engleski

Effect of Dipping Treatments on the Quality of Dried Plums

The quality of dried plums depends on the drying parameters, as well as the pretreatments used prior to drying. Since plums are covered naturally with a thin layer of wax, it is necessary to increase water transport from plums to drying medium. Chemical pre-treatments normally break down the waxy fruit surface and create microscopic cracks which increase moisture permeability. The best pre-treatment method for drying any fruit should optimally reduce drying time while keeping product quality high (color, nutrient content, taste, etc.). Therefore, the aim of this research was to select an appropriate chemical and thermal pre-treatment combination for plum drying at low and moderate temperatures occurring in a laboratory tray dryer to minimize the plums’quality loss. In order to select the best plum cultivar for drying four cultivars (Prunus domestica L.) President, Topend, Tophit and Topper are investigated in terms of physical and chemical parameters (total dry matter, total soluble solids, pH, total acidity) and phenolics (total phenols (TP), total flavonoids (TF) and total nonflavonoids (TNF)). Compared to other cultivars, Topend demonstrated the best characteristics for drying showing the highest phenolic content, soluble solids and lower total acidity, therefore is chosen for drying process. Topend plums were dipped in one of two different pre-treatment solutions (1% KOH or water) at two dipping temperatures (23 or 60 °C) for 1 min to accelerate the skin moisture diffusivity by breaking down the waxy cuticular surface of plum. Subsequently the plum samples were dried at low or moderate temperatures (<70 °C) and completed approximately over the 13 hours. Physical and chemical parameters are not markedly differing among plums dipped in 22 °C or 60 °C hot water. However, plums treated by 1% KOH at 60 °C dipping temperature showed higher total dry matter, pH and total acidity in comparison to plums treated by 1% KOH at 22° C dipping temperature. The pretreatment combinations caused variations in the prune phenolics, too. Obtained results indicate that dipping at 60 °C results with higher concentrations of phenolics regardless of solution type. The highest concentrations of TP and TNF were found in plums pre-treated with 1% KOH (60 °C), while the highest concentrations of TF were found in plums pre-treated with water at 22 °C. In conclusion, the experimental results show that the selection of dipping temperature and chemical solution is an important step for successful dried plum production at low and moderate air drying temperatures.

dried plums; drying at moderate temperature; dipping treatment; phenols

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