Lecture 10 - Fiber

Question 1

dietary fiber definition according to AACC

Answer 1

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

Question 2

dietary fiber definition according to Codex Alimentarius

Answer 2

carbohydrate polymers with ten or more monomeric units, which are not hydrolysed by the endogenous enzymes in the small intestine of humans

Question 3

what categories of fiber are there according to codex alimentarius?

Answer 3

• CHO polymers consumed in food
• CHO polymers isolated from food raw material
• CHO polymers made synthetically

Question 4

relevance of fiber to health?

Answer 4

• lower cholesterol
• lower blood sugar
• reduced risk of intestinal ulcers
• improves laxation
• reduced colon cancer risk

Question 5

what fibers make up crude fiber?

Answer 5

• cellulose
• hemicellulose
• lignin

Question 6

what are the non-major kinds of fiber?

Answer 6

• pectins
• hydrocolloids & gums
• resistant starch
• waxes, cutin, tannin

Question 7

how can fiber be classified and what’s the most widely accepted method?

Answer 7

• by plant function
• type of polysaccharide
• digestion and physiological function
• solubility
  solubility is the most widely accepted

Question 8

list examples of soluble fibers

Answer 8

Pectins , inulins , Gums (e.g. guar gum, xanthan, carrageenan and gellan ) and mucilages

Question 9

list examples of insoluble fibers

Answer 9

includes cellulose, hemicellulose and lignin

Question 10

how can dietary fiber be further fractionated?

Answer 10

H or L MWDF (high or low molecular weight dietary fiber)

Question 11

how do you determine crude fiber?

Answer 11

weight of residue retained after treating the defatted specimen with heat, acid and alkali, and then subtracting the weight of the ash (550C)

Question 12

what acid and base are used for crude fiber determination?

Answer 12

acid - H2SO4

base - NaOH

Question 13

true or false: crude fiber includes physiologically relevant fiber

Answer 13

false

Question 14

which method was the crude fiber method replaced with?

Answer 14

dietary fiber method

Question 15

how do you determine dietary fiber?

Answer 15

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

Question 16

how do you determine soluble and insoluble fibers?

Answer 16

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

Question 17

what is NDF and ADF?

Answer 17

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)

Question 18

how do you determine NDF?

Answer 18

boil neutral solution of sodium dodecyl sulfate and EDTA

Question 19

how do you determine ADF?

Answer 19

• H2SO4
• acetyl trimethyl ammonium bromide
  boil

Question 20

how can you determine TOTAL DF and include non-digestible oligosaccharides?

Answer 20

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

Question 21

why is the total DF method advantageous?

Answer 21

good for measuring DF in foods enriched with prebiotics by consolidating procedures