Vernon L. Singleton

Phenolic substances in grapes and wine, and their significance.

Publisher Summary This chapter attempts to gather some of the threads of physiological and chemical theory underlying the practice of handling meat, with special consideration of the problem of ripening. It is found that there is a necessary preponderance of the space devoted to the discussion of physiological and chemical facts over that devoted to consideration of the opportunities that have been taken or can be suggested for the application of the facts. There are two points to which concentration of interest have been directed. The first is the vital role that the pH of flesh plays in every phase of meat technology. This general principle affords a useful plane to which the complicated events that take place in muscle post-mortem can be related, and upon which they can be oriented. The second focal point to which particular attention is drawn is the technique of evaluation of quality by panel judgments based on sensory tests.

Naturally Occurring Food Toxicants: Phenolic Substances of Plant Origin Common in Foods

Publisher Summary The risks to humans of serious poisonous effects caused by natural phenols present in normal foods consumed under usual circumstances seem vanishingly small, as determined by experiment, as well as common sense and long-term observation. Conclusions involving evolution obviously are speculative, but some putative relationships appear worthy of discussion to clarify the durability of animal life and the threat of plant toxins generally or of phenols particularly. Phenols are probably the most important group of substances, useful in chemotaxonomic differentiation among plant species. Plants have evolved toxins to combat herbivores, but herbivores have also evolved to tolerate or avoid plant toxins. Phenol itself, and other small phenols, such as catechol, the cresols, guaiacol, orcinols, and pyrogallol, are commonly considered to be industrial chemicals. Gallic acid is widely distributed in plants, but the concentration is usually very low. The flavonoids contribute color, flavor, and processing characteristics important in food. The most often cited effect of phenols that is discussed in this chapter is the inhibition of catechol-O-methyltransferse (COMT) and competition for methyl groups by phenols that serve as a substrate for this enzyme. The chapter discusses that many plants contain secondary metabolites toxic or deterrent to members of the animal kingdom attempting to feed on them. Plant phenols that are highly toxic to animals are rarely found. The phenols that occur widely in plants or in large amounts in common food plants have very low acute oral toxicity and most are also of low toxicity when given parenterally.

Identification of three flavan-3-ols from grapes

Abstract Three phenolic substances present in sizable amount in grapes, particularly in underripe grape seeds, are relatively easily extracted into ether and were isolated and unequivocally identifed as (+)-catechin, (+)-(2R:3S)-5,7,3′,4′-tetrahydroxyflavan-3-ol; (−)-epicatechin, (−)-(2R:3R)-5,7,3′,4′-tetrahydroxyflavan-3-ol; and (−)-epicatechin-3-gallate. These identifications clear up previous conflicting and incomplete reports and show that the grapevine synthesizes the catechin isomers to be expected from work with other plants.

Caftaric and coutaric acids in fruit of Vitis

Abstract The contents of trans and cis caftaric and coutaric acids were determined by HPLC under conditions fully protecting against oxidation in berry juices from five non- Vitis species, 28 Vitis species, 20 white and 17 red Vitis vinifera cultivars, six Vitis labrusca cultivars and 11 other varieties. These components appear to be genetically determined to a considerable degree. Replicate samples of the same variety from different sources generally gave similar composition. The compounds were absent from or present only in trace amounts in Vitis rotundifolia and four (of five) non- Vitis species. Other Vitis species all contained them but the content ranged from 5 mg/1 to 1350 mg/1 of caftaric and from a trace to 340 mg/1 of coutaric acid. Cultivars of Vitis vinifera did not differ appreciably whether white or red berries were involved, but ranged from 16 to 430 mg/1 of trans-caftaric acid, averaging 145 mg/1. Vitis labrusca and its cultivars averaged notably higher and hybrids were generally intermediate with their parent species. The cis percentage increased, particularly for coutaric with the varieties arranged in order of decreasing caftaric concentration, but appeared to reflect environmental rather than genetic influences. The proportion of coutaric acid, however, appeared quite variable (3-33 % of the caftaric content in the vinifera cultivars) by variety and was apparently genetically controlled.

Colour and Sensory Characteristics of Merlot Red Wines Caused by Prolonged Pomace Contact

Pigment analytical parameters and sensory characteristics of Merlot red wines made with pomace contact during fermentation and subsequent maceration were investigated. The fermenting (at 25 ° C) musts were pressed at 0 (free-run juice), 1, 2, 4, 8, 16, 32 and 64 days after crushing and addition of the yeast. All wines were allowed to finish fermentation after pressing. High scores were given for wines made with 4, 8 and 16 days’ pomace contact. The sensory characteristics correlated with the wine component and pigment parameter results.

The effect of sulfur deficiency on the amino acids of alfalfa.

Abstract Sulfur-deficient alfalfa plants grown in sand culture contained increased amounts of aspartic acid and arginine, and decreased amounts of 16 other amino acids when compared with normal control alfalfa plants. The data suggest that asparagine acts as a primary, and arginine as a secondary storage form for nitrogen in the sulfur-deficient plant, and that important changes in the protein make-up of the plant take place during sulfur deficiency.

Removal of red blush and bitterness from white wine by partial hyperoxidation of juice from the pink-skinned koshu variety

Abstract White wine which is produced using sulfited juice from koshu grapes, the most important cultivar native to Japan, sometimes has bitterness and/or astringency and a red blush. Blowing compressed air through unsulfited juice for a short period of time results in less bitterness and/or astringency and no red blush, thereby improving wine quality, whereas conventional hyperoxidation produces thin, watery wine with little colour and poor body. It was found that the bitterness and/or astringency of wine made from sulfited juice is due to oligomeric and polymeric tannins extracted from skin and perhaps seed of soft koshu grape berries during crushing, stemming, and pressing, whereas the red blush is probably due to excess caffeic acid derivatives, anthocyanins or anthocyanin–flavonoid complexes, and cyanidins produced from procyanidins. Partial hyperoxidation removed the phenols responsible for the bitterness and/or astringency and the red blush via enzymatic oxidation (uninhibited by SO2), polymerisation, and insolubilisation.