High-level expression and characterization of a novel aspartic protease from Talaromyces leycettanus JCM12802 and its potential application in juice clarification.

Aspartic proteases are promising fining agents used in the production of fruit juices. In this study, a novel aspartic protease gene (Tlap) was identified in Talaromyces leycettanus JCM12802 and heterologously expressed in Pichia pastoris. Using casein as the substrate, purified recombinant TlAP showed optimal activities at pH 3.0 and 55 °C with a specific activity of 1795.4 ± 62.8 U/mg, and remained stable over a pH range of 3.0-6.0 and at temperatures of 45 °C and below. Moreover, the enzyme was highly resistant to most metal ions and chemical reagents except for Fe3+ and β-mercaptoethanol. When added to apple, orange, grape and kiwi fruit juice, it showed excellent proteolytic activity against haze-forming proteins, decreasing the turbidity by up to 49.9 nephelometry turbidity units (NTU). These favorable enzymatic properties make TlAP attractive for potential use in the juice industry.