Digestibility and starch structure: the key to tailored energy release

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1 Digestibility and starch structure: the key to tailored energy release Undine Lehmann & Frédéric Robin, Department of Food Science & Technology PO Box 44, Vers-chez-les-Blanc, CH-1026 Lausanne, Switzerland 59. Starch Convention, April 17, 2008

2 Starch main CHO in nutrition Starch - main carbohydrate in human nutrition (intake about 250 g/d) Main energy source Functional properties (e.g. thickening, texturising) Varying nutritional qualities and health benefits depending on the starch structure 2

3 3 Physiological starch classification (according to Englyst et al. 1992) Rapidly digestible starch (RDS) Example: freshly cooked potatoes, fresh white bread Benefit: rapid source of energy Slowly digestible starch (SDS) Example: certain granular starches, partially retrograded starch Benefit: slow and sustained source of energy Key to tailor energy release Resistant starch (Type 1-4) (RS) Example: Raw potatoes, staled bread Benefit: special dietary fiber, effects on gut health (prebiotic, fermentation to butyrate anticancerogenic etc)

$fractions granular level Starch fraction$ Rapidly digestible starch (RDS) Slowly

2) (RS) Example (granular) (B) wheat (C) maize

4 Structural differences between starch fractions granular level Starch fraction Rapidly digestible starch (RDS) Slowly digestible starch (SDS) Resistant starch (Type 2) (RS) Example (granular) (B) wheat (C) maize (A) potato SEM of starch granules, magnitude 600 (Galliard, 1987) 4

$Structural differences between starch fractions molecular level Starch fraction$ (Type 3) (RS) Molecular level Amylopectin Amylose Retrogradation Coil Double

(Type 3) (RS) Molecular level Amylopectin Amylose Retrogradation Coil Double

5 Structural differences between starch fractions molecular level Starch fraction Rapidly digestible starch (RDS) Slowly digestible starch (SDS) Resistant starch (Type 3) (RS) Molecular level Amylopectin Amylose Retrogradation Coil Double helix Structure amorphous amorphous/ crystalline Aggregation of double helix crystalline 5

6 What makes a starch slowly digestible? Starch digestion kinetic is depending on the complex structure of starch Main SDS examples: Certain granular structures Optimised Retrogradation Interaction with other components (e.g. protein, fat, fiber) Maize starch (Shin et al. 2004) Starch embedded in protein matrix Retention of granular structure Delivery in the product by: Retrogradation before/ during the processing Optimized food matrix 6

7 Factors favoring SDS structures A-type crystallites favor SDS compared to B- type (Jane et al. 1997) High amylopectin content, high branching (Backer and Saniez 2005) Unit chain length of amylopectin (long and intermediate/short favor SDS (Benmoussa 2007) Granular starches maize (Axelsen et al. 1999), waxy starch (Weurding et al. 2001), millet and sorghum (Benmoussa et al. 2004) and legumes (Hoover and Zhou 2003) HMT / annealing (Anderson 2002) Retrogradation at nucleation temperature (Guraya et al. 2001) Unit cell of A and B type amylose Waxy maize starch 7

8 Features of SDS and challenges for the food industry Less perfect arranged crystallites and amorphous regions (Guraya et al. 2001; Shin et al. 2004) Low / Intermediate crystallinity Low thermal stability Challenge of developing SDS ingredients and incorporation into food products / retention of structural properties during processing Solution integral application development 8

9 A particular dietary fiber - RS RS Type I: physically unavailable starch Type II: resistant starch granules Type III: retrograded starch Type IV: chemically modified starch Example Partly milled grains and seeds Raw potatoes, green bananas Cooked and cooled potatoes, bread Acetylated starch (Englyst et al.: Eur. J. Clin. Nutr. 1992, 46, Suppl. 2, S33-50; Eerlingen, R.: Doctoral thesis 1994) 9

10 RS properties and applications Retrograded RS vs. SDS: Semi-crystalline perfect arrangement of (mini)amylose chains High thermal stability allows processing Thermal stability of the pea starch products (DSC) Sample T 0 T p ( C) T c native debranched, retrograded (25 C, 20% starch in gel) To = onset temperature; Tp = peak temperature; Tc = conclusion temperature (Lehmann et al. 2003) Commercial products on the market 10

11 Physiological effects of SDS related to the areas: Metabolic (e.g. blood glucose) response / diabetes management Satiety / weight control Mental performance (reviewed in Lehmann and Robin, 2007)

12 SDS proof of physiological benefits - challenges No suitable SDS ingredient on the market SDS structures have low process stability, difficulty of incorporation into food products Food products with claimed slow digestibility questionable effects Differentiation RDS/SDS/RS in several studies unsatisfying High SDS does not mean low Glycaemic Index (GI)! Studies linking low GI and health benefits are not directly claimable as SDS benefits 12

13 Beneficial metabolic response after SDS intake In vivo glucose kinetic data after SDS intake mmol/l glucose * p< g glucose 10 g glucose + 10 g SDS * * * * time (min) Blood glucose levels of healthy subjects after consumption of 20 g available CHO including 0% or 50% SDS (Schmitt, Lehmann et al., performed at Maastricht University, NL) SDS reduces peak blood glucose response and sustains glucose release over 2-4 h pp compared to RDS; beneficial effects on insulin levels 13

14 SDS delivers benefits for diabetes management SDS delivers beneficial effects on blood glucose / insulin level and distinct metabolic parameters (e.g. lower fluctuation, lower levels of circulating triacylglycerols (Harbis et al. 2004) and thus significant benefits for diabetes management SDS at breakfast can improve CHO metabolism in diabetic patients (Golay et al. 1992) 14

15 Open questions related to SDS physiological benefits Link blood glucose response and physiological benefit satiety / performance? Active dosages, thresholds Mechanism Further clinical studies needed to verify benefits 15

16 SDS and satiety Mechanistic link starch and satiety: Blood glucose / insulin levels: glucostatic theory of Mayer 1953, 1955: low blood glucose concentrations trigger the onset of feeding and high blood glucose levels signal satiety Viscosity, stomach emptying Effects on gut peptides, hormones, other metabolites 16

17 SDS and satiety Blood glucose / SDS on satiety: Reviews: Ludwig (2000): inverse correlation between glycemic and insulinemic response and satiety Campfield & Smith (2003): Review linking blood glucose dynamics and meal initiation, supporting the fact that transient declines in blood glucose promote hunger Studies: P. Leathwood & P. Pollet (1988): Delayed return of hunger after intake of g of slow release CHO in the form of bean purée compared to rapidly digestible potato purée Alvina & Araya (2004): Rapid CHO digestion produced less short term satiety in obese preschool children than slow digestion (spaghetti) High GI food may have beneficial effects on short-term (60 min) satiety whereas low GI food promotes satiety in long-term and postabsorptive period (Anderson and Woodend 2003, Sparti et al. 2000, Warren et al. 2003) Barkeling et al. (1995): no effect of low GI food on satiety 17

18 Potential timeline of starch effects on satiety Timeline hours postprandial Food intake meal initiation second meal Potential effects of starch fractions RDS SDS RS Main effects: RDS: SDS: RS: Blood glucose, insulin; viscosity Blood glucose, insulin, hormones; contact intestine Fermentation products; contact with intestine; hormones; lipid metabolism 18

SDS and mental performance Glucose is the main fuel for the brain Glucose levels mainly affect higher demanding tasks like memory Breakfast high in slowly digestible

19 SDS and mental performance Glucose is the main fuel for the brain Glucose levels mainly affect higher demanding tasks like memory Breakfast high in slowly digestible starches (SDS) counteracts performance decline over the morning (compared to rapidly available carbohydrates) (Benton, 2003; Wesnes, 2004), effective 8 g SDS in children 19

20 Physiological effects of RS Reduction of the energy content of food Reduction of the postprandial glucose response and impact on metabolism (e.g. lipid metabolism) Benefits for satiety / weight control? Substrate for the intestinal microflora Formation of SCFA (especially butyrate) Trophic effects on the colonocytes (therapeutic for IBD) Inhibition of the conversion of primary into secondary bile acids (anti-carcinogenic) 20

21 Physiological effects of butyrate Substrate for the colonocytes Signal metabolite Influence on cell cycle Stimulates proliferation of colonocytes Butyrate paradox: increased apoptosis in cancer cells Prevention and therapy of colorectal diseases? (Velázquez et al. 1996) 21

22 Summary Structural starch features determine the digestion kinetic and are the key to tailored energy release and health benefits Slow digestion kinetic can be achieved either by protection of SDS structures in a food matrix or generation of SDS during food production Physiological benefits of SDS on blood glucose/ insulin level well established, further benefits need further verification in clinical studies RS ingredients and food products available, certain benefits well established / under investigation The challenge for the food industry is to deliver health promoting foods with tailor-made digestion and to overcome current stability or organoleptic issues 22

Resistant Starch A Comparative Nutrition Review. James M. Lattimer Ph.D., PAS Assistant Professor Animal Sciences & Industry

Resistant Starch A Comparative Nutrition Review James M. Lattimer Ph.D., PAS Assistant Professor Animal Sciences & Industry Personal Background Education B.S. Kansas State University Animal Sciences &