Enzymatic valorization of an agricultural by-product

Abstract

Agro-industrial by-products derived from sugar crops represent a significant source of waste and an environmental burden. Among these, molasses, a by-product of sugar processing, is particularly cost-effective and rich in sugars such as sucrose, glucose, and fructose, making it an ideal substrate for bioconversion processes. This research focuses on valorizing molasses by converting it into a high-value product, D-mannitol. This study aims to develop and optimize a three-enzyme cascade reaction utilizing invertase, NADH-dependent mannitol dehydrogenase (MDH), and NAD⁺-dependent glucose dehydrogenase (GDH) to produce D-mannitol. Invertase was used to hydrolyze sucrose into D-glucose and D-fructose, enhancing substrate availability for downstream reactions. Subsequently, a coupled MDH- GDH cascade converted D-fructose into D-mannitol while regenerating the NADH cofactor through the oxidation of D-glucose. The invertase-catalyzed step achieved efficient sucrose hydrolysis, generating high yields of D-fructose and D-glucose. The introduction of invertase maximized the utilization of carbon source, sucrose in molasses, increasing substrate availability for downstream reactions. This step ultimately enhanced overall D-mannitol production efficiency compared to systems without invertase. The MDH-GDH cascade demonstrated approximately 95.6% conversion efficiency for D-fructose to D- mannitol, maintaining high enzyme activity and stability in the complex mixture of sugar beet molasses without requiring additional cofactor supplementation. The study highlights the feasibility of utilizing sugar beet molasses as an economical and renewable feedstock for value-added D-mannitol production. The three-enzyme cascade offers an efficient and sustainable approach for industrial applications, valorizing agro-industrial by-products into high-value products.