NBA5 Food matrix and digestion: starch and sugars
26 important questions on NBA5 Food matrix and digestion: starch and sugars
What are starchy foods
- Bread
- Cereals
- Pasta
- Pizza
- Rice
- Potatoes
- Beans
- Chestnuts
- Bananas
Starchy foods are staple in every country
Most important source of energy in human diet (>40%)
The physiological relevance of starch digestion in humans
- Amount of starch digested
- Kinetics of starch digestion (appearance of hydrolysis products in the gastrointestinal lumen and glucose in the blood)
- Amount of starch digested
- caloric content of food
- amount of resistant starch reaching the colon
- Kinetics of starch digestion (appearance of hydrolysis products in the gastrointestinal lumen and glucose in the blood)
- glucose level in the blood (diabetes, metabolic syndrome)
Glycemic index (GI) =
GI (%) = 100 x AUC food / AUC reference
Glycemic load = GI x g CARB / 100
- 50g of carbohydrates to test
- blood sampling
- blood glucose content
- comparison with the reference (glucose)
- average on 8-10 volunteers
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What is the supramolecular structure of starch?
- Amylopection & amylose
- crystalline lamellae
- amorphous lamellae
- amylose
- Maltese cross: partially crystalline material
What varies with botanical species?
Starch granules varies for:
- AM/AP ration
- MW distribution of AM and AP
- AP branch chain length and branching point density
- Lamellar thickness, molecular density
- Degree of crystallinity and Type (A, B and C) of crystallinity
- Size, shape and porosity
What is the starch and digestibility of native starch
Amylase catalytic activity is proportional to granule surface (available surface area per unit mass) because amylases act on the surface of the granule (heterogeneous catalysis)
- Typical of type A starches (cereals)
- pore and channels. High available surface area per unit mass - Faster digestion
- Typical of type B starches
- No pores and channels. Low surface area per unit mass - Slower digestion
increase degree of crystallinity, decrease lamellae thickness and increase molecular density = decrease native starch digestion
What is starch granule gelatinisation?
- swelling
- loss of crystallinity (and thus loss of birefringence and Maltese cross)
- amylose leaching
- increase in viscosity
What is the digestibility of gelatinised starch?
What is differential scanning calorimetry (DSC)
Gelatinization parameters differ among starches from different sources!
What is the degree of gelatinisation (DG%) and digestibility?
- positive correlation between DG% and digestibility
- correlation is not linear
- correlation varies among botanical sources
- correlation varies depending on physiological conditions (e.g. Level of amylase)
DG% in food with temperature gradient
thermal properties of the matrix (heat capacity, density, thermal conductivity)
DG% in food with amount of water available
- Starchy products that are thermally treated under relatively low-moisture conditions
- some extruded-cooked snacks
- foods that experience low moisture during cooking, e.g. Bread crust
- Permeability of the matrix to water (water diffusivity coefficient) in case of wet heating
- e.g. Cooking of un-soaked legumes
- Presence of compounds that compete with starch for water (e.g. Dietary fibre, sugars, salts, etc..)
- e.g. Sugar cookies
DG% in food with crowding and confinement
- Space available for complete swelling may be limited
- more compact structure, more impermeable to amylase
- less amylose leaching
What is starch retrogradation
- rapid crystallisation of amylose molecules formation of amylose network
- slow crystallisation of amylopectin molecules
What is the digestibility of retrograded starch?
where do you expect retrograded starch?
What are the factors affecting starch retrogradation?
- Starch properties
- degree of retrogradation increases with amylose content
- time-temperature
- storage time increases degree of retrogradation
- retrogradation faster at lower temperatures but virtually absent at freezing T
- Water content
- highest retrogradation at 40-50% water content
- Food additives
- beta-cyclodextrin, lipid and emulsifiers can retard retrogradation by association with amylose and inhibit/retard their re-association
- No consistent effect of added sugars or carbohydrates. Competition for available water?
Review os starch digestibility in relation to cooking and storage
- Raw starch, RS2
- Melting of retrograded AP
- Fully gelatinised starch
- Some retrograded starch, RS3
What is modified starch (MS)
chemically modified starche
- cross-linked
- esterified
- etherified
- oxidation
- dextrinized & acid treated
Physically modified starch
- Heat-moisture treatment
- annealing
- pre-gelatinized
- retrograded
Enzymatically modified starch: de-branching, addition of branches, elongation or shortening of chains
- pullulanase
- amylosucrase
- branching enzymes
- cyclodextrin glycosyltransferase
What are the starch physical-chemical properties and digestibility of gelatinised starch?
- No consensus on properties of starch and digestibility of fully gelatinised starch
- Digestibility of gelatinised starch decreases with amylose content. Amylose content varies from 0-5% (waxy starch) to 50-90%
(high amylose starch)
- degree of retrogradation
- higher amount of lipid associated, (amylose-lipid complexes are indicated as resistant starch types V)
- molecular features of AM and AP likely more important than supramolecular parameters (e.g. High fraction of AM medium chain decreases digestibility in cooked wheat starch)
Plant matrix and starch digestion; the digestion of intact cells, broken cells and intact cells with big pores
starch undigested because encapsulated in cell walls (resistant starch type 1) for intact cells and intact cells with bigger pores
Bakery products [food matrix and starch digestion]
pasta: dense, close microstructure [slow digestion]
bread: porous macrostructure, open microstructure [fast digestion]
denser macrostructure, slower digestion
Extruded products are ... [food matrix and starch digestion]
- Variety of products and conditions
- matrix de-structures and expanded to different degrees: e.g. Puffed products vs pasta
- gelatinisation level varies, often <100%
- starch granule often molten and disintegrated, replaced by a honeycomb structure
- starch digestibility higher than raw material and often very high
Dietary fiber and ... [ dietary modulators of starch digestion
- Dietary fiber, cereal fibre and vegetable fiber intake, but not fruit fibre, are associated with a lower risk of diabetes
- certain soluble fibre can reduce postprandial blood peak by increasing digest viscosity
- release of digestion-related gut hormones (CCK, GLP-1, PPY)
- when incorporated in starchy matrixes (e.g. Bread, pasta) additional effect on the matrix must be considered:
- destabilisation of the gluten (protein) network
- coating of starch by dietary fibre
- competition for water (e.g. Effect on gelatinisation and retrogradation)
Polyphenols .... [dietary modulators of starch digestion]
Which of the following statements on starch is wrong?
- it contains only one type of monosaccharides
- starch retrogradation decreases starch digestibility
- it is stored in partially crystalline granules
- its hydrolysis by amylase produces glucose
Which of the following statements on starch is correct?
- insoluble DF decreases GI after consumption of starchy foods
- native starch is more digestible than partially gelatinised starch
- intact cereals and legumes contain some RS type 1
- on average gelatinised starch with lower AM/AP is digested more slowly
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