| Mackerel is one of the important migration fishes in China, which contains high levels of histidine in protein and endogenous protease with high activity. Spoilage occurs easily in mackerel and high levels of histamine are produced by the combination of endogenous protease and histamine-producing bacteria during the spoilage. Scombroid poisoning results from ingestion of mackerel containing high levels of histamine, and it hindered the processing and utilization of mackerel seriously. Therefore, study on histamine variation, relationship between histamine production and bacterial growth and identification of histamine-producing bacteria were carried out in the thesis. Results obtained in this study would be helpful to safety and histamine control of mackerel. The main results of the thesis were as follows:The characteristics and spoilage microorganisms of raw material of mackerel were analyzed firstly. Contents of moisture, ash, crude protein and crude fat were66.3%,0.89%,17.1%and15.5%, respectively. Results of chemical, sensory and microbial indexes of fish freshness detected in raw material showed that mackerel was fresh. Enterobacteriaceae and Vibrio spp. were not detected in raw material of mackerel while counts of Pseudomonas spp. and S. putrefaciens reached to58.9cfu/g and39.8cfu/g, respectively.Scombroid poisoning has a great effect on safety and processing of mackerel, the thesis studied the variation of histamine in mackerel dutring storage at0℃,4℃,15℃and25℃, relationship between histamine and freshness was analyzed. Shelf life of mackerel stored at0℃,4℃,15℃and25℃were10days,4days,3days and1day, respectively. Results also showed that temperature was an important influencing factor for histamine production in mackerel during storage, and the variation of histamine correlated well with TVB-N content, colony counts, K value and sensory indexes at different storage temperatures. It indicated that histamine could be used as a freshness index for mackerel during storage, and it was also referential to enterprises for simultaneous detection of freshness and safety of mackerel.To analysis the microbial factors which accelerated histamine production, the thesis studied the variation of Pseudomonas spp. Knterobacteriaceae, Vibrio spp. and histamine-producing bacteria in mackerel during storage at0℃,4℃,15℃and25℃. Results showed that Pseudomonas spp. was predominant microorganism in mackerel stored at0℃-25℃. Growth rate of Enlerobacteriaeeae, Vibrio spp. and histamine-producing bacteria were enhanced while stored at15℃-25℃, however, they were inhibited below4℃. Pseudomonas spp. was the main contributor to histamine production in mackerel stored at0℃-4℃However, the main histamine contributors at15℃and25℃were linterobacieriaeeae and histamine-producing bacteria, respectively.To confirm the species of histamine-related bacteria, identification of isolated bacteria was carried out, histamine production of high histamine-producing bacteria (HHPB, produce>1000mg/kg histamine) was also studied. A total number of305bacteria were isolated from mackerel, only32of them could produce histamine. Histamine-producing bacteria were mostly isolated from mackerel stored at15℃and25℃. Pholobaclerium damsela and Actinobacilhs ureae were the main contributors to histamine production in mackerel stored at0℃-4℃while Morgcmella morgana was the one at15℃-25℃. Study on histamine production of HHPB showed that temperature and NaCl concentration had a great effect on the growth and histamine production of HHPB. Therefore, low temperature and high NaCl concentration could be used to keep the freshness of mackerel and controlling histamine production. |
