revisión del efecto de la tasa de dosis en la irradiación de alimentos.pdf

7/28/2019 Revisin del efecto de la tasa de dosis en la irradiacin de alimentos.pdf

1/72

AECL10343ATOMIC ENERGYOF CANADA LIMITED

ENERGIE ATOMIQUEDU CANADA L1MITEE

DOSE RATE EFFECT IN FOOD IRRADIATION: AREVIEWL'EFFET DE DEBIT DE DOSE EN IRRADIATION DES ALIMENTS: UN EXAMEN

H a rw a n t Singh

W h it e sh e ll L a bo rato ries La bo ratoires de WhiteshellPinawa, Ma n it o b a ROE 1LO

Au g u s t 1991 a o u t


2/72

AECL RESEARCH

DOSE RATE EFFECT IN FOOD IRRADIATION: A REVIEV

by

Barwant Singh

Vhiteshell LaboratoriesPinawa, Manitoba ROE 1LO1991 AECL-10343


3/72


4/72

- - - - - - - - - - - - - - - - - - - - - - -i

CONTENTS

1.

2.

3.

4.

5.

6.

INTRODUCTION

BASIC ASPECTS OF DOSE RATE EFFECT2.1 INITIATION OF RADIOLYTIC REACTIONS2.2 DOSE RATE EFFECT2.3 OXIDATION AND DOSE RATE EFFECT2.4 SPUR OVERLAP AND DOSE RATE EFFECT2.5 COMPUTER MODELLING2.6 SUMMARY

IRRADIATORS AND DOSE RATES

DOSE RATE EFFECT ON FOODS: EXPERIMENTAL ASPECTS4.1 MICRONUTRIENTS4.1.1 Vater-Soluble Vitamins4.1.1.1 Thiamin (Vitamin Bl )4.1.1.2 Pyridoxine4.1.1.3 Riboflavin (Vitamin B2 )4.1.1.4 Ascorbic Acid (Vitamin C)4.1.1.5 Other Vater-Soluble Vitamins4.1.2 Lipid-Soluble Vitamins4.1.2.1 Vitamin E4.1.2.2 Other Fat-Soluble Vitamins4.2 HACRONUTRIENTS4.2.1 Amino Acids and Proteins4.2.1.1 Amino Acids4.2.1.2 Proteins4.2.2 Carbohydrates4.2.3 Lipids4.3 VOLATILE COMPOUNDS4.4 SPROUTING

SENSORY CHARACTERISTICS

CONCLUSIONSACKNOvLEDGEMENTSREFERENCES

1

22610111213

14

14141616222223262627303131323738414345

47

525454

b

APPENDIX AAPPENDIX B

SPUR OVERLAP: AN ESTIMATERADIOLYTIC REACTIONS OF VATER

6568


5/72

1. INTRODUCTION

Although most foods lose some vitamins and other nutrients duringprocessing and storage, food is generally processed in a manner thatminimizes nut ri en t los s and maximizes product safety. The nutrient contentof food is a lso a ffec ted by preprocessing factors such as geneticvariation, degree of matur ity, soil conditions, use of fert i l izer, climateand handling (Archer and Tannenbaum 1979). Vhile radiation processing offoods can lead to some losses of the sensitive vitamins (e.g., thiamin,vitamin E) , in general, food irradiation at the doses 10 kGy) recommendedby the Codex Alimentarius Commission (1983) causes no significant loss innutritional quality (Tajuma et al. 1970, Taub et al. 1979a, 1979b, Graham1980, Hurray 1983) .

I t has been suggested (Hannah and Simic 1985, Raica et al. 1972,Skala et al. 1987, Thayer 1987, Thomas et al. 1981) that the observedminor losses of nutrients may even be decreased when foods are irradiatedat high dose rates (electron beams from accelera tors ), rather than at thelower dose rates typical of gamma irradiation (60CO or 137CS). Thepossible beneficial effect of higher dose rates has often been referred toas the "dose rate effect" (DRE). Brasch and Huber (1947) considered theultrashort exposure times that a re possibl e with highly acceleratedelectrons to be a vi tal factor in suppressing undesired s ide react ions infood irradiation. Studies of dilute solutions of organic compounds, e.g . ,phenol, glucose, linoleic acid, asco rbic acid and vitamin A-acetate,support the suggest ions that there is lower loss of these compounds athigher dose rates (Dorfman et al. 1962, Head 1952, Schuchmann and vonSonntag 1977, Simic 1983, Taimuty and de LaRue 1957). On the other hand,Taub et al. (1979a) concluded that, in general , such a DRE should not beexpected from the irradiation of foods, since the first-order reactions ofthe primary species from water (hydroxyl radicals, hydrated electrons andhydrogen atoms) with the main components of foods (proteins, carbohydrates,etc.) will predominate. However, there seems to have been no comprehensivereview of the relevant data on DRE in food irradiation. This is partlybecause of the paucity of data on the electron-beam irradiation of foods,which, until recently, was no t considered practical.


6/72

- 2 -

The main objective of this review is to consider briefly thebasic aspects of DRE and evaluate the available comparative data on thegamma and electron irradiation of foods. A particular aim is to determinewhether any significant differences in the effects of irradiation of foodsat different dose rates exist, based on known chemical and sensory effects.Although microbiology is not covered in this review, a few s tudies indicateonly a minor DRE, i f any, on microorganisms and insects (Adem et al. 1979,Hansen 1966, Shamsuzzaman, personal communication, Taimuty and de LaRue1957, Tilton and Brower 1983, Veber 1983). One exception appears to be theDRE on adult Mexican frui t fly emergence where larvae were exposed to 10 Gytotal dose at dose rates between 0.1 and 40 Gy/min (Lester and Volfenbarger1990).

2. BASIC ASPECTS OF DOSE RATE EFFECTl

2.1 INITIATION OF RADIOLYTIC REACTIONSThe exposure of a substrate to ionizing radiation (radiolysis)

results in the formation of a spectrum o f ionized and excited species,which are either deactivated to the starting substrate or converted toother products, usually via free radicals (Draganic and Draganic 1971,Simic 1983, Singh and Singh 1982).

In radiolysis, the absorbed energy of a mixture is distributedapproximately in proportion to the mass ratio of i ts constituents (Klots1968). In a biological system, fo r example, the energies deposited in theorganic (R'RH) part (di rect e ffec t) and in the water part (indirect effect)are -25 and -75% respectively. (In foods, the water content varies; forexample, in meats i t is -75% in fresh beef but only -50% in smoked bacon,while i t may be as l i t t le as 15% in grains and as much as 80% in fruits(Singh 1989). Radiolysis leads to the formation of reactive intermediatesin water (Reaction (1 and organic components (Reaction (2 , as follows:

lPrepared in consultation with A. Singh


7/72

- 3 -

R'RH RH. + R'. + R'R + .B + e- + R'RH+ + R'RH'(1)

(2)

The free radicals formed from the organic components (Reaction (2 includethose formed by the C-C (R'.) and the C-B (R'R.) bond breakages.

On the microscopic scale, energy deposited in the liquid and thesolid phases is not distributed homogeneously but deposited in units of 20100 eV in regions called spurs (Samuel and Hagee 1953), about 5 nm indiameter (Hozumder 1969, Schwartz 1969). A typical spur, based on theparameters used by Schwartz (1969) to model radiolytic reactions in water,is shown in Figure 1. The spur consists of a spherical core, where thecationic and free radical species a re formed, and an outer sphere definingthe space within which the e;q is formed. In liquid water, the resultingdistribution of the major reactive species (.OB, B and e;q) is ini t ial lyinhomogeneous at _10- 12 s af ter each energy deposition event, but becomeshomogeneous by d if fu sion in _10- 7 s, as shown in Figure 2. Theconcentrations of the primary reactive species formed in spurs are quitehigh (Figures 1 and 2). For example, in water, the primary concentrationsof hydrogen atoms (.B), hydroxyl radicals (.OB) and hydrated electrons(e;q) in spurs average _10- 2 , _10- 1 , and _10- 1 mol.dm- 3 respectively, whilein the spur core (central 0.75 nm), the ini t ial concentrations of .B and.OB could be as high as -0.5 and -2 mol.dm- 3 (Figure 1) respectively (Singhand Singh 1982). Figure 2 is a qualitative representation of how spurformation in liquid water would appear i f the radiolysis were done with asingle gamma photon and a s ingle e lect ron. I t is meant to indicate thatthe in i t ia l spur concentration would be much higher in the case of electronirradiation than in the case of gamma irradiation. This difference is dueto much higher energy loss per unit volume of water from electron than fromgamma irradiation (Klots 1968).

Diffusion during the f i rs t 10- 7 s reduces these concentrations inwater at room temperature by many orders of magnitude, e.g. , to_109 mol.dm- 3 for gamma irradiation and to 10- 3 to 10- 6 mol.dm- 3 fo relectron irradiation. This large difference in concentration in thesteady-state homogeneous system of the reactive species formed on


8/72

G(e-aq)N' 5G('OH) I'V 6

0.75 nm I I2.3 nm

[e-aq] ~ [. OH] '; f 0.1 mol'dm-3(Av)a[. OH] -;:: 2 mol'dm-3(Spur Core)b

..,..

FIGURE 1: A Typical Spur in Vater, Based on the Parameters Used by Schwartz (1969), Adapted fromSingh and Singh (1982). The G-values given ar e based on the data of Jonah and Killer(1977) and Singh et al. (1978). Init ial concent ra ti on : ( a) averaged over total spurvolume (diameter 4.6 nm); (b) within the spur core (diameter 1 .5 nm).


9/72

- 5 -

( i ) o o o o [Spur] - Lowoo

(11) G(e-aq)N 2.7G(-OH)'" 2. 7

HOMOGENEOUSDISTRIBUTION

(. OH, e-aq, H etc.)

[Spur] - Very high

-3 b[. OH] ~ 2 mol dm (spur core)

oo 000 0o 0o 00

(11i)

FIGURE 2: Transition from Inhomogeneous to Homogeneous Distribution ofFree Radical Species in Liquid H20. ( i ) represents spurformation on energy absorption from a single gamma photon in10. 12 s or less; ( i i) shows homogeneous distribution of reactivespecies on diffusion of spurs in about 10. 7 s and ( i i i )represents spur formation on energy absorption from a singlee lectr on in 10. 12 s or less. The higher spur concentration[spur] on electron irradiation is not drawn to scale. (a )Averaged over total spur volume (diameter 4.6 nm); (b ) ini t ia lconcentration within the spur core (diameter 1.5 nm); (c ) 1refers to gamma irradiation; (d ) e- refers to electronirradiation.


10/72

- 6 -

radiolysis is due to the large differences generally seen in dose ratesbetween gamma and electron irradiation. However, the concentrations withinthe spurs are normally independent of dose rate, except at extremely highdose rates ()10 Gy/s) where significant spur overlap may occur (seeSection 2.4 and Appendix A).2.2 DOSE RATE EFFECT

To i l lustrate the basis of the ORE, one may consider a generalcase where a radiolytically produced free radical, R., reacts either withi tself (recombination Reaction (3 or with food components (e.g.,nutrients, Nutr) to cause damage (damaging Reaction (4 .

k 3R. + R. - - - ) R-Rk.R + Nutr - - - ) Nutrient Damage

(3)

(4)The radical R may be produced by direct or indirect effect. Two differentcases can be considered: a dilute solution (one solute, e.g., Nutr_10- 5 mol.dm 3 ) and a food item (e.g., beef containing 75% water and 25%organic food components; [Fe], 2.5 mol.dm- 3 , Table 1). Further, i t isassumed that k3 = 1010 mol- 1 .dm3 .s 1 and k. = 10' mol 1 .dm 3 ,s 1 fo rReact ions (3) and (4 ) respectively, based on the known rates of reactionsof .OH radicals (Buxton et al. 1988). The estimated relative importance ofReact ions (3) and (4 ) based on these assumptions is shown in Table 1.

The importance of Reaction (3) increases by a factor of 106 goingfrom gamma to electron irradiation, both fo r dilute solution and for beef.However, one important difference exists: in the case of the dilutesolution, Reaction (3) occurs only about once for every 1000 times Reaction(4 ) occurs during gamma irradiation, while during electron irradiationReaction (3) becomes dominant (at 1000 to 1). On the other hand, in thecase of beef, React ion (3) (compared with Reaction (4 increases from aninsignificant share of 4 in a billion in the case of gamma irradiation to alarger but s t i l l negligible share of 4 in 1000 in the case of e lect ronirradiation. Thus the relative importance of Reaction (4) as compared withReaction (3) decreases with increasing dose rate, mainly in dilutesolutions.


11/72

- 7 -TABLE 1

RELATIVE IMPORTANCE OF RECOMBINATION REACTION (3) ANDDAMAGING REACTION (4) (k3 = 1010 and k{ - 109 mol- 1 dm 3 .s- 1)

FOR THE SAME TOTAL DOSE1,2

Free Radical Food Component Relative ImportanceSystem Irradiator Concentration Concentration of Reactions[.R) mol.dm- 3 [FC) mol.dm- 3 (3) (4 )Dilute Gamma 10- 9 10- 5 1 : 10 3solution3Dilute Electron 10- 3 10- 5solution 3 1 : 10- 3Beef Gamma 10- 9 2.5 4 : 10 9Beef Electron 10- 3 2.5 4 : 10 3

l .2.

3.

I (3 /R i (4 k) [R . )Re ative importance of Reaction ) eact on ) = k{[FC) I t is assumed that beef behaves as an aqueous solution, since th erelative values of k3 and k{ in beef are not known. The calculationsare made fo r the systems at room temperature.Vater solution with only one solute.

In general, a similar ORE would be expected for a l l free radicalspecies, whether primary or secondary, formed by direct or indirect actionof radiation. The differences in the relative importance of the relevantanalogues of Reactions (3) and (4) would depend on the relative reactionrates, and the complexities of the exact mechanisms of reactions. Vheresimple mechanisms analogous to Reactions (3 ) and (4) dominate, one wouldexpect an observable ORE in dilute solutions but a negligible ORE in thecase of foods, based on the data in Table 1.

This expectation is borne out in r ad io ly si s s tudi es of diluteaqueous solutions as shown by data on the gamma and electron radiolysis ofsolutions of vitamin A-acetate (Figure 3) and ascorbic acid (Figure 4), asreported by Taimuty and de LaRue (1957). In both cases, Taimuty andde LaRue (1957) observed a g reate r l os s from gamma irradiation, for thesame absorbed dose. Schuchmann and von Sonntag (1977), and Simic (1983)


12/72

- 8 -

w 100-et O / ~-wUet 80etZ:2E 60 "yOt!::> /0u. 400 /0II I /0II I0 00-l 20 Electron ~ .l - +-+#-+-- --r-+#+ +- t-wu 0I:W 0 0.8 1.6 2.4 3.2 4.0.

DOSE (Rep x 10-5 ~ 1(f 3Gy)

FIGURE 3: Loss of Vitamin A-Acetate in Isopropanol Solution from Gamma(Dose Rate - 10 Gy/s) and Electron (Dose Rate - 10 Gy/s)Irradiation. Data from Taimuty and de LaRue (1957).


13/72

IIIIfI - 9 -

100Cl 90 0 0 Gammau + + electron~ 80uco 70:0U(J ) 60~u.0 50(J )(J ) 400- Jt - 30zUJu 20 +t:UJc. 10

o 0.4 0.8 1.2 1.6 2.0 2.4

FIGURE 4: Loss of Ascorbic Acid in Aqueous Solution from Gamma (Dose Rate- 10 Gy/s) and Electron (Dose Rate - 104 Gy/s) Irradiation.Data from Taimuty and de LaRue (1957).


14/72

- 10 -reported similar conclusions from work on glucose solutions.also reported higher product yields at lower dose rates from

Mead (1952)the

irradiation (using the Picker 250-KVP Therapy Tube) of l inoleic acid (in 5%methanol) in buffered aqueous solution, pB 9.0, as shown in Table 2. Theradiolytic products were not identified by the author. In this case,however, the free radical species reacting with linoleic acid would be theradicals derived from methanol by reaction with .OB and B radicals, asfollows:

.OB + CB 3 0B - - - ) .CB20B + B20

.B + CB 3 0B - - - ) .CB20B + B2

.CB 20B + Linoleic Acid - - - ) Reaction Products

.CB20B + .CB20B - - - ) (CB20B)2

TABLE 2DOSE RATE EFFECT ON PRODUCT FORMATION FROM LINOLEIC ACIDl

Dose Rate2 [Product)(Gy/min) (10- 5 mol.dm- 3 )-0.10 28.2-0.33 11.8-0.98 5.0-5.40 2.0

1. Data from Mead (1952). Irradiationtemperature not g iven. Irradiation source,Picker-250 KVP Therapy Tube. Linoleic acid,5.8 x 10- 3 mol.dm- 3 in borate buffer, pH 9.2. Given as r/min for a total dose of 1000 r(-10 Gy).

2.3 OXIDATION AND DOSE RATE EFFECT

(5)(6)(7)(8)

In the presence of oxygen, organic free radicals may react withoxygen to form peroxy radicals:

R + 02 -) RO' 2 (9)


15/72

- 11 -This reaction would compete with the recombination reaction of the freeradicals:

.R + .R -> R-RSo, as the dose rate increases, the recombination reaction would befavoured over the peroxy radical formation. As a consequence, loweroxidation of food components may be expected from irradiation at higherdose rates. I t appears, however, that no relevant work has been done totest this expectation.2.4 SPUR OVERLAP AND DOSE RATE EFFECT

(3)

As noted in Section 2.1, concentrations of free radical specieswithin spurs do not change with dose rate, except at very high rates(>10 Gy/s), where spur overlap becomes significant. In add it ion to thedose rate, spur overlap would also increase i f spur lifetime increased,e.g. , because of the low temperature of frozen systems.

The diffusion rates of reactive species in spurs depend on theviscosity of the system. Thus, the diffusion rate would be lower in solidfoods (e.g., grain and frozen meats, fo r which spur diffusion rates do notseem to be available), which would decrease the DRE except where spuroverlap occurred (see below). However, even in the solid phase, the DREwould s t i l l depend on the relative changes in the importance of Reactions(3 ) and (4 ) (and their analogues). Spur overlap would become importantduring electron irradiation of frozen samples (e.g., meats irradiated at-15 to -40C) at dose rates lower than those required in liquid H20 forspur overlap; as the temperature was lowered, the diffusion rate of spurs(and hence of free radicals) would be dramatically reduced in frozenaqueous systems. Unfortunately, no est imates are available on spurdiffusion rates in frozen systems (A. Hozumder, personal communication) andsolids. I t is not even certain whether homogeneous concentrations of freeradicals could ever be reached in frozen systems (particularly in the caseof meats at -15 to -40C). The overall effect of spur overlap in frozensystems would be to increase the DRE, owing to slow spur diffusion.


16/72

- 12 -

Since the rate and extent of spur diffusion would be much lowerin s olid s, one would expect much less damage to nutrients in frozen foods(-30 10C) than in foods at 0 to sC, for both gamma and electronirradiation. In the case of e lectron irradiation, DRE would also be afactor, owing to much greater spur overlap in the case of frozen meats . I tshould be pointed out that the total number of spurs formed, for the sametotal dose, would be th e same for gamma and electron irradiation. The spurdiffusion rate would be reduced in frozen solution and th e consequentlifetime of the spur would be increased enough (e.g., 10- 3 s instead of10- 7 s in liquid H20) to allow spur overlap dur ing electron irradiation butnot during gamma irradiation. Data support ing these expectations arediscussed in Section 4.1.1.1 for thiamin.

I t is relevant to point out that, at low temperatures(-30 10C) or in solids at ambient temperature (e.g. , grains), th e spurswould s t i l l diffuse, though slowly. The diffusion rates of the three mainreactive species (derived from water, for the sake of this discussion) inthe above systems will roughly be inversely proportional to their molecularweight. Thus, H atoms would be the most mobile, e;q less mobile and OHthe least mobile. This would affect the DRE in foods at low temperatures.The mobility of e;q would depend on i ts diffusion mechanism: i f i t acted asa hydrated species (e;q) ' i t would diffuse most slowly. However, i f i tmigrated from one hydration si te to another, i t would diffuse qUickly (A.Singh, personal communication). Information on this subject is not readilyavailable.

2.5 COHPUTER HODELLING

In principle, i t should be possible to use computer modelling tocalculate the expected dif fe rences in the effects of various dose rates i fthe mechanisms of the relevant radiolytic react ions are known. The numberof radiolytic reactions that occur from the irradiation of a puresubstrate, such as water, is large (-50, Appendix B). This numberincreases rapidly with the number of components/solutes to >100 for onesolute and to >1000 for mult isolute solut ions.


17/72

- 13 -

A solution of tryptophan (I) may be taken as an example of waterplus a one-component/solute system (Singh et al. 1984), to i l lustrate theincrease in the number of reactive species, and hence in the reactions thatoccur as a solute is added t o water.

CH2 - CH - COOHINH2

1NH

I

In this case, the addition reaction of hydroxyl radicals can give up to sixdifferent free radicals (assuming the hydroxyl radical additions to be atcarbons 2-7, in I above). The hydrogen atom abstract ion react ion ofhydroxyl radicals can give four more free radicals (assuming theabstraction of H from the CH 2 , CH and NH 2 groups from the side chain and ofthe NH group from the ring structure, in I above). Additional freeradicals would also be expected from reactions of hydrated electrons andhydrogen atoms with t ryptophan (Armstrong and Swallow 1969).

Host foods are multicomponent systems and thus the expectednumber of radiolytic reactions in a food is very larg e ( 100 ). Since a llthe possible react ions have yet to be identified and th eir rate constantsestablished, i t is impossible to model the reactions by computer to predictthe expected DRE. The only practical alternative is to review theavailable relevant experimental data to identify any significant DRE.2.6 SUHMARY

The existence of DRE in a system should depend on the followingfactors:


18/72

- 14 -

(1 ) the rate constants for the analogues of Reactions (3) and (4 ) foreach of the reactive free radical species;

(2 ) the concentra tions of various reactive food components in thesystem; and

(3) the viscosity of the system.The above factors should apply to a simple mechanism involving

analogues of Reactions (3) and (4). Food systems are too complex to allowa prediction of the extent of DRE in a particular system on the basis offundamental principles.

3. IRRADIATORS AND DOSE RATES

Although gamma irradiators (60CO and I37CS sources) have been themost common sources o f food irradiation, electron-beam irradiators,particularly 5-MeV X-ray sources and 10-MeV electron accelerators , arebecoming increasingly important. Characteristics of typical irradiatorsare given in Table 3, a long with their dose rates, where available.

4. DOSE RATE EFFECT ON FOODS: EXPERIMENTAL ASPECTS

4.1 MICRONUTRIENTS

Vitamins are an important group of micronutr ients present infoods and a re a ff ec ted by processing conditions (Archer and Tannenbaum1979, Erdman and Klein 1982, Osborne and Voogt 1978, Sauberlich et a l.1982). Their concentrations are generally small ( ~ g / g ) , a notableexception being vitamin C (mg/g). They are usually subdivided into waterand fat-soluble vitamins. Their physical environment (water or l ipids)determines the types of free radical reactions they undergo on irradiation


19/72


20/72


21/72

- 17 -TABLE 4

DOSE RATE EFFECT ON THIAMIN IN SOLUTIONl

Current ( ~ ) 2 40 80 200 400Average PulseDose Rate (Gy/s ) 10' 2 x 10 ' 5 X 10' 10 8Average ScanningBeam Dose Rate (Gy/s) 12.5 25.0 62.5 125.0Duration ofIrradiation (s) 40 20 8 4Percent Lossof Thiamin 51.2 48.8 47.2 53.01. Data from Diehl 1975.2. 10-MeV linear electron accelerator; irradiations of 1 mg/mLthiamin dichloride solutions at OC, total dose0.5 kGy.

However, in the case of high-dose irradiation of meats, dataexist t ha t ind icate only a minor DRE on thiamin destruction fromirradiation above freezing temperatures. Raica et al. (1972) reportedthat, al though the destruction of thiamin in meats containing relativelyhigh levels of the v itamin was slightly greater, irradiation to dosesbetween 20 and 60 kGy at 0 to 5C re su lted in no significant difference(s10%) in i ts retention as a function of dose rate, as shown in Figure 5.

On the other hand, data repor ted by Thomas et al. (1981) on theradappertization (radiation sterilization) of pork at very low temperatures(frozen samples) show a very high retention of thiamin at high dose rates.The data in Figure 6 show that thiamin loss is lower at lower temperaturesand higher dose rates (electron irradiation), thus establishing DREclearly. As explained earl ier, this is attributable to spur overlap fromlow-temperature electron irradiation


22/72

r- 19 -

90

-45C

-15C50 7000

'


23/72

- 20 -Skala et al. (1987) and McGown et al. (1979a) have reported

results on frozen radappertized beef and chicken i rr ad ia ted a t -30 10C,which also suggest better thiamin r et en ti on in electron-irradiated samplesthan in gamma-irradiated samples (Table 5). These results are consi sten twith the trend seen in pork irradiation at very low temperatures (-15 to-45C, Thomas et al. 1981, Figure 6) and in chicken irradiation(-25 15'C, Thayer 1990, Table 5). The reasons for the difference indegree of thiamin r et en tion in chicken (Table 5) between the resultsreported by Skala et al. (1987) and those reported by Thayer (1990) are notclear but may be related to different thiamin detection methods; whileThayer (1990) used a chemical method, Skala et al. (1987) used amicrobiological assay.

TABLE 5DOSE RATE EFFECT ON VITAMINS IN MEATS

Irradiation (at -30 WC)AverageVitamin System Total Gamma Electron ReferenceDose(kGy) Percent RetentionThiamin Beef 58 1 23 44 Skala et al.(1987), McGownet al. (1979)

Chicken 58 1 26 66 Skala et al.(1987)Chicken 45-68 2 -68 -86 Thayer (1990)

Pyridoxine Chicken 58 1 50 62 Skala et aL(1987)Chicken 45-682 73 93 Thayer (1990)

1. Gamma and electron dose rates not given but assuaed to be -14 Gy/s and_106 Gy/s respectively, based on data from Shults and Vierbicki (1980).2. Gamma and electron dose rates 9.6 and _106 Gy/s respectively (Thayer,personal communication).


24/72

- 21 -Limited data are available from which to compare the DRE at doses


25/72

- 22 -I t would therefore be worthwhile to repeat some of this work to

obtain a clearer picture of ORE in the case of low doses of irradiation, ato to 5C, using a much wider range of dose rates, especially for meats.4.1.1.2 Pyridoxine

Pyridoxine is a member of the vitamin B6 group widely distributedin living systems and an essential growth factor. I t is present in meatsat a concentration of 1 to 5 ~ g / g . Pyridoxine is frequently added toprocessed foods (Archer and Tannenbaum 1979, Fennema 1985).

In radappertized frozen chicken, the trend of ORE for pyridoxinelevels is similar to that for thiamin, except that damage from both gammaand electron irradiation is less extensive (Table 5, Skala et al. 1987,Thayer 1990). The reason for the differences in the percentage retentionof pyridoxine (Table 5) in the work of Skala et al. (1987) and Thayer(1990) is no t clear. Both used a microbiological assay for pyridoxine.There appear to be no data in the l i terature from which to compare ORE atlow doses ( ~ 1 0 kGy) on pyridoxine content in foods.

4.1.1.3 Riboflavin (Vitamin B2 )Riboflavin is not as radiation-sensitive as thiamin or pyridox

ine. Day et al. (1957) reported tha t r iboflav in in beef is f ai rl y r es is tant to irradiation, since only 8% was destroyed by the irradiation processat a dose of 30 kGy. Beat process ing of beef apparently has a greaterdestructive effect on riboflavin than radiation processing at either 28 or56kGy (Kraybill 1982). Taimuty and de LaRue (1957) could not observe aORE (103 and 10 6 rep/s, -10 and 10 Gy/s) on r ibof lavin in solut ion,contrary to the general observation of a ORE on other systems in dilutesolutions, mentioned earl ier in Section 2.2.

At low doses (1 kGy) , Lu et al. (1989) reported no ORE on riboflavin content between 0.27 and 3.75 Gy/s in sweet potato tubers (Table 6).In the case of radappertized chicken (Table 7), Thayer (1990) observed noinactivation of riboflavin at high doses. In fact, the levels of riboflavin in both gamma- and electron-irradiated chicken were slightly higherthan those in the unirradiated control, showing no significant ORE.


26/72

- 24 -In their study of ORE, Taimuty and de LaRue (1957) reported

reduced destruction of asco rb ic acid (1% solution) at higher dose rates(Figure 4). Vork on the r et en tion o f ascorbic acid in foods as a functionof dose rate has been limited to low-dose irradiations. Somogyi et a l.(1975) studied such effects on two varieties of potatoes (Haritta andBintje) using 3-HeV electron (dose rate not given but expec ted to be-10' Gy/s) and gamma (5.5 and 6.3 kGy/h for Bintje and Hari tta varietyrespectively) irradiation, up to a total dose of 1.5 kGy (Figure 7). Theyobserved no significant ORE on the level of ascorbic acid in eithervariety. I t should be mentioned here that the levels of ascorbic acidreported in this study (-85 mg/l00 g) are much higher than those generallyreported for potatoes (about 20 mg/l00 g, Bowes et al. 1975). The authorsdo not comment on this difference.

Similarly, Umeda et al. (1970) observed no ORE on citrus fruitsections irradiated with a 1- to 5-kGy total dose (Table 8), usingelectron (1 HeV at 0.4 ~ / c m 2 , dose rate not given but expec ted to be4.8 x 104 Gy/h) and gamma (dose rate 0.6 to 2.3 kGy/h) irradiation. Infact, they reported no significant loss of ascorbic acid, even at doses ashigh as 5 kGy. A recent study (Lu et al. 1989) reported a slightly higherr et en tion o f ascorbic acid at higher dose rates in sweet potatoes(Table 6). Since the irradiation times (for a total dose of 1 kGy) rangedfrom 3.9 to 60 min at 24C using a ,oCo source (Table 6), the possibili tyof ascorba te loss at this temperature during long periods of irradiationwas raised by the authors. In view of these contradictory results, i twould be useful to optimize the irradiation temperature, which is likely tobe lower than 24C.

In an earlier study, Lu et al. (1987) found no ORE on theascorbic acid content of onions irradiated with a 2-HeV electron source(dose rate not given) and a gamma source (dose rate 0.38 Gy/s) up to atotal dose ranging between 0.1 and 3 kGy.


27/72

MARITTA BINTJE

20 J I I I I

0-- - - - - - - - - -0 ..... - t > ' ~ - - - - _ . . (>1----------->

DOSE (kGy) DOSE (kGy)

FIGURE 7: Effec t o f Gamma and Electron Irradiation on the Content of Vitamin C(Ascorbic Acid) in Two Varieties of Potatoes. Data from Somogyi et al.(1975). X = electron (3-HeV) irradiation (dose rate not g iven butassumed to be _106 Gy/s); 0 = gamma irradiation (6.3 kGy/h fo r Harittaand 5.5 kGy/h fo r Bintje variety).


28/72

- 26 -TABLE 8

EFFECT OF GAMMA AND ELECTRON IRRADIATION ON ASCORBIC ACID(VITAMIN C) CONTENT OF CITRUS FRUIT SECTIONl

Ascorbic Acid Content(mg per fruit section)Treatment Dose (kGy)1 2 3 5Unirradiated 16.6 21.2 18.9 18.6(control)Electron irradiation 17.0 22.5 18.9 17.9(1 MeV, 0.4 ~ A / c m 2 )Gamma irradiation 17.2 21.2 18.6 17.2(0.6-2.3 kGy/h)1. Data from Umeda et al. (1970). Al l fruit sectionsassumed to be of equal weight.

4.1.1.5 Other Vater-Soluble VitaminsThayer (1990) has reported on the DRE on several other water

soluble vitamins in radappertized chicken (Table 7). The retention valuesfo r a l l the vitamins except choline and niacin (bound) are slightly higherin the case of electron irradiation than in the case of gamma irradiation.Incidentally, many of the values for irradiated chicken are higher thanthose for the unirradiated controls. Vhile the reason for this is notclear, one possibility may be that relevant enzymes are activa ted onirradia tion.

4.1. 2 Lipid-Soluble VitaminsVitamin E, the most sensitive of the fat-soluble vitamins, is

easily degraded by irradiation. The sensitivity of the fat-solublevitamins follows the order: vitamin E > carotene> vitamin A > vitamin D >vitamin K (Kraybill 1982).


29/72

II 4.1.2.1 Vitamin E- 27 -

j

This fat-soluble vitamin is found in nature in the form oftocopherols and tocotrienols. Vhile vitamin E has multiple physiologicalfunctions, i ts exact biochemical role remains to be defined (Tannenbaum eta l. 1985). I ts activity is widely distributed among food groups of animaland vegetable origin, including oils (Davis 1972, Slover 1971). The mostactive form of vitamin E is a-tocopherol (Fennema 1985). The levels ofa-tocopherol in different foods (Hachlin 1980, Sebrell and Harris 1972)range from 1 to 15 pg/g in g rain s (Herting and Drury 1969), from 0.15 to3 pg/g in meats, poultry and fish (Ames 1972), and from 0.2 to 0.8 mg/g inmargarine and sunflower oil (Diehl 1970).

Although a-tocopherol i n soluti on is very sensitive toirradiation, solutions are not affected by different i r radia t ion doserates. Diehl (1979a) irradiated a-tocopherol so lu tion in isooctane, undernitrogen, with gamma radiation (1.8 Gy/s) and electrons (107 Gy/s) andfound identical patte rn o f destruction, as shown in Figure 8. Although theauthor does not mention the temperature during irradiation, his otherpublished work refers to the irradiation o f s im ila r systems at 20C (Diehl1979b, Diehl and Kim 1981). Earlier, Diehl (1970) showed that, althougha-tocopherol loss was prevented to some extent by the exclusion of oxygen(nitrogen vs. air , Figure 9), there was no significant difference betweeni t s degradation in air and in nitrogen at dose rates between 103 and105 Gy/s. Similar results were obtained with a-tocopherol acetate inisooctane solution (Diehl 1970), but this compound was found to be lesssensitive than a-tocopherol to irradiation.

There have been only a few studies of DRE on a-tocopherol contentin foods. One such study (Diehl 1979a) used four different radiationsources: 1-HeV Van de Graaff accelerator, 2.5 x 10 Gy/s; 10-HeV linearelectron accelerator , 10 7 Gy/s; 5-mA X-ray, 4 Gy/s; and 60CO, 1.8 Gy/s.No significant differences were observed in a-tocopherol loss from th eirradiation of sunflower oil at a total dose of 1 kGy at the four differentdose rates (Table 9). Samples under nitrogen l os t s li gh tl y less


30/72

- 28 -

100

(J )(J )o....I -ZW(Ja:wa.

80

60

40

20

o 5 10 15

o

20DOSE (kGy)

FIGURE 8: Dose Rate Effect on a-Tocopherol in 0.1% Solution in Isooctane,Under Nitrogen. Data from Diehl (1979a) . e ---e, gammairradiation (1.8 Gy/s); 0 ---0 I electron irradiation (lO-MeVl inear electron accelerator, 107 Gy/s).


31/72

----------------- 29 -

100 r - - - - - - r - - - - , - - - - . - - - - ~

80

enen0 60...JI- 0 AIR0 0UJ +-N2) : 40UJDo

20

DOSE RATE (kGy/s)

FIGURE 9: Electron I r r a d i a t i o n of a-Tocopherol in Solution in Isooctane,Under Ai r and Nitrogen. Data from Diehl (1970). Total dose ofi r r a d i a t i o n (10-HeV l i n e a r electron accelerator) was 1 kGy.


32/72

- 30 -TABLE 9

DOSE RATE EFFECT ON a-TOCOPHEROL IN SUNFLOVER OILl

Radiation Dose Tocopherol Loss (%)Source Dose Rate(kGy) (Gy/s) in Nitrogen in AirCo 1 1.8 30.1 36.510 1.8 89.4 94.6X-ray (5 IDA) 1 4 30.1 1.0 34.8 0.6(20 IDA) 10 16 86.0 1.3 90.7 1.2Van de Graaff 1 2.5 x 104 27.8 0.4 33.5 0.3(1 MeV) 10 2.5 x 10 4 91.1 1.4 95.9 0.5Linear 1 107 27.0 32.2accelerator(10 MeV)1. Data from Diehl (1979a) .a-tocopherol than those under air (Table 9). Similar results for DRE wereobtained when sunflower oil samples were irradiated at a total dose of10 kGy (Table 9), a lthough the loss of a-tocopherol was greater, as wouldbe expected (Diehl 1979a). Diehl (1979a) concludes that the slightapparen t t rend (Table 9) in loss of a-tocopherol at low dose rates (e.g. ,1.8 and 4 Gy/s) of 30.1% vs . high dose rates (e.g., 2.5 x 104 and 107 Gy/s)of -27% with a 1-kGy dose is not significant, especially since the sametrend dose not exist fo r the 10-kGy dose.4.1.2.2 Other Fat-Soluble Vitamins

Most other fat-soluble vitamins are less sensitive to radiationthan is vitamin E. Litt le work has been done on these vitamins, especiallyon the DRE, either in solution or in foods. In a study of DRE, Taimuty andde LaRue (1957) reported greater destruction of solubilized retinyl acetate(vitamin A derivative) in isopropanol by gamma than by electron irradiation(Figure 4). However, no DRE on vitamin A was observed in radappertizedchicken (Thayer 1990, Table 10). Thayer (1990) also repor ted data on DREon vitamins D, K and B12 in radappertized chicken (Table 10). Theelectron-irradiated sample shows a much higher vitamin D content than does

,


33/72

- 31 -either the gamma-irradiated or the frozen control sample. Since the valuefor electron-irradiated samples is much higher than for the frozen controlor gamma-irradiated sample (Table 10), this work needs to be repeated inorder to confirm these results.

TABLE 10DOSE RATE EFFECT ON FAT-SOLUBLE VITAMINS INENZYME-INACTIVATED RADAPPERTIZED CHICKENl

Vitamin Frozen Control Gamma2 Electron3(9.6 GY/S)4 (106 GY/S)4Vitamin A IU/kg' 2716.0 2270.0 2270.0Vitamin DIU/kg 375.1 354.0 466.1Vitamin K mg/kg 1.3 0.8 0.8Vitamin B12 ~ g / k g 8.3 13.7 8.8

1. Data from Thayer (1990).2. 60Co, irradiation dose 46-68 kGy at -25 15'C.3. 10-MeV electron accelerator dose, 45-68 kGy at -25 15'C.4. Thayer, personal communications.5. IU/kg or and mg/kg of dry weight of chicken.Lu et a l . (1989) have observed lower or no loss of carotenoids in

sweet potatoes at higher dose rates than at low dose rates (Table 6).However, the authors suggest that the longer irradiation times at 24'Cplayed a role in the greater loss of carotenoids at the lower dose rate.

4.2 MACRONUTRIENTS

Amino acids , p ro te ins, carbohydrates and lipids are themacronutrients in foods. Many studies have focussed on the radiolysis ofthese components of foods and relevant model systems. The basic aspects ofradiolysis that lead to chemical effects and the factors tha t inf luencethese effects (irradiation temperature, oxygen effect, stabili ty of freeradicals) have been described (Singh 1987, 1988 and references therein).However, work on DRE has remained rather neglected.4.2.1 Amino Acids and Proteins

The radiation chemistry of amino acids and proteins remains anactive field of research, owing to i ts relevance in radiobiology and food


34/72

- 32 -irradiation (Biaglow et al. 1988, Davies 1988, Delincee 1983, Griffiths etal. 1988, Simic 1983, Singh and Singh 1982, Taub 1983). The range of possible chemical and physical changes from the irradiation of proteins infoods is similar to that from other treatments. Potential react ions include deamination, decarboxylation, reduction of disulfide linkages,oxida tion of sulfhydryl groups, breakage of pep tide bonds and changes invalency states of co-ordinated metal ions in enzymes (Delincee 1983, Taub1983, Taub et a l. 1979a). The products of protein irradiation includecarbonyl compounds, ammonia, free amino acids, hydrogen peroxide andorganic peroxides. Some free amino acid-protein bonding, protein-proteinaggregation and cross-linking, and protein-lipid cross-linking can alsooccur, particularly at high doses . Vhen pro te ins a re irradiated, crosslinking and scission can proceed simultaneously (Bailey et al. 1964).Oxygen and t he presence of radical scavengers inhibit cross-linking, asreported for col lagen (Bailey 1967), whereas increasing proteinconcentrations favour cross-linking, as in the case of myoglobin(Lycometros and Brown 1973). The overall decomposition of proteins at lowdoses ( ~ 1 0 kGy at 1 to 4C) and even at radappertization doses, is minimal.4.2.1.1 Amino Acids

Vhile many amino acids in solution are susceptible to decomposition on i rr ad ia tion a t high doses (Diehl and Scherz 1975, Liebster andKopoldova 1964), their sensitivities in meats are much lower (Partmann andKeskin 1979). Therefore, while a DRE may be expected in dilute solutions,i t should become negligible in foods, as in the case of the micronutrientsdiscussed in Section 4.1. This is supported by the available experimentaldata. Bound amino acids in proteins are known to be more stable againstirradiation than free amino acids (Diehl and Scherz 1975, Haslennikova1969, Rhodes 1966). From an analysis of the amino acids in beef, no significant differences were found between those i rr ad ia ted in the frozen state(-30 10C) to a dose of 47 to 72 kGy (by gamma or electron irradiation),the unirradiated controls and the thermal ly treated samples (Taub et al.1979a). Table 11 gives the amino acid content of electron- and gamma-irradiated raw beef (6 kGy), as cited by Josephson et al. (1978 from thedata of Frumkin et al. (1972). These authors found no significant DRE onamino acid composition.


35/72

- 33 -TABLE 11

DOSE RATE EFFECT ON THE AMINO ACID CONTENT(g/100 g DRY VEIGHT OF PROTEIN) OF RAV BEEFl

60CO Electron IrradiationControl Irradiation 2 MeV 4 MeVAminoAcid Dose Rate (Gy/s)0 5.3 2 x 102 2 X 103 2 X 102 2 X 10 3

Cystine 0.72 0.86 0.71 0.87 0.65 0.62Lysine andhistidine 15.42 14.95 13.46 15.07 14.29 13.79Arginine 7.95 7.23 7.72 8.09 7.32 7.65Aspartic acid 7.04 7.15 6.85 6.65 6.41 6.78Serine 2.82 2.79 2.97 2.60 3.04 2.96Glycine 3.37 3.42 3.39 3.61 3.91 3.75Glutamic acid 11.82 11.50 11.75 11.11 12.04 11.72Threonine 4.64 4.67 4.23 4.52 4.52 4.54Alanine 4.64 4.82 5.10 4.95 5.12 5.19Tyrosine 2.84 3.03 2.74 2.89 3.02 2.77Methionine 2.48 2.52 2.38 2.46 1.91 2.30Valine 5.35 5.15 5.21 5.08 5.71 5.63Phenylalanine 4.10 4.15 4.57 4.90 4.69 4.96Leucine andisoleucine 9.19 9.32 10.04 9.74 9.96 9.93

1. Data cited by Josephson et al. (1978). Irradiation to a total dose of6 kGy. Irradiation temperature not given but assumed to be ambient.The electron and gamma irradiation of enzyme-inactivated beef at

very low temperatures (-40'C) causes no significant DRE in terms of theloss of cystine, methionine or tryptophan, considered the most radiationsensitive amino acids (Table 12, Josephson et a l. 1978). An earlier study(Johnson and Moser 1967) compared the DRE on ground beef of gammairradiation (60CO, 28 Gy/s) and electron-beam irradiation from anaccelerator (11 and 24 MeV at 20 and 200 ~ current levels), with doserates of about 10 and 109 Gyls respectively (also see Diehl 1982). Theauthors reached the fol lowing conclusions:

(1) the destruction of amino acids i n p ro te in s by irradiation waslimited to t ryptophan and cystine, and


36/72

- 34 -TABLE 12

DOSE RATE EFFECTS ON THE AMINO ACID CONTENT(VEIGHT PERCENT OF ENZYME-INACTIVATED BEEFl

T r e a t m e n tAmino Frozen 6GCO 10 MeVAcid Control (47-71 kGy) (47-71 kGy)

Cystine 0.28 0.26 0.28Methionine 0.53 0.57 0.59Tryptophan 0.25 0.25 0.26

1. Data from Josephson et a l. (1978). Vacuum-packaged beefirradiated at -40C.(2 ) damage to amino acids was slightly less from gamma

irradiation than from 24-MeV electron irradiation.However, the latter conclusion is

tryptophan, histidine and cystine/cysteine.generally indicate the following:

not supported by their data onThe data given in Table 13

(1 ) histidine and tryptophan lo ss es a re similar for gamma andelectron (24-MeV) irradiation;

(2 ) the differences in the case of cystine/cysteine are minor;and

(3) the re a re wide and unexplained differences in amino acid lossesfrom 11- and 24-MeV electron irradiation, even though, for thesame current, the dose rate in the two cases would be expected tobe similar.

The authors also report differences when the electron dose rateis increased by a factor of 10 fo r II-MeV electrons which are notparalleled for 24-MeV electrons in the case of tryptophan (Table 13).


37/72

TABLE 13CONCENTRATION (g/100 g PROTEIN) OF AM INO ACIDS IN GROUND BEEF

AT AMBIENT TEMPERATURES. AT DIFFERENT DOSE RATESl

Radiation 11-MeV Electrons 24-MeV Electrons 60CODose 20 jlA 200 jlA 20 jlA 200 jlA

(kGy) gllOO g proteinTryptophan

0 1. 703( 100) 1. 703(100)2 1.703(100) 1.703(100) 1.703(100)20 1.665(98) 1. 605(94) 1.498(88) 1.510(89) 1.477(87)45 1. 615(95) 1.575(93) 1. 515(89) 1.485(87) 1. 475(87)100 1.595(94) 1.488(87) 1.505(88) 1.480(87) 1. 475(87)Histidine

0 3.43 3.43 3.43 3.43 3.4320 3.43 3.44 3.33 3.20 3.4345 3.45 3.32 3.32 -- 3.41100 3.43 3.30 3.33 3.03 3.46Cvstine/Cysteine0 1.27(100) 1. 27 (100) 1.27(100) 1.27(100) 1.27(100)20 1.11(87) 1.04(81) 0.92(72) 0.82(65) 0.89(70)45 1.08(85) 0.96(76) 0.88(69) 0.74(58) 0.84(60)100 1.08(85) 0.95(75) 0.83(65) 0.74(58) 0.84(66)

1. Data from Johnson and Moser (1967). Dose rate fo r gamma irradiation 28 Gy/s; fo relectron irradiation assumed to be 108 and 109 Gy/s respectively, from informationgiven (20 and 200 j lA).2. Numbers in brackets show percentage retention.

UJIJ '


38/72

- 36 -More recen t data (Thayer 1990) on the amino acid content of

gamma- and electron-radappertized chicken show no significant ORE(Table 14).

In general , therefore , considering a ll of the available data, i tis concluded that there is no ORE on amino acids in foods.

TABLE 14CONTENT OF AMINO ACID (g/100 g PROTEIN) IN

ENZYME-INACTIVATED CHICKEN TREATED VITH ELECTRONS AND GAHHASl

Amino Acid Frozen Control Electron 2 Gamma3(106 Gy/s)4 (9.6 Gy/s)4Alanine 5.76 5.85 5.84Arginine 6.24 6.38 6.37Aspartic acid 8.94 8.84 8.98Cysteine 0.91 0.93 0.96Glutamic acid 14.33 14.17 14.19Glycine 5.83 5.87 5.96Histidine 4.05 4.36 4.21Hydroxyproline 0.28 0.28 0.27Isoleucine 4.51 4.67 4.70Leucine 7.53 7.64 7.69Lysine 8.34 8.49 8.55Methionine 2.52 2.57 2.48Phenylalanine 3.78 3.79 3.74Proline 4.02 4.34 4.45Serine 3.72 3.60 3.73Threonine 4.11 3.94 4.14Tryptophan 1.16 1.20 1.25Tyrosine 3.38 3.22 3.34Valine 4.79 4.93 5.02

1. Data from Thayer (1990).2. 10-MeV electron-irradiated chicken, 45-68 kGy at-25 15C.3. 60CO, gamma-irradiated chicken, 46-68 kGy at -25 15C.4. Thayer, personal communication.


39/72

- 37 -4.2.1.2 Proteins

Klein and Altmann (1972) reported some decrease in the molecularweight of so lub le protein fractions at high doses (20 to 50 kGy), but nochange at low doses (up to 7.5 kGy), under controlled temperature (4C) wasdetected in irradiated chicken meat. On the other hand, Zabielski et a l.(1984) have suggested that myosin solubility from chicken breast muscle isreduced with increasing irradiation dose (to 10 kGy), resulting in reducedwater-holding capacity. Other protein solubilities were only slightlyaltered at these doses. The temperature during irradiation in theseexperiments was very high (up to 32C), which may have affected theirresults. In contrast, Taub (1981, 1983) showed that sterilization doses atlow temperatures have only a minor effect on myosin. His findings suggestthat the irradiation of muscle proteins in meat does not lead tosignificant alteration and, therefore, is not of nutritional orphysiological concern (Taub et al. 1977). However, no data are availab leto compare the effects of gamma and electron irradiation on the structuralaspects of p ro te in s, e.g. , water-holding capacity and solubili ty.

Proteolytic enzymes are only partially inactivated at dosesrequi red for radurization (radiation pasteurization). Their inactivationdepends on irradiation temperature and dose (Shults et al. 1975). Forexample, pork irradiated at 21C loses about 75% of i ts proteolyticactivity at a dose of 20 kGy, whereas the same meat irradiated at -30Closes only about 60% of i ts activity, even when exposed to 40 kGy. Thus,the proteolytic and l ipolytic enzymes are not fully inactivated at dosesoptimum for food irradiation (Diehl 1982, Josephson 1983). In fact,i rr ad ia tion a t low doses may increase the activities of some enzymes (Diehl1982, Singh and Singh 1982). For example, the increase observed in levelsof certain vitamins (Table 7) from the irradiation of meats could be due tothe activation of relevant enzymes. Glew (1969) reported on what appearsto be a DRE on the denaturat ion of the protein ~ - l a c t o g l o b u l i n in solution,at dose rates from lOS to 10 7 Gy/s (Table 15). The results show that thehigher the dose rate the lower the degree of denaturat ion at a given dose.This denaturation effect was enhanced by the presence of oxygen (Glew 1969,results not shown). Apparently, no data on DRE on the cross-linking ofproteins in foods have been reported.


40/72

- 38 -TABLE 15

DOSE RATE EFFECT ON DENATURATION OF 1% SOLUTIONOF 8-LACTOGLOBULINl

Dose Dose Rate2(kGy) (Gy/s)1.11 x 107 1.11 X 108 1.11 x 10 9

%Protein Denatured)2.5 37 19 143.5 37 24 205.0 52 35 327.5 65 44 3810.0 73 60 5615.0 84 71 78

1. Data from Glew (1969).2. 4-HeV linear accelerator.3. Denaturation was measured as the proport ion ofprotein insoluble in 20% sodium sulphate solutionat 40'C, at pH 2.4.2.2 Carbohydrates

The carbohydrates found in foods exist in forms ranging fromaqueous solutions of simple sugars, as in fruit juices, to solid complexpolysaccharides, such as starch in potatoes. Despite these differences,their radiation chemistry is quite similar (Taub 1983). This similaritystems from the structural similarity of the sugars to each other and fromthe fact that the polysaccharides are composed of repea ting units of asmall number of sugars.

Fundamental changes that can occur in carbohydrates a re s imilarto those that take place in proteins and include decomposition(degradation) and cross-linking. Hexoses are degraded by dehydrogenationand complex polysaccharides exhibit, breaks in the glycosidic linkages.Though many of these radiolytic aspects have been investigated, very l i t t lework has been done on DRE on carbohydrates in foods. In dilute solutions,DRE is observed from the irradiation of glucose solution (Simic 1983), as


41/72

- 39 -shown by the yields (G-values) of some of i ts products (Table 16). TheG-values fo r these products are lower at the high dose rates delivered byelectron irradiation. Somogyi et al. (1975) reported work on DRE on thecarbohydrate content of two varieties of potatoes (Bintje and Haritta).The potatoes were irradiated using 3-HeV electrons (dose rate not g iven)and 60CO (dose rate 1.7 Gy/s) fo r total doses of 0.08, 1 and 1.5 kGy. Theresults for the Bintje var ie ty are shown in Figure 10. Any d if fe rences inthe resulting glucose and sucrose levels from electron and gamaairradiation are minor. However, there appears to be a larger increase inthe fructose content (Figure 10) in the case of electron irradiation thanin the case of gamma irradiation, at the higher total doses (>1 kGy). Luet al. (1987) saw somewhat greater sugar loss in onions subjected to gammairradiation (60CO; dose rate 22.8 Gy/s) than in those subjected to electronirradiation (2-HeV Van de Graaffj dose rate not given); the authors suggestthat this difference may l ie in the shallow penetration of onions by theelectron beam, as one might expect, and thus may not be a true DRE.

TABLE 16RADIOLYSIS OF AQUEOUS SOLUTION OF D-GLUCOSE:

DOSE RATE EFFECT1.2

Product G-ValueElectron3 Gamma4

D-Gluconic acid 0.80 0.90D-Arabinohexosulose 0.61 0.90D-Ribohexos-3-ulose 0.40 0.57D-Xylohexos-4-ulose 0.41 0.50D-Xylohexos-5-ulose 0.20 0.60D-Glucohexodialdose 0.90 1.551. Data from Simic (1983) .2. Radiolysis in N20/0 2 (4:1) saturated aqueous solution at roomtemperature.3. Van de Graaff, electron-irradiated 5 x 10- 3 mol.dm- 3 D-glucosesolution at 2.5 Gy/pulse (4-Hz frequency, l - ~ s pulse).4. 6Co, gamma-irradiated, 5 x 10- 3 mol.dm- 3 D-glucose solution at0.18 Gy/s.


42/72

- 40 -

-loo,..-lE--ZWI -Zooa:


43/72

4.2.3 Lipids

- 41 -

Lipids are a heterogeneous group of organic compounds that makeup a large proportion of the human diet. They are distributed widely inboth plant and animal tissue and influence many qualities of foodsincluding contributions of essential nutrients, energy, mouth-feel, flavor,and emulsifying and complexing characteristics. The physical and chemicalmakeup of lipids in foods, whether natural or added, can be greatly alteredby processing, and these changes may be either benef ic ia l or detrimental .

Lipids containing unsaturated fatty acids are readily autooxidized, and enzymatically oXidized, during normal chemical and metabolicactivity. They are also oxidized during irradiation in the presence ofoxygen. Irradiation in air produces volatile products by the process oflipid peroxidation. However, these effects can be minimized by irradiationat low temperatures (Brasch and Huber 1947, Merritt 1984, Vierbicki 1985,Singh 1987) and in the absence of oxygen (Kraybill 1982, Merritt et al.1985, Singh 1987). Most of these oxidizing reactions proceed through freeradicals (Delincee 1983; Nawar 1983; Taub 1983; Singh 1987, 1988). Some ofthe many products formed from such oxidations, such as peroxides,hydroperoxides and carbonyl compounds (ketones and aldehydes), can affectthe flavor o f meat, including the development of off-flavors (Merritt etal. 1978, Merritt and Taub 1983, Lillard 1978, Pearson et al. 1983, Pryoret al. 1976, Francis and Vood 1982, Singh 1988). However, i t is generallyreported that at low doses and controlled temperature conditions (0-5C),irradiation has no significant effect on the total fat content of foods (o fchicken, for example; Kahan and Howker 1978). Only minor differences havebeen reported in fatty acid profiles (Food Chemical News, 1987) byirradiation at 1 to 10 kGy.

As discussed in Section 2.3 above, lipid peroxidation levels infoods may be slightly lower after electron irradiation than after gammairradiation. This view is reflected in a review article by Kraybill


44/72

- 42 -(1982). Unfortunately, as there seem to be no data dfrectly comparinglipid peroxidation levels after electron and gamma irradiation, theexpectation of lower peroxidation after electron irradiation remains to betested. Vhile two studies do give the peroxide values fo r enzymeinactivated radappertized chicken rolls (Vierbicki 1985, Table 17) and beef(Raica et al. 1972), these data are not r elevant to lipid peroxidation inair , since the samples were vacuum-packaged in the absence of oxygen.

Vierbicki (1985) also published data on free fatty acids producedin low-temperature (-25 lS"C) electron- and gamma-radappertized chickenrolls (Table 17) during storage at ambient temperatures. The resultsindicated no DRE after 3 or 81 months of storage. Similarly, nosignificant DRE on total free fatty acids or individual fatty acids wasseen by Thayer (1990) in the case of radappertized chicken.

TABLE 17EFFECT OF DOSE RATE AND STORAGE ON PEROXIDE VALUE

AND FREE FATTY ACID CONTENT OF CHICKEN ROLLSl

Fat FrozenOxidation Control Gamma2 Electron3Index4

Storage Time (months)3 81 3 81 3 81

Peroxide value 38.1 1.6 11.3 0.6 14.1 0.9Free fatty acid 0.7 0.9 0.9 4.6 0.9 5.01 Data from Vierbicki, 1985. Irradiation dose 46-68 kGy at-25 15 "C.2. 60CO, dose rate -5 x 102 Gy/s.3. 10-HeV linear electron accelerator, dose rate not given but,based on Shults and Vierbicki (1980), assumed to be_106 Gy/s.4. Peroxide value as milliequivalent 02/kg fat, free fatty acidas % oleic acid in extracted fat.


45/72

- 43 -4.3 VOLATILE COMPOUNDS

As discussed above (Section 4.2.3) enzymatic reactions, autooxidation and irradiation produce small-molecular-weight volatile components, such as aldehydes and ketones, from fats that impart particularflavors to foods. Similarly, some products obtained from proteins, such assulfur-containing compounds, impart characteristic flavors to meats. Inaddition, a number of other classes of organic compounds, including furansand chlorinated compounds, are related to meat flavors and off-flavors(Ramaswamy and Richards 1982, Merritt et a l. 1978, Merritt 1984). Inirradiated meats, the undesirable components (off-flavors) are produced asa funct ion of radiation dose and temperature (Merritt et al. 1975); theirlevels are reduced by irradiation at subfreezing temperatures. Thevolatile compounds from chicken, pork, beef and other meats arequalitatively similar (Merritt 1972, Merritt et al. 1975).

The DRE on the volatiles formed from many of these meats has beencompared by Merritt (1984). The effect of irradiation at a dose of 45 kGyat -30'C, is shown by the data on the low-molecular-weight volatiles inTable 18. Although the Table indicates some differences in the absolutenumbers for various volatiles, both between gamma and electron irradiationand between different production lots, the authors suggest in one publication (Merr it t et al . 1978) that the amounts of volatile products obtainedare independent of the type of radiation used, based on the statist icalevaluation of their original data. However, i t is not clear whether thestatist ical analyses and the conclusion that no DRE is present (Merritt etal. 1978) apply to all other data reported by this group (Merritt 1984).

Data for the solvent-extracted high-molecular-weight volatilesfrom chicken are compared in Table 19 (Merritt 1984). Clearly, differentabsolute amounts of some volatiles, such as octadecenal, are produced bygamma and electron irradiation. In both the low-molecular-weight (Table18) and the high-molecular-weight (Table 19) volatile compounds, theelectron-irradiated (high dose rate) chicken samples appear to give higheryields than the gamma-irradiated samples. Also, the values of many of theproducts differ between the two production lots (Table 18). However, i t isnot clear whether these differences are important.


46/72

- 44 -

TABLE 18VOLATILE RADIOLYSIS PRODUCTS ISOLATED FROM CHICKEN MEAT

BY DIFFERENT TREATMENTS'

Prosen G.__ ElectronControl 11'1'&4. Irrad.Ro. Ib Bo . 2b Wo. I b Ro. 2b .0. I b Ro. 2b1 Ethan. 110 134 181 1962 Propane 116 129 167 2053 X-Butane 109 137 172 1954 X.abutalle 17 22 24 305 . Pantane 2 3 107 13. 157 1916 Xaopantana 11 16 H 197 . -Haxan. 9 5 173 219 24. 301 2-Methylpantana + 2 19 ]-Methylpantana +

10 .-Haptane 12 8 271 235 392 47711 . -Octane 336 331 489 58112 Jletbylbaptana 5 4 4 3 +13 . -Ronan. 101 131 153 187H X-Dacan. 135 149 20. 23215 Unclacana 182 191 210 30316 Dod.cana 242 253 373 39 '17 Tridacana 19 93 137 15118 Tetrad.cana 12 13 18 2019 Ethane 13 21 21 2620 Butane 16 23 22 2721 Pantan. 93 186 135 16422 Haxana + 67 95 81 11423 Haptane + + 115 107 169 20724 Octan. 241 156 347 42725 Wonana 51 55 79 1626 Dacan. 115 123 177 19527 unclacana 92 97 H2 15.2 ' Dod.cana 164 171 253 27129 Trid.ean. 56 59 16 9530 Tetrad.can. 15 92 109 12331 .a n na 12 H 18 2032 Toluene 1 + 2. 31 43 4833 Xylane 1 2 2 234 Methyl alcohol 31 35 48 5235 Bthy l a lcoho l 50 55 77 U36 Acatona 1 1 41 43 63 6937 But.nona + 1 16 17 25 273 . Acataldehyde 77 81 119 13139 Carbonyl sulf ide + +40 Bydro9an sulf ida + + + +41 Methyl rcaptan + + + +42 Etbyl .arcapten 6 7 3 643 Dt thyl sulf ide + + 3 4 4 344 nt t hy l d is u lf id a 16 H 15 1945 Hethyltbiophana 0 046 Ithane nitr i le + + + 047 Di thylfuran + +U Chlorofor. 12 I 13 I 1349 D.cyn. 26 25 40 U50 und.eyn. 13 15 20 2251 Dod.eyn. 6 7 9 1052 T r i ~ s . . e . d i . n . + +53 ' l ' . trad.cadi.n. 17 17 26 28

8a 4 on data of H.rritt (19 ' . ) , 9iv.n in uni t . o f . i cro9ra . of product p.rkil09ra. of chick.n at. S pl w . r. i rr a di at .d .t ~ 3 0 - c f or .SkGy t o t . l do b S p l . . f ro . two dif t .r .nt production l o t . (Ro. 1 and Ro. 2) v . r . proc d. i .u l tan .ou . ly .


47/72


48/72

- 46 -TABLE 20

DOSE RATE. TOTAL DOSE AND TIME OF IRRADIATION USED FORCOMPARATIVE SPROUT INHIBITION IN POTATOES AND ONIONS

Number of Total Dose Rate Conclusion1 ReferenceProduct Dose (Gy/s)Varieties (Gy) High LowPotatoes

3 _2 100 0.016 HDR-B Jaarma (1969)2 60 30(2)3 2.5(24) HDR-B Mathur (1963)90 30(3) 2.5(36) HDR-B1 50 6.3(7.9) 0.4(125) HDR-B Kruschev eta1. (1964)1 70 12(5.8) 1.0(70) HDR-B Metli tsky eta1. (1968)1 - 0.45 0.04 HDR-B Scheid andHeilinger(1968)1 105 83 0.083 HDR-Bt Furuta et a1.(1979)1 100-140 12.6(7.9-11) 3.16(79-110) NAD Kahan andTemkin-Gorodeiski(1968)1 50-70 16.6 0.83 NAD Kume et a1.(1976)

Onions1 20 83 0.083 HDR-Bs Furuta et al.(1979)1 100 2 MeV' 22.8 NAD Lu et al.(1987)1 30 and 16.7 0.83 HDR-B KUlle et al.50 (1977)

1. HDR-B, high dose rate is better; NAD, no apparent dose rate effect.2. Not available.3. Numbers in brackets indicate calculated times (lI in) of irradiation.4. Optillum dose rate 0.83 Gy/m.5. Optimum dose rate 0.166 Gy/m.6. Dose rate not given.


49/72

- 47 -TABLE 21

DOSE RATE EFFECT ON PERCENTAGE OF TUBER SPROUTINGIN TVO VARIETIES OF POTATOESlDose Rate (Gy/m)Potato TotalVariety Dose 0 2.5 30(Gy) Percent Sprouting

Gola 60 100 15 0Up-to-Date 90 100 20 0

1. Data taken from Mathur (1963).

Furuta et al. (1979) andKume et al. (1977) observed a DRE ononion sprouting in which a higher dose rate had a greater inhibitory effectthan a low dose rate, although Lu et al. (1987) observed no difference atthe dose relevant fo r sprout inhibition (100 Gy). The DRE on theinhibition of onion sprouting is shown in Figure 11. Furuta et a l. (1979)observed that the dose required for complete sprout inhibition on onionbulbs was about 20 Gy at a dose rate of 10 Gy/h. Below 10 Gy/h the doserequired increased rapidly, while above 10 Gy/h i t decreased slowly withincreasing dose rate (Figure 11). I t appears therefore that this is agenuine DRE, since the increase in dose rate reduced the total doserequired fo r sprouting.

5. SENSORY CHARACTERISTICS

The measurement of sensory or organoleptic characteristics andthe determination of consumer product acceptance represent very importantand necessary steps in food processing. The former is usually conducted bytrained taste panels and the latter by randomly chosen consumer groups.The two are, of course, complementary.


50/72

-C'l-oI-a l::czI-:::loa:0ena:ou.CIUJa:-::loUJa:UJenoc

40

30

20

10

- 48 -

\

Ol-..- .J . .--I-. .1-l. .L--l---1.-L.. . .L.L---l_.L-.JL.. . .L.L.-. .L.. .--L.-L-U1 10 1 10 2 10 3 10 4

DOSE RATE (Gy/h)FIGURE 11: Dose Required for Inhibition of Sprouting of Onion Bulbs After8 Months of Storage as a Function of Dose Rate. Valuesobtained during 1976-77, 0 - 0 and 1977-78, A-A . Data fromFuruta et al. (1979).


51/72

- 49 -Some data are ava ilab le on ORE on the sensory characteristics of

irradiated food. Josephson et al. (1973) have reported consumer acceptancetest results for gamma- and electron-irradiated roast beef. As the data inTable 22 show, there is no significant dif fe rence in the average preferenceratings for the two types of irradiation.

Shults and Vierbicki (1980) described t he ir r esul ts from thesensory evaluation of gamma- and electron-radappertized lamb rolls (dose47 kGy). The data in Table 23 indicate no significant differences in termsof sensory characteristics between samples irradiated at two different doserates (gamma, -5 x 102 Gy/s and electron, _106 Gy/s). Though the authorsdo not make a distinction, the scores for the frozen control appear to besomewhat better than for either of the irradiated samples. The authorsfound no change in the results shown in Table 23, whether the samples wereanalyzed after zero, one or six months of s to rage .

TABLE 22CONSUMER ACCEPTANCE OF ROAST BEEF

IRRADIATED VITH GAMMA OR ELECTRONSl

Average Preference Rating2Experiment No. ofNo. Raters 60C0 3 Electron3 Control1 32 5.5 5.4 5.52 32 6.2 5.6 6.13 32 5.4 5.8 6.04 32 6.6 5.9 6.25 32 5.6 6.3 6.06 30 5.0 5.6 4.87 30 5.8 6.3 5.4

1. Data from Josephson et al. (1973).2. Nine-point hedonic scale: 9 = like extreaely;5 = neither like nor dislike; 1 = dislikeextremely.3. Irradiation dose 47 to 71 kGy at -30 10C.


52/72

- 50 -TABLE 23

SENSORY CHARACTERISTICS OF GAMHA- AND ELECTRONIRRADIATED LAMB ROLLSl

Sample Discolora tion Off- Irradia tion MushinessOdor FlavorGalllllll 1.9 0.81 1.9 0.99 2.0 1.20 2.4 1.29Electron 1.7 0.70 2.1 0.99 2.0 1.50 2.4 1.50Frozen control 1.0 0.00 1.0 0.00 1.0 0.00 1.6 0.731. Data from Shults and Vierbicki (1980). Irradiation dose 47 kGy at-30 10'C; seven-member trained panels, probably nine-point scale.

Characteristics ranged from 1 = none, 2 = trace, 3 = slight to 9 =extreme. Gamma dose rate, -5 x 10 2 Gy/s; electron dose rate (10-MeVLINAC), _106 Gy/s.Vierbicki (1985) has published the results of expert panel

evaluation (Table 24) and consumer acceptance (Table 25) of gamma- andelectron-radappertized chicken meat. In general, no significant

TABLE 24EXPERT PANEL EVALUATION OF DOSE RATE EFFECT ON THE SENSORYCHARACTERISTICS OF ENZYME-INACTIVATED RADAPPERTIZED CHICKEN MEATl

Overall Score2Treatment Colour Odor Flavor TextureGamma3 6.28b 0.736 6.04' 0.536 5.43' 0.386 5.40b 0.586Electron 6.3Gb 0.73 5.98' 0.58 5.40 b 0.56 5.35b 0.54FCs 6.45b 0.44 6.68b 0.48 6.4Gb 0.47 6.11 c 0.42

1. Data from Vierbicki (1985).2. Expert panel, n = 10; Average data for 4 storage times x 2 prepara-tions fo r serving (n = 80). Details of cooking conditions not given.3. 60CO, dose rate - 5 x 102 Gy/s.4. 10-MeV LINAC _106 Gy/s (Shults and Vierbicki 1980).5. Frozen control.6. Mean values with different superscripts in the same column (a, b, c)are signif icantly different (P < 0.05).


53/72

- 51 -TABLE 25

CONSUMER PREFERENCE RATINGS OF GAHHA- ANDELECTRON-IRRADIATED CHICKEN HEATl

Treatment2 RatingServed ColdGamma-irradiated 5.00" 1.643Electron-irradiated 4.62" 1.77Frozen control 6.37b 1.60Served ReheatedGamma-irradiated 5.78" 1.64Electron-irradiated 5.91" 1.91Frozen control 6.88b 1.45

1. Data from Vierbicki (1985). Nine-point hedonic scale: 9 =like extremely; 5 = neither like nor dislike; 1 = dislikeextremely.2. Gamma irradiation dose 56 kGy (dose rate - 5 x 102 Gy/s) andelectron irradiation dose 59 kGy (dose rate - 106 Gy/s; Shultsand Vierbicki 1980); i rrad ia tion a t -30C; the unirradiatedcontrols from the same batch were kept frozen at -29C untilrequired.3. Hean values with different superscripts (a, b) in the samecolumn are significant ly different (P < 0.05).

differences were found between gamma- and electron-irradiated chickenmeat in e ith er set of data (Table 24 and 25). The consumer preferenceratings for (electron- or gamma-) irradiated chicken meat weresignificantly lower than those fo r the controls, part icularly in the caseof chicken meat served cold (Table 25). Vierbicki (1985) reported betterconsumer preference ratings in a subsequent run involving a lowerradappertization dose (45 to 55 kGy) and a better temperature control(-30 10C).

Lu et al. (1987) have reported a comparison of onions irradiatedto doses of 5 kGy with either an electron or a gamma source (Table 26).Even though the authors report some differences at the 5% level, theiroverall evaluation is that there are no major differences.


54/72

- 52 -TABLE 26

SENSORY EVALUATION OF GAHHA- AND ELECTRON-IRRADIATEDVALLA VALLA ONIONSl

Irradiation Fresh Cooked 2Treatment Dose Firmness Flavor Taste Firlllless Flavor Taste(kGy)None 0 7.0 6.7b 6.4 6.4 4.Sb 4. geElectron 0.1 6.1 7.3 6.S 7.3 7.3 7.0(2 MeV) 1.0 6.6 6.7 b 6.6 5.93 5.5 b 5.4be2.0 6.S 5.6b 6.4 7.0- 6.5 b 7.0

3.0 6.7 6.7 b 6.7 S.6 6.6 b 5.7 b5.0 6.7 5.6b 5.9 7.0 6.2 b 6.7 bNone 0 6.6 be 6.4 6.6 b 7.1 6.5 7.0Gamma 0.1 6.2 be 6.0 6.0b 6.S b 6.3 6.5(22.S Gy/s) 0.3 7.4 7.3 7.6 S.O 7.3 7.0LO 7.0 b 7.2 7.1 b 6.4 b 5.5 5.92.0 6.S be 6.6 6.5 b 6.7 b 6.2 5.93.0 5.6 e 6.5 6.Qb 5.5b 5.7 5.51. Data from Lu et al. (19S7). A nine-point hedonic scale was used forsensory evaluation: 9 = like extremely; 1 = dislike extremely. Mean

values with the same superscripts (a, b, c) in the same columns are notdifferent (P < 0.05).2. Chopped onions were cooked fo r 2 min at 250C.

6. CONCLUSIONS

Basic mechanistic considerations suggest that, although the lossof key micro- and macronutrients in dilute solut ions are expected to belower froll electron irradiation (high dose rate) than froll gammairradiation (low dose rate), the difference, i f any, should be negligiblefor irradiated foods. Experimental data comparing gamma and electronirradiation of foods, though rather limited, do support this expectation.Available results give no ind icat ion of any DRE on aaino acids, proteins,carbohydrates, fats, or most of the vitamins in irradiated foods. However,a DRE favoring electron irradiation over gamma irradiation has beenreported in two processes:


55/72

- 53 -

(1 ) Thiamin loss in pork and other meats is significantly lower fromelectron irradiation than from gamma irradiation, at lowtemperatures (-15 to -4SC). Spur diffusion is much slower atthese temperatures than at OC, le ad ing to significant spuroverlap in the case of electron irradiation. In comparison, nospur overlap is lik ely in the case of gamma irradiation at lowtemperatures, even with slower spur diffusion. Hence theobserved DRE on thiamin in the low-temperature irradiation ofmeats, favoring electron irradiation.

(2 ) Sprouting in potatoes and onions is inhibited more effectively byelectron irradiation than by gamma irradiation. However, themechanistic reasons fo r th is e ff ec t are unknown.Mechanistic considerations suggest that electron irradiation may

also be favoured over gamma irradiation for foods normally i rr ad ia ted inair , since electron irradiation should result in lower peroxidation levelsin the food. However, experimental data supporting such a conclusion areunavailable.

Vhile computer modelling of irradiation of simple systems isbeing done, no data are available from which to predict a DRE in the caseof irradiated foods on this basis.

Somewhat higher amounts of volatile compounds appear to begenerated by electron irradiation than by gamma irradiation. However, i tis not certain whether the dif ferences are significant and outside theoverall experimental error.

The sensory characteristics, as judged by expert panels and ratedby consumer acceptance panels, show no significant differences betweengamma- and electron-irradiated foods, thus supporting the overallconclusion that the two irradiation methods are equally effective.

,.J


56/72

- 54 -ACKNOVLEDGEHENTS

I t is a pleasure to thank Dr. Ajit Singh for discussions on thebasic aspects of DEE. I thank Dr. John Barnard for providing informationon dose rates of irradiators and Drs. Jos. Borsa, Stu Iverson and KishorHehta for comments on this manuscript.

REFERENCES

Adem, E., R.H. Uribe, and F.L. Vatters.survival of two insect species whichRadiat. Phys. Chem. 14, 663.1979. Dose rate e ffec ts oncommonly infest stored corn.

Ames, S.R. 1972. Tocopherols. In The Vitamins, Vol. V (V.H. Sebrell, Jr .and R.S. Harris, eds.). Academic Press, New York, 233-247.Anbar, H. , H. Bambenek, and A.B. Ross. 1973. Selected specificreactions of t rans ient s from water in aqueous solution. 1.electron. National Standard Reference Data Series Report,NSRDS-NBS 43.

rates ofHydrated

Anbar, H. , Farhataziz, and A.B. Ross.reactions of transients from wateratom. National Standard Reference1975. Selected speci fic rates ofin aqueous solution. I I . HydrogenData Series Report, NSRDS-NBS 51.

Archer, H.C. and S.R. Tannenbaum. 1979. Vitamins. In Nutr it ional andSafety Aspects of Food Processing (S.R. Tannenbaum, ed.). Food ScienceSeries, Vol. 6. Harcel Dekker, Inc., New York, 47-96.Armstrong, R.C. and A.J. Swallow. 1969. Pulse- and gamma-radiolysis ofaqueous solutions of tryptophan. Radiat. Res. 40, 563.Bailey, A.J. 1967.temperature and

Res. 11, 206.Irradiation-induced changes in the denaturationintermolecular cross-linking of tropocollagen. Radiat.

Bailey, A.J., D.N. Rhodes and C.V. Carter. 1964. Irradiation-inducedcrossl inking of col lagen. Radiat. Res. 22, 606.Basson, R.A. 1983. Recent advances in radiation chemistry of vitamins.In Recent Advances in Food Irradiation (P.S. Elias and A.J. Cohen,eds.). Elsevier Biomedical, Netherlands, 189-216.


57/72

- 55 -Beyers, H., A.C. Thomas and A.J. Van Tonder. 1979. Gamma-irradia tion ofsubtropical fruits . I . Compositional tables of mango, papaya, strawberry, and l i tchi fruits at the edible-ripe stage. J. Agric. FoodChem. 27, 37.Biaglow, J.E., H.E. Varnes, E.R. Epp, E.P. Clark, S. Tuttle, and K.D. Held.1988. Cellular protection against damage by hydroperoxides: role ofglutathione. In Oxygen Radicals in Biology and Hedicine (H.G. Simic,K.A. Taylor, J.F. Vard and C. von Sonntag, eds.). Plenum Press, NewYork, 567-573.Bielski, B.H.J., D.E. Cabelli, R.L. Arudi and A.B. Ross. 1985.of HOz/Oi radicals in aqueous solution. J. Phys. Chem. Ref.1041.

ReactivityData 14,Bowes, A. de P., C.F. Church and H.N. Church. 1975. Food Values ofPortions Commonly Used (12th ed.). J .B. Lippincot t Company, New York,138.Brasch, A. and V. Huber. 1947. Ultrashort application time of penetra tingelectrons: a tool for sterilization and preservation of food in the rawstate. Science lOS, 112.Buxton, G.V., C.L. Greens tock, V.P. Helman and A.B. Ross. 1988. Crit icalreview of rate constants for react ions of hydrated electrons, hydrogenatoms and hydroxyl radicals (.OH/.O') in aqueous solution. J. Phys.Chem. Ref. Data lI , 513.Chung, 0., K.F. Finney and Y. Pomeranz. 1967. Lipids in flour from gamma-irradiated wheat. J. Food Sci. 32, 315.Codex Alimentarius Commission. 1983. The microbiological safety ofirradiated food. (CX/FH 8319).Davies, K.J.A. 1988. A secondary antioxidant defense role fo r proteolyticsystems. In Oxygen Radicals in Biology and Hedicine (H.G. Simic,K.A. Taylor, J.F. Vard and C. von Sonntag, eds.). Plenum Press, NewYork, 575-585.Davis, K.C. 1972. Vitamin E: adequacy of infant diets. Am. J. Clin.Nutr. 25, 933.Day, E.J., H.D. Alexander, H.E. Sauberlich and V.D. Salmon.

of gamma radiation on certain water-soluble vitamins inbeef. J. Nutr. 62, 27.1957. Effectsraw ground

Delincee, H. 1983. Recent advances in radiat ion chemistry of proteins.In Recent Advances in Food Irradiation (P.S. Elias and A.J. Cohen,eds.). Elsevier Biomedical, Netherlands, 129-147.Diehl, J.F. 1970. Effect of ioniZing radiation on vitamin E in foods, ontocopherol and on tocopherol acetate. Influence of different radiationconditions. Z. Lebensm. Unters. Forsch. 142, 1.


58/72

- 56 -Diehl, J.F. 1975. Thiamin in irradiated foods. I . Influence ofdifferent radiation conditions and of time after irradiation. Z.Lebensm. Unters. Forsch. 157, 317.Diehl, J.F. 1979a. Effect of various irradiation conditions and storage

on radiation-induced vitamin E losses in foods. Chem. Hikrobiol.Technol. Lebensm. 2, 65.Diehl, J.F. 1979b. Reduction of radiation-induced vitamin E and B1 lossesby irradiation of foods at low temperatures and by exclusion ofatmospheric oxygen. Z. Lebensm. Unters. Forsch. 169, 276.Diehl, J.F. 1982. Radiolytic effects in foods. In Preservation of Foodby Ionizing Radiation, Vol. I (E.S. Josephson and H.S. Peterson, eds.).

CRC Press, Inc., Boca Raton, FL, 279-357.Diehl, J.F. and Ch. Kim. 1981. Formation of vitamin E-destroyingsubstances during aerobic s to rage of electron-irradiated or heated

sunflower oil . Lebensm. Viss. Technol. 14, 82.Diehl, J.F. and H. Scherz. 1975. Estimation of radiolytic products as abas is for evaluating the wholesomeness of irradiated foods. Int. J.Appl. Radiat. Isot. 26, 499.Dollar, A.H., H. Hanaoka, J.H. Hoy, A.D. Cinnamon, E. Hammill, D. Helber,S.T. Hsia, and N. Venkam. 1970. Physiological, chemical and physicalchanges during ripening of papaya. In Hawaii food irradiation programfo r the period June 1, 1968 to June 30, 1969, contract Nos. AT(26-1)374 and AT(04-3)-235, project agreement No.5. Division of IsotopesDevelopment, U.S. Atomic Energy Commission, Vashington, DC, 85-128.Dorfman, L.H., I.A. Taub and R.E. Buhler. 1962. Pulse radiolysis studies.I . Transient spectra and reaction-rate constants in irradiated aqueoussolut ions o f benzene. J. Chem. Phys. 36, 3051.Draganic, I.G. and Z.D. Draganic. 1971. The Radiation Chemistry of Vater.Academic Press, New York.Erdman, J.V. Jr . , and B.P. Klein. 1982. Harvesting, processing andcooking influences on vitamin C in foods. Advances in Chemistry 200(Ascorbic Acid: Chemistry, Hetabolism, and Uses), 499-532.Farhataziz, and A.B. Ross. 1977. Selected speci fic r ates of r eact ions o ftransients from water in aqueous solution. III . Hydroxyl radical and

perhydroxyl radical and their radical ions. National StandardReference Data Series Report, NSRDS-NBS 59.Fennema, O.R. 1985. Food Chemistry (2nd ed.). Harcel Dekker, Inc., NewYork.Food Chemical News. 1987. Nutrient loss during irradiation tied to meat,poultry temperature and changes in polyunsaturated fat levels inirradiated chicken. April 27, 42.


59/72

I

- 57 -Fox, Jr . , J.B., D.V. Thayer, R.K. Jenkins, J.G. Phillips, S.A. Ackerman,G.R. Beecher, J.H. Holden, F.D. Horrowand D.H. Ouirbach. 1989.Effect of gamma irradiation on the B vitamins of pork chops and chickenbreasts. Int. J. Radiat. BioI. 55, 689.Franc is , B .J . and J.F. Vood. 1982. Changes in the nutritive content andvalue of feed concentrates during storage. In Handbook of NutritiveValue of Processed Foods, Vol. II (H. Recheigl, Jr . , ed.). CRC Press,Inc., 161-189.Friedman, L., G.H. Shue, C.D. Douglas and D. Firestone. 1961.effects of feeding rats non-urea-adducting (urea-filtrate)Fed. Proc. 20, 369.

Acutefatty acids.Frumkin, H.L., L.P. Kovalskaya and S.Y. Gelfand. 1973. Technologicalfoundations fo r radiation treatment of food products. Cited inNutritional aspects of food irradiation: an overview. J. Food Process.Preserv. Z, 299.Furuta, J . , E. Hiroaka, S. Okamoto, H. FUjishiro and T. Kanazawa. 1979.The gamma-ray dose-rate effect in the sprout inhibition of onion andpotato. Annu. Rep. Radiat. Cent. Osaka Prefect., Vol. 19, 69-73. ISSN0474-7879.Glew, G. 1969. Changes in enzyme activity and protein solubility duringstorage after radiation treatment. In Enzymological Aspects of FoodIrradiation. Proceedings of a panel. Leeds University, Leeds,England, 83-90.Graham, H.D. 1980. Safety and wholesomeness of irradiated foods. In The

Safety of Foods (2nd ed.). AVI Publishing Co., Vestport, CT, 546-592.Griffiths, H.R., J. Lunec, D.R. Blake, and R.L. Villson. 1988. Freeradical denaturat ion of immunoglobulin G due to amino acid oxidation:implications for rheumatoid arthritis. In Oxygen Radicals in Biologyand Hedicine (H.G. Simic, K.A. Taylor, J.F. Yard and C. von Sonntag,eds.). Plenum Press, New York, pp. 357-360.Hannah, K.V. and H.G. Simic. 1985. Long-term preservation of bacon byhigh-energy electrons. Radiat. Phys. Chem. 25, 167.Hannan, R.S. 1955. Scientific and technological problems involved inusing ionizing radiations fo r the preservation of food. Spec. Rep. No.

61, Her Hajesty's Stationery Office, London.Hansen, P.I.E. 1966. Radiation treatment of meat products and animal byproducts. In Proceedings of a Symposium on Food Irradiation, IARA/FOA,STI/PUB 127, 411-426.Herting, D.C. and E.E. Drury. 1969. Alpha-tocopherol content of c erealgrains and processed cereals. J. Agr. Food Chem. 17, 785.


60/72

- 58 -Jaarma, H. 1969. Effect of ion iz ing radiations on inhibition of sp rout ingand biochemical and physiological changes in potato tubers, Riso Report16, Danish Atomic Energy Commission, Riso, Denmark, 70. Cited inP. Thomas. 1984. Radiation preservation of foods of plant origin.Part 1. Potatoes and other tuber crops . In CRC Critical Reviews inFood Science and Nutrition, Vol. 19, 327-379.Jenkins, R.K., D.V. Thayer and T.J. Bansen.irradiation and post-irradiation cookingcontent of fresh pork. J. Food Sci. 54,

1989. Effect o f low-doseand storage on the thiamin1461.Johnson, B.C. and K. Hoser. 1967. Amino acid des truc tion in beef by highenergy electron beam irradiation. Advances in Chemistry 65 (RadiationPreservation of Foods), 171-179.Jonah, C.D. and J.R. Hiller. 1977. Yield and decay of the OH radical from200 ps to 3 ns. J. Phys. Chem 81, 1974.Josephson, E.S. 1983. Radappertization of meat, poultry, finfish,shellfish, and special diets. In Preservation of Food by IonizingRadiation, Vol. III (E.S. Josephson and H.S. Peterson, eds.). CRCPress, Inc., Boca Raton, FL, 231-251.Josephson, E.S., A. Brynjolfsson, E. Vierbicki, D.B. Rowley, C. Herritt

Jr . , R.V. Baker, J .J . Killoran, and H.H. Thomas. 1973.Radappertization of meat, meat products and poultry. In RadiationPreservation of Food. International Atomic Energy Agency, Vienna,STI/PUB/317, 471-489.Josephson, E.S., H.H. Thomas and V.K. Calhoun. 1978. Nutritional aspectsof food irradiation: an overview. J. Food Process. Preserv. 1, 299.Kahan, R.S. and J.J. Howker. 1978. Low-dose irradiation of fresh, nonfrozen chicken and other preservation methods for shelf-l ife extensionand for improving i ts public-health quality. In Food Preservation byIrradiation. Proceedings of an international symposium jointlyorganized by the IABA, the FAO and the VHO, Vageningen, 21-25 November,1977, Vol. II . International Atomic Energy Agency, Vienna,IABA-SH-221/36, 221-242.Kahan, R.S. and N. Temkin-Gorodeiski. 1968. Storage tests and sproutingcontrol of up-to-date variety potatoes and on an experimental onionvariety (Beit Alpha). In Preservat ion o f Fruits and Vegetables byRadiation. International Atomic Energy Agency, Vienna, 29-37.Kent, J.A., G.B. Taylor, V.R. Boyle and A.V. Vinston. 1968. Radiationinduced polymerization of vinyl monomers impregnated in wood. Chem.Eng. Prog. Symp. Ser. 65, 137.Klein, V. and H. Altmann.proteins from chicken135.

1972. Investigations of changes in the solublemeat after ionizing irradiation. Kerntechnik 14,


61/72

- 59 -Klots, C.E. 1968. Energy deposition mechanisms. In Fundamental Processesin Radiation Chemistry (P. Ausloos, ed.). Interscience Publishers, NewYork, 1-57.Kraybill, H.F. 1982. Effect of processing on nutritive value of foodirradiation. In Handbook of Nutritive Value of Processed Food, Vol. I(H. Recheigl, Jr . , ed.). CRC Press, Inc., 181-208.Kruschev, V.G., B.A. Rubin, L.V. Hetlitsky, A.I. Rytov, N.H. Gaisin,U. Ya. Hargulis, V.S. Grammatikati, G.V. Flasov, A.V. Petrov. 1964.Gamma unit for continuous irradiation of potatoes. In Proceedings ofthe Tashkent Conference on the Peaceful Uses of Atomic Energy, Vol. II ,239. Cited in P. Thomas. 1984. Radiation preservation of foods ofplant origin. Part 1. Potatoes and other tuber crops. In CRCCritical Reviews in Food Science and Nutrition, Vol. 19, 327-379.Kume, T., H. Tachibana, S. Aoki and T. Sato.

dosage and dose rate in sprout inhibitionResearch Institute Report, JAERI-H-6408.1976. Effective gamma rayof potatoes. Japan Atomic

Kume, T., H. Tachibana, S. Aoki, K. Umeda and T. Sato.dose and dose rate of gamma radiation on the sproutonions, J. Jpn. Soc. Food Sci. Technol. 24, 37.1977. Effects o finhibition of

Lester, G.E., and D.A. Volfenbarger. 1990. Comparisons of cobalt-60 gammairradiation dose rates on grapefruit flavedo tissue and on Hexicanfruit fly mortality. J. Food Prot. 53, 329.Liebster, J. and J. Kopoldova. 1964. The radiation chemistry of aminoacids. Adv. Radia t. BioI. 1, 157.Lillard, D.A.in foods.Symposium

1978. Chemical changes involved in the oxidation of lipidsIn Lipids as a Source of Flavor, (H.K. Supran, ed.). ACSSeries 75. American Chemical Society, Vashington, DC, 68-80.Lu, J.Y., C. Stevens, P. Yakubu, P.D. Loretan, and D. Eakin. 1987. Gamma,electron beam and ultraviolet radiation on control of storage rots andquality of Valla Val la onions. J. Food Process. Preserv. 12, 53.Lu, J.Y., P. Hiller and P.A. Loretan. 1989. Gamma radiation dose rate andsweet potato quality. J. Foo

revisión del efecto de la tasa de dosis en la irradiación de alimentos.pdf

Documents