Effects of four faba bean extracts on growth parameters, textural quality, oxidative responses, and gut characteristics in grass carp

Faba bean (Vicia faba) is proven to improve muscle textural quality in fish, but also causes growth retardation possibly inducing oxidative damage and/or nutritional disturbances. Here we used ultrasonic processing to isolate four faba bean extracts (FB water extract, alcohol extract, proteins, and residues), and then these extracts were mixed with commercial feed. Whole faba bean and commercial feed were used as controls. After grass carp (Ctenopharyngodon idellus) were fed with the six experimental diets for 100 d, their growth, textural quality, oxidative response, and gut characteristics were analyzed. Results showed that whole faba bean and FB water extract significantly increased textural parameters (hardness, springiness, and chewiness), collagen content, and fiber density in grass carp muscle (P < 0.05). Also, the whole faba bean and FB water extract contained similar contents of vicine, a pro-oxidant that has been supposed to improve the textural quality, suggesting that vicine may be responsible for the improvement of textural quality in grass carp. However, importantly, vicine was not likely to be the growth inhibitor in faba bean because the growth rate of the FB water extract group was much higher than that of the whole faba beans group (P < 0.05). The presence of other oxidative substance(s) and anti-nutritional factors was suggested because both FB water and alcohol extract groups showed reduced intestinal oxidative damage and improved hematological indexes compared with the whole faba beans group (P < 0.05); indeed, FB residues group showed the worst oxidative responses and the lowest growth rate among all group tested. Taken together, this study highlights the potential usefulness of FB water extract in aquaculture and warrants further identification of functionally active component of faba bean.