Pasteurization of onion juice by continuous UV-C reactor

The objective of this study is to investigate the continuous pasteurization of onion (Allium cepa L.) juice by ultraviolet (UV-C) irradiation by a designed coiled-tube type UV-C reactor. System is composed of four vertical low-pressure mercury lamps (20 W/lamp, 254 nm) coiled using a teflon tube. A reflector and a cooling jacket were placed outside the coiled tube. A secondary eddy flow effect was achieved with a Dean number of 0.073. The population of Escherichia coli K-12 strain (a surrogate of E. coli O157:H7) inoculated in onion juice was reduced by 4.83 log after being exposed to UV-C light for 8.13 min at an estimated UV-C dosage of 38.1 J/mL with the flow rate of 1.26 L/min. As a result of this UV-C treatment, the total color change (ΔE) of the onion juice was recorded as 1.15 which can be referred as slightly noticeable. Total aerobic mesophilic bacteria count of UV-C irradiated samples was below acceptable limits after 6 weeks of storage. Meat marination in UV-C treated onion juice reduced the hardness of meat by 78%. Combination of UV-C treatment (15.24 J/mL) with mild heat treatment (55 °C) resulted in more than 5log reduction in E. coli K-12. This study revealed that the designed coiled-type UV-C reactor was able to meet demand of consumers of fresh-like and pasteurized onion juice. This study provides some important findings which will form a basis for the further pilot-scale UV-C reactor design.