X Fermented fish products
X Fermented fish products
Various types of fermented fish products are found in the world. A range of fish–rice and fish–vegetable products are produced in South East Asia and the Pacific Islands and depend on acid production by endogenous lactic acid bacteria (and possibly yeast) for safety and stability of the product. The fermentation, which is run at ambient tropical temperature (30 ◦ C), rapidly becomes anaerobic. These products typically contain low levels of NaCl (less than 10%). A range of products with much higher NaCl-content is also found in South East Asia and Japan. These products, fish sauces and fish pastes, are not fermented by microorganisms but rather are the result of slow hydrolysis by endogenous enzymes. The microbiology of these products is discussed in the chapter on spices. In Alaska and the Canadian Arctic territories, Inuits prepare a variety of fermented fish and marine mammal products by simple means including burying them in the ground or storing them behind a warm stove. Several of these products have been the cause of botulism (Wainwright et al., 1988).
Little is know about the microbiology of these products. A mixture of lactic acid bacteria and yeasts are isolated from South East Asian products (Adams et al., 1985; Paludan-M¨uller et al., 2002) and L. plantarum are probably responsible for the acidification of several of these products. Fish contains very little carbohydrate and the fermentation therefore requires the addition of carbohydrates. Addition of rice and cassava to the products has been thought to serve this purpose, however, it has recently been found that garlic (or rather the fructan of garlic) is the important carbohydrate source for the fermentation of several of the South East Asian products (Paludan-M¨uller et al., 2002; Figure 3.10).
These products rely on NaCl and acidification and/or putrification and particularly the products from arctic territories have caused botulism. The problem of botulism in fermented seafood products is related to failures to control the process. The main categories of fish products that cause trouble are produced by traditional, poorly controlled techniques, which are intrinsically dangerous. If acid is produced too slowly Cl. botulinum may grow and produce toxin. Thus, a fish-rice fermented product was the cause of type E botulism in Japan in 1951 (Dolman and Iida, 1963; Iida, 1970).
The changes in protein/lipid fractions are of questionable value in stabilizing the product or protecting against growth of Cl. botulinum type E. Consequently, there are a significant number of cases of botulism each year among these Eskimo and Inuit people (Wainwright et al., 1988; MMWR, 2001).
MICROORGANISMS IN FOODS 6
without garlic 6.5 with garlic
pH
days of fermentation
Figure 3.10 Fermentation of Thai som-fak with and without the addition of 4% garlic (Paludan-Müller et al., 2002).
A third ethnic fish food type causing botulism are whole fish, which are salted and air dried with viscera intact. Where this is done without refrigeration, there is good possibility that Cl. botulinum will grow. Examples of such outbreaks have been reported in the United States involving kapchunka and moloha (MMWR, 1985, 1992b; Badhey et al., 1986; Slater et al., 1989; Telzak et al., 1990), and a massive outbreak of botulism occured in Egypt where 91 people were hospitalized following consumtion of faseikh—an uneviscerated, salted mullet fish (Weber et al., 1993). A related source of botulism is home prepared ceviche, which was responsible for three cases in Puerto Rico in 1978 (CDC, 1981).
Little is know about disease caused by parasites transferred by fermented products, but one must assume that the processes (and time) involved are not sufficient to inactivate parasites. Thus unless the products are consumed cooked, there is a high risk from parasites.