Lecture 2- Proximate Analysis

Question 1

Moisture Limitations/ Applications

Answer 1

• Limitation/ Sources of Error
○ Drying can remove other volatile compounds (easily burned or evaporated), such as short chain fatty acids (SCFA) and some minerals
• Human/Agricultural Applications
○ Agriculture industry more interested in composition of dry feed
Human food labelling is based on wet weight

Question 2

Ash (Mineral Content) Limitations

Answer 2

• Potential Sources of Error/ Limitations
○ Volatile minerals may be lost when burning the residue
○ Doesn’t give information about individual minerals
Now mandatory for food labels to indicate sodium content

Question 3

Nitrogen Limitations

Answer 3

• Potential Sources of Error/ Limitations
○ Assumes all protein has 16% nitrogen (actual range is 13-19%)
○ Other sources of nitrogen
§ Nitrates, nitrites, urea, nucleic acids…etc in the food sample would therefore be part of the crude protein calculation
Causes a slight over estimation of crude protein content

Question 4

Crude Fibre (Fibre) Limitations

Answer 4

• Crude fibre =/= dietary fibre
○ Crude fibre is mainly cellulose and lignin (what remains after processing in proximate analysis- soluble fibres are lost during analysis)
○ Dietary fibre is all fibre (soluble and non soluble)
• Potential Source of Error/ Limitations
○ Unable to distinguish different fibre components
Measuring crude fibre under estimates the actual dietary fibre content of feed up to 50% because soluble fibres are lost

Question 5

General Comments on Proximate Analysis:

Answer 5

• No information provided on “digestibility of food
○ Don’t know what will actually be absorbed by an organism
• No information provided on specific amino acids, minerals, lipids, or carbohydrates
• Still used as the basis for food labelling and animal feed analyses
Has promoted the development of more advanced analytical assays to improve food characterization

Question 6

Dietary Fibre:

Answer 6

• Non digestible complex carbohydrates
Structural part of plants

• Insoluble fibres help maintain pH (bacteria sensitive to pH in digestive system)
• Soluble fibres hag onto other nutrients, slow down their absorption (i.e. glucose)
	○ Slowing down absorption of glucose puts less strain on system, lowers risk of diabetes Slowing down absorption of cholesterol lowers blood cholesterol, lowers risk for heart disease

Diagram

Question 7

Van Soest Method (Detergent Fibre Analysis):

Answer 7

• Differentiates between insoluble fibres
○ Cellulose and Hemicellulose
○ Lignin (poorly fermented, prevent fermentation of other fibres)
• Determines fermentable and non fermentable CHO
○ Determines whether bacteria in system have enzymes capable of breaking down non-digestible CHOs
○ Important for agricultural applications (fermenting non-soluble fibres in cows is very important, necessary for them to survive)
Poorly differentiates sugars, starches, and soluble fibres

Question 8

Southgate Method:

Answer 8

• Provides information about sugars, starch, and various fibres
• Used for human nutrition and food labeling
Does not differentiate between various fibre components adequately, so this method is not used for agricultural applications