Proceedings of the Third World Fisheries Congress: Feeding the World with Fish in the Next Millenium—The Balance between Production and Environment

Enzymatic Hydrolysis of Lipids in Muscle of Chinese Freshwater Fish

Masaki Kaneniwa, Masahito Yokoyama, Chunhong Yuan, Dewen Deng, Shunsheng Chen, Yutaka Fukuda


Fisheries production in the People’s Republic of China in 1995 was about 29 million tons, and now China is the world’s leading fisheries producer (Fisheries Agency 1998). Regarding the fisheries products of China, production of freshwater fish was about 11 million tons and accounted for about 10% of world fisheries. Most of the freshwater fish in China are cultured fish. They are widely consumed in large cities near culture ponds as fresh fish but are not available as processed foods. It is expected that the production of Chinese freshwater fish will be increased in the future by the application of new technology in aquaculture. Further development of new processing technology for Chinese freshwater fish is also necessary for stabilizing this valuable food supplement not only in China but also in the rest of the world.

For successful processing, it is necessary to determine the properties of the materials. Lipid components of the fish affect the nutritional value and the preservation period of the fish products. Nutritionists and food scientists need lipid and fatty acid composition data to aid them in dietary formulation, nutrient labeling, processing, and product development (Ackman 1989).

In previous research, enzymatic hydrolysis of lipids in fish muscle has been reported in some lean and fatty fish such as cod, skipjack Euthynnus pelamis, carp, sardine Sardina pilchardus, and rainbow trout Oncorhynchus mykiss (Olley and Lovern 1960; Olley et al. 1962; Wu et al. 1974; Toyomizu et al. 1977; Hanaoka and Toyomizu 1979; Ohshima and Koizumi 1983; Ohshima et al. 1983a, 1983b, 1984a; Hwang and Regenstein 1993; Aubourg et al. 1998; Ingemansson et al. 1995; Ben-Gigirey et al. 1999). It is known that free fatty acids (FFAs) accumulate in muscle lipids from the enzymatic hydrolysis of lipids, and they degrade the quality of the fish muscle (Dyer 1951; Dyer and Fraser 1959; Ohshima et al. 1984b).

There have been several studies on the lipid components of Chinese freshwater fish (Liu 1991; Yu and Wang 1994; Yang et al. 1994), but few studies have dealt with changes of lipid components during storage or processing. In our previous study (Kaneniwa et al. 2000), we elucidated the lipid components of nine species of Chinese freshwater fish and that the lipid hydrolysis occurred in silver carp Hypophthalmichthys molitrix muscle during storage at 20°C for 8 d. It is necessary to purify lipid hydrolases in fish muscle and elucidate their properties for the prevention of enzymatic hydrolysis of fish muscle lipids. In most previous studies, examinations were done at a low temperature (<5°C) and for long storage (>1 week). These conditions are unsuitable for purification of the enzymes. Wu et al. (1974) elucidated the formation of glycerylphosphorylcholine (GPC) by enzymatic decomposition of phosphatidylcholine in carp ordinary muscle during incubation at 37°C for 2 h using 14C-labeled phosphatidylcholine. They analyzed the GPC contents for the measurement of phospholipid hydrolysis. However, analysis of the FFA contents, the other product of lipid hydrolysis, can be readily carried out. In this study, we examined high-temperature (37°C) and short-term (<6 h) incubations for the detection of the enzymatic hydrolysis that occurs in the muscle of some Chinese freshwater fish.