Malaysia SummaryProteins from Oreochromis mossambicus, a freshwater fish, were hydrolysed, using alkalase 0.61, to produce a soluble, spray-dried hydrolysate. The hydrolysis was carried out at 50°C, using a ratio of one part water and one part fish mince, an enzyme:substrate ratio of 1:50 at pH 8.0. Reaction was terminated by heating to 90°C for 20min. After neutralization, the soluble fraction obtained after centrifugation was spray dried in a mini spray-drier, at an air inlet temperature of 170°C and a feed rate of 41-'. The spray-dried hydrolysate was incorporated into crackers which are fried before eating. Ten per cent hydrolysate was found to give maximum linear expansion. Sensory evaluation with 20 experienced assessors showed that in terms of appearance, crispiness and colour, crackers with hydrolysate had the highest scores, compared to crackers made with 0. mossambicus and Sciaena sp. (Jewfish). There were no significant differences in overall acceptability in all three samples. Crackers with hydrolysate also had the highest nitrogen content.

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A variety of significantly odorous compounds of yellowtail (Seriola aureovitata) developed during storage at 3ºC for 15 days. Trimethylamine (TMA) and dimethylamine (DMA) were the major volatile basic components. Volatile organic acids which include acetic acid, propionic acid, butyric acid, isobutyric acid and valeric acid were found and their contents increased during six days of storage, but the level of contents didn’t reach their odor threshold. Fat oxidation products of carbonyls and alkenals increased greatly during storage. The important compounds were hexanal, hexenal, octanal, octenal, 3,5- octadien-3-one, nonanal, and pent-1-en-3-ol, octen-3-ol. Sulphide compounds were identified after six days of storage.

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