Isolation and Screening of Microorganisms Associated with Locust Bean (IRU) for the Ability to Ferment Soya Bean to Produce Soy Iru

Abstract

Aims: This study was conducted to isolate, identify and screen microorganisms associated with soy iru for the ability to be used as starter in the fermentation of soya bean (Glycine max) to produce soy iru. Study Design: To control the fermentation of soya bean (Glycine max) to produce soya iru using functional starter culture in order to improve the quality of the product. Place and Duration of Study: Soybeans (Glycine max) samples were collected from markets in Ibadan, in Oyo State Nigeria. Analyses of the samples were conducted in the Department of Microbiology, University of Ibadan and Central Multidisciplinary Research Laboratory in the University of Ibadan, Nigeria. The sampling and analyses were done between August 2014 to January 2015. Methodology: Soybean (Glycine max) seeds were purchased from markets, in Ibadan, Oyo State, Nigeria. Spontaneously fermented locust bean iru samples were also purchased from iru seller from markets, Ibadan, Oyo State and they were analysed using Nutrient agar, DeMann Rogosa and Sharpe medium (MRS), MacConkey Agar and Malt Extract Agar and isolates were also screened for enzymatic activity. The antibacterial activity of LAB metabolites against some indicator organisms was also determined; Results: A total of thirty eight (38) strains of bacteria were isolated, seven (7) isolates from locust bean iru (LBI) and thirty one (31) isolates from soya bean iru (SBI). Bacillus subtilis SBI 13 and Leuconostoc mesenteroides SBI 15 produced the three enzymes and the highest protease activity was produced by Bacillus subtilis SBI 13. All the isolated LAB produced antimicrobial compounds; lactic acid, diacetyl and hydrogen peroxides with Leuconostoc mesenteroides SBI 15 producing the highest quantity of diacetyl (0.91 g/l) and hydrogen peroxide (1.10 g/l) while the highest quantity of lactic acid (1.61 g/l) was produced by Lactobacillus plantarum. Bacillus subtilis SBI 13 and Leuconostoc mesenteroides SBI 15 were chosen as starter cultures for further study. Conclusion: Bacillus subtilis and Leuconostoc mesenteroides exhibit the best potentials of a good starter so they can be used as starter culture in the fermentation of soya beans to produce Soy Iru.