Effect of ultrasound pre treatment on drying behavior, ascorbic acid, lycopene, color and other related properties of tomato slices

Drying of tomatoes is a process commonly used to preserve the product and to prolong its shelf-life. This study aims to investigateeffect of ultrasonicpre-treatment on drying time andqualityproperties of tomatoslicesdriedbymicrowavecombinedwith hot air at 60°C with the intent to reduce drying time and to improve quality properties. The influence of ultrasound pre-treatment (20 and 40 min) and different microwave power levels (120, 150 and 180 Watt) on drying time, vitamin C, lycopene, total phenolics content, shrinkage, rehydration and color values of dried slices of tomato was studied. Results showed that as microwave power level increased, drying time to a final moisture content of 17.65 % decreased significantly. On the other hand, ultrasound pretreatment reduced drying time about 1.68-7.38 %. Depending on drying conditions, vitamin C and lycopene contents reduced from 433.94 to 81.89 mg AA/100 g dry solids and 3920.57 to 415.40 mg/100 g dry solids, respectively. The change in total phenolics content was not severe as much as vitamin C and lycopene contents. Rehydration capacity of ultrasound pretreated samples was larger than non-treated samples. The color values of dried tomato slices were in the acceptable range (TCD: 0.92 - 8.25 and a*/b* ratio:1.30- 1.59). Key words: Drying, tomatoes, microwave, ultrasound pre-treatment, vitamin C, lycopene.