BIOCONVERSION OF MOLASSES FOR GLUCONIC ACID PRODUCTION

Abstract

The present study was undertaken to isolate a potent microbial strain having ability of gluconic acid production and to economize the fermentation process by utilizing sugarcane molasses as cheaper carbon source. The following strategy was undertaken to fulfill the aim of the present study. A total of 38 fungal strains were isolated from sugarcane industry wastes, garden soil and from the decomposing food and horticultural materials. Strain AR-12 was selected on the basis of its maximum gluconate production ability and identified as Aspergillus niger (ITCC 5483). The isolated strain Aspergillus niger AR-12 was evaluated for its ability to use sugarcane molasses for gluconic acid production under various fermentation systems. Among submerged, surface and solid-state fermentations, solid-state fermentation was found to be promising and more productive in comparison to other fermentation systems. Attempts were further made to develop a productive strain by physical and chemical mutagenesis of strain AR-12 having improved ability for production. Among the various mutants obtained following mutagenesis, mutant ARN-30 obtained by NTG mutagenesis had improved ability of production. Mutant ARN-30 was further mutagenised with UV, which had resulted into mutant ARNU-4 with increased production ability under solid-state fermentation. The distinction between the wild type Aspergillus nigerAR-\2 and mutant Aspergillus niger ARNU-4 was not limited to their gluconic acid production ability but also to their morphological features. Various parameters and factors for solid-state fermentation using untreated molasses as a low cost substrate were evaluated for gluconic acid production. Among the seven different solid supports viz., bagasse, corn cob, polyurethane sponge, tea waste, luffa sponge, jute and wheat bran, tea waste was found to be preferable solid support for maximal levels of production. The moisture level, spore age, aeration level and incubation period were also derived to achieve the maximal acid accumulation. Among the various additives evaluated, supplementation of fermentation medium with yeast extract had led into a further increase in the production levels. Mutagenesis and derivation of various factors appears to have resulted into induced levels of glucose oxidase resulting into higher levels of production. The various parameters thus derived were followed to scale up and develop a semi-continuous process for gluconic acid production. The designed bioreactor was exploited for recycling of the fungal biomass for multiple cycles of fermentation.