1Hokkaido Kushiro Fisheries Experimental Station, Kushiro, Hokkaido 085-0027, 2Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, 3Hokkaido Industrial Technology Center, Hakodate, Hokkaido 041-0801, Japan
The effects of pre-pickling chum salmon (Oncorhynchus keta) fillets with vinegar on the chemical and microbiological characteristics of Izushi (cured and fermented fish meat) were investigated during the ripening process at about 5°C. During the ripening process of Izushi prepared with pickled fillets, microbial counts did not significantly increase, the pH values remained below pH 5.3, and organic acids were mostly the acetic acid of the vinegar. In contrast, in Izushi prepared with non-pickled fillets, aerobic bacteria, lactic acid bacteria, and yeast obviously increased during the ripening. Lactic acid was produced and the pH declined from 6.4 to 4.9 during ripening. Consequently, the main organic acid in the non-pickled Izushi was lactic acid. Also, free amino acids remarkably increased during the ripening of the non-pickled Izushi. Regardless of the pre-pickling process, the Izushi reached an acceptable state by ripening for 36 d and had similar microflora. During the ripening process, Leuconostoc mesenteroides subsp. cremoris and Saccharomyces cerevisiae became the dominant groups of lactic acid bacteria and yeast, respectively.