Radiochromic film dosimetry for UV-C treatments of apple fruit

Abstract

UV-C can inactivate foodborne pathogens on surface of fruit such as apples. However, the practical application of the technology has been limited by lack of methods to measure UV-C doses received by fruit and difficulty of achieving uniform UV-C doses on the same pieces of fruit. In the present study, radiochromic films were evaluated for their suitability to estimate UV-C doses and dose uniformity on apple fruit surface. Parameters investigated included film type, color changes of the films in response to different UV-C doses, color stability of films, UV-C light intensity, and temperature. In addition, apples with films attached to six locations on the surface were exposed to UV-C in a treatment chamber without reflective material, with an aluminum foil and a stainless steel sheet in the bottom of treatment chamber as reflectors, in comparison with the use of a rotating device to study the UV-C dose uniformity of the fruit received. Results showed that the radiochromic films were sensitive to UV-C light as they changed to blue or pink upon exposure to UV. The developed color after UV-C irradiation was stable for at least 15 d at dark and ambient temperature (21±2°C). The temperature (21°C vs 4°C) at which the films were exposed did not affect the changes in color as a result of UV-C exposure. Films exposed to UV-C at an intensity of 60Wm−2 developed a more intense color compared to those at 94Wm−2. The changes in color of the films as a function of UV-C dose were measured as absorbance at 510 and 600nm. The relationship between A510nm and the UV-C dose could be expressed as polynomial equations, and the equations were used to predict UV-C doses on the surface of apples. The rotating device provided higher UV-C uniformity on the apple surface than other UV-C reflective materials as indicated by the coefficient of variations and the ratio of maximum/minimum doses. Therefore, the radiochromic film can be used as a UV dosimeter to determine UV dose distributions on individual fruits. Fruits treated with UV-C on a roller received uniformed UV-C exposure.