Inactivation of Escherichia coli, Salmonella enterica and Listeria monocytogenes on apple peel and apple juice by ultraviolet C light treatments with two irradiation devices

Following the market trends, the consumption of fresh and cold-pressed juice in Europe is increasing. However, a primary concern – particularly in apple juice – is the related outbreaks caused by food-borne pathogens. One of the challenges is to find methods able to reduce pathogenic loads while avoiding deterioration of nutritional properties and bioactive compounds that occur in thermal pasteurization processes. In this study, the inactivation of Escherichia coli, Salmonella enterica and Listeria monocytogenes was evaluated under different ultraviolet C (UVC254nm) light treatments (up to 10,665.9 ± 28.1 mJ/cm2), in two different steps of the production chain (before and after juice processing): on apple peel discs and in apple juice. The systems proposed were a horizontal chamber with UVC254nm emitting lamps treating the product disposed at a distance of 12 cm, and a tank containing UVC254nm lamps and in which the product is immersed and agitated. Final reductions ranged from 3.3 ± 0.5 to 5.3 ± 0.4 logarithmic units, depending on the microorganism, matrix and used device. The survival curves were adjusted to Weibull and biphasic models (R2-adj ≥ 0.852), and UVC doses needed for the first decimal reduction were calculated, being lower for the apple peel discs (0.20 to 83.83 mJ/cm2) than they were for apple juice (174.60 to 1273.31 mJ/cm2), probably for the low transmittance of the apple juice compared to the surface treatment occurring on the peels. Within the treatments evaluated, the UVC254nm irradiation of apple peels immersed in water was the best option as it resulted in a reduction of the tested microorganisms of ca. 2–3 log units at lower UVC254nm doses (< 500 mJ/cm2) when compared to those occurring in apple peel treated with the UVC chamber and in juice. As contamination can proceed from apples, the sanitization of these fruit prior to juice production may be helpful in reducing the safety risks of the final product, reducing the drawbacks related to the poor transmittance of the fruit juices.This research was funded by the Spanish Ministry of Science and Innovation (MICINN), research project QUALISAFEJUICE [PID2019- 106645RB-I00], and the Spanish Ministry of Economy, Industry and Competitiveness (MINECO), with a postdoctoral orientation period grant [BES 2017 079779] (I. Nicolau-Lape ̃na)