Sustainable production of gellan gum from enzymatically hydrolyzed wheat bran: fermentation optimization and...

The valorization of agro-industrial by-products into high-value functional biopolymers represents a central objective of circular bioeconomy strategies. Gellan gum is a microbial polysaccharide widely used in food, pharmaceutical, and biomedical applications. In this context, the present study develops an integrated bioprocess that valorizes wheat bran (WB), an abundant underutilized cereal by-product, for gellan gum production via microbial fermentation. This study follows an integrated approach in which gellan gum was biosynthesized by Sphingomonas paucimobilis ATCC 31461 using an enzymatically hydrolyzed WB as the sole carbon source. Gellan gum synthesis was primarily affected by inoculum size, whereas the initial total reducing sugar (TRS) concentration had a secondary effect within the investigated range. The highest gellan titers (11.07 ± 0.21, 11.60 ± 0.52, and 11.76 ± 0.48 g/L) were obtained at an initial TRS concentration of 50 g/L and increased with inoculum size. The highest conversion yields (24.82 ± 2.58, 26.82 ± 1.59, and 29.35 ± 2.40%) were observed at the lowest TRS level tested (20 g/L), with yield decreasing as substrate concentration increased; moreover, lower inoculum levels were associated with higher yields, indicating more efficient substrate-to-polymer conversion under biomass-limited conditions. Structural characterization confirmed that the recovered biopolymer matches commercial gellan gum, indicating that WB hydrolysates can effectively replace refined sugars in gellan gum production. The results demonstrate that WB hydrolysate can support gellan gum biosynthesis without refined sugars, while preserving the structural integrity of the biopolymer. These findings highlight the potential of lignocellulosic-derived carbon sources for sustainable microbial polysaccharide production.