Antibacterial Effect of Noni Juice In Vitro and Applied to Fresh-Cut Papaya to Control Escherichia coli O157 : H7

Abstract

This study aimed to evaluate the effect of noni (Morinda citrifolia L.) juice (NJ) in vitro and applied it to fresh-cut papaya to control Escherichia coli O157 : H7. Furthermore, the NJ effect on the physicochemical characteristics of fresh-cut papaya was evaluated. We determined the minimal inhibitory concentration (MIC) in a microplate reader by the microdilution method using TSB using an initial concentration of 1 × 107 cells of E. coli/mL. Cubes of fresh-cut papaya fruit were immersed in an E. coli suspension (1 × 105 cells/mL) and after that in NJ three times (0, 2.5, and 5 min) and then stored at 4 ± 1°C for 18 days. The presence of E. coli and total coliforms, as well as pH, TSS, and titratable acidity, were evaluated every three days. The results of in vitro assays showed that NJ at 20% inhibited the microbial growth of E. coli, finding a maximum growth rate (μmax) of −0.0066 h−1. Immersion in NJ for 5 min presented a reduction of E. coli of 3.72 ± 1.43 log10 CFU/g of fresh-cut papaya fruit treated with this bacteria on day 9 of storage regarding control. Likewise, fresh-cut papaya fruit immersed in NJ for 5 min maintained the total coliforms between 1 and -1 log10 coliforms CFU/g for 18 days. However, the immersion treatment in NJ modified some physicochemical parameters of the fresh-cut papaya fruit, such as acidity and pH (P < 0.05). The application of NJ to fresh-cut papaya fruit showed in vitro and in vivo inhibition of E. coli and total coliforms, evidencing it as a possible bacterial control agent in the precut fruit industry for up to 18 days.