PROXIMATE ANALYSIS

Question 1

proximate analysis

Answer 1

series of methods used to determine the nutritive value of food

• dry matter
• ether extract
• ash
• crude protein
• crude fibre
• van Soest detergent fibre analysis
• nitrogen-free extract

Question 2

Dry Matter

Answer 2

The moisture content of a food item 
Method: 
- weigh sample
- dry sample in the oven at 100ºc
- reweigh sample 
- repeat until no change in weight pre/post drying

weight loss from original sample= moisture content

potential problems:
- Maillard reaction product formation

Question 3

Ash

Answer 3

inorganic ( mineral) content of a food item
Methods:
- weigh a portion of the dried sample
- heat sample in the oven at 500-6000º for 8 hours
- reweigh sample

weight loss from original dried sample = mineral content (inorganic)

potential problems:

• some trace minerals may be lost to volatilization
• does NOT provide the amount of specific minerals

Question 4

Crude Protein (CP)

Answer 4

nitrogen content of a food item 
Methods: 
- dried sample analyzed for nitrogen using Kjeldahl methods 
- calculate CP (%CP = % N x6.25)
- reweigh sample 

Potential problems

• assumes all nitrogen is from protein
• assumes all proteins are 16% nitrogen (100/16 = 6.25)

Question 5

Ether Extract (EE)

Answer 5

Crude fat content of a food item

methods:
- weigh dried sample
- dried sample in extracted with diethyl ether
- ether is then separated and evaporated
- residue that remains is weighed

Potential problems

• assumes all dissolved lipids are fats
• error is generally small

Question 6

Crude Fiber

Answer 6

insoluble carbohydrate fraction (cellulose, hemicellulose, lignin)

Methods:

• fat-free portion of ether extraction is weighed
• sample is boiled in dilute acid, filtered washed,
• sample is then boiled in dilute alkali, filtered and washed
• residue that remains is weighed

potential problems

• underestimates true total fibre
• no differentiation between fibre sources

Question 7

Van Soest Fiber Analysis

Answer 7

insoluble carbohydrate fraction (NDF/ ADF)
Method (step 1)
- weight dried sample
- sample is boiled in neutral detergent (pH 7), filtered, washed, dried
- separated NDF contents and NDS

NDF (neutral detergent fiber): cellulose, hemicellulose, lignin

NDS (neutral detergent soluble): soluble carbs, proteins, fats

(step 2):

• weigh dried NDF sample
• sample is boiled in acid detergent, filtered, washed, dried
• separates ADF and NDF contents

ADF(acid detergent fiber): cellulose, lignin

(step 3):

• weigh dried ADF sample
• sample is boiled in concentrated sulfuric acid, filtered, washed, dried
• separates ADL adn ADF contents

ADL (acid detergent lignin)

Question 8

Nitrogen Free Extract (NFE)

Answer 8

soluble carbohydrate fraction (starch and sugars)
method:
- calculate
%NFE = 100 - (%EE + % ash + % CP + % moisture)

potential problems
- accumulates error from all other analyses (CF= largest error)

Question 9

Dry Matter vs As-fed

Answer 9

as fed basis = represents the nutrient content of food including moisture

dry matter basis= represents the nutrient content of food without moisture

Question 10

Dry matter to as-fed conversion

Answer 10

% nutrietn (as fed) / % dry matter of food = % nutrient (dmb)/ 100% DM