Utilization of astaxanthin from red yeast, Xanthophyllomyces dendrorhous, in rainbow trout, Oncorhynchus mykiss:: effects of enzymatic cell wall disruption and feed extrusion temperature

The aims of this study were to assess the effects of enzymatic cell wall disruption and feed extrusion temperature on utilization of astaxanthin from red yeast (Xanthophyllomyces dendrorhous, formerly Phaffia rhodozyma) supplied to experimental diets for rainbow trout. The red yeast was subjected to three different degrees of enzymatic cell wall disruption, resulting in 45%, 70% and 97% increase in acetone extractability of carotenoids compared to untreated yeast. Each of the three yeast preparations was included in the dry mix of feeds that were extruded at 102 and 137 degreesC, respectively. Each of the six diets was fed to three groups of rainbow trout with an initial weight of 0.5 kg, kept in 7-8 degreesC freshwater, for 92 days. The trout nearly doubled their weights during the experiment, and feed conversion ratios ranged from 0.8 to 0.9 kg intake per kg gain. Increasing the degree of enzymatic cell wall disruption increased flesh astaxanthin concentrations from 2.2 to 6.7 mg kg(-1), the CIE (1976) a*-value (redness) from 5.5 to 10.7 and b*-value (yellowness) from 11.7 to 16.7, Roche SahnoFan(R) values from 22.6 to 28.6, and astaxanthin retentions in the muscle from 3.7% to 17.4%. Extrusion temperature did not affect utilization of dietary astaxanthin or flesh colour significantly, but cell wall disruption of red yeast cells is crucial to optimize carotenoid utilization. (C) 2003 Elsevier B.V. All rights reserved.