Sustainable carotenoid production using amylaceous agro-industrial byproducts: process efficiency and environmental assessment

Agro‑industrial brans are abundant residues that can be valorized as low‑cost feedstocks for microbial bioprocesses within a circular‑economy framework. Here, we investigated the use of corn, soybean, rice and wheat bran hydrolysates as sole nutrient sources (no detoxification and no supplementation) for carotenoid production by the yeast Rhodotorula mucilaginosa. After standardizing total fermentable sugars to 10–12 g/L, the yeast successfully consumed mixed sugars and produced biomass and carotenoids in all hydrolysates. Rice bran hydrolysate led to the highest carotenoid titer (28.41 ± 0.23 mg/L) and the highest specific carotenoid content (1.11 ± 0.05 mg_carotenoids/g_{dry cells}), whereas soybean bran hydrolysate favored biomass formation (29.74 ± 0.18 g/L). UV–Vis/FTIR analyses of the pigment-rich extract showed spectral features consistent with carotenoids (absorption maxima at 480–490 nm and characteristic FTIR bands), supporting the qualitative identification of a carotenoid mixture. Finally, a cradle‑to‑gate life cycle assessment (LCA) showed that the RBH scenario presented the lowest impacts across the evaluated categories, with electricity demand during fermentation as the main hotspot. Overall, rice bran emerges as a promising residue for sustainable carotenoid bioproduction coupling process performance and environmental benefits. This study highlights the valorization of agro-industrial residues as an efficient strategy to reduce production costs and environmental impact, contributing to the development of more sustainable biotechnologies for carotenoid synthesis and beyond.