Sugars and acid analysis and effect of heating on color stability of Northwest Concord grape juice
1982
Montgomery, M.W. | Reyes, F.G.R. | Cornwell, C. | Beavers, D.V.
Carbohydrate and nonvolatile acid composition of concord grapes grown in the Northwestern United States were studied, as well as color changes of grape juice during storage. Nonvolatile acids in Northwest Concord grapes ranged from 0.071 mEq/100 g fruit for coumaric to 2.660 mEq/100 g fruit for malic. Malic acid concentration was twice that of tartaric, the second major acid. Gas-liquid chromatography and an enzymatic analysis were used to examine soluble sugars; each method identified fructose, glucose and sucrose. The fructose/glucose ratios for the two methods were 1.08 and 1.18, respectively. Heating of crushed concord grapes to 88 and 98 degrees C inactivated the polyphenoloxidase, increased the extraction of anthocyanins (ACN), and reduced polymeric color in the grape juice but did not affect the rate of ACN degradation and color density decrease during 8 months of storage. (emc)
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