Dietary supplementation of phytosterols improves meat quality by increasing intramuscular fat, improving fatty acid composition and enhancing antioxidant capacity in Hu lambs

Abstract

Phytosterols (PS) play an important role in regulating lipid metabolism. This study aimed to investigate the effects of PS on intramuscular fat (IMF) deposition, fatty acid composition, meat quality, and antioxidant capacity in Hu lambs. Forty-eight 4-month-old male Hu lambs with similar body weight (23.90 ± 0.83 kg) were randomly divided into four groups (n = 12 per group): basal diets supplemented with 0 (Control), 500 (500PS), 1000 (1000PS), or 1500 mg PS/kg diet (1500PS) on a dry matter basis. After a 75-d feeding trial, feces, ruminal fluid, longissimus dorsi (LD) muscle and serum samples were collected for subsequent analysis. The results showed that all PS-supplemented groups had a significantly higher average daily gain than the Control group during the 26–50-day period (P = 0.002). The digestibility of dry matter (DM), organic matter (OM), crude protein (CP), and neutral detergent fiber (NDF) was significantly affected by PS supplementation (P < 0.05). Compared with the Control group, ruminal pH significantly decreased, while total volatile fatty acids (VFA) and propionate concentrations significantly increased in the 500PS group, which also had a significantly lower acetate-to-propionate ratio (P < 0.05). Meat quality was improved with PS supplementation. Specifically, pH24 h significantly increased in 500PS group, yellowness significantly decreased in 500PS group, cooking loss and water loss significantly reduced in 500PS or 1500PS groups compared with Control group (P < 0.05); shear force decreased linearly and quadratically with increasing PS supplementation (P < 0.05). Additionally, compared with Control group, IMF and CP contents significantly increased only in 500PS group in LD muscle (P < 0.05). The GR value, an indicator of carcass fatness, exhibited a quadratic decreasing trend with increasing PS supplementation (P = 0.027). The activities of fatty acid synthase (FAS) in all PS-supplemented groups and acetyl-CoA carboxylase (ACC) in 500PS group in LD muscle significantly increased compared with Control group (P < 0.05). The mRNA relative expression levels of FABP4, FAS, PPARγ, ACC, SREBP-1, and C/EBPα significantly upregulated in LD muscle with PS supplementation (P < 0.05). Compared with Control group, C11:0 and C18:0 contents in all PS-supplemented groups in LD muscle significantly decreased (P < 0.05), while the 500PS group significantly increased beneficial fatty acid contents including C18:1, C18:2, C18:3n3, C22:6n3, monounsaturated fatty acid (MUFA), and polyunsaturated fatty acid (PUFA) (P < 0.05). Compared with Control group, serum and muscle total antioxidant capacity (T-AOC) significantly elevated in the 500PS group, serum superoxide dismutase (SOD) activity significantly increased in the 1000PS group, and serum malondialdehyde (MDA) content was significantly reduced in the 500PS group, while muscle MDA content was significantly reduced in all PS-supplemented groups (P < 0.05). In summary, dietary PS supplementation improved growth performance, nutrient digestibility, ruminal fermentation, meat quality, and antioxidant capacity of Hu lambs. Phytosterols supplementation could increase IMF content in the LD muscle, promote lipid droplet accumulation, and optimize fatty acid composition by upregulating lipid metabolism-related genes.