A Potential of Agro-Industrial Biowaste as Low-Cost Substrates for Carotenoid Production by Rhodotorula mucilaginosa

The sustainable production of natural pigments is gaining attention as industries seek alternatives to synthetic additives. This study explored agro-industrial biowastes as feedstocks for carotenoid biosynthesis by Rhodotorula mucilaginosa (natural isolate from Jerusalem artichoke), aiming to identify an optimal substrate that combines high productivity with economic and environmental feasibility. Thirteen biowastes, including grape pomace, crude glycerol, chicken feathers, sugar beet juice, and pea protein isolate, were systematically evaluated for their impact on yeast growth and pigment accumulation. Carotenoid yields ranged from 21.4 to 187.2 mg/100 g dry weight, with the highest volumetric productivity achieved in pea protein isolate (14.98 mg/L), untreated white grape pomace (14.09 mg/L), and crude glycerol (13.87 mg/L). To assess scalability, a simplified techno-economic and sustainability analysis was applied, revealing that although pea protein isolate offered the best yields, its high market cost limited industrial feasibility. In contrast, untreated grape pomace and crude glycerol emerged as low-cost, abundant alternatives with strong circular bioeconomy potential. Fed-batch bioreactor validation using untreated grape pomace confirmed its suitability, achieving a 43% improvement in carotenoid productivity (20.1 mg/L) compared to shake-flask trials. These results position untreated grape pomace as the optimal substrate–strategy combination for sustainable carotenoid production linking agro-waste valorization with high-value bioproduct generation. This study provides both experimental evidence and economic rationale for integrating winery residues into industrial pigment production chains, advancing yeast biotechnology toward more circular and resource-efficient models.