Impact of different processing mulberry leaf on growth, metabolism and liver immune function of largemouth bass (Micropterus salmoides)

Abstract

Mulberry leaf is abundant in bioactive ingredients, and their release could be affected by different treatment technologies. In this study, the mulberry leaf was treated with methods of superfine grinding (MG), wall-broken (MB), and water extraction-methanol precipitation (ME). Three processing mulberry leaves were equally added to the feed of largemouth bass (Micropterus salmoides), respectively, and the growth, liver health and intestinal microorganisms were analyzed. According to statistical analysis, the growth of the three experimental groups was remarkedly better than that of the control group fed with a basic diet. The MB group had a higher specific growth rate (SGR) and weight gain rate (WGR) than the MG and ME groups. Mulberry leaf supplementation could significantly reduced blood glucose and serum total cholesterol (TC), very low-density lipoprotein (VLDL) and triglyceride (TG) levels, improved hepatic glycogen, lipid and TG levels, and these parameter values of the MB group were superior to the other treatments. Additionally, MB treatment could up-regulate the expressions of gpx and cat in the liver compared with the control and boost the activities of antioxidant enzymes (GSH-Px and CAT). Meanwhile, MB supplementation suppressed the expressions of pro-inflammatory cytokines (TNFα and IL-8) and up-regulated anti-inflammatory cytokines (IL-10 and TGF-β) in liver compared to the control group. Accordingly, the hepatic histostructure showed an improvement in the treatment group, and mulberry leaf could also dramatically lower the apoptosis of hepatic cells, particularly in the MB group. Furthermore, MB treatment reduced gut dysbiosis by limiting the development of gram-negative and possibly dangerous bacteria. In sum, this study firstly disclosed that the biological effectiveness of mulberry leaf might be impacted by various processing techniques. Especially MB-treatment effectively ameliorates glucose, lipid metabolism and liver immunology in largemouth bass.