Sugars, Alcohols, and Hydroxymethylfurfural in Authentic Varietal and Commercial Grape Juices

Abstract

The quantity of fructose, glucose, and sucrose present in authentic varietal grape juices produced by cold and/or hot pressing from 56 cultivars was determined by liquid chromatography for the 1988 and 1989 seasons. The concentration of fructose, glucose, and sucrose and the fructose:glucose ratio ranged from 5.97 to 10.92, 4.91 to 9.99, trace to 1.04 g/100 mL, and 0.92 to 1.41, respectively. Sorbitol and hydroxymethylfurfural were not detected in the authentic grape juices. Genotype had no significant effect on the fructose and glucose contents. The labrusca-type cultivar group was significantly higher in the sucrose concentration and fructose.glucose ratio than either the vinifera or the French hybrid groups. The pressing method had no significant effect on the sugar composition. The glucose, fructose, total sugar, and total soluble solids contents were significantly higher in the juices from the warmer and sunnier 1988 season. The total sugar contents correlated highly with total soluble solids, but the latter averaged 1.81 units more than the former. Most commercial grape juices had a composition similar to that of the authentic juices, except that they had only traces of sucrose. Also, most commercial grape juices contained measurable quantities of ethanol, glycerol, and hydroxymethylfurfural.

Sugar Composition of Varietal Juices Produced from Fresh and Stored Apples

“…The sugar composition of apple juice provides excellent means for the detection of adulteration (Lee and Wrolstad, 1988b; Mattick, 1988). Unlike in grapes (Fuleki and Pelayo, 1993), the concentration of fructose in apples is much higher than that of glucose, and sorbitol is present as well. Most pear cultivare contain significantly higher concentrations of sorbitol than apple (Weiss and Sámann, 1979), and this can be used to detect substitution of apple juice with that of pears.…”

“…The sample preparation method was designed to inactivate native enzymes and separate neutral from acid components. The procedures used were the same as described for grape juice (Fuleki and Pelayo, 1993) except that centrifuging after heating of the neutralized juice was omitted. No (hydroxymethyl)furfural (HMF) formation was observed as a result of this mild heat treatment.…”

“…No (hydroxymethyl)furfural (HMF) formation was observed as a result of this mild heat treatment. The methods used for determination of total soluble solids (TSS), individual sugars, sugar-alcohols, and statistical analyses were described in a previous publication (Fuleki and Pelayo, 1993).…”

“…Since the peaks for stachyose and raffinose were very small, where peak area integration values are not reliable, regression equations based on peak heights were established for the chromatographic procedure described previously (Fuleki and Pelayo, 1993) and 50-mL injection volume as follows: stachyose 1 g/L = (peak height, mm -1.36601)/3.2902 raffinose 1 g/L = (peak height, mm -1.83088)/3.659804…”

Nonenzymatic Browning and Chemical Changes During Grape Juice Storage

“…At that point the accumulated HMF became noticeable. Two practical conclusions drawn from this study are these: F:G ratio can be used simultaneously with the assay of sorbitol (Fuleki and Pelayo 1993) to detect blends of grape juice with other subtropical fruit juices, and, HMF content can be used to complement color data in estimating the storage capacity of grape juice concentrate.…”