Practical and Project Work
This section covers Practical and Project Work: laboratory analysis, sampling, sensory evaluation, record keeping and the structure of a project report in fish processing. The exam tests correct method, calculation and interpretation, not only the final number.
Core rules
- Proximate analysis commonly includes moisture by oven drying at 105 degrees C to constant weight, ash by muffle furnace, crude protein by Kjeldahl, and fat by Soxhlet extraction.
- Use duplicate samples, calibrated balances and a desiccator for cooled crucibles. Report results on a stated basis, usually wet weight.
- TVB-N, salt, pH and peroxide value are routine quality tests. Sensory evaluation needs a defined score sheet and trained panellists.
- A project report should state title, aim, introduction, materials and methods, results, discussion, conclusion and references. Raw data belong in tables.
- Sampling must be representative; do not take only the best-looking fish.
Worked example
Kjeldahl titration shows 2.24 percent nitrogen. Using the fish protein factor 6.25, crude protein = 2.24 x 6.25 = 14.0 percent. If the sample moisture was 76 percent, the result is on a wet-weight basis. Reasoning: state the factor and the basis; changing either changes the reported protein.
Traps
- Using one sample and reporting it as the lot value.
- Weighing hot crucibles and getting a false low moisture.
- Using the wrong nitrogen factor without stating it.
- Reporting protein on dry matter when the method says wet weight.
- Leaving methods out of the project report so results cannot be reproduced.