THESIS

2.2 Method determination
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Total nitrogen content of tested samples was determined using the
Kjeldahl method, according to the AOAC procedures (2002). Sample (2.0000 g) was
weight in the Kjeldahl digestion tube. Fifteen ml of conc. H2SO4 and 15 g of catalyst
(mixed CuSO4 with K2SO4 in a weight ratio of 0.5:1) were added to the sample and
digested in a digester at 420°C until a clear solution was obtained. Distilled water (55
ml) was added to the tube and the mixture steam distilled using a distillation unit,
while 85 ml of 40% NaOH solution were added automatically via a built in dispensing
system. The distillate was collected in a 50 ml saturated boric acid with mixed
indicator. The mixed indicator solution was prepared by mixing 0.1% (w/v) of
bromocresol green with 0.1% (w/v) of methyl red. Titration was done using 1.0 N
HCL until the color changed to pink-red. The total nitrogen content and protein
content was calculated as following formula;
Total nitrogen = Volume of HCL × Normality of HCL ×14.007 × 100
Weight of sample (g)
Protein content = ( % total nitrogen × 5.70)
3. Determination of crude fat content
3.1 Regents and apparatus for analysis
3.1.1 Analytical balance (at least 1 mg sensitivity).
3.1.2 Electrical drying oven to be operated at 102ºC± 1ºC.
3.1.3 Soxhlet extraction unit comprising:
- Round bottom flask, 150 mL
- Soxhlet extractor with 60 mL
- siphoning capacity and condenser
- Cellulose extraction thimbles (28 x 80 mm)
3.1.4 Fume cupboard