Effect of ultrasonic vibration on pineapple drying

Abstract

Thailand is known to have various types of tropical fruits. Fruits are generally produced in large quantities annually. Preservation can add value and extend the shelf life of these fruit products. One of the most popular methods of preservation is the drying process. A solar-powered dryer is widely used in fruit drying because of its low cost in terms of energy use. Ultrasonic vibration technology can be used to induce water movement in a product resulting in a faster dehydration rate. This can shorten the overall drying time and preserve the vitamins and nutrients in the product. In this work, the application of ultrasonic vibration to fruit drying was investigated. The raw material tested was pineapple. Drying was carried out in a hot air oven set to a temperature of 60 °C, with an applied vibration frequency of 40 kHz continuously for a short duration of 1 min. Three periods of the applied ultrasonic cycle (on for every 10, 20, 30 min) were tested for an overall drying time of 10 h. The results showed that for a cycle of every 10 min with vibration turned on, the initial moisture content of pineapples was reduced from 86.9 to 47.9 % wet basis at a maximum drying rate of 48.6 g/h, compared to 40.5 g/h from normal drying without applied vibration. The reduced drying time led to reduced energy consumption. This technique has the potential to be applied to other types of fruits and dryers.