Fermentation of foods by lactic acid bacteria is a useful way to improve the nutritional value of foods. In this study, the health-promoting effects of fermented papaya juices by two species, Lactobacillus acidophilus and Lactobacillus plantarum, were determined. Changes in pH, reducing sugar, organic acids, and volatile compounds were determined, and the vitamin C, total phenolic content, and flavonoid and antioxidant capacities during the fermentation process were investigated. Juices fermented by Lactobacillus acidophilus and Lactobacillus plantarum had similar changes in pH and reducing sugar content during the 48 h fermentation period. Large amounts of aroma-associated compounds and organic acids were produced, especially lactic acid, which increased significantly ( < 0.05) (543.18 mg/100 mL and 571.29 mg/100 mL, resp.), improving the quality of the beverage. In contrast, the production of four antioxidant capacities in the fermented papaya juices showed different trends after 48 hours' fermentation by two bacteria. Lactobacillus plantarum generated better antioxidant activities compared to Lactobacillus acidophilus after 48 h of fermentation. These results indicate that fermentation of papaya juice can improve its utilization and nutritional effect.

This study aimed to evaluate the effects of black pepper petroleum extract (BPPE) on pathogenic bacteria. The extraction from black pepper showed intense antimicrobial activity against the Gram-positive ATCC 19115 and the Gram-negative bacteria ATCC 14028. The minimum inhibitory concentrations of BPPE against and were 0.625 and 1.25 mg/ml, respectively. Detection of Alkaline phosphatase outside the cell revealed that BPPE treatment destroyed the cell wall integrity. BPPE also altered the membrane integrity, thereby causing leaching of 260 and 280 nm UV-absorbing materials into the medium, particularly, nucleic acids and proteins. Propidium iodide infiltration experiments also indicated that BPPE treatment altered the permeability of bacterial cell membrane. Moreover, Na/K-ATPase activity was inhibited by BPPE. And the results of scanning electron microscopy showed that BPPE treatment damaged the morphology of the tested bacteria. These results indicated that BPPE could destroy cell wall integrity, alter the permeability of cell membrane, and inhibit the activity of intracellular enzyme, which could kill bacteria.