Grain Constituents Flashcards
Constituents of Grain
Water
Protein
Carbohydrate
Lipid
Lignin
Minerals
plus minor constituents.
Which crops have the highest protein %
Pea and Chickpea
Which crops have the lowest protein %
Corn and Rice
Which crops have the highest fat %?
canola, flax, soybean, peanut (oilseeds)
Which crops have the highest starch %?
Wheat, corn, oat, rice, barley (cereals)
How to measure water/moisture determination?
- dry sample in an oven (130ºC for 1 hr).
- measure weight loss
- express weight loss as % moisture.
There are other rapid methods including capacitance, near-infrared reflectance spectroscopy (NIRS).
What is Protein
polypeptides that are polymers of amino acid
Some essential amino acids
Leucine, Lysine, Methionine, Tryptophan.
Protein Determination
- Determine %N
- Multiply by conversion factor (6.25 to obtain % crude protein).
Problem: not all N is from protein, so what factor to use?
Grains and seeds contain 8-40% protein.
Kjeldhal method (flask)
Dumas Method (combustion)
NIRS
Amino Acid Determination
- hydrolysis of protein to constituent amino acids
- chromatographic separation and identification of amino acids
Classification of Proteins Based on Solubility (1924, Osbourne)
Albumins - water soluble
Globulins - salt, acid, and alkali soluble
Prolamins - alcohol soluble
Glutenlins - detergent and extreme pH soluble.
What are carbohydrates?
a substance that only contains C, H, and I.
starch, fibre, and simple sugars.
Starch
a carbohydrate polymer (polysaccharide). consists of polymers of glucose (amylose and amylopectin).
Starch granules are formed in amyoplasts. Occur in grains as layered, particulate granules.
granule size and shape and amylose/amylopectin ratio are genetically determined.
starch is important to dietary energy and its pasting and other functional properties.
grains and seeds contain 0-80% starch
Starch Assay
- glucose after enzymatic hydrolysis
- measure glucose chromotographically or chemically
Amylose vs Amylopectin
amylose - straight chain
amylopectin - branched chain
Fibre
crude, detergent, and dietary fibre.
grains and seeds contain up to 40% fibre. contain 5-25% total dietary fibre (TDF)
2 kinds of fibre
Non-starch polysaccharides (NSPs)
Resistant Starch
NSPs (Non-Starch Polysaccharides)
NSPs - cell wall consists of variety of carbohydrate polymers (5 and 6-carbon sugars).
Cellulose, hemicellulose, pectins, beta gluten.
Indigestible dietary component for monogastrics.
Resistant Starch
non-diegestible in the small intestine of humans.
Simple Sugars
glucose, fructose, sucrose, raffinose, etc.
grains and oilseeds contain 2-5% simple sugar
Simple Sugar Assay
extraction with aqueous alcohol, chromatographic separation, and identification.
Lignin
carbohydrate-like material associated with fibre.
Complex polymer network of simple phenolics derived from phenylalanine and tyrosine.
grains and oilseeds contain low levels of lignin.
Lignin Assay
- soak material in 72% H2SO4 for 12 hours
- wash, dry, weigh residue
Lipids
Neutral lipids (vegetable oils and fats)
Polar Lipids (cell membrane lipids)
consist mainly of triglycerides.
grains and seeds contain 1-50% neutral lipid and 2-3% polar lipid.
Polar Lipids
Primary phospholipid.
Not extracted in the assay for crude fat.
total lipids extracted with a mixture of chloroform and methanol.
Total lipid - neutral lipid = polar lipid.
grains and seeds contain 2-3% polar lipid.
Minerals (Ash)
inorganic material.
Burn away organic material (650ºC), residue is ash.
Specific minerals (Ca, Mg, Fe, etc.) may be determined by a variety of methods – atomic absorption or plasma spectroscopy, neutron bombardment.
