Effects of ultraviolet light emitting diodes (LEDs) on microbial and enzyme inactivation of apple

In this study, the effects of Ultraviolet light-emitting diodes (UV-LEDs) on the inactivation of E. coil K12 (ATCC 25253), an indicator organism of E. coil 0157:H7, and polyphneoloxidase (PPO) in cloudy apple juice (CM) were investigated. The clear (AJ) and cloudy apple juice were exposed to UV rays for 40 min by using a UV device composed of four UV-LEDs with peak emissions at 254 and 280 nm and coupled emissions as follows: 254/365, 254/405, 280/365, 280/405 and 254/280/365/405 mn. UV-LEDs at 254 sun achieved 1.6 +/- 0.1 log(10) CFU/mL inactivation of E. coil K12 at UV dose of 707.2 mJ/cm(2). The highest inactivation of E. coil K12 (2.0 +/- 0.1 log(10) CFU/mL and 2.0 +/- 0.4 log(10) CFU/mL) was achieved when the cloudy apple juice was treated with both 280 nm and 280/365 nm UV-LEDs. For clear apple juice the highest inactivation 4.4 log(10) CFU/mL obtained for E. coil 1(12 was achieved using 4 lamps emitting light at 280 nm for 40 min exposure time. For the same treatment time, the experiments using a combination of lamps emitting light at 280 and 365 nm (21amp/21amp) were resulted in 3.9 +/- 0.2 log(10) CFU/mL reductions. UV-A and UV-C rays in combination showed a better inactivation effect on PPO than UV-C rays used separately. Residual activity of PPO in CAJ was reduced to 32.58% when treated with UV-LED in combination of UV-C (280 nm) and UV-A (365 nm) rays. Additionally, the total color change (Delta E) of CM subjected to combined UV-LED irradiation at 280/365 nm was the lowest compared to other studied processing conditions. This study provides key implications for the future application of UV-LEDs to fruit juice pasteurization.