Changes in Ellagic Acid and Other Phenols in Muscadine Grape (Vitis rotundifolia) Juices and Wines during Storage

Abstract

This study followed the changes in gallic acid, catechin, epicatechin, ellagic acid, epicatechin gallate, and ellagic acid sediment during storage of muscadine (Vitis rotundifolia) juices and wines. Juices and wines from cv. Carlos and Welder (both white) and juices from Noble (red) were produced following standard methods. Samples were heated at 94°C for 5 min to accelerate sediment formation and then stored at 25°C for up to 52 wk. Other studies examined the effects of spiking juice with 50mg/mL of gallic acid and hydrolyzing juices using trifluoroacetic acid. In white cultivars, all phenolic compounds, except catechin, were higher in Carlos than in Welder. Ellagic acid sediment formed in the juices from both white cultivars after approximately 2 wk, compared to 24 wk in the wines. In all samples, there was an increase in gallic acid immediately after heating, followed by a decrease. There was also an increase of ellagic acid in solution followed by a decrease, as the ellagic acid started to form a sediment. The amount of ellagic acid sediment did not change much over time in the wine, whereas in the juice, the ellagic acid sediment increased over time. The ellagic acid in solution generally declined after appearance of ellagic acid sediment, and the ellagic acid sediment reached a maximum of 24 mg/mL in Carlos juice after 24 wk and 98 mg/mL in Noble hot press juice after 42 wk. When juice was spiked with 50 mg/mL gallic acid, there was no significant increase in ellagic acid in solution or in ellagic acid sediment. However, juice hydrolysis resulted in a significant increase in ellagic acid in solution and ellagic acid sediment. Ellagic acid is likely coming from hydrolysis of higher molecular weight compounds and perhaps some from the dimerization of gallic acid.