Detection of Phenolic Compounds and Hydroxy Acids in Grapes, Wines, and Similar Beverages

Abstract

Solvents and developers for the detection of phenol-like compounds and hydroxy acids in grape juice, wine, pomace wine, and wine-like beverages have been listed.

The compounds are d-catechin, I-epicatechin, I-epigallocatechin, gallic acid, protocatechuic acid, and ellagic acid, in addition, gallocatechin in apples.

Among the polyphenols are: chlorogenic acid, isochlorogenic acid, cis- and trans-caffeic acid, and probably caffeic acid lactone.

Among the phenols were found cis- and trans-coumaric acid and probably a coumaric acid lactone.

The positions of the substances on the chromatograms, their Rf-values with various solvents and developers are reproduced.

In juice of green grapes were found: d-catechin, I-epicatechin, I-epigallocatechin, ellagic acid, chlorogenic-and isochlorogenic acids and shikimic acid. Absent in juice from green grapes are: free gallic acid, caffeic acid, p-coumaric acid, quinic acid, and flavonols.

Catechins are mostly in seeds and stems and in lesser amounts in skins. Chlorogenic acid was not found in these parts.

Chlorogenic acid is always present in wine and later also caffeic acid. Gallic acid disappears on maturation of wine. Old white wines contain as a rule no condensable tannins.

In the pomace wine are present condensable tannins of the woody parts and of the seeds. Free gallic acid and ellagic acid are present in large amounts. Chlorogenic acid is present in pomace wine in an insignificant amount.

A blend of wine and pomace wine cannot be identified with certainty because gelatine and egg white finings remove free gallic acid and catechins. When no condensabe tannins are present one is assured of the purity of grape wine.

Young apple wine contains much more chlorogenic acid than grape wine. Caffeic acid and quinic acid are also present. d-Catechin and I-epicatechin are present in small amounts.

Old apple wines contain no chlorogenic acid, instead very large amounts of caffeic, quinic, and shikimic acids are present. Some coumaric also is present.

Strawberry dessert wine contains no chlorogenic acid and normal amounts of caffeic acid. There is much quinic acid, but no shikimic acid. Gallic acid, d-catechin and I-epigallocatechin were found. There is also present a red-violet fluorescent spot characteristic of oak extracts used in brandy manufacture.

Cherry wine contains much chlorogenic, caffeic and quinic acids and little shikimic acid. d-Catechin, I-epicatechin and gallic acid were found.

Gooseberry dessert wine contains practically no chlorogenic acid but much caffeic, quinic and shikimic acids. Small amounts of gallic acid were found, but no condensable tannins.

Caffeic acid occupies a key position and serves, evidently, for the construction of the flavonoid structure. Chlorogenic acids are present in live plants in large amounts probably as reserve material for caffeic acid. Caffeic acid appears only in dead tissue of the plant—in must and in wine.

It was possible to separate the isomers of caffeic and coumaric acids with 2% solution of acetic acid as second solvent. Since three spots appear in each instance along with the cis- and transforms, the formation of a lactone is assumed.

Caffeic, p-coumaric, and ellagic acids are formed as secondary compounds.

Acetaldehyde and glucose are not the only substances that bind sulfurous acid. Derivatives of cinnamic acid such as caffeic and p-coumaric acids can also bind the acid.

The sulfurous acid is a poison for polyphenoloxidase and a reducing agent for the quinones formed from the polyphenols. Its reducing action can also be performed by ascorbic acid.

The caffeic acid lactone is identical with esculetin and the p-coumaric acid lactone is identical with umbeliferon. Therefore, these two terms can be used for the designation of lactones.