Unit 2A: Food Composition and Proximate Analysis Flashcards
What is proximate analysis and what is its purpose?
A combination of several chemical analytical procedures. Used to estimate the nutrient content and molecular components of food.
What are the basic steps of proximate analysis?
First take the water out of the feed, them determine the 5 proximate principles of the dry matter
(crude protein, ether extract, ash, crude fibre, and nitrogen-free extract)
What are the 5 proximate principles?
1) Crude protein
2) Ether extract
3) Ash
4) Crude fibre
5) Nitrogen-free extract
What is left in dry matter after the water is eliminated?
Inorganic content like minerals, and organic content like macronutrients and vitamins
Why does water need to be extracted for proximate analysis?
Because it allows for comparison between different feeds since they vary in water content
How do you determine the dry matter % ?
Bonus: what are the SOE?
dry weight/fresh weight x100 =%DM
SOE: fatty acids, essential oils, lactic acid, fermented products
How do you get crude protein from nitrogen (eqn) ?
__g of N x 6.25 (g of protein/ g of N) = crude protein
**N is measured, not protein!
What are the steps in determining the nitrogen content for finding the crude protein?
Dry sample.
Boil sample in sulfuric acid which converts N into ammonium sulfate.
Cool and neutralize with sodium hydroxide which stops the denaturing process.
Ionized ammonium is released, dry sample and titrate with sulfuric acid.
What are the possible limitations of the process used to determine nitrogen content for crude protein?
- we assume all of the N is coming from the protein which it doesn’t; it is also present in urea and DNA/RNA
- time consuming
- hazardous materials
- accurate and repeatable though
What is the goal of the ether extract principle?
To isolate the high caloric fraction/crude fat - lipids and lipid soluble compounds
(fats, fatty esters, fat soluble vitamins)
How is crude fat isolated during ether extract and what are possible limitations?
The sample is boiled in ether, an organic solvent, for 4 hours.
A possible limitation is that the test does not indicate what type/quality of fat is isolated and present, like saturated and unsaturated.
What is the proximate principle ash measuring?
Measures inorganic compounds (minerals). Refers to leftover after all organic nutrients have burned off or oxidized.
How is the ash content determined and what are possible limitations?
The sample is heated at 500-600 °C for 2-4 hrs.
- high ash values = contaminated/diluted feed
- can underestimate the mineral value of the feed
- high temperatures can burn off Cl, Zn, Se, I
What is crude fibre and what is the proximate analysis measuring?
It measures the indigestible portion of feed that is fermented by the hind gut and resistant to digestive enzymes. Made up of cellulose, hemicellulose, lignin, and pectin
How is crude fibre determined? (phased out approach)
Sample is dried, baked in weak sulfuric acid, and then filtered.
The residue is then boiled in weak alkali solution, filtered, dried, and ashed.
