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 – GBP). Its carbohydrate and protein-rich composition makes it a suitable substrate to produce value-added compounds through solid-state fermentation (SSF). For the first time, GBP was used in SSF with Aspergillus ibericus and Aspergillus niger for carbohydrases production and protein enrichment. SSF was performed with unsupplemented GBP, supplemented with Mandel salt solution, and mixed at equal dry mass proportion with plant feedstuffs and with the seaweed Ulva rigida. A. niger CECT 2915 was the best strain under SSF obtaining the maximum xylanase activity (498 ± 49 U g-1), in GBP mixed with sunflower cake and the maximum of cellulase activity (382 ± 37 U g-1) in GBP mixed with rapeseed cake. In these mixtures, protein content increased 1.2-fold by SSF, as well as in GBP mixed with rice bran (1.3-fold). Scale-up of SSF using GBP mixed with sunflower cake from flasks to tray-type bioreactors demonstrated SSF reproducibility, achieving similar xylanase and cellulase activities. In the stirred-drum bioreactor, aeration and low agitation favored both enzymes production. Bioprocessing of GBP with plant feedstuffs using SSF was a cost-effective strategy to produce high-value enzymes, valorizing this seaweed by-product.