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

Abstract

Red seaweed Gelidium is used for agar extraction, generating large quantities of by-products (red seaweed by-product RSB). Its carbohydrate and protein-rich composition makes it a suitable substrate to produce value-added compounds through solid-state fermentation (SSF). In this study, RSB was used in SSF with Aspergillus ibericus and Aspergillus niger for carbohydrases production and protein enrichment. RSB was used for unsupplemented SSF, supplemented with Mandel salt solution, and in 50% (w/w) mixtures of RSB with agro-industrial by-products and Ulva rigida. SSF of RSB mixed with sunflower cake with A. niger resulted in the maximum xylanase activity (498 ± 49 U g-1), while RSB mixed with rapeseed cake led to the maximum cellulase activity (382 ± 37 U g-1). Protein content increased in RSB mixed with rice bran (30%), rapeseed (18%), and sunflower cakes (15%) after SSF with A. niger. Scale-up of SSF was performed using RSB mixed with sunflower cake, and A. niger. In tray-type bioreactors there were no variations in xylanase and cellulase activities compared to small scale. In the stirred-drum bioreactor, aeration and low agitation favored both enzymes production. Bioprocessing of RSB with agro-industrial by-products using SSF was a cost-effective strategy to produce high-value enzymes, valorizing this seaweed by-product.