3242 JOURNAL OF FOOD SCIENCE—Vol. 67, Nr. 9, 2002 © 2002 Institute of Food Technologists Food Chemistry and Toxicology TMAOase Activity of European Hake ( Merluccius merluccius ) Organs: Influence of Biological Condition and Season M. REY-MANSILLA, C. GONZÁLEZ SOTELO, AND R.I. PÉREZ-MARTÍN ABSTRACT: Trimethylamine N-oxide demethylase (TMAOase) activity of several internal organs of hake were studied for 2 consecutive y. The correlation between enzymatic activity and season of year, sex, weight, and length were analyzed. While kidney and spleen showed the highest activities, liver, heart, bile, and gall bladder activities were much lower, and in some cases they were below the detection limit. A correlation between TMAOase activity of kidney and season was found. During winter and spring (February to May), the months matching the spawning peak, high activities were detected, while in summer months the activity level was lower. TMAOase activity in the rest of the organs did not seem to have a seasonal influence. Keywords: TMAOase, season, biological condition, hake, soluble protein Introduction T RIMETHYLAMINE N-OXIDE (TMAO) IS present in most marine animals, both vertebrate and invertebrate (Hebard and others 1982). However, the presence of Tri- methylamine N-oxide demethylase (TMAOase) activity has been detected in only 30 species of fish, mostly marine, and 8 invertebrates, mainly molluscs (Sikorski and Kostuch 1982). Among fish, the Ga- didae and Merluccidae families account for most of the species having measurable TMAOase activity (Sotelo and Rehbein 2000). In fact, many research studies have described the presence of this enzymatic activity in a number of organs and tissues of these species (Hebard and others 1982; Rehbein and Schreiber 1984; Sotelo and Rehbein 2000). The occurrence of this enzymatic activity has been detected either indirectly—deter- mining the products of its catalytic reac- tion, formaldehyde (FA) or dimethylamine (DMA) in postmortem tissues (Amano and others 1963a, 1963b; Amano and Yamada 1964, 1965) and frozen stored fish (Babbit and others 1972; Tokunaga 1964, 1965, 1974, 1980; Castell and others 1970, 1971 1973; Mackie and Thomson 1974; Lall and others 1975; Gill and others 1979; Regen- stein and others 1982; Sotelo and others 1994, 1995a)—or directly, estimating TMAOase activity by a specific assay (Par- kin and Hultin 1982; Rehbein and Schreiber 1984; Rehbein 1988, 1997; Reh- bein and others 1997). The level of TMAOase activity is charac- teristic of a given species, and it can vary widely between species (Castell and others 1971; Rehbein and Schreiber 1984). For spe- cies, different organs and tissues have dif- ferent enzyme levels. Generally, TMAOase activity in viscera is higher than in muscle tissues. Low levels of FA and DMA have been detected in the muscle of Pacific cod (Gadus macrocephalus), Alaska pollack (Theragra chalcogramma), and Japanese hake (Lotella maximoniczi), while high con- centrations of these compounds have been found in viscera, especially in the pyloric caeca, gall bladder, and stomach of these species (Amano and Yamada 1965; Tokuna- ga 1980). The TMAOase activity is depen- dent on the type of muscle (Rey-Mansilla and others 2001). While red muscle pre- sents a low TMAOase activity (Castell and others 1971), enzymatic activity is almost nonexistent in the light muscle (Rehbein and Schreiber 1984). Rehbein and others (1997) reported that in most gadoid species the activity of bellyflaps was somewhat higher than activity of white muscle. The only reported exception is the significant activity found in the light muscle of red hake (Urophycis chuss) (Parkin and Hultin 1982). As mentioned above, the TMAOase level in viscera varies among species. Few stud- ies, however, have dealt with this matter. Rehbein and Schreiber (1984) compared the different TMAOase activity levels of 4 internal organs (liver, pyloric caeca, kidney, and spleen), muscle, and blood of 9 com- mercial species of gadoids. These authors reported different TMAOase activity pat- terns depending on the species. While in some species, such as cod (Gadus morhua), blue whiting (Micromesistius poutassou), Alaska pollack (Theragra chalcogramma), cusk (Brosme brosme), and grenadier (Cory- phaenoides rupestris), kidney and spleen have, in this order, shown the highest activ- ity levels. In other species, like saithe (Pollachius virens) and lings (Molva molva and Molva dypterygia), pyloric caeca and spleen presented the highest activity, re- spectively. The influence of certain factors, like the season of y and biological condition, have been described as relevant in order to ex- plain the large TMAOase activity differenc- es found in a given species (Rehbein and Schreiber 1984). Some authors have attrib- uted the differences found in DMA produc- tion among frozen stored specimens to the season of y they were caught (Castell and others 1971; Lall and others 1975). We are, however, unaware of any studies that aimed at establishing the real influence of any of these factors on TMAOase activity levels or DMA production during frozen storage. The dependence of the TMAOase activ- ity on the biological condition and on the season of year is a question of great inter- est, not only from an academic point of view, but also from the industrial perspective. FA produced by TMAOase activity during fro- zen storage of gadoid fish reacts with muscle proteins, causing muscle textural changes as toughening, sponginess, and loss of juic- iness (Tokunaga 1980; Shenouda 1980; Sikorski and Kostuch 1982; Regenstein and others 1982; Hebard and others 1982; Sote- JFS: Food Chemistry and Toxicology