| Because of its delicious taste, abundant nutrition, high value and large amounts of catching, yellow croaker (Pseudosciaena crocea) played a significant role in Chinese aquaculture. The yellow croaker which was mainly cultured in FuJian coastal waters, was circulated in the way of ice-storage. It was very meaningful to study the effect of unstandardized operation in the actual processing on the quality change of yellow croaker and how to prolong its shelf life by economical and effective way. By doing this study the consumer can eat high quality and fresher fish, the income of fishermen can be increased too.This study stimulated the operation of yellow croaker in the actual processing and the effect of delayed-icing as well as different pre-icing temperature were studied by analyzing the microbiological, biochemical and organoleptic changes occurring in fish samples. The influence of low dose gamma irradiation (1 kGy and 2 kGy) on quality and shelf life of iced Pseudosciaena crocea was also discussed by analyzing the microbiological, biochemical and organoleptic changes occurring in fish samples. The following are the main results obtained in this study:(1) The results of delayed iceing showed that Total viable counts, Psychrobacter, Pseudomonas spp., H2S-Producing bacteria and Total volatile basic nitrogen (TVBN) significantly increased during the delayed-icing duration; sensory quality significantly decreased; trimethylamine (TMA) did not change obviously. Delayed icing led to significant increase in every kind of microorganism throughout the period of storage, the accumulated rate of TVBN and TMA increased as well. The shelf life and the time when off-odour was produced were significantly shortened by delayed icing. Results of this study according to sensory data indicated that the shelf-life of Pseudosciaena crocea iced immediately and delayed in icing for 4h and 8h was 27 days, 23 days and 17 days, respectively. Compared with delayed icing, the shelf life of Pseudosciaena crocea was prolonged 4 days and 10 days by immediate icing, so it is absolutely necessary to add ice immediately after catching.(2) High pre-iceing temperature can lead to the increase of total viable counts, Pseudomonas spp., H2S-producing bacteria and TVBN during the pre-iceing period, but TMA does not change obviously during this period. High pre-iceing temperature would induce adverse effects to keep the specific body color of yellow croaker, the accumulated rate of microbiology, TVBN and TMA could be increased as well. The shelf life of yellow croaker could be significantly affected by the pre-iceing temperature, results of this study according to sensory data indicated that the shelf-life of Pseudosciaena crocea with different pre-iceing temperature was 23 days (2℃), 21.5 days (10℃) and 18 days (18℃) respectively. So, it is very significant pre-icing sufficiently after catching.(3) The results of low dose gamma irradiation showed that the numbers of total viable counts, Pseudomonas spp. and H2S-Producing bacteria significantly decreased after irradiation; during storage the bacteria numebers of Pseudosciaena crocea treated with irradiation were always less than the control simples; the concentrations of total volatile basic nitrogen and trimethylamine were conspicuously reduced by irradiation, whereas lipid oxidation was accelerated. At the end of storage the smell of lipid rancidity could be smelled for fish treated with 2 kGy dose, but that smell could not be smelled for 1 kGy and control simples. The shelf life can be remarkably prolonged by irradiation, compared to a shelf life of 17 days for non-irradiated samples, the shelf life of Pseudosciaena crocea treated with 1 kGy and 2 kGy were extended to 30 days and 26 days, respectively. |
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