Effect of the fish oil, oxidation status and of heat treatment temperature on the volatile compounds of the produced fish feeds

This study aimed at giving information on the fish feeds’ volatile compounds and factors affecting them, since no respective data are currently available in the literature. Two different fish oils, a standard fish oil (FO) and a sardine oil (SO) were subjected to forced oxidation (50 °C and stirring for 120 h) and their non-oxidized and oxidized forms were incorporated in four produced fish feeds, respectively. The manufactured fish feeds were subjected to three different heat treatments (85, 115 or 140 °C). The SO diets had higher eicosapentaenoic (EPA 20:5 ω3) contents, higher total saturates and ω6 fatty acids and lower total monounsaturates, ω9 and docohexahenoic (DHA 22:6 ω3). Both oil oxidation and heat treatment resulted in higher TBA values in manufactured feeds. The volatile compounds characterizing the fish feeds were mainly hydrocarbons, carbonyls and alcohols, but also cyclic hydrocarbons, aromatics, ketones, esters ethers, furans, terpenes and miscellaneous compounds were present in lower quantities. The FO and SO diets differed (p<0.05) to their volatile profiles. In general sardine oil (SO) resulted in a higher number of feeds volatiles. Oxidation of the incorporated fish oil was found to have a significant impact on the volatile compounds. Among the above volatile compounds, butanal 2-methyl and toluene contents were affected by the fish oxidation status, the temperature of the heat treatment as well as by the interaction of these factors. These indicate that these two volatiles can be useful indexes of the feed quality.