Value added fish by-products - Nordic Innovation

4.2 Comparison of the effect of injected protein solutions on fillet properties
The process of injection and storing conditions were the same as described above in
paragraph 1.2 and 1.2.1 on page 83 and 84 respectively.
4.2.1 Effects of fish protein solutions on chemical and physicochemical
characteristics of fresh and lightly salted cod fillets
4.2.1.1 Physical properties
Water holding capacity and T2 transversal relaxation times were evaluated for the fillets. See
description of methods above, paragraphs 1.1.1.1 and 1.1.1.2, respectively.
4.2.1.2 Chemical analysis
Salt and water content was determined by standard methods, AOAC no. 976.18 (2000) and
ISO 6496 (1999), respectively. The total protein contents of the fish muscle were estimated
by Kjeldahl method (ISO, 1979) with the aid of a Digestion System 40 (Tecator AB,
Hoganas, Sweden) and calculated using total nitrogen (N) x 6.25. Salt, water and protein
content were determined for the fillets and the fish protein solutions.
TVB-N content of samples was measured using direct distillation into boric acid (based on
AOAC 1990). The acid was then titrated with a diluted sodium hydroxide solution. The
unbound ammonia was calculated as g/16gN.
4.2.1.3 Microbiological analysis
A sample was taken from a muscle of each fillet and analysed for psychotropic bacteria
(colony forming units) and H2S-producing bacteria on Iron agar with overlay (IA). The plates
were incubated at 15°C for five days. Bacteria forming black colonies on this agar produce
H2S from sodium thiosulphate and / or cysteine. One of the main spoilage bacteria in chilled
fish, Shewanella putrefaciens, forms black colonies on this agar. This bacteria forms
trimethylamine (TMA) from trimethylamine oxide (TMA-O), but TMA has often been used
as a parameter on fish freshness.
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