인간의 삶과 역사 속의 미생물

2010-2 학기

강의자료 ppt-6

미생물은어떤 존재인가?

The Impact of Microorganisms on Humans

음식물과 미생물

Microorganisms and food production

• Many common foods are produced or enhanced by the actions of microbes

– Fermentation is the anaerobic catabolism of organic com-pounds (generally carbohydrates)

– Important bacteria in the fermented food industry are lactic acid bacteria, propionic acid bacteria, and acetic acid bac-teria

– Products of fermentation include yeast bread, cheese, yo-gurt, buttermilk, sausage, sauerkraut, and soy sauce

Fermented foods

• Most wine is made from grapes• Wine fermentation occurs in fermentors ranging in size

from 200 to 200,000 liters– Fermentors are made of oak, cement, glass-lined steel, or

stone• White wine is made from white grapes or red grapes that

have had their skin removed• Red wine is aged for months or years• White wine is often sold without aging

Wine

racking – removes sedi-ments

or

Wine making

Commercial wine making

Equipment for Transporting Grapes to the Winery for Crushing

Large Tanks Where the Main Wine Fermentation Takes Place

Comercial wine making

Large Barrel Used for Aging Wine in a Large Winery

Commercial wine making

Smaller Barrels Used for Aging Wine in a Small French Winery

Commercial wine making

• Brewing is the term used to describe the manufac-ture of alcoholic beverages from malted grains

• Yeast is used to produce beer• Two main types of brewery yeast strains

– Top yeast — ales – Bottom yeast — lagers

Brewing, distilling and commodity alcohol

• Lager beer – Use bottom yeasts (e.g. Saccharomyces pastorianus, S. carlsbergensis)

• Fermentation: 8-14 days at 6-12oC• Aged several weeks at -1oC

• Ales– Use top yeasts (Saccharomyces cerevisiae)

• Fermentation: 5-7 days at 14-23oC• Aged for short periods at 4-8oC

* CO2 usually added at bottling

* Beer can be pasteurized or sterilized by filtration

Lager beer and ales

(pitched)

Beer production

Brewing Beer in a Commercial Brewery

The copper brew kettle is where the wort is mixed with hops and then boiled. From the brew kettle, the liquid passes to large fermentation tanks where yeast ferments glucose to ethanol plus CO2.

Brewing Beer in a Commercial Brewery

If the beer is a lager, it is stored for several weeks at low temperature in tanks where particulate matter, in-cluding yeast cells settle.

The beer is then filtered and placed in storage tanks from which it is packaged into kegs, bottles, or cans.

Brewing Beer in a Commercial Brewery

• Distilled alcoholic beverages are made by heating

previously fermented liquid to a temperature that

volatilizes most of the alcohol

– Whiskey, rum, brandy, vodka, gin

Distilled spirits: Dark rum, Brandy, and whiskey (left to right)

• Zymomonas– A bacterium that carry out vigorous fermentation of

sugars to ethanol– Used in production of fermented beverages (e.g.

pulque in Mexico)

Ethanol production using Zymomonas

Korean traditional alcoholic beverages

• 막걸리• 동동주• 기타 전통주 : 홍로주 , 문배주 , 안동소주 , 이강주 , 복분자주 , 가양주 등

• Citric acid– A widely used food industry additive

• Supplement in beverages, confections, and other foods• Used in leavening of bread

Citric acid and other organic compounds

• Majority of fermented milk products rely on lactic acid bac-teria belonging to the genera Lactobacillus, Lactococcus, Leuconostoc, Streptococcus, and Bifidobacterium

Fermented milks

Lactobacillus helveticus

Lactobacillus delbrueckii sub. bulgaricus

Lactobacillus lactis

Bifidobac-terium

milklactic acid bacteria and rennin

curd removal of whey

ripening by microbial action cheese

Cheese production

Major types of cheese and microorganisms used in their production

Gouda cheese

Cheddar cheese

Roquefort cheese(goat cheese; Penicillium)

Swiss cheese(Propionibacterium)

Brie cheese (soft/ripened; Penicillum camemberti)

Limburger cheese (soft/ripened; Bre-bibacterium linens)

Cottage cheese (soft/un-ripened)

cream cheese (soft/unripened)

Cheddar cheese production

• Sausages• Hams• Bologna• Salami• Izushi – fish, rice, and vegetables

(Lactobacillus spp.)• Katsuobushi – tuna (Aspergillus glaucus)• 가자미 식혜

• 젖갈

Fermented meat and fish

• Involves growth of Saccharomyces cerevisiae (baker’s yeast) under aerobic conditions– maximizes CO2 production, which leavens bread

• Other microbes used to make special breads (e.g., sourdough bread)

Production of breads

된장 , 청국장 , 고추장 , 간장 등 / cocoa

Fermented foods produced from fruits, vegetables, beans, and related substrates

– Results from conversion of ethyl acohol to acetic acid– Incomplete oxidation of ethyl alcohol

Vinegar

• Acetic acid bacteria– Commonly found in alcoholic juices– Some can synthesize cellulose (Acetobacter xylinum)

Diagram of a vinegar generator

• Variety of bacteria, yeasts, and mushrooms are used as animal and human food sources

• Probiotics– microbial dietary adjuvants : e.g. Spirulina, lactic acid bacteria, etc. – microbes added to diet in order to provide health benefits

beyond basic nutritive value

Microorganisms as foods and food amendments

• Immunodilation• Control of diarrhea• Anticancer effects• In beef cattle

– Lactobacillus acidophilus decrease E. coli (O157:H7)

• In poultry– Bacillus subtilis limit Salmonella colonization of the

gut by the process of competitive exclusion

Benefits of probiotics

• Lactic acid bacteria– Lactobacillus and Bifidobacterium– addition of microbes to the diet to improve health be-

yond basic nutritive value

Bifido-amended dairy products

Bacteria as probiotics

• Spirulina

Bacteria as probiotics

• Chlorella

Algae as probiotics

• Yeast for baking or nutritional purposes are grown in aerated fermentor ( 醱酵槽 )– Molasses ( 糖蜜 ) is the major ingredient of growth

medium• Cells are recovered from broth by centrifugation

– Compressed yeast cakes– Active dry yeast– Nutritional yeast

Yeast as a food and food supplement

Stages in industrial production of yeast cells

Mushroom as a food source

Agaricus bisporus The shitake mush-room, Lentinus edulus

Microorganisms and food spoilage

Spoilage of a dairy product

Spoilage of bread and corn

Both are spoiled by fungi

Bread also can be spoiled by Bacillus species that produce ropiness

• Food Spoilage– Any change in appearance, smell, or taste of a food product

that makes it unpalatable to the consumer– Food may still be safe to eat, but is regarded as unacceptable

• The chemical composition of a food determines its susceptibility to microbial spoilage– Perishable– Semiperishable– Nonperishable

Microbial growth and food spoilage

Food classification by storage potential

• Susceptibility to food spoilage is based in large part on moisture content– Perishable foods have higher moisture content than non-

perishable foods• Fresh foods are spoiled by both bacteria and fungi

– Spoilage organisms are those that can gain access to the food and use the available nutrients

– I.e., E. coli frequently contaminates meat products be-cause it is found in animals’ digestive tracts

Microbial growth and food spoilage

• Methods for slowing spoilage and foodborne disease– Cold– Pickling and acidity– Drying and dehydration– Heating– Aseptic food processing– Chemical preservation– Irradiation

Food preservation

• Removal of microorganisms– Usually achieved by filtration

– Commonly used for water, beer, wine, juices, soft drinks, and other liquids

Food preservation

• Cold– Slows microbial growth rate and delays spoilage

– Psychrotolerant bacteria can grow at refrigerator temper-atures

– Freezing allows for longer storage, but isn’t suitable for all foods

Food preservation

• Pickling and Acidity– pH is an important factor in microbial growth

– Most foods are neutral or acidic

– At pH less than 5 most spoilage organisms are inhibited

– During pickling process acetic acid is added to a solution with sugar or salt

• Pickled foods include pickles, fish, peppers and fruits

Food preservation

• Drying and Dehydration– Moisture content is critical for microbial metabolic pro-

cesses– Sugar and salt reduce the availability of water for micro-

bial growth (in effect, dehydrating it)• I.e., jams, jellies, meats, fish

– Lyophilization (freeze-drying) is the physical removal of frozen water under vacuum

• Very expensive, but very effective

Food preservation

• Heating– Used to reduce the bacterial load (i.e., pasteurization) of

a product or to actually sterilize it (i.e., canning)

– Canning isn’t always 100% effective• Results in swollen cans (DO NOT EAT!)

Food preservation

• Kills pathogens and substantially reduces number of spoilage organisms

• Different pasteurization procedures heat for different lengths of time– shorter heating times result in improved flavor

Pasteurization

Canning

• Food heated in special containers (retorts) to 115°C for 25 to 100 minutes

** Spoilage of canned goods• spoilage prior to canning• underprocessing• leakage of contaminated water into cans during cool-

ing process

Changes in sealed cans as a result of microbial spoilage

• Aseptic Food Processing– Several foods are now processed and packaged asepti-

cally

– This food can be stored on shelves for months or longer

– Involves flash heating and packing in sterile containers

– I.e., juice boxes and milk substitutes

Food preservation

• Chemical Preservation– Over 3,000 compounds are used as food additives

– A small number of these are used to control microbial growth

• I.e., sodium propionate, sodium benzoate, nitrites, etc.

• Some, such as nitrates, are controversial because stud-ies show they may be harmful to human health

– Significantly extends shelf life of finished foods

Food preservation

Chemical Food Preservatives

• Bacteriocins– bactericidal proteins active against related species : some inhibit energy generation of susceptible bacteria : some form pores in plasma membranes : some inhibit protein or RNA synthesis

e.g., nisin - used in low-acid foods to inactivate Clostridium botulinum during canning process

Microbial product-based inhibition

Food preservation

• Irradiation– Food is irradiated with ionizing radiation to reduce bacte-

rial, fungal, and insect contamination

– Uses gamma or beta radiation, or X-rays

– Irradiated foods must be labeled

Food preservation

The Radura, the International Symbol for Radiation

Irradiated Foods by Category, Dose, and Purpose