Abstract:

The extract extracted from grape residue left after making wine with 70% ethanol under the assistance of ultrasonic was tested for its total phenolic content and in vitro antioxidant and antimicrobial activities in the present study. Total phenolic quantification was performed using Folin-Ciocalteu reagent. FRAP assay was used for the assessment of total antioxidant capacity, and the abilities to scavenge DPPH, superoxide anion, hydroxyl and 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate (ABTS) radical free radicals and to inhibit β-carotene/linoleic acid system were also measured. The inhibitory effects against five tested strains including Gram positive and negative strains were evaluated. It was found that the extract contained 106.4 mg/g total phenolic content, and had a FRAP value of (3.215 ± 0.017) mmol/g and IC50 values of 20.5, 52.5, 566.4 mg/L and 16.8 mg/L for DPPH, superoxide anion, hydroxyl and ABTS free radicals, respectively. The IC50 value of the extract forβ-carotene/linoleic acid system was 28.2 mg/L. It presented the best inhibitory effect against Staphylococcus aureus, with a minimum inhibitory concentration (MIC) of 900 μg/L, followed by Bacillus subtilis, Bacillus cereus, Escherichia coli and Aspergillus flavus. To sum up, the extract has excellent antioxidant performance, and its inhibitory effect against Gram positive strains is higher than that against Gram negative strains, but its anti-fungus effect is relatively weaker.

Key words: grape residues, extract, antioxidant activity, antimicrobial activity, polyphenol