Acid protease production by Aspergillus oryzae on potato pulp powder with emphasis on glycine releasing activity: A benefit to the food industry

•Production of acid protease with glycine realizing properties is reported.•Potato byproducts were transformed using Aspergillus oryzae.•Improved strain and statistical optimization enhanced enzyme production.

Potato pulp powder is a major byproduct generated in huge amounts globally from potato processing industry. The disposal of these residues causes environmental pollution. Considering the use of agro byproduct as economic and environmental benefits, biotranformation of Potato pulp powder by solid state fermentation for the production of acid protease a valuable food enzyme is explored. Screening of food grade and industrial Aspergillus oryzae strains on enriched media identified A. oryzae RIB 40 (ATCC 42149) yielding 20.5 U/ml of acid protease as a potential candidate. Further, the productivity of the parent strain was improved by UV mutagenesis with a lethality of 1.8 × 10−4. The mutant strain (F6) produced 5.6 fold higher than the parent. The solid state fermentation of A. oryzae (F6) with potato pulp powder as a sole source and along with supplementation of nitrogen yielded 2.85 ± 5.0 and 18.68 U/g of acid protease, respectively. Statistical optimization of biovariables, namely moisture (50%), temperature (30 °C) and fermentation time (120 h) accomplished using a central composite rotatable experimental design, led to an 11-fold increase in protease activity (31 U/g dry substrate). Model validations indicated 95% agreement between the experimental results and the predicted responses. The acid protease from A. oryzae liberated glycine (0.57 ± 0.25 U/g), which can enhance food palatability. Thus, the present study established fermenting potato pulp, with a starter culture of A. oryzae F6 strain and optimized variables can produce acid protease that has great potential for use in the food industry. This will also contribute to sustainable management in the potato industry and adds value-addition.