STABILITY OF SYNTHETIC TAURINE THROUGH EXTRUSION PROCESSING AND SUBSEQUENT BIOAVAILABILITY TO RAINBOW TROUT Oncorhynchus mykiss
Numerous research trials have reported the efficacy of taurine as a nutritional supplement in aquafeeds particularly when fish are fed plant-based feeds. Potential may exist for the destruction or reduction of taurine to unavailable complexes during feed manufacturing. For example, taurine is susceptible to forming Maillard reaction products. The formation of these products or others could decrease the biological value of taurine in the feeds. Therefore, the following experimentation was performed to determine the stability of taurine during extrusion processing, drying, and long term storage. Thereafter, the bioavailability of taurine from cold-pelleted and extruded feeds was evaluated in rainbow trout.
Five diets were formulated utilizing plant-based ingredients to minimize endogenous taurine. Taurine was supplemented at 0, 0.5, 1, 2 and 4% of the diet on a dry-weight basis and diets were manufactured in cold-pelleted or extruded forms. Samples were taken pre-extrusion, post-extrusion, post-drier, and from the finished feeds which had been top-coated with fish oil for taurine analysis. Samples of the 0.5 and 2% taurine complete diets were stored in a cool, dry location to assess stability of taurine during long-term storage. The complete diets were fed to 25-g rainbow trout for 9 weeks to assess fish growth performance, efficiency and taurine content of fillets.
Across all diets pre-extrusion taurine concentration was 98.8% of target values with a coefficient of variation of 4.1%. Post-extrusion taurine concentration was 98.9% of target values with a coefficient of variation of 2.4%. Post-drying taurine concentration was 98.8% of target values with a coefficient of variation of 5.2%. In complete feeds the taurine concentration was 98% of target values with a coefficient of variation of 3.8%. Over time taurine concentration were quantified at 0.49% at day 74 post-extrusion and 0.47% at day 214 post-extrusion in the 0.5% taurine diet and at 1.97% and 1.94% for those respective dates in the 2.0% taurine diets.
Taurine supplementation had limited effects on trout performance metrics while extrusion processing improved most performance metrics. No interactive effects between feed processing methods (cold-pelleted versus extrusion) were noted for any response variable.