PRODUCTION AND SOME PHYSICOCHEMICAL PROPERTIES OF ACID PROTEASE FROM Aspergillus niger (NRRL 1785)

Abstract

The effect of growth of Aspergillus niger (NRRL 1785) on acid protease production was investigated over a five day fermentation period. The production of acid protease by Aspergillus niger (NRRL 1785) using five saccharides (glucose, sucrose, lactose, maltose and starch), glycerol and six nitrogenous compounds (peptone, beef extract, groundnut meal, yeast extract, casein and. urea) was also investigated. The physicochemical properties of the acid protease were also examined. Results show that Aspergillus niger (NRRL 1785) was found to be a very good source of acid protease. Maximum enzyme production was obtained at the 96th hour. Glucose was the best saccharide that supported its production while peptone was the best nitrogenous compound. These two compounds produced highest enzyme unit of 26.05Umr1. The acid protease produced had optimum pH of 4.0 while the enzyme was stable (60% relative activity and above) over a wide range of pH 2.0 - 5.5. The optimum temperature for acid protease was determined to be 50°C. The enzyme was also stable up to this temperature (50°C) at pH 4.0 for 1 hour. Calcium ions had an activating effect on acid protease while mercury, lead and sodium ions had inhibitory effects. Furthermore, the stability of acid protease at 50°C was enhanced in the presence of calcium ions and reduced in the presence of sodium ions. The characteristics of the acid protease obtained in this study are reminiscent of typical acid protease reported , in literature.