Valorization of Gelidium corneum by-product through solid-state fermentation

Abstract

Industrial agar extraction of red seaweed Gelidium produces a significant amount of by- products (red seaweed by-product - RSB), which are often discarded. Nevertheless, their rich composition in carbohydrates and proteins makes them appropriate for value-added compound production through solid-state fermentation (SSF). In this study, RSB was utilized as substrate for SSF with Aspergillus ibericus MUM 03.49 and Aspergillus niger CECT 2915. RSB was initially characterized, and after was used as substrate for SSF as unsupplemented RSB, RSB supplemented with Mandel salt solution, and in a 50% (w/w) mixture of RSB with agro-industrial by-products (rice bran, sunflower cake, rapeseed cake, and corn gluten feed) and green seaweed Ulva rigida. The changes in crude protein content and carbohydrases production in the fermented biomass were assessed. The maximum xylanase activity (498 ± 49 U g-1) was achieved with SSF of RSB mixed with sunflower cake using A. niger, while the mixture between RSB and rapeseed cake led to the production of the highest cellulase activity (382 ± 37 U g-1). Additionally, protein content increased after SSF with A. niger in RSB mixed with rice bran (30%), rapeseed (18%), an sunflower cakes (15%). As a proof of concept, an SSF scale-up of up to 20-fold of dry substrate was done with A. niger using a mixture of RSB and sunflower cake. The effect of aeration and agitation on xylanase and cellulase production was studied using two types of bioreactors. In tray- type bioreactors enzyme activities were similar with values obtained at small scale, while in the stirred-drum bioreactor, forced aeration and low agitation enhanced both enzymes production. SSF-based bioprocessing of RSB mixed with agro-industrial by-products was demonstrated to be a costeffective and sustainable approach for producing high-value enzymes and valorizing this seaweed by-product.