Effects of salinity treatment on muscle quality and off‐flavour compounds of grass carp (Ctenopharyngodon idella) and black carp (Mylopharyngodon piceus)

To investigate the effects of short‐term salinity treatment on muscle quality and earthy and musty off‐flavour compounds of freshwater fish, adult grass carp (1.25 ± 0.25 kg) and black carp (1.50 ± 0.30 kg) were reared at water salinities of 0‰, 5‰ and 7.5‰for 48 h. Muscle nutrients, amino acid, and fatty acid contents, texture properties, and earthy and musty off‐flavour compounds were then determined. The content of total amino acid (TAA), Lys, Arg and essential amino acid index (EAAI) in the muscle of C7.5 group were elevated significantly compared with that in the control group (p < 0.05). The content of delicious amino acids (DAA) and EAAI in the muscle of M7.5 group was significantly higher than M0 and M5 groups (p < 0.05). The fatty acid content of the muscle was affected by salinity. In grass carp, the saturated fatty acid (SFA) content level was decreased significantly in the C5 and C7.5 groups (p < 0.05), while the monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) content levels were increased significantly in the C5 and C7.5 groups (p < 0.05). The ratio of n3/n6 PUFA increased significantly in the C7.5 group (p < 0.05). The PUFA content and the n3/n6 PUFA ratio were increased significantly in the M7.5 group (p < 0.05). With increasing salinity, the relative content levels of volatile compounds causing earthy and musty off‐flavour in muscle were decreased significantly in 5‰ and 7.5‰ salinity groups both grass carp and black carp (p < 0.05). The textural properties of muscle, such as hardness, springiness, gumminess and chewiness, were improved in the C7.5 and M5 groups. These results suggest that a short‐term salinity treatment in freshwater fish prior to selling can effectively improve muscle quality and decrease the content of earthy and musty off‐flavour compounds, with ideal salinities of 5‰ or 7.5‰ for grass carp and 7.5‰ for black carp.