food science tutorial 2
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what are 2 major components of foodstuffs
protein and oil
what does protein and oil contribute to
sensory, nutritional, shelf life, quality control and data for labelling
what are lipids
materials from biological origin that dissolve with organic solvents including, ether, petrol, sprits
what is the method for oil estimation
Soxhlet extraction
what is the theory for soxhlet extraction
. Lipid extracted with solvent * Difference in weight measured = weight of the oil
what does protein contain
Protein is the major nitrogen (N) containing component of food (reminder: Pr = %N * 6.25)
what does the Estimation of total N allow
Estimation of total N enables total protein to be estimated – basis of the classical Kjeldahl method (=crude protein values)
what 2 assumption does the kjeldahl method rely on
• all N is present as protein • the N content of protein is a constant %
what does 1g N =
6.25 G protein
when are Kjeldahl Factors Used
when food proteins deviate from average 16% N
what is the kjeldahl method
eveloped by Danish chemist, Johan Kjeldahl in 1883 * Determination of N in organic substances Used for >130years 2 step process…
what are the 2 steps of the kjeldahl process
• Digestion= N(food) + acid –> (NH4)2SO4 • Neutralization (NH4)2SO4 +NaOH –> NH3 (volatile) –>(Distill & Add to boric acid trap) –>NH4 + Borate
how is water determined
by a drying oven at 105 degrees for 16 hours and the weight difference is calculated
what is the equation for % dry matter
final weight / initial weight x 100
how is ash quantified
by combustion of food in a furnace at 550 degrees for 16 hours and the weight left over
what is the equation for organic matter
100 - ( %ash + %water) e.g FW - ash + water
what is the equation for protein
(g/100g FW) % nitrogen x 6.25
what the equation for oil
(g/100g FW) oil in grams / sample in grams x 100
how you convert DW –> FW
DW = FW / [1- (% moisture / 100)]
how you convert FW –> DW
FW = DW * [1- (% moisture / 100)]
is DW always higher than FW
yes