Drying kinetics, heat quantities, and physiochemical characteristics of strawberry puree by Refractance Window drying system

Abstract

AbstractAttempts were made to understand the drying kinetics, different heats involved, and change in physiochemical properties during Refractance Window (RW) drying of strawberry puree on an in‐house fabricated RW drier. RW drying of puree was conducted at 75°C water temperature with 1.5 mm thickness. The drying was carried out from initial moisture content 614% (db) to 5.1% (db) with1.2 m/s exhaust air velocity. RW drying took place only in the falling rate period. The sensible heat of strawberry puree, convective heat loss from puree surface to air, and convective heat loss from the bottom surface (hot water to air) of the dryer were 70, 205, and 61.96 W, respectively. The evaporative capacity of 5.28 kg m−2 hr−1 was calculated at experimental parameters. This confirms that the drying system is advantageous. RW dried strawberry puree was rehydrated as exact of fresh strawberry puree considering total solids. Total phenolic content and ascorbic acid were significantly (p < .05) reduced from 246.33 mg gallic acid equivalent (GAE) (fresh strawberry puree) to 204.67 mg GAE per 100 g (reconstituted RW dried strawberry puree); 33.31–28.54 mg/100 g, respectively. Color characterization through L*, a*, b*, darkness factor (b*/a*), chroma (C), and hue angle (h*) revealed that reconstituted RW dried puree sample was darker compared with fresh puree.Practical ApplicationsAmong various drying methods of fruit purees, hot air drying is the most widely used. It results in an unpleasurable taste and color. During the falling rate drying period, the less thermal conductivity of fruit puree restricts heat transfer in conventional drying. Refractance Window (RW) drying adopts low‐temperature drying for less time, which leads to advantages like effective and economical drying. RW drying technology can be promising at the commercial level in product quality and much‐reduced production cost.