Raisins are dried grapes usually through sun drying, shade drying, or mechanical drying. Due to its good flavor and high nutritional value, raisin is a popular snack and is also used as part of many other food products. Since grape epidermis contain a waxy layer, the removal of water from grapes is difficult, which makes the drying of grapes a very slow and complicated process. To overcome this problem, most of the grapes are pre-treated with soaking chemicals to crack or dissolve the waxy layer before drying. However, the use of chemical may result in the presence of unwated residual materials in the end product. Plasma, a neutral gas in an ionized state that consists of a large number of different species such as electrons, positive and negative ions, free radicals, and gas atoms. These active particles have great energy that collide with the target, on which the surface is etched and stripped through rapid chemical reactions. Non-thermal plasma, also called cold plasma, can channel energy to produce high-energy particles that remains near the room temperature making it a good alternative to process heat-sensitive materials. Currently, cold plasma is used as a novel food processing technology that uses highly reactive gases to inactivate microorganisms in food and could be extended to other area such as food drying. The objective of this study is to investigate the potential of reducing drying time through changing the chemical properties of the waxy grape surface using cold plasma treatment. The change in the structural and chemical properties of the grape surface is observed using scanning electron microscopy(SEM) and Fourier transform infrared spectroscopy (FTIR). The effect of cold plasma pretreatment on the drying rate and other quality parameters like color, appearance, total soluble solids (TSS) were compared with that to the chemicals soaking pretreated, untreated and peeling-treated raisin dried at 70 degrees Celsius. The result from this study indicated that cold plasma is an effective drying pretreatment that can effectively decrease the drying time by more than 50% while maintain great product quality. This work is by-far the first to demonstrate the application of cold plasma technology in food drying and could be used for future reference to further applied to other fruits and vegetables which contain heat-sensitive factors or functional ingredients.

Cold Plasma pretreatment modified the chemical properties of grape surface: Enhancing the drying rate and final raisin quality

254th National Meeting (2017)

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