Rice Bran Biorefinery: A Zero-Waste Approach to Bioactive Oil and Biopolymer Production

Rice is a staple food for global nutrition, and its processing generates large volumes of waste with a consequent environmental impact. The industry needs to improve its capacity to manage and treat this waste with more sustainable options than traditional management methods, thereby mitigating the environmental impact of the rice industry. Among the waste streams generated, rice bran represents a significant fraction that is largely underutilized. This study proposes a comprehensive approach to rice bran recovery, aiming to transform 100% of the waste into bio-based products through a three-stage biorefinery approach that combines chemical and biological operations. The process began with the ethanolic extraction of rice bran, which yielded 20.58% (w·w−1) rice bran oil. This oil, evaluated through both in vitro and in vivo trials, has demonstrated effectiveness when combined with commercial edible coatings, reducing post-harvest damage in grapes and lemons by 15–20%. Following extraction, the remaining defatted rice bran, accounting for 79.42% (w·w−1) of the initial material, was used as a carbon-rich substrate for microbial fermentation by Haloferax mediterranei. This step converts 28.75% (w·w−1) of rice bran into microbial biomass and 12.75% (w·w−1) into polyhydroxybutyrate-valerate. The undigested residual biomass, comprising 37.95% (w·w−1) of the starting material, was further valorized through the purification of high-value products such as cellulose (13.08% (w·w−1)), hemicellulose (14.58% (w·w−1)), and lignin (10.29% (w·w−1)). Overall, the biorefinery model recovers 100% of the initial waste and demonstrates, under laboratory conditions, the model’s ability to transform rice bran into six products of industrial interest, offering an option with the potential to effectively manage rice bran waste and help circularize the production model of an industry that traditionally operates under a linear production model.