Application of Ultrasound in Convective Drying of Fermented, Frozen-Thawed, and Osmotically Dehydrated Beetroot Slices

Abstract

The aim of the study was to assess the benefits of using high-power ultrasound (HPU) during convective drying of raw beetroot slices and beetroot slices subjected to fermentation, pulsed vacuum osmotic dehydration, and freezing-thawing (in selected combinations). Beetroot slices were dried at a temperature of 80°C. The HPU treatment (200 W) was applied in 5-min cycles with 10-min intervals in between. The dried products were assessed for color, microstructure, total phenolic content, antioxidant capacity, and sugar content. Additionally, a Fourier-transform infrared spectroscopy analysis was performed. The HPU treatment during convective drying exerted the most beneficial effect on raw beetroot slices by shortening drying time by 23.5% and decreasing energy consumption by 18.4%. The above treatment also shortened the drying time of fermented and osmotically dehydrated beetroot slices by 17.6%, increased the total phenolic content of product by 17.1%, and increased the ferric reducing antioxidant power by 13.7%. In addition, the ferric reducing antioxidant power of fermented beetroot slices dried with HPU assistance increased by 12.2% compared to sample dried without HPU. In the remaining cases, HPU-assisted drying did not lead to significant improvements in the evaluated parameters. All analyzed treatments decreased the intensity of red color in dried beetroot slices.