Assessment of taurine bioavailability in pelleted and extruded diets with red drum Sciaenops ocellatus
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2015 Elsevier B.V. Taurine has been reported to be efficacious in supporting growth of carnivorous fish species, particularly when supplemented to diets primarily containing plant feedstuffs. Although taurine may become unavailable to some extent by heat and moisture, and is susceptible to the Maillard reaction with reducing sugars, information is lacking on the stability and bioavailability of taurine subjected to extrusion processing in the manufacture of compounded fish feeds. Therefore, a feeding trial was conducted with juvenile red drum to determine the bioavailability of synthetic taurine in diets processed by cold pelleting and extrusion technology. Experimental diets were formulated without animal ingredients to contain 38% digestible protein and 20% lipid. Diets were supplemented with taurine at either 0, 0.5, 1, 2 or 4% of diet. Half of each diet was processed using conventional cooking extrusion conditions, and the other half of each diet was processed at cold temperatures, with minimal shear and pressure, resulting in 10 experimental diets. Taurine was very stable to manufacturing by cold extrusion or extrusion cooking. Post-extrusion taurine concentration was 98.9% of target values with a coefficient of variation of 2.4%. Groups of 12 juvenile red drum (averaging 4.3. g/fish) were sorted by size and stocked into each of 30, 38-L aquaria as part of an indoor brackish water (6-7. ppt) recirculating system. Each diet was fed to three replicate groups of fish twice daily at rates close to apparent satiation for 6. weeks. Fish were group weighed weekly to adjust feeding rations. At the end of the trial, three fish per aquarium were collected for determination of body condition indices and whole-body proximate composition, as well as basal taurine concentrations in plasma and muscle. Three additional fish per aquarium were bled at 5. h post-feeding for determination of post-prandial plasma taurine concentrations. Best performance of red drum in weight gain and feed efficiency was observed with the supplementation of taurine up to 1% of diet while proximate composition and condition indices were not affected by dietary taurine. Plasma and muscle taurine concentrations showed that extrusion processing significantly reduced the bioavailability of taurine. Slope ratio analysis of plasma taurine data indicated cooking extrusion reduced taurine bioavailability by 36.6%. This study, demonstrated that red drum gained more weight when fed plant-based diets supplemented with taurine regardless of diet processing technique. Statement of Relevance: Tuarine supplementation to plant-based diets for carnivorous fish species is becoming more common. This study assessed the bioavailability of taurine in cold pelleted and extrusion processed diets to red drum, and found that extrusion processing reduced taurine bioavailability by approximately 37% compared to cold pelleting.
