Fish roe lipids and lipid hydrolysis in processed roe of certain Salmonidae fish as studied by novel chromatographic techniques

This publication summarizes the studies directed towards the development of modern chromatographic methods in lipid research and their applications to the investigations of roe lipids of common food fishes in Finland. The lipid class composition of the total lipid extracts was determined by quantitative thin-layer chromatography - flame ionization detection (TLC-FID) and detailed studies on phospholipids were performed by HPLC. An automatic phosphorus analyzer was introduced for the firts time as a detector for an HPLC system to monitor and quantify phospholipids. Fatty acid methyl esters of the total lipids and lipid fractions were analysed by gas-liquid chromatography on glass capillary columns with mass-spectrometry being used to confirm the identifications. According to the fish species, lipid content and the major components in the roe vary considerably. An exceptional lipid composition with wax and sterol esters as the major lipid was recorded in perch and burbot roe. The fatty acid composition of whitefish roe was similar to that of flesh and followed the pattern typical of freshwater fish with a proportion of about 50 % polyunsaturates. During the storage of various whitefish and rainbow trout roe products both triglycerides and phospholipids were hydrolysed and cephalins broke down faster than lecithins. The HPLC study revealed an accumulation of lysophospholipids suggesting a stepwise hydrolysis process in the roe. With regard to lipid hydrolysis the unpasteurized cold stored roe became non-acceptable within a few months while frozen and pasteurised roe products retained their quality over one year of storage.