Abstract

In a screen of 175 fungal strains, Aspergillus oryzae LL1 and LL2 were identified as having the highest extracellular leucine aminopeptidase (LAP) activity. LAP activity was optimal when A. oryzae LL1 was subjected to submerged fermentation with an inoculum size of 10⁵ spores per ml and an agitation of 100 rpm at 30°C in media containing defatted soybean and rice husk with a pH of 4.5 for 72 h. Partial characterization of A. oryzae LL1 LAP revealed that it could be greatly inhibited by 2 mmol L^-1 of Pb²⁺, Cu²⁺, or Fe²⁺. In contrast, 2 mmol L^-1 Zn²⁺ stimulated LAP activity about one-fold compared to adding 30 mmol L^-1 zinc increased D_H to 33.3% for LAP LL1 during a piolot plant scale experiment hydrolysis of chopped chicken breast meat (Lin et al., 2008; Eur Food Res. Technol., 2008). To determine the stability of A. oryzae LL1 LAP, the samples were stored at -80, -20, 4 and 25°C for eight weeks with residual activities being reduced to 84, 72, 61 and 58%, respectively. Taken together, our data suggest that A. oryzae, LL1 LAP has tremendous potential for use in the food industry.

Key words: Leucine aminopeptidase, Aspergillus oryzae, culture conditions, fermentation, Zn²⁺