Effect of UV-Vis processing on enzymatic activity and the physicochemical properties of peach juices from different varieties

This work evaluated the effect of ultraviolet and visible light (UV-Vis) processing on the enzymatic activity (polyphenol oxidase and peroxidase) and physicochemical characteristics (pH, °Brix, acidity, formol index, phenolics, ascorbic acid, sugars and colour) of peach juices from three different varieties (Baby Gold, Calanda and Planet Top). Irradiation was performed for 120 min, at 25 and 45 °C, using a multi-wavelength emission lamp which provided a radiation power of 4.49 · 10−2 W·cm−2 at the liquid surface. After the treatments, no significant changes were observed in the pH value, acidity, vitamin C content, sugar content, or lightness. The phenolic content was reduced for the Planet Top juices, while the formol index decreased for the Calanda variety. a* and b* CIELab parameters decreased with processing time, contrary to that reported for thermal treatments. In most cases, UV-Vis irradiation was effective at inactivating polyphenol oxidase (PPO) and peroxidase (POD), although sometimes an initial activation was observed. The inactivation stage was described by a first-order model. At 45 °C, PPO was almost totally inactivated for the three juices studied, while reductions in POD of up to 60% were registered. Further experiments are suggested to improve the effectiveness of this technology for inactivating enzymes in peach juices.