Lecture 10 - Fiber Flashcards
dietary fiber definition according to AACC
edible parts of plant that are resistant to digestion and absorption in the human intestine or partial fermentation in the large intestine
- polysacch
- oligo
- lignin
- associated plant substances
dietary fiber definition according to Codex Alimentarius
carbohydrate polymers with ten or more monomeric units, which are not hydrolysed by the endogenous enzymes in the small intestine of humans
what categories of fiber are there according to codex alimentarius?
- CHO polymers consumed in food
- CHO polymers isolated from food raw material
- CHO polymers made synthetically
relevance of fiber to health?
- lower cholesterol
- lower blood sugar
- reduced risk of intestinal ulcers
- improves laxation
- reduced colon cancer risk
what fibers make up crude fiber?
- cellulose
- hemicellulose
- lignin
what are the non-major kinds of fiber?
- pectins
- hydrocolloids & gums
- resistant starch
- waxes, cutin, tannin
how can fiber be classified and what’s the most widely accepted method?
- by plant function
- type of polysaccharide
- digestion and physiological function
- solubility
solubility is the most widely accepted
list examples of soluble fibers
Pectins , inulins , Gums (e.g. guar gum, xanthan, carrageenan and gellan ) and mucilages
list examples of insoluble fibers
includes cellulose, hemicellulose and lignin
how can dietary fiber be further fractionated?
H or L MWDF (high or low molecular weight dietary fiber)
how do you determine crude fiber?
weight of residue retained after treating the defatted specimen with heat, acid and alkali, and then subtracting the weight of the ash (550C)
what acid and base are used for crude fiber determination?
acid - H2SO4
base - NaOH
true or false: crude fiber includes physiologically relevant fiber
false
which method was the crude fiber method replaced with?
dietary fiber method
how do you determine dietary fiber?
with the help of enzymes
1) have dry, defatted, sample
2) add a-amylase at 95C to gelatinize starch, then cool
3) add protease at 60C
4) adjust pH to 4.1-4.8
5) add amyloglucosidase
6) precipitate with 95% ethanol
how do you determine soluble and insoluble fibers?
part of the dietary fiber method.
after adding amyloglucosidase, then you filter it directly. residue left behind is insoluble while the filtrate is soluble.
for residue:
- dry and weigh
- determine protein and ash and apply to formula
for filtrate
- precipitate with ethanol
- filter dry and weight residue
- determine protein and ash and apply to formula
what is NDF and ADF?
NDF = neutral detergent fiber. leftover residue from boiling with neutral detergent (lignin, cellulose, hemicellulose) ADF = acid detergent fiber. leftover residue from boiling with acidic detergent (lignin, cellulose)
how do you determine NDF?
boil neutral solution of sodium dodecyl sulfate and EDTA
how do you determine ADF?
- H2SO4
- acetyl trimethyl ammonium bromide
boil
how can you determine TOTAL DF and include non-digestible oligosaccharides?
1) amylase at 37C
2) protease at 60C
3) SDF and IDF HMWDF are precipitated with 78% ethanol & determined gravimetrically
4) non-digestible oligosaccharides are measured in filtrate by HPLC
why is the total DF method advantageous?
good for measuring DF in foods enriched with prebiotics by consolidating procedures