Integrated enzymatic hydrolysis of crude red onion extract and yeast treatment for production and purification of short-chain inulin and inulin neoseries oligosaccharides

Abstract

As has been confirmed in our previous study, red onion is a promising source of inulin-fructan, inulin neoseries fructan, and their fructooligosaccharides (FOSs). Short-chain FOSs (SCFOSs) are potential prebiotics as they provide many health promoting benefits. However, short-chain inulin neoseries oligosaccharides isolated from plants have scarcely been studied. After prebiotic production, a purification step is essential to produce a functional prebiotic. The aim of this study was to develop new processes of integrated enzymatic hydrolysis of crude red onion extract and yeast treatment for production and purification of SCFOSs. Endo-inulinase is a key enzyme for hydrolysis of crude red onion extract to produce SCFOSs, while Candida orthopsilosis FLA44.2 was employed for purification of the produced SCFOSs. Three different strategies, including two-step (TSP), simultaneous (SP), and semi-simultaneous (SSP) production processes, were designed and investigated as potentially simple, cost-effective, and timesaving production processes. The SP and SSP processes met the objective criteria by exhibiting desirable yields of SCFOSs and the optimal purity of SCFOSs when compared with the TSP process. Notably, the SP process was highlighted as it was simpler than the SSP process. Under optimal conditions (0.4 U of endo-inulinase/g total fructans, 5 % v/v of yeast inoculum and reaction time of 72 h), the SP process conducted in 1-dm³ flasks produced SCFOSs of 87 g/dm³ with neo-GF₂ as the main constituent (42 g/dm³) and a purity of 100 %. The ratio of total SCFOSs to total fructans was 0.93 indicating that fructans of the red onion extract have been transformed to SCFOSs.