| Summary: | 碩士 === 國立中興大學 === 食品科學系 === 90 === 英文摘要
Bacteria with histidine decarboxylase are the main histamine producers in scombroid fish. This enzyme is responsible for the conversion of free histidine in fish muscle to histamine (commonly known as the scombroid toxin), which is the most common cause of fish intoxication. Histamine does not present in the fresh fish when it is caught, but it will occur when histamine-producing bacteria decarboxylate histidine to histamine during the spoilage process.
Mackerel fish muscles normally contain high amount of free histidine, and this why mackerel is the major fish category of scombroid intoxication. Histamine—producing bacterial species and strains vary considerably in amounts of histamine formation, and the type of spoilage bacteria present depends on the aquatic environment.
Rapid detection of histamine producers has been a great concern for seafood safety recently, and the objective of this study was to develop a rapid and precise isolation and identification method for histamine-forming bacteria in mackerel tissue.
Niven’s differential medium was used to isolate bacteria from mackerel tissue, and the histamine-forming bacteria showed clearly purple colonies on Niven’s differential medium. Forty-one bacterial isolates were obtained from Niven’s agar plates and 40 isolates were confirmed as histamine producers by TLC test. Morphological study showed that all isolates were gram-negative bacilli with 2~2.75μm in length, 1~1.5μm in width.
Identification of bacterial isolates was first conducted by biochemical tests with API 20E strip. The bacterial isolates were further identified by genotyping methods of polymerase chain reaction (PCR) amplification and DNA sequencing of 16S rDNA. The results from API 20E strip test and 16S rDNA sequencing indicated that the bacterial isolates could be divided into 8 groups, which belonged to the bacterial genus of Klebsiella and Enterobacter.
Histamine production of bacterial isolates was studied by growing them in trypticase soy broth. The histamine concentration in growth broths was detected with Bateman’s method (copper chelation histamine assay). Group Ⅶ bacteria showed the highest histamine production among the eight groups of bacterial isolated and the optimal temperature for histamine formation was 20℃.
|
|---|
