Optimization of Critical Fermentation Parameters for Improved Yield, and Characterization of Curdlan Biopolymer Produced by Agrobacterium Species Utilizing Agro-Waste

Abstract

The utilisation of agro-waste as an inexpensive alternative carbon source for curdlan production is increasing. However, low curdlan yields have been reported for Agrobacterium species utilising agro-waste. This study therefore optimised critical fermentation parameters to improve curdlan yield. Agrobacterium species isolated from legume fields were inoculated onto rice husk and corncob as carbon sources; the curdlan production process was optimised, and the produced curdlan was characterised using Fourier-transform infrared spectroscopy (FTIR). The results showed that 25 g/L rice husk produced the highest curdlan yield (0.73 g/L), with a reduction in yield at higher rice husk concentrations; a maximum curdlan yield of 0.7 g/L was achieved at 1 g/L urea, whereas the lowest yield (0.3 g/L) was recorded at 2 g/L urea; curdlan yield increased with pH, with the highest yield (0.76 g/L) recorded at pH 7; at 25°C, the curdlan yield was 0.4 g/L and increased to 0.62 g/L at 30°C; combined optimisation of the fermentation parameters produced a maximum curdlan yield of 0.91 g/L; and the curdlan produced by the Agrobacterium spp. exhibited peak values of 1071.44, 1366.57, and 3292.73 cm⁻¹, with the FTIR spectrum confirming the presence of the β-1,3-glucan (curdlan) polysaccharide structure. Rice husk and corncob are inexpensive carbon sources for curdlan production, and curdlan yield generally increased following process optimisation.