甘露寡糖对高糖饲喂下尼罗罗非鱼肌肉品质的影响

甘露寡糖是一种新型饲料添加剂，它具有保护肠道健康和降血糖的功能。然而，甘露寡糖对于鱼类肌肉品质的影响并无系统性报道。为此，本实验选择均重为2g左右的健康尼罗罗非鱼幼鱼315尾，随机分成对照组（Control，糖含量为35%）、高糖处理组（HC，糖含量为45%）和高糖饲料中添加甘露寡糖处理组（HM，糖含量为45%，甘露寡糖添加量为0.5%），每组3缸，每缸35尾，投喂10周后，测定其生长指标、肌肉营养成分和质构特性等相关指标。结果显示，与对照组相比，HC组尼罗罗非鱼肝体比，肌肉内聚性，肌纤维数量、肌苷酸含量、鲜味氨基酸占比、支链氨基酸/芳香族氨基酸比例、甘油三酯含量以及可促进肌肉生长的钙蛋白酶抑制蛋白基因CAST 相对表达量均显著升高；肌肉硬度、胶着性、咀嚼性、肌纤维直径、蒸煮损失，必需氨基酸占比以及在肌纤维的分化中起着重要作用的MyoG基因 相对表达量以及脂肪酸、甘油二酯和磷脂酰肌醇含量显著降低。与HC组相比，HM组尼罗罗非鱼的肌肉弹性、必需氨基酸占比，脂肪酸和甘油二酯含量以及CAST基因相对表达量显著增加；肌肉粘力、肌纤维数量、肌苷酸含量，磷脂酰乙醇胺和磷脂酰胆碱含量以及MyoG基因相对表达量均显著降低。与对照组相比，HM组尼罗罗非鱼增重率和肌肉内聚性，支链氨基酸/芳香族氨基酸比例，甘油三酯和脂肪酸含量显著增加；肝体比，肌肉硬度、咀嚼性以及磷脂含量均显著降低。上述结果表明，高糖饲喂可以使罗非鱼肌肉的保水能力增强，其肌肉更嫩更柔软紧密，提升肌肉鲜味，但会降低氨基酸营养价值。在添加甘露寡糖后，可以促进尼罗罗非鱼生长，提高产肉率和肌肉持水力，并且肌肉更加柔软紧密且富有弹性，提高氨基酸营养价值，但是会降低磷脂含量。

Effects of manna oligosaccharides on flesh quality of Nile tilapia (Oreochromis niloticus) fed with high carbohydrate diet

Mannan oligosaccharide is a new kind of feed additives, which can protect intestine and control blood sugar. However, the effects of manna oligosaccharides on fish flesh quality has not been well studied. In this study, 315 healthy juvenile Nile tilapia with an average body weight of about 2g were randomly divided into three treatment groups: control group (35% carbohydrate), high carbohydrate diet group (HC, 45% carbohydrate) and high carbohydrate diet supplemented with mannan-oligosaccharide (HM, 45% carbohydrate, 0.5% mannan oligosaccharide). Three tanks for each group, and 35 fish reared in each tank. After the feeding trial for 10 weeks, the growth indicator, muscle nutritional composition and flesh texture were determined. Compared with the control group, the hepatosomatic index, muscle cohesiveness, the myofiber number, the content of inosinic acid and triglyceride, the proportion of delicious amino acids, the ratio of branched amino acids to aromatic amino acids and the relative expression of CAST gene, which could improve muscle growth, in the fish of HC group were significantly increased; the muscle hardness, gumminess and chewiness, myofiber diameter, cooking loss, the proportion of essential amino acids, the contents of fatty acids, diglyceride and phosphatidylinositol, and the relative expression of MyoG gene, which functions in the differentiation of muscle fibers, in the fish of HC group were significantly decreased. Compared with the HC group, muscle springness, the proportion of essential amino acids, contents of fatty acids and diglyceride and the CAST gene relative expression were significantly increased in Nile tilapia of HM group; the muscle adhesion, the number of myofiber, the contents of inosinic acid, phosphatidylethanolamine and phosphatidyl choline, and the MyoG gene relative expression in Nile tilapia of HM group were significantly decreased. Compared with the control group, the weight gain rate, muscle cohesion and contents of triglyceride and fatty acids were significantly increased in fish of the HM group; the hepatosomatic index, muscle hardness and chewiness, content of phospholipid in the fish of HM group were significantly decreased. The above results indicated that the muscle of Nile tilapia fed with high carbohydrate diet was softer and tighter, the muscle water holding capacity and umami were improved, but the nutritional value of amino acids was reduced. With the addition of manna oligosaccharides, the growth and meat yield of Nile tilapia were improved, the muscle was softer and tighter than the fish in the HC group, the nutritional value of amino acids was elevated, but the phospholipid content was reduced.