Evaluation of Monascus ruber Inoculum Preparation Strategies and Surfactant Supplementation to Enhance Biopigment Production in a Xylose-Based Medium Derived from Ethanol Biorefinery By-Products

Bioenergy biorefineries generate lignocellulosic by-products rich in fermentable sugars that can serve as renewable feedstocks for the production of high-value bioproducts, including microbial pigments with promising bioactive properties (antioxidant, antimicrobial, and anticancer). Therefore, this study aimed to identify a suitable inoculum preparation strategy, to optimize the culture medium, and to evaluate biopigment production using xylose-based media derived from sugarcane bagasse hemicellulosic hydrolysate (SBHH). Different inoculation strategies were evaluated (cell suspension, whole mycelial discs, and fractionated mycelial discs) and supplementation with Tween 80 (TW80). The medium composition was optimized using a Box–Behnken design, with xylose, yeast extract, and TW80 as variables, and fermentations were then conducted under selected inoculum conditions in semi-defined media and SBHH. The mycelial disc inoculation strategy was selected due to its high biopigment production and lower operational complexity, yielding 8.99, 8.48, and 11.78 AU of yellow, orange, and red biopigments, respectively. The optimized culture composition consisted of 55.65 g/L of xylose, 4.18 g/L of yeast extract, and 15.38 g/L of Tween 80. The cultivation of M. ruber in SBHH resulted in 12.73, 10.75, and 14.56 AU of yellow, orange, and red biopigments, respectively. Thus, the strategy of inoculum preparation associated with non-ionic surfactant proved promising for application in bioenergy biorefineries.