Efficient Whole‑Cell Biosynthesis of Curcumin Monoacetate by Rhizopus arrhizus With Improved Stability and Tyrosinase Inhibitory Activity

Curcumin, a natural food colorant and functional ingredient, suffers from poor stability, low lipophilicity, and limited oral bioavailability. This study, for the first time, employs a whole-cell catalyst (Rhizopus arrhizus MQ1 isolated from lipid-rich soil) to achieve green acylation of curcumin in a non-aqueous system, aiming at efficient synthesis of curcumin monoacetate (CA). Using vinyl acetate as the acyl donor, the reaction conditions were optimized (DMSO, 40 mg/mL whole-cell catalyst, substrate ratio 1:62.5, 60°C), reaching a conversion >90%. To investigate the substrate specificity of the whole‑cell catalyst towards acyl donors of different chain lengths, vinyl butyrate and vinyl octanoate were also tested, yielding the corresponding monoacylated derivatives-curcumin monobutyrate (CB) and curcumin monooctanoate (CO). All three derivatives showed increased Log P relative to curcumin; CA (3.32) fell within the optimal range and exhibited the highest aqueous solubility (Log S = -4.11) among the series. All three derivatives exhibited improved photothermal stability, stability in simulated body fluids, and tyrosinase inhibitory activity compared to curcumin. Among them, CA showed superior overall performance: >75% retention after 6 h at 100°C and an IC₅₀ of 125.94 µmol/L (23.8% higher potency than curcumin), making it a promising candidate for functional food ingredients, anti‑browning agents, and natural colorant improvement. This study provides a green whole-cell acylation strategy that not only achieves high conversion of CA but also demonstrates substrate specificity towards acyl donors of different chain lengths.