Grape polyphenolic extracts are promising antimicrobials.

Wine grape pomace is an excellent source of phenolic extracts for potential use in oral health. Scientists at Cornell University wanted to fractionate and characterize grape polyphenolic extracts prepared from pomace to investigate their antimicrobial properties. Their work indicates that phenolic grape extracts composed mainly of flavan-3-ols and flavonols are promising natural antimicrobial agents for preventing juice spoilage and oral disease.

In experiments, the researchers prepared phenolic extracts from Pinot noir grape pomace or seeds, which are known to have a high polyphenolic content. To obtain pomace, the grapes were crushed, fermented on their skins, pressed, freeze-dried and ground.

The researchers separated the seeds from the pomace. Polyphenols were extracted using methanol, ethanol and water, and were separated by solid-phase extraction to produce powdered total phenolic and whole seed extracts. The extracts were fractionated into anthocyanin, neutral, polymeric and oligomeric fractions.

The investigators analyzed the extracts for total phenolic (gallic acid equivalent--GAE), monomeric anthocyanin (malvidin-3-glucoside equivalent--MGE), and flavan-3-ol content (catechin equivalent--CE), as well as for their antioxidant capacity (vitamin C equivalent antioxidant capacity--VCEAC) and yield. Then they determined the effects of powdered extracts on the growth of A. acidoterrestris, a juice spoilage bacterium, and on the biofilm formation of S. mutans, an oral pathogen.

The total phenolic content of the extracts ranged from 8 g to 62 g GAE per 100 g. The antioxidant capacity was highest in the polymeric fraction and lowest in the anthocyanin fraction (85 g and 6 g VCEAC per 100 g, respectively). The flavan-3-ol content ranged from 48 g to 76 g CE per 100 g. The polymeric fraction had the most yield: 4.8 g of extract per 100 g of fresh weight. All extracts, except the anthocyanin fractions, were effective in inhibiting the growth of A. acidoterrestris at concentrations as low as 1000 ppm, and in reducing biofilm and insoluble polysaccharide production (oral plaque) by S. mutans.

Further information. Randy W. Worobo, Department of Food Science and Technology, New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456; phone: 315-787-2279; fax: 315-787-2284; email: rww8@cornell.edu.

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