Characterization of a Low Glycemic
Index Potato Cultivar
Les Copeland
University of Sydney, Australia
Kai Lin Ek
Jennie Brand-Miller, Shujun Wang
Glycemic Index Foundation
Agrico Holland
Mitolo Group (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
Van Gogh, The Potato Eaters
6
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
o Glucose
• Potato
3.0
2.0
1.0
0.0
0
-1.0
30
60
Time (min)
90
Cultivar
Carisma
Nicola
Desiree
Russet Burbank
Virginia Rose
Bintje
Maiflower
120
DE
4.0
3.0
2.0
1.0
0.0
-1.0
0
30
60
Time (min)
90
GI
53 ± 7
69 ± 5
74 ± 8
82 ± 3
93 ± 10
94 ± 8
103 ± 8
120
Change in BG (mmol/L)
CA
4.0
Change in BG (mmol/L)
Change in BG (mmol/L)
GI of seven potato cultivars
RB
4.0
3.0
2.0
1.0
0.0
-1.0
0
30
60
Time (min)
Classification
Low
Medium
High
High
High
High
High
90
120
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?
Carisma
Russet Burbank
Thickness of cell walls?
10
Why is Carisma low GI?
Differences in potato starch?
• 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
-4
-4.5
-5
Endothermic heat flow (W/g)
• Good correlation between GI value and
in vitro starch hydrolysis
• Carisma starch has higher melting
temperature than the other starches
-5.5
VR
DE
-6
BJ
NI
-6.5
CA
MF
-7
RB
-7.5
-8
Carisma
-8.5
-9
• Differences likely to be at level of
starch fine structure
50
60
70
80
90
Temperature (⁰C)
11
Starch is made up of two glucose polymers
Amylose
• 20-35% of most starches
 low degree of branching
 low solubility in water
Amylopectin
 65-80% of most starches
 highly-branched with complex architecture
 semi-crystalline
 soluble 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, ...
Heating
Cooling
Gelatinization
Retrogradation
Goesaert et al. 2005
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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