NBA1 (molecular aspects of) protein digestion and absorption
17 important questions on NBA1 (molecular aspects of) protein digestion and absorption
Are there alternative pathways for protein absorption?
- transcytosis of larger peptides
Increase intestinal permeability
- Paracellular transport
- Epithelial integrity
- Exercise
Large peptides; incl. Allergens
image is a study that they have done --> with exercise the peak of peanut allergie was higher....? Exercise has a negative impact on the intestinal impermeability
Protein quality; how many are essential and how many are nonessential?
- Nonessential AA - 11
- Essential AA - 9
- conditionally essential AA (synthesised in limited amounts; diet in case status of rapid protein synthesis [e.g. Growth])
What is the definition of protein quality? And what is its relevance?
- Nutritive value of a protein depends on its capacity to provide nitrogen and amino acids in adequate amounts to meet the requirements of an organism
- relevance
- growing population
- specific groups
- children
- disease
- elderly
- Higher grades + faster learning
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Protein quality is dependent on...
- AA composition
- AA bioavailability
nutritive value of a protein depend on its capacity to provide nitrogen and amino acids in adequate amounts to meet the requirements of an organism
By what is the amino acid bioavailability influenced?
- Digestibility
- net absorption of an amino acid
- Chemical integrity
- the proportion of the amino acid that, if absorbed, is in a utilisable form (e.g., bioavailable/reactive lysine)
Name the scoring system for the evaluation of protein quality and what the formula is.
- recommended in 2011 by FAO
- DIAAS% = 100 x lowest value [(mg of digestible dietary indispensable amino acid in 1g of the dietary protein)/(mg of the same dietary indispensable amino acid in 1g of the reference protein)]
in 1989 the PDCAAS [protein digestibility corrected amino acid score] was recommended. Sinds 2011 the DIAAS
What are the improvements & limitations of the DIAAS
- Digestibility at ileal level, not faecal
- determined in human > growing pig > growing rat
- Measurement bioavailable lysine (no Maillard products)
- AA pattern of reference protein
- age-groups (birth-6; 6m-3y;>3y)
- no truncation at 100%
- except sole food source or already mixed diet
- Limitation
- still one score per protein --> AA individual nutrients
In which 3 ways can the digestibility be measured in humans?
- Naso-ileal intubation
- liquids, powders, non-fibrous food
- Ileostomates
- fibrous, coarse food
- Less-invasice techniques
- isotope methods
Ileostomates -- Proteos study =
- 'healthy' subjects
- breakfast with protein or protein-free meal
- collection of digest - 9 hours
Considerations
- not completely healthy
- microbiota ileum
- total collection & marker recovery
What is the principle dual isotope approach?
- Intrinsically labelled test protein
- different labelled standard protein/free AA
- known digestibility
- postprandial ratio of appearance of differently labelled amino acids --> evaluation absorption of test protein
--> less invasive: useful to determine digestibility in children, elderly, patients
Dual tracer approach - 15N & 2H
- Cystic fibrosis patients
- Quantify protein maldigestion - Pancreatic enzyme
Dual tracer approach - 2H & 13C
- relative to free amino acids
Digestibility of legumes, eggs, meat, rice (2H)
- relative to spiruline
What is the protein origin [digestibility]
- Dietary protein
- Endogenous protein
- Basal; depends on quantity of intake, independent of diet
- Specific; depends on diet
- fiber (type and concentration)
- anti-nutritional factors
What is the apparent vs true digestibility?
- Difference in correction for endogenous losses
- Digestibility(%) = (ingested - digestive losses) / ingested x 100
True:
- Digestibility(%) = (ingested - (digestive losses - endogenous losses)) / ingested x 100
What are the methods to determine endogenous losses?
- Protein - free diet
- basal endogenous losses
- labelled protein sources
- 15N labelled protein source
- total endogenous losses --> 'real' digestibility
- recycling
- hydrolysed proteins with ultrafiltration of digesta
Age & protein digestibility
- rats: 5 weeks or 20 months
- true faecal protein digestibility
- results
- low differences for properly processed protein products
- larger differences for proteins products with anti-nutritional factors
Scoring protein quality - calculation
[example for a single food ingredient - milk powder]
- (mg of digestible dietary indispensable amino acid in 1 g of the dietary protein)
- lowest value
13 * 0.9 = 12
12/17= 0,69
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