Abstract
The purpose of this study was to investigate the effect of pre-treatment in ethyl alcohol for 5, 15, 60 and 180 s with the application of ultrasound on the course of convective drying and properties of carrot tissue directly after the treatment and after the drying process. The treatment in ethanol resulted in loss of mass, increase of dry matter, ethanol conductivity, extractivity of carotenoids with a slight effect on the colour of carrot tissue after the treatment. The utilization of ultrasound during immersion in ethanol contributed to additional increase of conductivity of ethanol, and extractivity of carotenoids. The immersion in ethanol virtually did not affect the drying kinetics, which can be explained by the increase of shrinkage of the tissue in relation to the untreated dried tissue. Despite the lack of the influence on the drying course in the ethanol-immersed carrot, an increase of the carotenoid content (up to 135%) and the rehydration ability (up to 19%) was noted with the simultaneously unchanged colour of dried carrot in comparison to untreated dried material, which indicates the possibility to improve the quality of dried carrot after immersion in ethanol.
Highlights
Carrot is one of the most widely grown root vegetables around the world
The most commonly used convective drying is a thermal process of simultaneous heat and mass exchange, the purpose of which is to evaporate some of the water from the material into the surrounding air, which is both the medium providing heat and carrying moisture away from the material
Considering the further use of dried carrot as a component of, e.g., instant soups, seasoning mixes, etc., it is especially important to select a processing method to provide a product characterizing by a good rehydration ratio, high content of carotenoids and stable colour
Summary
Carrot is one of the most widely grown root vegetables around the world. Consumption of carrots and carrot products is constantly increasing due to their richness in natural nutrients, including carotenoids or dietary fibre [1,2]. The drying of vegetables is predominantly carried out by the means of the convective method due to its simplicity, ease of process control and low costs of such dryers [4]. The disadvantages of this method, include high energy consumption and relatively low quality of the dried product, in particular low rehydration ability, high shrinkage and high losses of nutrients [5,6,7]. Considering the further use of dried carrot as a component of, e.g., instant soups, seasoning mixes, etc., it is especially important to select a processing method to provide a product characterizing by a good rehydration ratio, high content of carotenoids and stable colour. Novel pre-treatment methods are sought in order to reduce the negative aspects of convective drying
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