Investigation of antifungal activity of lactic acid bacteria isolated from sorghum, corn and barley sour doughs against Aspergillus flavus, Penicillium expansum and Rhizopus coriniformis molds

Abstract

Objective: In recent years, the use of biological methods to control the activity of molds with the help of lactic acid bacteria and their metabolites has received much attention. The aim of this study was to isolate and molecularly identify of lactic acid bacteria with antifungal ability from corn, sorghum and barley sour doughs. Methods: The anti-fungal properties of 68 cell bacterial isolates, bacterial supernatant and autoclaved cells were investigated on Aspergillus flavus, Penicillium expansum and Rhizopus coriniformis molds. Also, the anti-mold properties of the supernatant treated with pepsin and proteinase K enzymes were tested. Results: The results showed that the percentage of inhibition of live bacterial cells on the molds of A. flavus, P. expansum and R. coriniformis was between 0-16, -0.33 and -0.56 percent, respectively. The lowest inhibitory effect of live bacterial cells was observed on R. coriniformis and the highest inhibitory effect was observed on P. expansum. The supernatants of most isolates had an inhibitory effect on R. coriniformis in the range of 0-30 percent, while this inhibition of growth on P. expansum mold was in the range of 100-90 percent, indicating that this mold is sensitive to the supernatant of most isolates. Regarding the inhibitory effect on P. expansum and R. coriniformis, the highest frequency of isolates was in the range of 91-100 percent, which indicated that these two molds were more sensitive to the heated cell of the most bacterial isolates. Based on the results, finally three isolates were selected as superior isolates, all of which were identified as Lactobacillus plantarum. The supernatants from these three bacterial isolates when treated with pepsin, inhibited the growth of A. flavus only and had no inhibitory effect on the other two molds. Conclusion: The results of this study showed that it is possible to use L. plantarum and its supernatant for control of mold growth.

Keywords

• lactic acid bacteria
• pepsin
• heated cell
• cell-free supernatant
• anti-fungal activity