Proteolytic Yeasts Isolated from Mackerel (Scomber japonicus)

고등어에서 분리된 부패성 효모

Microbiological spoilage of marine fish is complex process occurring by bacteria, yeasts and molds. There have been rare study for saprophytic yeasts although having enormous numbers of bacteriological studies on the spoilage of marine fish. The 14 genera of yeasts isolated from mackerel (Scomber japonicus) with high frequency of occurrence were Candida sp., Rhodotorula sp., Torulopsis sp., Cryptotoccus sp. and Tricosporon sp. Among these ones Candida lipolytica was identified as the strongest proteolytic yeast, then named Candida lipolytica FM5 (C. lipolytica FM5). C. lipolytica FM5 showed optimum growth at $25^{\circ}C$, pH 7.0 and could grow at $5^{\circ}C$ and in medium containing $10\%$ sodium chloride, To evaluate the saprophytic activity of the selected strain, C, lipolytica FM5 and Pseudomonas fluorescens ATCC 17571 which is one of representative spoilage bacteria were individually inoculated into the sterilized fish muscle homogenates, and then pH changes and volatile basic nitrogen (VBN) values were checked during the storage at various temperatures. According to the experimental results, the productions of VBN by C. lipolytica FM5 in the fish muscle homogenates were 50 mg-N/100 g at $5^{\circ}C$, 152 mg-N/100 g at $15^{\circ}C$ and 379 mg-N/100 g at $25^{\circ}C$ for 1 week storage, respectively. Above results were nearly same as in case of Ps. fluorescens ATCC 17571 inoculation. It suggest that sapyophytic yeasts also have important role in spoilage of marine fish.

우리나라 남해안의 다획성 어종인 고등어로부터 부패 활성이 강한 효모를 분리하여 그 균학적 특성을 조사하고 어육의 부패에 미치는 영향을 조사한 결과를 요약하면 다음과 같다. 1. 고등어로부터 분리된 효모 14균주 중 12균주 ($86\%$)가 저온성 효모였으며, 6균주 ($43\%$)가 단백분해활성을 가지는 것으로 나타났다. 2. 분리된 효모 14균주 중 저온생육능 및 단백분해능이 가장 강한 Y-5가 C. lipolytica로 동정되어 C. lipolytica FM5로 명명하였다. 3. C. lipolytica FM5의 최적 생육조건은 $25^{\circ}C$, pH 7.0이었으며, 염농도 $10\%$에서도 생육이 가능하여 강한 내염성을 나타내었다. 4. 멸균어육을 이용한 부패실험에서 C. lipolytica FM5를 접종한 경우 $5^{\circ}C$, $15^{\circ}C$, $25^{\circ}C$에서 저장 1주일만에 VBN생성량이 각각 50mg-N/100g, 152mg-N/100g, 379mg-N/100g를 나타내어, 대표적인 어류부패세균인 Ps. fluorescens ATCC 17571을 접종한 경우와 유사한 속도로 부패가 진행되었다.