Effects of Ulva prolifera polysaccharide calcium on flavor compound deposition, myofiber conversion and gut microbiota profiles in broilers.

Ulva prolifera polysaccharide (UPP), a bioactive compound derived from marine algae, exhibits potent antioxidant, anti-inflammatory, and lipid-regulatory activities. However, the mechanism by which its calcium chelate form (UPP-Ca) affects muscle development remains largely unknown. The purpose of this study was to evaluate the patterns of flavor compound deposition and muscle fiber composition across different muscle regions in broilers at different developmental stages and to determine the effects of UPP-Ca (200, 400, and 800 mg/kg) and UPP on meat quality and gut microbiota in vivo (1-day-old yellow-feathered broilers) or in vitro (C2C12 myoblasts). We found that flavor fatty acids were gradually deposited with age, and unsaturated fatty acids and slow-type muscle fibers were mainly accumulated in the thigh muscle of broilers. Dietary supplementation with 200 mg/kg UPP and UPP-Ca improved final body weight, average daily gain, and muscle redness; however, these benefits were weakened at higher UPP-Ca doses (400 and 800 mg/kg). Both 200 mg/kg UPP and UPP-Ca selectively promoted and optimized the contents of favorable flavor-related amino acids and polyunsaturated fatty acids at 28 or 70 d. However, only 200 mg/kg UPP-Ca increased C20:4n6 and C20:5n3 in thigh muscle, along with serine content and the PUFAs/SFA ratio in breast muscle. Furthermore, 200 mg/kg UPP-Ca enhanced the expression of MYH1B, MYH1E, MYH7, MyOD, and Myf5 in thigh and breast muscle, and this was also confirmed by in vitro experiments, showing that UPP-Ca promoted myoblast proliferation and lipid metabolism and also modulated myofiber differentiation and conversion towards type I. Additionally, 200 mg/kg UPP-Ca administration reshaped gut microbiota profiles at 28 d, with a significant rise in the Rikenellaceae_RC9_gut_group and Subdoligramilum in intestinal chyme, which were significantly associated with flavor substrates and muscle fiber types. Collectively, these results indicate that 200 mg/kg UPP-Ca improves growth performance and meat quality by selectively promoting flavor compound deposition and myofiber type conversion in muscle of broilers, while modulating beneficial gut microbiota profiles at an early age.