Effects of different drying methods on the physicochemical properties of pomegranate leather (pestil)

- Refractance window drying was used in pestil production for the first time.
- Hydrocolloid formulation retained high levels of bioactive compounds.
- Microwave-assisted drying promotes non-enzymatic browning reactions.
- Refractance windows drying improve ascorbic acid retention.

The present study examines the effects of various formulations (traditional and hydrocolloid) and drying techniques [hot air drying at 50, 60 or 70 °C, microwave-assisted hot air drying (90 or 180 W) at 50, 60 or 70 °C and refractance window drying 90, 95 and 98 °C), in order to develop new methods for pomegranate pestil production. Water activity, pH, color, textural properties, total phenolic content, total flavonoids, total proantocyanidins, total monomeric anthocyanin, ascorbic acid, HMF content, antioxidant activity, phenolic and anthocyanin profiles and volatile compounds of the pestils were determined. Hydrocolloid formulation resulted in superior physicochemical properties of the pestils compared to traditional formulation. While microwave-assisted drying (MWD) provided higher phenolic content, refractance window (RW) drying provided higher ascorbic acid and anthocyanin content, and lower content of 5-hydroxymethylfurfural. Volatile compounds in the pestils showed that MWD promoted non-enzymatic browning reactions. Overall, the hydrocolloid formulation and the RW drying technique are the most promising processing methods for high-quality pestil production with high content of bioactive compounds.