engleski

Drying assisted with high intensity ultrasound

Drying in food technology is usually based on the use of conventional methods such as heat exchange by conduction or convection, which may have negative effects on textural issues of final products. Although drying is energy intensive and consequently cost intensive because it is a simultaneous heat and mass transfer process accompanied by phase change, it is still indispensable in food industry. Drying extends shelf life, but also lead to undesirable changes in color, texture, and partial loss of nutritive components. The conventional ways of drying are still present in the industry but their disadvantage lies in quality loss of the final product In order to achieve high quality of final products, new and sophisticated techniques for food treatments are required. One of such methods is power ultrasound aided drying. This method is proven efficient for preserving main characteristics and quality of products. Fresh Pear (Williams) was hand-peeled and cut to the rectangular shaped slices, with dimensions 30 x 30 x 5 mm, the samples had total weight of 15 ± 1 g for each of 4 samples. The ultrasonic pre-treatments were carried out in 250 mL laboratory glass for each sample. The sample was put into glass then poured over with a 100 mL of distilled water. The aim of this research was to investigate the impact of high-intensity ultrasound as pre-treatment, using different amplitudes, on the duration of drying and texture characteristics of infrared dried pear slices. Titanium probe with 22 mm in diameter was mounted on the ultrasonic device, UP400S (Hielscher, Teltow, Germany) with declared maximal output power of 400 W. Ultrasonic frequency was 24 kHz. Amplitudes used in research were 35, 60, 80 and 100% of nominal output power. Cycle of ultrasound was set to 1, which is the full time period. Sonication was performed for 5 min. The experiments were carried out under ambient temperature (25°C). Each assay was carried out in triplicate. The control sample was not treated with ultrasound and was placed directly into the dryer. Drying was performed in an infrared dryer, at 75⁰C temperature. Obtained results showed how application of ultrasound with various amplitudes influenced on shortening of treatment time of drying and allows elimination of more water from the pear slices. The results showed that hardness of samples gradually decreases with increase of ultrasound intensity. As a result, hardness of untreated pear slices was significantly higher than treated sample.

ultrasound; drying; pears

nije evidentirano