TOP-DRESSING OF FISH STEARIN OIL BY STEP-COATING PROCESS ELEVATES THE WATER STABILITY OF HIGH-FAT FEED FOR LARGEMOUTH BASS (MICROPTERUS SALMOIDES)

The current study was aimed to test if step-vacuum coating with fish stearin oil can elevate the water-stability of high-fat feed for largemouth bass. A batch of uncoated pellet was obtained from a commercial extrusion line, based on the current practical feed formulation of largemouth bass. Four groups of high-fat experimental feed were prepared by direct vacuum coating or step-coating with fish stearin oil and winterized fish oil to the uncoated pellet from the same batch, and named as winterized fish oil direct-coating (WOD) group, homogenized fish oils direct-coating (HOD) group, “1/2” fish stearin oil top-dressing (“1/2” SOT) group and “1/3” fish stearin oil top-dressing (“1/3” SOT) group. The parameters on water stability of feed were measured after soaking in water for 10, 20, 40, 60, 90, and 180min. under the conditions of water temperature at 26℃ with slight oscillation respectively. The results showed that the loss rates of dry matter (DM), crude protein (CP), and crude fat (CF) of each feed increased gradually with soaking time, and the average loss rates of DM, CP, and CF were 22.34%, 10.26% and 4.60%, respectively, after soaking for 180min. Soaking within 60min, the WOD group performed the worst, the loss rates of CF and DM were significantly higher than that of other groups, and the “1/2” SOT group performed the best, the loss rates of CF and DM were significantly lower than that of the other groups, while no significant difference was found in the loss rate of CP among all groups (P>0.05). After soaking for 90min, the CF loss of both “1/2” and “1/3” SOT groups were significantly lower than that of WOD and HOD groups, however, no significant difference was found between the two SOT groups. The DM loss of “1/2” SOT group was significantly lower than that of WOD group, but there was no significant difference among WOD, HOD, and “1/3” SOT groups. The loss of CP in WOD group was significantly higher than that of other groups. After soaking for 180min, the CF loss in “1/2” SOT group was significantly lower than that of the other groups, and the loss of DM and CP in WOD group were significantly higher than that of the other groups. Based on the comparative analysis furtherly, the results indicated that by increasing the saturation of oil for coating through blending the more saturated fish stearin oil with winterized fish oil, adopting the step-vacuum coating process to top-dress the fish stearin oil to feed pellet, or increasing the proportion of fish stearin oil for top-dressing was helpful to elevate the water stability of high-fat feed for largemouth bass. And each mean could effectively reduce the loss of CF and DM in the feed, but not the loss of CP.