Changes of non-protein nitrogens fractions in Antarctic krill (Euphausia superba Dana) during storage at 3� and 20 �C

Abstract

Quantitative changes in non-protein fractions (volatile bases, trimethylamine, free aminoacids, peptides and polypeptides) were followed in krill, harvested in Admiralty Bay (King George Island, South Shetlands), during storage at 3° and 20 °C were followed in an attempt to determine the respective contributions of autolysis (endogenous) and microbiological (excogenous) processes in the spoilage of krill treated as a potential raw food material. The deterioration can be devided into two stages, one with autolytic processes predominant, causing a rapid hydrolysis of proteins to non-protein fractions, and the other with microbiological process prevalent, manifesting themselves in an exponential increase in total volatile bases (mainly trimethylamine) content, leading to a deteriorating in odour and flavour. However, volatile base contents cannot be regarded as quantitative freshness criteria because various batches of krill examined were found to differ markedly in total volatile bases content, so that alternative freshness indicators should be looked for. Protein hydrolysis products soluble in 4% trichloroacetic acid and reacting with Folin-Ciocalteau reagent appear to be sensitive indicators of the suitability of krill for food processing, but autoproteolytic activity is dependent on the harvesting season, and separate studies are therefore necessary.