Purification and characterisation of an acid protease from theAspergillus hennebergiiHX08 and its potential in traditional fermentation

A protease AP3 from Aspergillus hennebergii HX08 was purified by ammonium-sulphate precipitation, followed by anion-exchange chromatography and gel filtration. The molecular weight of acid protease AP3 was 33 kDa (SDS-PAGE and MALDI-TOF-MS). The protease AP3 was identified as an acid protease with MALDI-TOF/TOF tandem MS. Its optimal temperature and pH were 60°C and 4.0, respectively. Its Kmax and Vmax were 57.92 mg/mL and 32.57 U/mL, respectively. The enzyme was active over a broad pH and temperature range (pH 3.0–5.0 and 30–60°C), and exhibited high activity and stability in 2–12% (v/v) ethanol solvent. Subsequent studies suggest that the enzyme presents a relatively high substrate affinity to wheat protein (98% of total activity). Its application to solid-state fermentation of wheat flour with Saccharomyces cerevisiae could increase the hydrolysis degree of wheat protein (28.26%) and amino acid nitrogen concentration of fermented grains (34.21%). Additionally, enhanced S. cerevisiae biomass (37.09%) and alcohol concentration (38.29%) were also observed during the process. Volatile compounds analysis of fermented grains by headspace solid-phase micro-extraction and GC-MS revealed more flavour compounds. These results suggest its potential in food and alcohol industries. Copyright © 2017 The Institute of Brewing & Distilling