Drying of persimmon fruit (Diospyros kaki L.) pretreated by different osmotic processes

Abstract

Persimmon is a short shelf life fruit with interesting potential for application in different industrial segments. The immersion of food in a hypertonic (30 and 45 °Brix) or even hypotonic medium can be used as a pretreatment for the drying process. In this study, the convective drying of persimmons was preceded by osmotic dehydration (OD) with fructose in a standard atmosphere, pulsed vacuum osmotic dehydration (PVOD), ultrasound (US)-assisted OD, and US pretreatment in distilled water. Pretreatment times were 0, 10, and 30 min. The samples were subjected to convective drying at 40 and 60°C, 0.5 m s−1. The effects of the pretreatments on the drying kinetics, volumetric shrinkage, and rehydration capacity were investigated. Fick's model and the Dincer and Dost model were used to fit the drying evolution. In addition to the influence of the osmotic solution concentration, moisture content and solid gain were functions of the treatment type. Convective drying required 260–740 min. The use of PVOD and US pretreatments resulted in the shortest drying times. The dried fruits showed particular characteristics with each different pretreatment. Both tested models presented satisfactory adjustments, but Fick's model was the best approach. In general, the treatments caused structural modifications in the persimmon fruits that modified the drying kinetics and the properties of the dried food.

Practical Applications Convective drying is a food processing method used to extend the shelf life of fruits, such as persimmons. The use of pretreatments is an interesting strategy to improve the drying process. However, the combination of these technologies can influence drying kinetics. Therefore, the use of mathematical models is important to represent the behavior of these processes.