NEW CHALLENGES IN FOOD AND NEW CHALLENGES IN FOOD AND HUMAN NUTRITION AT AAFCHUMAN NUTRITION AT AAFC

Nutritional Benefits of Cereal Nutritional Benefits of Cereal -Glucans-Glucans

Dr. Susan M. Tosh Research ScientistGuelph Food Research Centre

PRES2008-04-16

TETRAPARTITE 2008Bordeaux, France

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Food Research Map of CanadaFood Research Map of Canada

Summerland

Lacombe

Kentville

Guelph

Winnipeg

Ottawa

St-Hyacinthe

Charlottetown

• 600 Researchers• 19 Research Centres• 20% on Food Research

in 7 locations

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Food and Nutrition Research in AAFCFood and Nutrition Research in AAFC

20% of Research Branch

Safety40%

Processing30%

Nutrition30%

Antioxidants

Bioactive lipids

Probiotics

Polyphenolics

Dietary fibre

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Nutrition Research Areas - new challengesNutrition Research Areas - new challenges

Antioxidants

Bioactive lipids

Probiotics

Polyphenolics

Dietary fibre

Fruits & Grains

Meat &Dairy Products

Dairy Products

Pulses & Oil Seeds

Cereals & Pulses

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Investigation of the Impact of Dietary Fibre from Investigation of the Impact of Dietary Fibre from Cereals on Blood Glucose Levels in HumansCereals on Blood Glucose Levels in Humans

• Dietary fibre is found in the cell walls of cereal grains and other plant materials

• Insoluble fibres– Cellulose– Lignin

• Soluble fibres– Arabinoxylan -Glucan

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Mixed linkage -glucan

-Glucan in Oat Bran

Micrographs by Dr. Shea Miller, AAFC

Grain -glucan content (%)

Wheat 0.5 – 1.0

Rye 1.0 – 2.1

Oat groats 3.9 – 6.8

Barley 3.0 – 10.6

Corn 0.1

Rice 0.1

Oats and barley have the Oats and barley have the highest highest -glucan contents of -glucan contents of the cereal grainsthe cereal grains

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Oat and Barley Foods Prolong Oat and Barley Foods Prolong Glucose Release into the Blood StreamGlucose Release into the Blood Stream

• Attenuate postprandial blood glucose levels

• Prevent spike and overshoot of glucose concentrations after a meal

• Many oat and barley foods are considered low glycemic index

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-Glucan Identified as the Bioactive -Glucan Identified as the Bioactive Component for Glucose ControlComponent for Glucose Control

(Wood, AAFC)(Wood, AAFC)

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Human Subjects were given Drinks containing Human Subjects were given Drinks containing -Glucan and Available Carbohydrate-Glucan and Available Carbohydrate

(Wood et al., 1994, AAFC)

Their peak blood glucose was decreased as the viscosity Their peak blood glucose was decreased as the viscosity of the drink increasedof the drink increased

1

1.5

2

2.5

3

3.5

5 5.2 5.4 5.6 5.8 6 6.2 6.4

Log [Concentration x Mw]

Blo

od

Glu

cose

(m

mo

l/L)

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Efficacy of Efficacy of -Glucan can be Different in Different Foods-Glucan can be Different in Different Foods

-Glucan is not digested or absorbed– Activity is in the lumen of the gut– Thought to increase viscosity of intestinal contents

• Factors affecting development of viscosity– Aggregation causes loss of solubility– Enzymes cause depolymerization

• Food processing steps – Heating, freezing, shear, fermentation– Can affect bioactivity

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Concentration and Molecular Weight are the Major Concentration and Molecular Weight are the Major Factors Influencing Viscosity of Factors Influencing Viscosity of -Glucan Solutions-Glucan Solutions

h = 4x10-15 Mw2.89

r2 = 0.991

0.01

0.1

1

10

100

10000 100000 1000000

molecular weight (g/mol)

App

aren

t vis

cosi

ty (P

a.s)

(Tosh et al., 2004)(Ren et al., 2003)

Concentration EffectConcentration Effect Molecular Weight EffectMolecular Weight Effect

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Two Clinical Trials to Investigate Effects of Two Clinical Trials to Investigate Effects of Viscosity on Glycaemic ResponseViscosity on Glycaemic Response

• Investigate effects of processing– Oat bran muffin compared to whole wheat muffins– Changes in solubility and molecular weight

induced in some oat bran muffins• 11 or 12 healthy human subjects

– Age 20 – 50, BMI 20 – 36.2• Finger-prick capillary blood samples

collected over 2 hours• Blood glucose concentration measured

(Clinical trials conducted (Clinical trials conducted by Thomas M. S. Woleverby Thomas M. S. Wolever

at University of Toronto)at University of Toronto)

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Trial 1: Muffins with Modified Trial 1: Muffins with Modified -glucan Solubility-glucan Solubility

• Oat bran muffins contained 8g or 12g -glucan/serving (130g)

• Solubility reduced by freeze-thaw (FT) cycling– 2 FT or 4 FT cycles – – Up to 54% reduction in

solubility – Extracted at 37ºC under

physiological conditions0

5

10

15

20

25

30

35

40

45

50

% S

olu

bil

ity

.

Fresh 2FT 4FT

(Tosh, AAFC)(Tosh, AAFC)

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Freeze/Thaw Treatment Caused Aggregation and Freeze/Thaw Treatment Caused Aggregation and Reduced Solubility of Reduced Solubility of -Glucan in Muffins-Glucan in Muffins

8g -glucan/serving

No treatment Freeze/thaw treated

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Reduced Solubility Resulted in Diminished EfficacyReduced Solubility Resulted in Diminished Efficacy

3

4

5

6

7

8

0 20 40 60 80 100 120

Time (min)

Se

rum

Glu

co

se

(m

mo

l/L

)

. ControlFresh2F/T4F/T

• Fresh gave 45% reduction in peak blood glucose compared to control

(Lan-Pidhainy et al. 2007, AAFC)

8g -glucan/serving

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Trial 2: Muffins with Modified Trial 2: Muffins with Modified -Glucan -Glucan Molecular WeightMolecular Weight

• Added -glucanase enzyme to muffin batter to cause depolymerization

• Molecular weights – 2,210,000 to 120,000

-Glucan solubility also decreased

• Muffins containing 4g or 8g -glucan/serving

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Enzyme Treatment Caused Cell Wall Enzyme Treatment Caused Cell Wall Degradation and Aggregation of Degradation and Aggregation of -Glucan-Glucan

4g -glucan/serving

No treatment -Glucanase treated

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Depolymerization Reduced Depolymerization Reduced -glucan -glucan BioactivityBioactivity

• 2 Lowest MW’s not significantly different from whole wheat control

3

4

5

6

7

8

0 20 40 60 80 100 120

Time (min)

Blo

od

Glu

cose

(m

mo

l/L)

Control

120,000g/mol

390,000g/mol

620,000g/mol

2,210,000g/mol

8g -glucan/serving

(Tosh et al., 2008)

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Glycaemic Response was Correlated with Glycaemic Response was Correlated with Viscosity of Extractable Viscosity of Extractable -Glucan-Glucan

• Extractable -glucan– MW x concentration

• Pooled data from solubility and MW trials

• Correlation with peak blood glucose rise in clinical trial

0

1

2

3

4

10000 100000 1000000 10000000

MW x Concentration

Pea

k B

lood

Glu

cose

Ris

e (m

mol

/L)

.

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SummarySummary

• Cereal -glucans as part of a healthy diet can attenuate post-prandial serum glucose concentrations

• Distribution of -glucan, solubility and molecular weight affect bioactivity

• These factors can be affected by processing and storage conditions

• This information can assist food manufactures in producing low glycaemic index foods

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In Vitro In Vitro DigestionDigestion

-Glucan extracted from muffins at 37ºC

• Measure extract viscosity, concentration and molecular weight

(Beer et al., 1997)

CrumbsCrumbs

pH 6.9, Amylase pH 6.9, Amylase

pH 2, Pepsin pH 2, Pepsin

pH 6.9, PancreatinpH 6.9, Pancreatin

CentrifugeCentrifuge

Soluble FibreSoluble Fibre