Reduction of carotenoids in corn gluten meal: Effects on growth performance and muscle pigmentation of rainbow trout (Oncorhynchus mykiss)

Corn gluten meal (CGM) is an ingredient widely included in aquaculture feeds. The use of significant levels of CGM in diet formulation has been anecdotally related to the suboptimal pigmentation of the muscle of salmonid fish. The results of a few scientific studies that have examined the effect of CGM on muscle pigmentation in salmonids remain inconclusive. Therefore, a bench-scale study was carried out to reduce the content of yellow xanthophyll carotenoids in CGM using white soy flake flour as a bleaching agent. A 12-wk growth trial was then conducted to assess the effects of treated CGM on growth and muscle pigmentation of rainbow trout (Oncorhynchus mykiss) in comparison with regular CGM. Results of the pigment reduction study indicated that the concentration of lutein, zeaxanthin, beta-cryptoxanthin and beta-carotene was reduced by 86, 97, 100 and 100%, respectively, in the treated CGM. Results of the growth trial showed that the inclusion of treated or regular CGM in the diet did not significantly affect growth performance. However a significant (P<0.05) reduction in astaxanthin deposition was observed in the muscle of fish fed the diet supplemented with 190 g kg(-1) of regular CGM when compared with the fish fed the control diet (0 g kg(-1) of CGM). The muscle of fish fed the diet containing 190 g kg(-1) of treated CGM showed the lowest astaxanthin deposition. This could be attributed to the presence of reactive peroxy radicals produced during the reduction of carotenoids in the treated CGM. Further research is underway to improve the processing method for the reduction of carotenoids in CGM.