Effect of cold plasma pretreatment on drying kinetics and quality attributes of apple slices in Refractance window drying

Cold plasma (CP) is a state-of-the-art non-thermal technology with the potential to accelerate drying, preserve nutritional value, and inactivate enzymes in foods. The purpose of this study was to evaluate the impact of multipin atmospheric pressure CP pretreatment (5, 10, and 20 min) on Refractance window drying (RWD) of apple slices (2 mm thick). The results showed that CP pretreatment could accelerate the drying process and shorten drying time by up to, with the best results obtained after a 10-min CP exposure. Scanning electron microscopy revealed that the CP pretreatment significantly altered the surface morphology of apple slices by etching microchannels due to the bombardment of reactive plasma species, contributing to enhanced drying kinetics. The CP pretreatment also enhanced the rehydration ratio (up to 21.63%) and decreased the dried apple slices' hardness (up to 29.79%). CP pretreatment of 5, 10, and 20 min resulted in 18.33%, 39.4%, and 30.06% reductions in polyphenol oxidase enzyme activity, respectively. As a result, CP-pretreated samples showed better color values compared to other samples. Furthermore, compared to RWD samples alone, CP-pretreated apple slices retained significantly higher (P < 0.05) antioxidant activity, phenolics, flavonoids, and ascorbic acid content. Chemical dipping and thermal blanching are commonly used as pretreatments for inactivating enzymes and improving the drying process of fruits. However, chemical pretreatments can leave residues, while thermal blanching results in the loss of bioactive compounds. The findings of this study demonstrated that CP as a pretreatment can effectively inactivate enzymes and enhance drying kinetics while preserving nutritional quality. Moreover, the results also showed that RWD can preserve better physicochemical properties than conventional hot air drying. Therefore, CP pretreatment coupled with RWD can be a promising alternative to conventional methods for drying fruits in industrial settings.