Influence of pretreatment on plum drying rate

Abstract

Plum drying is a slow and time-consuming process because whole fruits are being dried. As drying period is limited, since conditioned by technological properties of plum suitable for this type of processing, in order to increase production, drying period should be reduced which is achieved by different pretreatments such as dipping. Another possibility of production increase is to extend drying season using frozen fruit, considering its availability throughout the whole year. Consequently, freezing can be considered as a pretreatment in prune production. In this study, plum cultivars of the Fruit Research Institute recommended for drying (‘Čačanska Rodna’ and ‘Nada’) and cultivar ‘Stanley’, most commonly used for drying, have been tested. Drying was done at an experimental convective drier at the air temperature of 90 °C and the air streaming rate of 4 m/s until 75% of total dry matter was reached. The aim of the work was to examine the drying rate of frozen plum fruits compared to dipped ones (conventional pretreatment) and non-treated fruits (control). Drying rate differed depending on varietal characteristics and pretreatments applied. The highest drying rate was in frozen fruits of cultivars ‘Čačanska Rodna’. In cultivars ‘Nada’ and ‘Stanley’, pretreatments had insignificant effect on drying rate.