Investigate the physicochemical properties of semi-dried yacon slices at different drying temperatures after being treated with ultrasound and microwave-assisted osmotic dehydration

Abstract

This study was carried out to examine the change in physicochemical properties of yacon (Smallanthus sonchifolius) dried at 50, 60, and 70°C after being pre-treated in an osmotic solution (sorbitol 60 Brix) with and without the aid of ultrasound and microwave. The water loss and solid gain during the pre-treatment were investigated. Moreover, the experimental data obtained during the drying processes were fitted with a Two-term model to predict the drying kinetics of yacon. The results showed that when ultrasound and microwave were applied, the more water loss (from 30.05 to 41.01 - 47.97%). The two-term model was found to be suitable for describing the drying process of yacon. The considerable differences in physicochemical properties of yacon after pre-treatment with an osmotic solution with and without ultrasound and microwave were observed. After being pre-treated in an osmotic solution with and without the support of ultrasound and microwave, the yacon samples show no noticeable effect on the product's color after drying. For example, in terms of brightness, before drying, the L* value ranged from 48.38 to 50.31 for samples that used supporting methods for osmotic dehydration and after drying, the value ranged from 47.64 to 52.15. In addition, the results also reveal that although the drying temperature does not affect the hardness of the yacon after drying, assisting methods such as ultrasonic waves and microwaves do. By destroying the internal structure of samples, these support methods contributed to the reduction in the hardness of yacon samples. In terms of total sugar content, after being treated with different supporting methods and drying temperatures, there was no significant difference in total sugar content of untreated samples and the samples that used the support method (except for samples that used microwave-assisting osmotic dehydration and dried at 50oC which has the highest total sugar content (30.38 mg/g (d.m.)).