Characteristics of durian flesh flour (Durio zibethinus Murr.) processed by ultrasonic wave and convective drying

The research was carried out to determine the characteristics of durian flesh flour, which was processed by implementing ultrasonic waves and convective drying. The durian flesh was separated from seeds and sonicated in an ultrasonic bath prior to drying in a convective drying oven. The frequencies of the ultrasonic waves were 20 and 40 kHz. The drying period in the oven was 12 h at the temperature of 55±2°C. The water content of durian flour was in the range of 10.66% to 11.54%, and the ash content was 2.14% to 2.83%. The L* (lightness) was 75.58 to 80.87, a* (redness) was 1.58 to 3.54, and b* (yellowness) was 6.735 to 19.385. The total soluble solid (TSS) was 10.43 to 11.54 °Brix. The swelling power was 4.05 to 4.70 g/g. The scanning electron microscopy images showed that durian flesh flour granules had a semi-round structure. The ultrasonication process caused the bonds between components in granules to be broken so that the structure appeared loose. The elemental analysis performed by Dispersive X-ray Spectroscopy indicated that more mineral elements were found in the frequency of 20 kHz and 20 min exposure time, and the minerals decreased with increasing frequency and duration of sonication. The ultrasonic waves prior to drying would maintain the color appearance of durian flesh flour but reduce the amount of minerals.