Characterization of a Low Glycemic

Index Potato Cultivar

Kai Lin Ek

Jennie Brand-Miller, Shujun Wang

Glycemic Index Foundation

Agrico Holland

Mitolo Group (Australia)

Les Copeland

University of Sydney, Australia

Faculty of Agriculture and Environment Research Symposium 15 July 2014

Grand challenges

Increase food supply

- 70% more food by 2050

Foods that deliver health benefits

- about one third of disease burden in Australians is related to poor diet

- over 30% of adults are obese, 25% have diabetes or pre-diabetes

Managing disease risks through diet

• Preventative• Small effects on many targets

• Changing the types of foods consumers eat will be difficult • Need to produce acceptable foods with health-promoting ingredients- carbohydrates with better glycemic control, prebiotic effects - oils to reduce saturated and trans fats, improved omega oils- increased bioavailability of micronutrients- reduced allergens

• Moderate glucose release• Increase satiety• Promote healthy gut microbiota

Dietary carbohydrates

• Source of energy, prebiotics, fibre for monogastric digestion

• Starch - 50-70% of dietary energy- source of essential pre-formed glucose

• The type of starch we eat has health implications

• Rapidly digested starch- high postprandial blood glucose levels, elevated insulin response, increased

risk of diseases

• Slowly digested starch- moderated glucose release

Measuring blood glucose-raising potential

• Glycemic Index- nutritional concept for ranking

carbohydrate-containing foods- measures a combination of physiological

processes

• Model systems ... simple to complex- measure glucose release under controlled

conditions as an alternative to GI testing- simulate digestion, but difficult to mimic

physiology- starch classified as rapidly digested, slowly

digested, resistant starch

• Resistant starch passes into the lower gut- good prebiotic, has no glycemic effect

MONA, Hobart

Potatoes

• Third most important human food crop

• Annual global production exceeds 3,000 million tonnes

• High biomass production- 40-50 tonnes tubers/ha ( 9 t dry matter/ha)- starch is 66-80% of dry matter

• Annual per capita consumption- 93 kg in Europe - 60 kg in North America- 22 kg in China

• Low GI potatoes will have health benefits

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Van Gogh, The Potato Eaters

Glycemic testing of potatoes

• Potatoes were peeled and cut into 5 cm slices

• Cooked in excess boiling water for 8 mins, drained and cooled by rinsing in tap water

• GI testing- potatoes served immediately as a portion of

25 g of available carbohydrate with 250 ml of water

- ISO standard method, using 25 g glucose in 250 ml of water as reference food

• In vitro enzymic digestibility of starch in cooked potatoes

Cultivar GI ClassificationCarisma 53 ± 7 LowNicola 69 ± 5 MediumDesiree 74 ± 8 HighRusset Burbank 82 ± 3 HighVirginia Rose 93 ± 10 HighBintje 94 ± 8 HighMaiflower 103 ± 8 High

GI of seven potato cultivars

o Glucose• Potato

CA RBDE

Carisma is a low GI potato

• First commercially grown low GI cultivar

• Bred by Agrico (Netherlands)

• Selected for firm cooking quality, size, agronomy

• Noticed by chef/potato grower with knowledge of nutrition (Graham Liney)

• Carisma was not differentiated from high GI cultivars by

- dry matter, total starch, reducing sugar and fibre content of the potato

Why is Carisma low GI?

Differences in potato tissue?

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Carisma

Russet Burbank

Thickness of cell walls?

Why is Carisma low GI?

Differences in potato starch?

•Good correlation between GI value and in vitro starch hydrolysis•Carisma starch has higher melting temperature than the other starches

•Carisma was not differentiated by- starch granule size distribution- amylose content of starch- relative crystallinity of starch- phosphate content of starch- amylopectin chain length distribution

•Differences likely to be at level of starch fine structure

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CA

NI

DE

RB

VR

BJ

MF

-9

-8.5

-8

-7.5

-7

-6.5

-6

-5.5

-5

-4.5

-4

50 60 70 80 90

End

oth

erm

ic h

eat

flow

(W

/g)

Temperature ( C)⁰

Carisma

Starch is made up of two glucose polymers

Amylose •20-35% of most starcheslow degree of branching low solubility in water

Amylopectin65-80% of most starcheshighly-branched with complex architecturesemi-crystallinesoluble in water

• Functional properties of starch are determined by the structure of amylose and amylopectin, and how these molecules are arranged inside granules

• Starches vary greatly in amylose content, length of amylopectin branches, spacing between clusters, stability of clusters

Organization of AM and AP in starch granules

• Starch granules have concentric growth rings made up of amylose and amylopectin arranged into amorphous and crystalline lamellae

- crystalline lamellae contain organized clusters of amylopectin chains in double helices

- amorphous lamellae contain inter-cluster amylopectin chains and branch points, and interspersed amylose

Kozlov, Krivandin et al. 2007

Digestibility of starch

• Digestibility of native granules is low• Digestibility of cooked starch is high ... 5-20 x faster than raw starch• Digestibility decreases on cooling• Affected by source and type of starch, amylose content, extent of

gelatinization and retrogradation due to hydrothermal processing, lipids, ...

CoolingHeating

Goesaert et al. 2005

Gelatinization Retrogradation

Digestibility

Conclusions

• Carisma potatoes are low GI

• Carisma potatoes were not differentiated from high GI potatoes by simple analyses

• Higher temperatures are required to melt crystallites in Carisma starch compared to other potato starches

- Carisma starch does not gelatinize to the same extent as starch in other potatoes that are cooked similarly

• Fine structural differences in the starch are likely to be sources of variation in digestibility

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