Modifications in fat content and fatty acid composition in white tuna, Thunnus alalunga, that take place at each stage of the canning process were studied. Steaming and two sterilization times ( 55 and (90 \mathrm{~min}) ) in soya bean oil were performed to this aim. The effects of storage for 1 and 3 years were also tested. Steaming had no effect on the relative distribution of fatty acid composition nor on the (\mathrm{n}-6 / \mathrm{n}-3) ratio of white tuna solids. but. duc to the fat content increase, the absolute content of all fatty acids tended to increase. Canned tuna absorbed soya bean oil during sterilization, becoming richer in fat and causing an increase in percentages of oleic. linoleic and linolenic acids. and a decrease in eicosapentaenoic and docosahexaenoic acids and increased polyunsaturated to saturated fatty acid and (n-6 / n-3) ratios compared with either raw or steamed tuna. However, due to the whole fat enrichment. canned fish ( (\mathrm{g} / 100 \mathrm{~g}) wet fish) showed only a slight loss of eicosapentaenoic acid, a (25-37 %) loss of docosahexaenoic acid. and an increase in oleic, linoleic, and linolenic acid contents in comparison to steamed tuna. Thus, the fat composition of the canned tuna tended to be similar to that of the soya bean oil used for coating. The latter effect was more marked with increased storage time. Small quantities of eicosapentaenoic and docosahexaenoic acids were present in the soya bean oil used for coating. 1994 Academic Press. Inc.