THERMOSTABLE ALKALINE PROTEASE FROM BACILLUS LICHENIFORMIS LBBL-11 ISOLATED FROM TRADITIONALLY FERMENTED AFRICAN LOCUST BEAN (PARKIA BIGLOBOSA)

Abstract

ABSTRACT Twelve strains of Bacillus licheniformis isolated from traditionally fermented African locust bean (Parkia biglobosa) were evaluated in respect to production of protease on skim milk agar. B. licheniformis LBBL-11 exhibited the highest proteolytic activity with an average area of clear zone measuring 960 mm2. Production of protease from B. licheniformis LBBL-11 was further studied by growing the strain on nutrient broth. Maximum protease production was 18.4 U/mL at 48 h of growth, which coincided with the end of exponential phase. The protease from this Bacillus sp. had optimum pH of 8.0 and was stable over a wide pH range of 5.0–11.0. The optimum temperature for the protease activity was 60C. The enzyme was 95% stable at 60C after 60 min of incubation. These properties indicate possible application of B. licheniformis LBBL-11 as potential starter culture for the fermentation of African locust bean under controlled conditions of temperature and pH. PRACTICAL APPLICATIONS African locust bean seeds (Parkia biglobosa) are rich in protein and usually fermented to a tasty food condiment (iru) used as flavor intensifier for soups. This is highly consumed in developing and under developed countries where there is high cost of animal protein. However, traditional fermentation techniques used in its production are often characterized by use of nonsterile equipment and unregulated conditions that lack control of microbial development that allow pathogens to survive or produce toxins in such products. Hence, for safety of consumers there is strong need for pure starter cultures that can be used under aseptic conditions, controlled pH and relatively high temperature, which make it very difficult for other microorganisms that might spoil the product to grow. As proteolysis is the main metabolic activity during the fermentation of African locust bean, a starter culture that produces a thermostable protease is highly desirable.