A Comparison of White Muscle Quality in Grass Carp Ctenopharyngodon idellus Fed with Commercial Feeds and Barley Malt

This study was the first report regarding the application of barley malt (BM) for diets of aquaculture species. Triplicate groups of grass carp Ctenopharyngodon idellus with an initial size of about 1.2 kg were selected and fed with either BM or commercial feed (CF) to apparent satiation for 8 weeks in outdoor ponds connected with a flow-through aquaculture system. The results showed that the final body weight (1651 g) was lower in the BM fish than in the CF fish (1791 g). The edible part was lower in the BM fish than in the CF fish as indicated by the viscerosomatic index. Except for ash levels, which were lower in the fillet of the BM fish than for that of the CF fish, moisture, protein, and lipid levels were not impacted by the application of BM. Water-holding capacity indicators (drop loss, frozen exudation rate, and cooking loss) of grass carp muscle were not relevant to dietary modifications. Hematoxylin-eosin (HE) staining showed that the diameter of the myofibers was decreased while density was increased in response to the application of BM, which contributed to the improvement in textural properties (hardness, gumminess, and chewiness) in the muscle of the BM fish as compared to the CF fish. Glutamic acid level was highest, followed by aspartic acid, lysine, leucine, alanine, and arginine in grass carp muscle. Except three amino acids (proline, phenylalanine, and histidine), the amounts of the other 15 amino acids, essential amino acids, semi-essential amino acids, nonessential amino acids, and delicious amino acids were not impacted by different treatments, suggesting that the application of BM had a minor effect on the amino acid composition of grass carp muscle. Oleic acid (C18:1n-9), linoleic acid (C18:2n-6), and palmitic acid (C16:0) were the most abundant fatty acids in grass carp muscle. The amounts of poly-unsaturated fatty acid (PUFA) in the muscle decreased in response to the application of BM as the diet of grass carp, and n-6 PUFAs (C18:2n-6 and C20:2n-6) rather than n-3 PUFAs accounted for this change, which is beneficial for human health. In conclusion, the application of BM had minor impacts on the proximate composition and amino acid composition but improved textural properties and decreased n-6 PUFAs in the fillet of grass carp.