The Efficacy of Mulberry Leaf Extract in Inhibiting Gram-positive Pathogenic Bacteria During the Post-fermentation Process of Fermented Fish (Pla-ra)

Abstract

Foodborne disease caused by consuming of pathogenic microorganisms contaminated food or drinking water is an important public health problem which causing of illness and death. Pathogenic microorganisms are highly contaminated from fermented foods, such as fermented fish (Pla-ra), which is popularly consumed in the northeastern region of Thailand. This study aimed to investigate the key chemical compounds of five mulberry (Morus spp.) cultivars and to evaluate the efficacy of their leaf extracts in inhibiting the growth of pathogenic bacteria during the post-fermentation process of Pla-ra. From the antioxidant activity testing and the content of phenolic compounds and flavonoids from five mulberry strains, which are Buriram 60, Khun Pai, Mon Pai, SakonNakhon 72 and SakonNakhon 85, found that, the ethanolic crude extracts from SakonNakhon 85 strain has the highest amount of these substances, 0.183±0.012 mg gallic acid equivalent /mg of crude extracts, 125.39±3.96 mg quercetin equivalent / mg of crude extracts, respectively, as well as an antioxidant activity. However, from the gram positive pathogenic bacterial growth inhibition results shown the best inhibitory effect in both water and ethanolic crude extracts from Mon Pai strain. The minimum inhibitory concentration of Staphylococcus aureus and Bacillus cereus were 12.5-25.0 mg/mL and 3.1-6.3 mg/ml, respectively, and the minimum bactericidal concentration of S. aureus and B. cereus were 25.0-50.0 mg/mL and 3.1-12.5 mg/mL, respectively. Moreover, when using crude extracts from Mon Pai strain at a concentration of 50.0 mg/ml in the process after fermentation for 28 days. It can effectively reduce the total number of bacteria and B. cereus, and moderately inhibited the growth of S. aureus compared to the control samples. From the results of this study found that the crude extract from the mulberry leaf was effective and can be used in the fermentation process of fermented fish to inhibit pathogenic bacteria which can reduce the risk of foodborne disease.