Abstract
Cellulose nanofibers biosynthesized by bacteria (BC) possess outstanding properties such as non-toxicity, high purity, high liquid holding capacity, high crystallinity, and high tensile strength. It is a more eco-friendly, bio-based material compared to cellulose isolated from plants via extraction/purification processes in which harsh chemicals are used. However, the low yield of BC limits the widespread production and usage of BC nanofibers. Hence, the purpose of this research was to study the effects of four different culture media, various carbon and nitrogen sources, initial pH, and static/dynamic cultivation conditions on BC yield. Suitable culture media formulations and cultivation conditions of cellulose-producing bacteria (Gluconacetobacter xylinus) were assessed. Moreover, BC production was examined in a modified Hestrin-Shramm (HS) medium by replacing the nitrogen source ingredients (yeast extract and peptone) with okara, an agricultural by-product from industrial soybean production. Nanocellulose yield and content in a hydrogel-like pellicle were compared. As a result, high BC pellicle yield (100-350 g/L) and nanocellulose content (3-12 mg/cm3) were observed in HS and Zhou media at pH 5.0 under static and combined static-dynamic conditions by adding mannitol and corn steep powder as carbon and nitrogen sources, respectively. When okara was used as an alternative nitrogen source, the resultant BC exhibited high crystallinity ((90%) and high molecular weight (7-9(106 g/mol) over the range of tested concentrations. The highest BC pellicle yield (85 g/L) and cellulose content (3.4 mg/cm3) were obtained when the culture was supplemented with 1 %w/v freeze-dried okara. The valorisation of non-valued okara waste through nanocellulose production can alleviate economic constraints around BC production and can simultaneously provide enhanced sustainability.
