The Effect Of Glycerol Monolaurate On Growth,health And Food Quality Of Cultured Large Yellow Croaker

Large yellow croaker(Larimichthys Croceus)is a typically marine economical fish in our country,which is very popular with consumers due to its delicious tastes.However,the overfishing resulted in the decreased production of wild yellow croaker in recent years,and the farmed fish was the main way to meet consumers' demands.Compared with wild one,some severe problems occurred in cultured fish,such as vague color,more fat content,and fishy smell,etc.The nutrition regulation may be considered as a safe and effective way to improve fish qualities.Glycerol monolaurate(GML)as a medium chain fatty acid monoglyceride naturally present in coconut oil and human breast milk has a variety of biological activities,such as antibacterial,antiviral,and anti-inflammatory properties.To date,many studies have found that GML had growth and health promoting effects and improved muscular properties in livestock.However,few reports were available on the effect of GML on the improvement of fish quality,and the relevant mechanism has not been established yet.In this work,GML was added to the diet of large yellow croaker.The serum biochemical indices and digestive enzyme activity of cultured large yellow croaker were meseasured,and the muscle nutrition,flavor,and texture were analyzed.The muscle metabonomics and gene expression were studied.Then,the effects and mechanism of GML on animal growth,health,and the meat quality were explored.The main reslts of this paper are as follows:1.Effects of GML on the growth,health,and nutritional composition of cultured large yellow croaker750 mg/kg GML supplementation significantly increased the final body height and muscle fatty content without inducing the hepatic hypertrophy.The intestinal protease and lipase activities were significantly increased(CON group: 1.13 U/mgprot,1.16U/mgprot;GML group: 2.09 U/mgprot,5.75 U/mgprot),but the level of LDL-C was significantly decreased,indicating the improved lipid metabolism of cultured large yellow croaker.In addition,the contents of Arg,Thr,Ala,and Pro were markly increased by the addition of GML(p < 0.05),as well as the contents of non-essential amino acids and total amino acids.Also,the contents of EPA and DHA were significantly increased.The results indicated that the addition of 750mg/kg GML to the basal diet could improve the muscle quality and nutritional value without affecting its own health.2.Effects of GML on the flavor of cultured large yellow croakerThe total content of the free amino acids in the GML group(228.90 mg/100 g fresh weight)was significantly higher than that of the CON group(192.57 mg/100 g fresh weight).The addition of GML significantly increased the contents of glycine,lysine,arginine,and proline(85.59,30.57,2.36,20.55 mg/100 g fresh weight).Though the addition of GML did not affect the contens of trimethylamine oxide and trimethylamine,the contents of the volatile compounds such as acetaldehyde,2-methyl-1-octanone,1-pentene,and 2-methylpentane were significantly increased,which may affect the muscle flavor of cultured large yellow croaker.Additionally,the electronic tongue could effectively distinguish the taste difference of large yellow croaker in the CON group and the GML group.The addition of GML in the feed can not only effectively enhance the bitterness and umami taste of fish,but also enhance the durability of umami taste.3.Effects of GML on the muscle texture of cultured large yellow croakerThe addition of GML could significantly increased the muscle cohesion(0.46)but did not affect the muscle hardness.Though the average diameter of the muscle fiber of large yellow croaker in CON group and GML group was not significantly different,the distribution range of the muscle fiber diameter was increased,and the muscle fiber space was significantly increased.We found that the muscle flavor and texture of large yellow croaker could be improved by amino acid,nucleotide and fatty acid metabolism pathways by means of nontargeted metabolomics,and the involved metabolites such as L-glutamine(FC = 1.05),glyceraldehyde-3-phosphate(FC = 1.26),D-proline(FC =1.03),and L-arginine(FC = 3.01)were significantly increased.Moreover,the addition of GML significantly up-regulated the expression levels of Myo D,Myo G,Myf-5,IGF-1,and m TOR,but down-regulated the expression levels of the MRF4 gene,indicating that the addition of GML in diets may increase the muscle fiber number of hyperplasia and swelling by regulating the expression of genes related to muscle growth and development,thus leading to the change of muscle texture.