Degradation Degree of Polyphenols Depending on the Drying Temperature of the Grape Pomace

Silvia Mariana PASCARIU, Ioan POP, Aida ALBU


Grape pomace provides a rich source of polyphenols, which have the capacity to act as powerful antioxidants. Grape pomace has been used mainly in ruminant feed as a source of fiber and for broiler chickens as a source of antioxidants. It has been proved that the polyphenols from grape pomace are discomposed during the drying process. Taking into consideration the incertitude of polyphenols thermal degradation, the aim of this study was to identify the degree of degradation of the polyphenols during the drying step at different temperatures. Red grape pomace (Black Maiden) from the same source was dried at room temperature (20°C) five days and three days at 38°C and 50°C. The total content of polyphenols (TP), tannins (Ta) and anthocyanins (An) was determined by different colorimetric methods. Our data reveal a significant degradation of the TP and An for all the three thermal variants. The Ta and non-adsorbed polyphenols on casein show a high degree of correlation, but with significant differences just between 20 and 38°C. Probably the lack of significant differences after 38°C, is determined by the thermal fragmentation of the polymer chain (Ta), that make this fragments unable to adsorbed with casein, an important proportion of Ta being affected by the first shock of heat. The correlation within Ta and non-adsorbed polyphenols on casein is the result of passage of the truncated Ta chains in non- adsorbed polyphenols fraction on casein. The drying and storing process is an important step for grape pomace usage as a feed additive because we demonstrated that the Ta presents a high level of degradation especially between 20 and 38°C.


anthocyanins, grape pomace, tannins, polyphenols

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