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.
