Abstract
The effect of ultraviolet irradiation on the activity of polyphenol oxidase and peroxidase in pear juices from six different varieties (Abate Fetel, Passa Crassana, Ercolini, Flor de Invierno, Blanquilla, and Conference) was investigated. The samples were irradiated for 120 min with a 400-W nominal power medium-pressure mercury lamp, emitting in a range between 250 and 740 nm. The temperature was kept at 25 ± 1 °C with help of a refrigeration system consisting on a metallic coil fed with cold water. Polyphenol oxidase was inactivated in different rates, depending on each variety’s properties. Besides, as irradiation time increased, there was a general decrease in the absorbance spectrum, which means that some of the juice’s pigments could have been damaged. This decrease was especially significant between 400 and 450 nm. These changes were also observed by means of CIELab parameters. Vitamin C also decreased during the treatment. No variations in the pH, soluble solids, and sugar content were observed.
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