Laboratory and Practical Skills in Food Science
Domain 10 covers laboratory and practical skills: sampling, proximate analysis, physical and chemical tests, microbiological counts and sensory trials.
Core rules
- Sampling must be representative; use clean, labelled containers and duplicate determinations.
- Moisture is measured by oven drying to constant weight; ash by incineration in a muffle furnace; fat by solvent extraction (Soxhlet); protein by Kjeldahl nitrogen × 6.25; crude fibre by acid-alkali digestion.
- pH is measured with a calibrated electrode; titratable acidity by titration with standard alkali; total soluble solids by refractometer.
- Microbiological work uses aseptic technique, serial dilution, plate counts, MPN for coliforms and proper incubation temperatures.
- Record raw readings and units; calculate on a dry or fresh basis and state which.
Worked example
A 5.000 g food sample is dried to 4.200 g. Moisture = (5.000 − 4.200) ÷ 5.000 × 100 = 16.0%. Reasoning: the loss in mass is water driven off under the specified oven conditions. The result is reported on a fresh-weight basis. If the dried sample were then ashed, ash would be expressed as a percentage of the original sample, not of the dried matter, unless a dry basis is explicitly stated.
Traps
- Weighing hot crucibles; cool in a desiccator to avoid moisture uptake.
- Reporting a single titration without duplicates or a blank.
- Mixing crude fibre with total dietary fibre; the methods measure different fractions.
- Using an uncalibrated pH meter or refractometer and reporting precise but wrong values.