Efficient Fermentation of Rhodotorula glutinis and Chlorella vulgaris Composite Feed Additives and Construction of Novel Microcapsule Carriers for Enhancing Carotenoids Stability and Bioaccessibility

Mixed-culture products of Rhodotorula glutinis and Chlorella vulgaris can enhance the antioxidant capacity of target organisms. However, their intrinsic carotenoids exhibit poor stability and bioaccessibility, which hinders the industrial application of related functional feeds. In this study, yeast-algal cells harvested from a 5 L fermenter were double-coated with gelatin and gum arabic. Process parameters were optimized by single-factor experiments and response surface methodology (RSM). Encapsulation efficacy was characterized by zeta potential analysis, Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The results showed that the maximum encapsulation rate reached 65.87% at the optimal conditions: wall material concentration of 1.34%, core-to-wall ratio of 58.80%, gelatin proportion in wall materials of 35.40% and curing agent addition of 0.17%. Characterization revealed that re-crystallization-regulated zeta potential facilitated the formation of dense wall structures. Storage stability tests demonstrated enhanced antioxidant retention, and in vitro digestion assays verified favorable sustained-release properties. This study effectively improves carotenoid stability and bioaccessibility, providing technical support for high-performance feed additives.