Harnessing soybean hulls for improved polygalacturonase production by Aspergillus sojae through fine-tuning of ambient pH

Abstract

BACKGROUND: Soybean hulls result from the processing of the bean for producing oil and protein products. This by-product generated massively in America has virtually no commercial value, so substantial effort is being applied to its exploitation for generating value-added goods. This work evaluates soybean hulls as inducer of the production of pectinolytic enzymes, through optimization studies regarding polygalacturonase production by Aspergillus sojae in submerged cultures. RESULTS: A 2-fold improvement in polygalacturonase yield was found by varying the initial pH of the culture in a very narrow acid pH range (2.40–2.80). The optimized fermentation process was successfully transferred to stirred-tank bioreactors in terms of volumetric productivity, and final polygalacturonase yields were 42 U mL-1 and 1.39 U g-1 soybean hulls, which are among the highest reported with this by-product. Morphological characterization of A. sojae during cultivation showed that the fungus mainly developed in dispersed mycelia at initial pH of 2.40–2.80 while, conversely, fungal pellets predominated in cultures performed at initial pH of 5.40. CONCLUSION: High enzyme titers are possibly connected to the formation of dispersed mycelia, as well as to acid-induced expression of the respective gene/s. It is foreseen that this data will be helpful regarding the production of fungal pectinases or other acid-induced enzymes. © 2017 Society of Chemical Industry.