Radiochromic film dosimetry for UV-C treatments of apple fruit

Authors: YAN, RUIXIANG - National Engineering Center For Vegetables; YUN, JUAN - Tianjin University Of Science And Technology; Gurtler, Joshua; Fan, Xuetong

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2017
Publication Date: 1/16/2017
Citation: Yan, R., Yun, J., Gurtler, J., Fan, X. 2017. Radiochromic film dosimetry for UV-C treatments of apple fruit. Postharvest Biology and Technology. 127:14-20.

Interpretive Summary: Ultraviolet light (UV-C) is lethal to a wide range of microorganisms. However, the technology has limited commercial applications on fresh produce, partially due to difficulties in measuring actual doses received by fruits and vegetables, as well as uneven UV exposure on the surface of fresh produce items. In the present study, we investigated the suitability of radiochromic film to estimate UV-C doses, and used the film to evaluate dose uniformity on apple fruit surfaces. Results show that radiochromic film develops stable color changes in response to UV-C treatments at different temperatures, and is suitable for measuring UV-C doses. Furthermore, a rotating device provides dose uniformity on the surface of apples. The information will help the fruit industry adopt the technology to enhance microbial safety of fruits.

Technical Abstract: 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 (black cloth), 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 UC-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 days at dark and ambient temperature (21 +/- 2 degrees C). The temperature (21 degrees C vs 4 degrees 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 6.0 mW/cm(2) developed a more intense color compared to those at 9.4 mW/cm(2). The changes in color of the films as a function of UV-C dose were measured as absorbance at 510 and 600 nm. The relationship between A(510 nm) 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 (CV) and the ratio of maximum/minimum doses. The CV for the estimated doses was 32.2, 59.6, 29.9 and 7.7% and max/min was 147.6, 86.4, 132.7 and 2.1 for fruit treated in the treatment chamber without reflective material, with stainless steel and aluminum foil, and with the rotating device, respectively. 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.