Effect of ultrasound treatment on microstructure, colour and carotenoid content in fresh and dried carrot tissue

•The effect of ultrasound treatment before drying of carrot were investigated.•The influence of ultrasonic application on carrot microstructure was studied.•The changes in colour and carotenoids content of ultrasound pre-treated and dried material were examined.•The properties of material after ultrasound treatment showed a visible difference in comparison to intact sample.•Ultrasound treatment induced changes of carrot microstructure.

The aim of the study was to investigate the influence of ultrasound treatment on the carrot tissue microstructure, colour and carotenoids content. To avoid adverse effects of rinsing out substances contained in the raw material, carrot slices were vacuum-packed and treated with ultrasounds in an ultrasonic bath using 21 and 35 kHz frequency for 10, 20 and 30 min. Images of the carrot tissue made by scanning electron microscope were analysed by calculating the cross-section area for each cell. The colour was measured using CIE L∗a∗b∗ method. To determine total carotenoid content spectrophotometric method was used. Obtained results indicate that the structural properties of carrots treated with ultrasound were significantly different from the samples without any treatment and it was clearly noticed during analysing images of scanning electron microscope. There was observed the influence of ultrasound treatment on colour L∗, a∗ and b∗ parameters, especially for carrot treated with ultrasound for 30 min, independent of the applied frequency of the ultrasonic waves. Similarly, sonic treatment resulted in substantial increase of carotenoid in comparison to raw carrot, especially in the case of 35 kHz frequency ultrasounds. Probably, such significant increase is caused by the destruction of the original structure and thus higher extraction ability of these compounds.