Topic 4 Organic Nutrients Proximate Analysis 2023
Topic 4 Organic Nutrients Proximate Analysis 2023
Topic 4 Organic Nutrients Proximate Analysis 2023
UDAA1124
AGRICULTURAL CHEMISTRY
Accuracy vs Precision
Accuracy Precision
How closely a How closely
measured value repeated
Proximate analysis
Accuracy Precision
How closely a How closely
measured value repeated
Proximate analysis
Air oven
Purpose:
The method is used for the
quantitative determination of
Proximate analysis
Definition:
Moisture in this method refers to the amount of free water and volatile
substances that are lost by drying the food under controlled
temperature in an air oven
Principle:
The method is based on the drying of food sample under controlled
temperature until constant weight is obtained. Moisture content is
required to express the nutrient content per dry weight basis.
In some foods, moisture is used to indicate their quality.
Moisture determination
Vacuum oven
Purpose:
The method is used for the
quantitative determination of moisture
in food products high in sugar and
Proximate analysis
Definition:
Moisture in this method refers to the amount of free water and volatile
substances that are lost by drying the food under vacuum and
controlled temperature
Principle:
Weighed samples are placed under reduced pressure (typically 25-100
mm Hg) in a vacuum oven for a specified time and temperature and
their dried mass is determined. The boiling point of water is reduced
when it is placed under vacuum. Lower temperatures can be used to
remove the moisture.
Crude protein determination
Kjeldahl method
Purpose:
The method is used for the
quantitative determination of crude
protein in all types of foods.
Proximate analysis
Definition:
Crude protein is total nitrogen multiplied by protein factor. Total
nitrogen content includes nitrogen primarily from proteins and to a
lesser extent from all organic nitrogen containing non-protein
substances
Principle:
Digestion
The method is based on the digestion of proteins and other organic
food components in the sample with sulfuric acid in the presence of
catalyst e.g. sodium or potassium sulfate to release nitrogen from
protein and retain it as ammonium salt.
Crude protein determination
Kjeldahl method
Principle:
Distillation
Ammonia gas is liberated upon addition of
Proximate analysis
Titration
The ammonia liberated from the complex is
titrated with standardised hydrochloric acid. The
amount of nitrogen in the sample is determined
from the milligram equivalent of the acid used.
Ash drying
Purpose:
The method is used for the quantitative
determination of ash in raw, cooked and
Proximate analysis
processed foods
Definition:
Ash content refers to the total mineral
residue left after incineration of organic
matter. The value for ash is a useful check
in summing up the proximate composition
of food and a measure of its mineral
content
Ash determination
Ash drying
Principle:
The method involves oxidation of all organic matter by incineration in a
furnace at a specified temperature (<550°C). Ashing above 650°C will
Proximate analysis
volatilise inorganic salts like alkali chloride and a portion of ash will fuse
and enclose some carbon, preventing them from being ignited. The
residue left after incineration is the ash content of the sample
Typically, a digestion
takes from 10 minutes
to a few hours at
temperatures of about
350oC
Crude lipid determination
Definition:
Oil and fat from solid material are extracted by
repeated washing (percolation) with an organic
solvent, usually hexane or petroleum ether,
under reflux in a special glassware
Principle:
The basic procedure calls for a solid sample
to be placed in a porous container and
allowing condensed solvent to extract
continuously.
Crude lipid determination
Definition:
The total lipid content determined by solvent extraction
depends on the nature of the organic solvent used to
carry out the extraction: the total lipid content
determined using one solvent may be different from
that determined using another solvent
Principle:
The efficiency of solvent extraction depends on the polarity of the lipids
present compared to the polarity of the solvent. Polar lipids (eg.
glycolipids or phospholipids) are more soluble in polar solvents (eg.
alcohols), than in nonpolar solvents (eg. hexane). On the other hand,
nonpolar lipids (eg. triacylglycerols) are more soluble in nonpolar
solvents than in polar ones
Crude lipid determination
aqueous phase is then decanted off, and the concentration of lipid in the
solvent is determined by evaporating the solvent and measuring the
mass of lipid remaining
Ash % = 4.3500%
Ash % (dry matter) = ?
43.500/88.8800%
=4.8942
Exercise
1.
Below are the various sets of results expressed in
mean ± s.e., choose the result(s) with high precision.
I. 1.0089 ± 0.0020
s.e standard error
II. 2.0030 ± 0.0002
Feed analysis
A. I only
B. IV only
C. I, II
D. I, II, III
Exercise
2.
Choose the correct statement(s).
I. Average values obtained from several
measurements are usually more reliable than
individual measurements.
II. Measurements are frequently repeated to improve
Feed analysis
A. I, II
B. III, IV
C. I, II, IV
D. All of the above
Exercise
3.
A. all foods
Feed analysis