NBA4 Food matrix and digestion: dietary fiber
25 important questions on NBA4 Food matrix and digestion: dietary fiber
Where does the food matrix has effect on?
- Amounts of nutrients available
- Rate of accumulation in lumen/blood
What is the definition of food matrix?
What are the food-related factors regulating nutrients digestion?
- Nutrients (supra)molecular structure
- Structural barriers
- Digestion modulators
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How much of a nutrient is digested/absorbed =
Rate at which nutrients are digested and/or absorbed =
What are dietary fibre (DF)
- naturally occurring
- extracted from natural sources and proven health effect
- obtained by synthesis and proven health effect
EU definition and FDA definition also includes carbohydrates with > 3 monomeric units
can be found in plant-based foods; fortification; food additives
Chemical heterogenicity of DF
- Oligosaccharides
- non-starch polysaccharides
- resistant starch
- lignin
DF polysaccharides varies by ... And has effect on:
- sugar composition
- water solubility
- type of linkages
- water holding capacity
- number of side-chains
- gel-forming capacity
- distribution of side-chains
- viscosity
- composition of side chains
- absorption/binding to molecules
- molecular weight
- fermentability
---> Physiological effect
What is the physiological effect of DF depends on its behaviour during digestion
- Barrier
- Rheology
- Binding
- Fermentation
In what way does DF (dietary fibre) in cell walls act as a barrier in the SI?
If cell integrity is retained upon swallowing, digestive enzymes must pass through cell wall to get to their substrate
What needs to be know about the cell wall permeability to digestive enzymes
- Diameter pores mostly >3nm
- Digestive enzymes radius of gyration 1.5-2.0 nm
- pore enlarged by processing (e.g. Heat treatments)
What happens when you are milling/grinding food
--->
ruptured cells, exposed nutrients high bioavailability / digestibility
Rheology; DF polysaccharides and digest viscosity ![]()
what is the in vivo digest viscosity? Name fluid phase and particulate fraction
- Fluid phase: newtonian or pseudoplastic behaviour
- Particulate fraction: pseudoplastic behaviour. Viscosity increases with the solids volume fraction
- insoluble fibre contributes to the particulate fraction and binds water; bulking effect and speeds up transit time
- soluble fibre may increase viscosity of the fluid phase
Certain soluble DF can increase viscosity of the fluid phase of digest. This in turn:
- Slows down propulsion and mixing of digest
- Slows down rate of gastric emptying
- Reduces diffusion coefficients in the lumen for nutrients/enzymes
- Reduces diffusion coefficient of nutrients in the unstirred water layer in contact with epithelium
Reduce rate of breaking down of macronutrients and absorption of nutrients
The viscosity of a polysaccharide in solution depends on its:
- Structuren: water soluble, rod-like (straight), poorly branched, HMW polysaccharides:
- Gums
- beta-glucans
- arabinoxylans
- carboxymethylcellulose
- pectins
- Concentration: viscosity increases with concentration; overlap concentration, C*
- Molecular weight: viscosity increases with MW
What is the viscous fibre and blood glucose response?
- Reducing rapid elevations in postprandial glucose is recommended in the prevention and management of several chronic conditions included cardiovascular disease, cancer and type2 diabetes
- Viscous dietary fibre frequently reported to reduce the post-prandial blood glucose peak after consumption of a variety of food/meals
- EFSA claims on reduction in the blood glucose rise after a meal:
- 4g of beta-glucans from oats of barley for 30g of available CHO
- 4g of hydroxypropyl methylcellulose per meal
- etc
- 10g of pectin per meal
What is know about viscous fiber and blood cholesterol?
- Viscous DF can decrease the baseline serum cholesterol level. Baseline serum cholesterol levels associat
ed to long mortality for CHD and CVD
- entrapped in a viscous solution/polysaccharide network; bile acids escape enterohepatic recirculation; cholesterol consumed to replenish the bile acids stock
Physiological effect of viscous fibre: importance of MW and concentration
&
importance fibre solubilization from food matrix
food matrix affects the amount of beta-glucan released during simulated in vitro digestion
Physiological effect of viscous fibre: changes during processing and storage, what happens
- Severe cooking, e.g. Dry heat or extrusion: solubility increases and MW decreases because of heat and shear
- Proofing/kneading/fermentation: solubility increases and MW decreases because of endogenous and exogenous beta-glucanases
- Frozen storage: reduced solubility because of aggregation
What needs the be known about soluble fibre and gels?
- DF with negative charge: pectin, alginate, gellan gum, carrageenan, etc
- Physical gels, often stabilised by cations, mostly Ca2+
- Gelation of DF in the GIT proposed to slow down digestion and improve satiety through manipulation of the gastric emptying and hormonal feedbacks (e.g. Ileal brake)
Binding; DF can bind and thus sequenster different actors in the food digestion drama, namely
- Digestive enzymes
- Phenolic compounds
- Bile acids
- Minerals
Binding requires the formation of a chemical bond (typically not covalent) between DF and other compounds. Chemical structure but also surface exposed for binding
What do phenolics do regarding DF binding in the SI
stacking mechanism is also possible
- involves several DF including pectins, starch and cellulose
- can occur during digestion or already in the food
- modulation of polyphenols bioavailability
- modification of polyphenols bioactivity in the GIT
What do bile acids do regarding DF binding in the SI
- Insoluble fibre: lignin, cellulose, cell wall material: hydrophobic interactions
- chitosan (positively charged): electrostatic interactions with negatively charged bile acids
- physiological significance not clear
What do minerals do regarding DF binding in the SI. And were does it have an effect on?
- Electrostatic interactions of DF with negative charges (pectin, alginate, carrageenan, etc) with cations (Ca2+)
Effect on:
- lipid digestion (Ca2+ sequestration)
- minerals bioavailability. Inconclusive evidence that DF decrease minerals bioavailability:
- release bound minerals in the large intestine where SCFA may enhance the absorption of minerals in the colon (lowering pH, epithelium proliferation)
- Effect of DF co-passengers (e.g. Phytates, polyphenols, tannins)
The DF fermentation in the colon
- little fermentation by SI microbiota
- little hydrolysis of ester bonds; limited cleavage of glycosidic bonds
- hydration and swelling
fermentability is to some extent related to solubility but also depends on chemical properties (type of sugars and linkages) and supramolecular aspects (e.g. Cell walls)
Which of the following statements on dietary fibre (DF) is wrong?
- DF intake is > from a vegan compared to an omnivorous diet
- Ingested DF reaches unmodified the colon
- DF chemical composition determines its effect in the small intestine
- Viscous DF interferes with reabsorption of bile acids
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