Chemical Chamges of Total Lipids in Salted Pollack Roe and Salted Herring Roe During Preservation

Abstract

The purpose of salting fish roes is primarily to maintain their good quality during preservation, but quality deterioration occurs markedly in short period depending on unsuitable conditions. Especially it is affected notably by containing lipids. In previous report, the authors studied on the changes in lipids contained in fish roes according to passage of time, and recognized the effect of preservation at low temperatures on oxidation of lipids by employing salted salmon roes that contain large amount of lipids (ca. 15%). In the present work, properties and compositions of total lipids in salted pollack roes (“Tarako”, ovary of Alaska pollack) and salted herring roe (“Kazunoko, ” ovary of herring) containing less lipids than salted salmon rose were clarified. In addition, to confirm the effects of temperatures and terms of preservation to oxidation of total lipids according to the passage of time, salted pollack roes and salted herring roes were stored at 5°C, -3°C and -18°C for a fixed period of time.
Salted pollack roes (“Tarako” in Japanese) and salted herring roes (“Kazunoko” in Japanese) were preserved at 5°C for 4 weeks, -3°C for 8 weeks and -18°C for 16 weeks. The changes in chemical properties, lipid composition and fatty acid composition of total lipids in both samples were investigated. The results obtained were as follows : The slight temporal decrease of total lipids contents in salted pollack roes (1.6%, before preservation) and salted herring roes (3.4%, before preservation) were obtained. Furthermore, acid value, peroxide value and carbonyl value of total lipids in both samples increased at each preservation temperature, while iodine value decreased during preservation, especially above changes were notable at higher preservation temperatures. Regarding the temporal changes in various lipid contents (g/100g sample) composed total lipids, the contents of compound lipid fraction, triacylglycerol as the principal lipid of neutral lipid fraction and phosphatidylcholine as the principal lipid of compound lipid fraction decreased at each preservation temperature in both samples, while neutral lipid fraction and free fatty acid contents increased with time, especially largely changed under preservation at 5°C. Regarding the temporal changes in main fatty acid composition of total lipids, neutral and compound lipid fractions, the composition of highly unsaturated fatty acid as 20 : 5, 22 : 6 acids and monoenoic fatty acid such as 16 : 1, 18 : 1 acids decreased at each preservation temperature in both samples. While, that of saturated fatty acid such as 14 : 0, 16 : 0 acids increased. Above changes were different from the case with salted salmon roes. These tendencies were the least conspicuous in case of preservation at -18°C. As the above experimental results were shown, the usefulness of the preservation at low temperature to cope with oxidation and decomposition of lipids and fatty acids was indicated.