Z Lebensm Unters Forsch A (1999) 208 : 267–269 Q Springer-Verlag 1999 ORIGINAL PAPER Mar Rey-Mansilla 7 Carmen G. Sotelo Jose Manuel Gallardo Decomposition of trimethylamine oxide during iced storage of blue whiting (Micromesistius poutassou) Received: 12 June 1998 M. Rey-Mansilla (Y) 7 C.G. Sotelo 7 J.M. Gallardo Instituto de Investigaciones Marinas (CSIC), Eduardo Cabello 6, E-36208 Vigo, Spain, e-mail: mar6iim.csic.es Abstract Products of the decomposition of trimethy- lamine N-oxide (TMAO) during iced storage of blue whiting were monitored over 15 days. Increasing amounts of trimethylamine (TMA) and dimethylamine (DMA) were found in the white muscle with increasing storage time. The production of TMA was interpreted as a consequence of bacterial growth, while DMA pro- duction was due to enzymatic activity of trimethylam- ine N-oxide demethylase (TMAOase). TMAOase ac- tivity was monitored with time in different organs. The highest activities always corresponded to kidney and spleen. Also, TMAOase was found to remain active during the 15 days of iced storage. A relationship was found between TMAOase in kidney and DMA concen- trations in white muscle. Key words TMAOase 7 Dimethylamine 7 Trimethylamine 7 Iced storage Introduction Gadoid fishes, such as hake, cod, haddock or blue whit- ing, are a wide group of lean species commercialized both fresh and frozen in the European Union. Frozen storage of gadoids is the common way of preserving their eating qualities, although refrigeration on board and in retail shops is a preservation method also quite usual for these species, especially in countries like Spain with a large fish-eating tradition [1]. Gadoids present as a distinguishing feature, unlike other fish species groups, the ability of enzymatically breaking trimethylamine oxide (TMAO) into dimethy- lamine (DMA) and formaldehyde (FA). The enzyme is usually known as TMAOase [2, 3]. This enzymatic ac- tivity has been regarded especially important for the quality of these species during frozen storage [4–6]. However, little is known about the behavior of the en- zyme during refrigeration. Blue whiting is a species quite abundant in the northeast Atlantic [7], and it has been previously shown to present a moderately high rate of total volatile bases nitrogen (TVB-N) production during iced storage [8] and that part of this TVB-N was due to DMA forma- tion [9]. Since the DMA present in the muscle is most proba- bly due to TMAOase activity, an experiment was de- vised for testing the hypothesis of enzymatic formation of DMA during iced storage. For this purpose, both pa- rameters were measured and correlations between them tested. Also, the levels of TMAOase in different tissues were evaluated during the period of storage. TMA was also measured as a means of determining the relative importance of bacterial and enzymatic TMAO breakdown. Materials and methods Fish samples. Blue whiting (Micromesistius poutassou) of 0.2–0.3 kg were obtained 12 h after catching in January 1998 and iced stored until required. The total storage time was 15 days. At each sampling period (0, 2, 5, 7, 9, 13 and 15 days), three samples were taken, each of them composed of three individual fish, so that nine fish were used at each sampling period. Preparation of extracts. Acid extracts of white muscle were car- ried out for DMA and TMA determinations. Ten grams of minced muscle were homogenized with 20 ml of an aqueous solu- tion of 5% trichloroacetic acid (TCA), using an Ultra Turrax tis- sue macerator (9500 rpm for 1 min). Extracts were kept for 60 min in ice and were filtered through a filter paper in order to obtain a clear extract. Extracts were made up to 25 ml with 5% TCA solution and kept frozen at –20 7C until analysis. TMAOase activity and protein concentration were measured in different organs which were taken out in each sampling, packed in polyethylene bags and kept frozen at –20 7C until anal- ysis. Extracts were prepared by blending the tissue with 9 vol- umes of 100 mM phosphate buffer (pH 7.0)/5 mM triton X-100 in the case of kidneys, and 4 volumes in the case of the other organs. Homogenates were prepared by using an Ultra Turrax tissue ma-