Antioxidant power, bacteriostatic activity, and characterization of white grape pomace extracts by HPLC-ESI-MS

Polyphenolic fractions obtained from white grape pomace by aqueous extraction were analyzed to determine their antioxidant power (DPPH and TBARS methods), bacteriostatic activity, the effect of particle size on total extractable polyphenols (expressed as gallic acid equivalents (GAE)), and to characterize by HPLC-ESI-MS. The extraction of polyphenols from Albario variety grape pomace was performed both on lab-scale and on pilot-plant scale using particles sizes of < 1 mm, 3-5 mm and entire particle. Lab-scale assays showed that the lower the particle size the higher the raw extract (RE) percentage (%w/w), which values were 21.3 +/- A 0.37% (SD), 12.6 +/- A 0.38%, and 6.6 +/- A 0.44%, respectively. Several fractions were obtained from RE, either as result of applying liquid-liquid partition or gel permeation chromatography. The antiradical activities of the fractions were lower than that of gallic acid (17.8 +/- A 0.1 mg GAE/mol DPPH) but similar to that of catechin or procyanidin B-2 (46.0 +/- A 2.3 mg GAE/mol DPPH and 52.3 +/- A 6.3 mg GAE/mol DPPH). Several fractions showed bacteriostatic activity both at 50 and at 100 mg/L. Total aerobic bacterial enumeration (TABE, log UFC/cm(2)) of treated samples revealed a significant lower TABE than that for control. HPLC-ESI-MS studies demonstrated that fractions V and VI included monomers, dimers, and trimers of procyanidins, few of them galloylated. Fraction VII contained several oligomers and galloylated procyanidins.