Effect of Drying Methods on Physicochemical Parameters of Different Red Beetroots (Beta vulgaris L.) Species

Abstract

The aim of this work was to study the influence of atmospheric, vacuum and microwave vacuum drying methods on the quality of dried beetroots. Three different red beetroot species ('Alto F1', 'Cylindra', 'Detroit') were chosen in this study. The microwave vacuum method reduced the total time of drying and decreased the shrinkage compared to the other drying methods. The quality of the dehydrated material was described by its color change, antioxidant capacity, total polyphenol, betacyanin, betaxanthin and each phenolic acids content. The attempts were made to suggest the microwave vacuum method for red beetroot samples as a gentle drying technology to reach a special texture that is favoured by costumers. During the experiments relevant differences could be observed between the investigated beetroot species on the effect of different drying methods. According to the examined parameters the 'Cylindra' species proved the most appropriate beetroot variety for microwave vacuum drying. Based on the results, the combined methods with hot-air at 60 °C followed by microwave vacuum finish drying was the most suitable assay to preserve the investigated parameters in the highest amount.

Analysis of physicochemical properties of beetroot dried by microwave-vacuum method

“…The two-way analysis of variance did not show any significant influence of the analyzed process parameters on the betanin content. Székely et al [2019] noted a higher content of betacyanin and betaxanthin in dried beetroot obtained by the microwave-vacuum method than after using convective drying. Removal of water from the beetroot samples increased the content of yellow pigment in all dried materials.…”

“…In the case of the two-stage program, the smallest difference in the color of the dried beetroot was achieved when initially higher microwave power was used, which was then lowered in the final stage. Among atmospheric, vacuum and microwave-vacuum drying, dried beetroot obtained by the last method showed the greatest color difference (5.06-13.39) [Székely et al 2019].…”

“…The lowest content of polyphenols was determined in the dried material obtained by the convective method. Among atmospheric, vacuum and microwave-vacuum drying, the last one, carried out with the microwave waves in a vacuum, resulted in dried beetroot with the highest content of polyphenols [Székely et al 2019]. Increasing the pressure in the drying chamber at the microwave radiation power of 300 W led to a reduction in the retention of polyphenols in the dried material, but it was not statistically significant.…”

“…Heat-transferring microwaves penetrate simultaneously and directly each particle of the dried material, thanks to which the drying time is shorter and the biochemical changes are significantly limited [Bondaruk and Markowski 2005]. The heating of the dried material and the reduction of its water content take place inside it, not on the surface [Jałoszyński et al 2008, Székely et al 2019. Depending on the used wave frequency, a different scale of its penetration into the material is observed.…”

Research of physicochemical properties and antioxidant activity of beetroots as affected by vacuum microwave drying conditions

“…The total color differences (∆E) of dried beetroots was bet ween 5.95 and 9.74 in comparison with fresh beetroots. It has been reported, that the ∆E parameters were between 5.06 and 13.39 for microwave vacuum drying of red beetroot samples [19]. The beetroots, dried at a vacuum degree of -0.09 MPa (T3), showed the lowest ∆E (5.95), while the beetroots with a sample thickness of 4 mm (T7) displayed the biggest ∆E.…”