Processing soybean meal for biodiesel production; effect of a new processing method on growth performance of rainbow trout, Oncorhynchus mykiss

A new method of soybean meal processing has been developed, which may simplify the process of biodiesel production. This method, ‘in situ transesterification’, eliminates hexane extraction to remove the oil, combining the extraction and transesterification steps so as to synthesize biodiesel via a single treatment conducted directly on a lipid-bearing solid material. If the resulting meal is comparable in nutritional value to commercially available hexane-extracted soybean meal (SE-SBM) the new process could become widely used in the bio-fuel industry. Two levels (17.5 and 35%) of each of three types of soybean meal were fed to triplicate lots of 30 (initial wt 22 g) rainbow trout for 9 weeks in flow-through 15 °C spring water. The three types of soybean meal included SE-SBM, an experimentally produced hexane-extracted SE-SBM (ESE-SBM), and a meal produced using in situ transesterification (IS-SBM) and each was fed at two levels for a total of 6 diets. Growth of fish fed the diets was good, averaging over 600% gain. There was no effect of source of soybean meal on weight gain of trout. The fish fed the meal processed by the new method, IS-SBM, gained as much weight as fish fed either of the two control meals, at each inclusion level. Fish fed the diets containing IS-SBM, however, did have higher feed intake (2.51% bw/d) compared to fish fed the ESE-SBM or SE-SBM, 2.38 and 2.46% bw/d, respectively. Since growth was equal, feed conversion ratios were higher for fish fed the IS-SBM diets. Protein and energy retention values were lower for fish fed the IS-SBM diets. There was no effect of soybean source on carcass composition. Apparent digestibility for protein was lower for the IS-SBM (85.9%) than for the ESE-SBM (89.3%). Feeding IS-SBM did not decrease weight gain in this study, but due to the increased feed intake and FCR, long term feeding trials should be conducted to further evaluate the meal.