Nonenzymatic Browning and Chemical Changes During Grape Juice Storage

The effect of storage on juice concentrate from 2 red grape (Merlot and Criolla) and 1 white grape (Yellow Muscat) varieties on color and chemical composition, at temperatures ranging from 10 to 30 °C, was investigated. Color deterioration as A420 occurred at a faster rate in juice made with Merlot variety. The same was true when the pigment destruction as A520/420 was studied. Total reducing sugar, fructose‐to‐glucose ratio, and proline (the only significant amino acid present in grape juice) remained practically constant during storage. The hydroxymethyl‐furfural (HMF) buildup reaction proceeded faster in Criolla grape juice. Independent of variety, a detectable amount of HMF was produced only after 12 wk of storage at any temperature.