Abstract
Grape pomace contains a complex of valuable and biologically active compounds. Drying is one of the main ways of microbiological stabilisation and preservation of the nutritional value of this secondary raw material. Kinetic parameters of dehydration of grape pomace from different industrially cultivated and processed varieties have been studied, namely, of the red grape varieties Cabernet and Shiraz, and of the white varieties Chardonnay and Riesling. Dependences of the moisture content in the process of convective drying at different drying agent rates have been obtained at a regulated temperature of 80 °C. The components of such an important technological parameter as the drying time have been determined. These components include the duration of the constant drying rate period Φ2 and the time of the decreasing drying rate period Φ1 of the two zones of the second drying period. The coefficients of the dehydration process have been calculated depending on the type of grape pomace processing. It has been shown that the discrepancy between the calculated and experimental results does not exceed ±3.9%. The specific features of the moisture yield of the pomace have been revealed, the pomace being viewed as a complex heterogeneous system with colloidal and capillary-porous properties. There are different types of its technological preparation: it can be fresh, frozen, fermented, and this makes for the fact that the drying time and drying rate may differ by 1.32–1.46 times. High preservation of valuable properties of grape pomace has been shown. Thus, the concentration of biologically active substances (BAS) in the total polyphenolic compounds is up to 69% of their initial concentration in the grape pomace samples, and the microbial contamination of the samples after drying is reduced by 51–82% of their initial contamination.
Highlights
Formulation of the problemGrapes are widely distributed in the Mediterranean and Black Sea regions
The work shows a possibility of increasing the efficiency of drying grape pomace, according to its structural and mechanical properties, to the ratio between free and bound moisture, and to the peculiarities of grapes processing
Specific features of the moisture yield of the pomace have been revealed, the pomace being viewed as a complex heterogeneous system with colloidal and capillary-porous properties
Summary
Grapes are widely distributed in the Mediterranean and Black Sea regions. The chemical composition of grape berries depends on climatic conditions, soil composition, and varietal characteristics [3,4]. A significant part of the grape pomace is formed. It contains valuable food ingredients and biologically active substances, due to which they are of considerable interest for various branches of the food industry, as well as for other types of industry [5,6]. The paper considers the problem of rational processing of grape pomace using methods that optimise moisture removal. The research is based on the data obtained about the structural and mechanical properties of grape pomace, on the ratio between the forms of free and bound moisture
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