Comparative study of drying methods of Vitis labrusca grape peels: greenhouse or Oshibana?

Herein we evaluated which drying processes preserve the bioactive compounds present in the grape peels (Vitis labrusca). The peels were dried by two methods: oven at 37±3 ºC and by the Oshibana method. The extracts were obtained by turbolysis followed by ultrasound using a hydroethanolic solution 50% (v/v) acidified, and after filtration both crude extract were concentrated by rotary evaporator at 80 °C and 150 rpm. The analysis of crude and concentrated extracts (triplicates) was: soluble solids(2), phenolic compounds(3), anthocyanin(4) and antioxidant activity(5) and statistical by Student T Test (p-valor < 0.05). The results presented statistical significance in the averages (Table); only the solids content of the crude extract did not present significant difference. Phenolic compounds presented higher values for the extracts obtained with the oven drying, while the anthocyanin content was higher for the Oshibana method. Antioxidant activity had lower IC50 values for oven drying, which suggests that the phenolic compounds significantly interfere in the antioxidant capacity. In both cases the soluble solids, anthocyanins and phenol contents increased from the crude extract to the concentrate, however, the antioxidant activity presented higher values of IC50, which indicates that the heat exposure decreases the antioxidant activity. This suggests that the glycosidic bonds were being broken down in the concentration process, increasing the content, but destabilizing the molecule and reducing its activity. In conclusion, the drying method of the plant material should be chosen based on the bioactive compound of interest.