Bioconversion of wheat and bean straw by thermo-alkaliphilic actinomycetes for enhanced polygalacturonase yield: statistical optimization and industrial application.

Extremophilic actinomycetes are promising microbial candidates in biotechnology due to their ability to decompose various agricultural wastes and are used to produce several enzymes with important applied properties. This study explored the biotechnological potential of Streptomyces griseorubens NBR14 and Nocardiopsis synnemataformans NBR9 by evaluating their polygalacturonase production from wheat and bean straw, and assessing the enzyme's efficacy in fruit juice clarification, as well as their ability to decolorize crystal violet. To optimize enzyme production, experiments with four variables were conducted using Box-Behnken design (BBD), followed by analysis of variance (ANOVA). The enzyme was then partially purified using acetone, followed by analyzing its properties and potential applications in fruit juice clarification. The optimal conditions for polygalacturonase (PG) activity by NBR14 and NBR9 were 40 °C, pH 9 and 7, incubation for 7 days, and substrate concentrations 2 and 3 g/100 mL, resulting in enzyme yields of 3.54- and 2.20-folds respectively. Partially purified polygalacturonase resulted in 7.07 and 2.99-fold purification, with recoveries of 33.5% and 16.61%, and specific activities of 177.9 and 72.13 U/mg, respectively. Both NBR14 and NBR9 partially purified polygalacturonase exhibited high relative activity at 40 °C and pH value 7. It remained 90% and 88% active at pH 9.0 and 64% and 81% at 60 °C, respectively. The maximum clarity recorded for apple juice was 82.75% and 85.75%, while orange juice clarity was noted at 61.77% and 83.31% for NBR14 and NBR9, respectively. These results highlight the potential of thermo-alkali stable polygalacturonase from extremophilic actinomycetes as a long-term and cost-effective biocatalyst for agro-waste valorization and industrial fruit juice processing.