Valorization of wheat milling by-products into bacterial nanocellulose via ex-situ modification following circular economy principles

Abstract

This study investigated the production of bacterial cellulose (BC) from wheat milling by-products and its post-modification to obtain nanostructures (BCNs). Crude enzyme consortia produced by Aspergillus awamori were involved in the enzymatic hydrolysis of wheat milling by-products to produce a nutrient-rich fermentation feedstock for BC production. The fermentation efficiency with Komagataeibacter sucrofermentans DSM 15973 was evaluated under various pH values and C/free amino nitrogen (FAN) ratios. The highest BC concentration (5.2 g/L) and productivity (0.74 g/L/day) were obtained at a pH value of 5.2 and a C/FAN ratio of 14.5 g/g. Sequential ex-situ modification of BC using H2SO4-assisted hydrolysis, led to BCNs with 45.8–73.1 nm fiber diameter (D) and length (L)/D ratio higher than 13. The crystallinity index (CrI) of BCNs was increased by 1.1 folds (90.1%), while thermogravimetric analysis revealed slight differences regarding the maximum decomposition temperature compared to the untreated BC (338 °C). The FT-IR spectra of BC and BCNs showed typical cellulose vibration bands while peaks at 748 cm−1 and 709 cm−1 indicated the presence of Iα and Iβ allomorphs. Size distribution of BCNs via dynamic light scattering exhibited polydispersity within the nanoscale (72 nm and 931 nm). Surface charge of BCNs (in absolute value) was increased by 44.5% compared to BC.