Changes in proximate composition and extractive components of rice-bran-fermented mackerel [Scomber japonicus] Heshiko during processing

To determine proximate composition and extractive components, a kind of fermented seafood, heshiko, was produced from fresh mackerel by salting for one week and subsequent pickling in rice-bran mixture for seven months. During salting period, fish were strongly dehydrated and decreased their body weights by the penetration of NaCl. During this period, lipid was mostly retained in the dehydrated fish meat, although a small amount of protein eluted out from them. During fermentation period in rice-bran mixture, as sugars permeated from rice-bran into fish, amounts of ash and lipid of the meat slightly decreased and that of protein did not vary. Throughout salting and fermentation, most of free amino acids and peptides markedly increased, although the His content extremely decreased. The increase of amounts of Glu, Asp, Gly, Ala, Val, Ile, and Leu, and low molecular peptides suggested that these components might contribute to the characteristic taste of heshiko. Nucleotides, such as IMP known as excellently taste active, decreased to trace amounts at the early stage of fermentation. Organic acids such as lactic, acetic, succinic, and malic acids increased remarkably during fermentation and fish meat pH decreased from 6.6 to 5.2.