engleski

Effect of freezing and different thawing methods on the content of polyphenolic compounds of red grape skins

Abstract Due to the short period of the grape fresh samples availability and their very complex analysis, appropriate grape samples storage is mandatory. In this study, samples were analyzed immediately after harvest and after storage at −20 °C. Frozen samples were thawed as follows: at the room temperature, in the microwave oven, in the refrigerator, and the skin was pulled off from the frozen grape berries. The freezing had a positive effect on the contents of anthocyanins and flavonol glycosides. These compounds are contained in cell vacuoles thus membrane degradation, throughout the freezing process, could enhance their extractability. The freezing had a negative effect on the content of the other polyphenols which can be bound to the cell wall. Among examined thawing methods, the most appropriate method was the peeling grape berry skin from the frozen berries samples with the receptacle. Suitable alternative to the aforementioned method could be the microwave thawing. Practical application One of the most important groups of compounds contained in grape berries are polyphenolic compounds. These compounds significantly affect the quality of grapes and wine. They also have a positive impact on human health. Most of the grapes are being processed into wine, but it also has many other uses. Besides the table grapes, raisins, juices, jams, and wine distillates, currently, various cosmetic and pharmaceutical preparations made from grapes whose functioning is based on the effects of polyphenols are encounter on the market. Given the short period of availability of fresh grape samples and complex procedure of their analysis and processing, samples must be stored in an appropriate manner. This study reported the effect of freezing and applied thawing method on retentions of polyphenolics in grapes. The information obtained by this study is essential for the development of specific applications of the grape berries skins.

phenolic compounds ; freezing ; thawing ; grape skins

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