Models based on ultraviolet spectroscopy, polyphenols, oligosaccharides and polysaccharides for prediction of wine astringency

Spectrophotometric Analysis of Phenolic Compounds in Grapes and Wines

Phenolic compounds are of crucial importance for red wine color and mouthfeel attributes. A large number of enzymatic and chemical reactions involving phenolic compounds take place during winemaking and aging. Despite the large number of published analytical methods for phenolic analyses, the values obtained may vary considerably. In addition, the existing scientific knowledge needs to be updated, but also critically evaluated and simplified for newcomers and wine industry partners. The most used and widely cited spectrophotometric methods for grape and wine phenolic analysis were identified through a bibliometric search using the Science Citation Index-Expanded (SCIE) database accessed through the Web of Science (WOS) platform from Thompson Reuters. The selection of spectrophotometry was based on its ease of use as a routine analytical technique. On the basis of the number of citations, as well as the advantages and disadvantages reported, the modified Somers assay appears as a multistep, simple, and robust procedure that provides a good estimation of the state of the anthocyanins equilibria. Precipitation methods for total tannin levels have also been identified as preferred protocols for these types of compounds. Good reported correlations between methods (methylcellulose precipitable vs bovine serum albumin) and between these and perceived red wine astringency, in combination with the adaptation to high-throughput format, make them suitable for routine analysis. The bovine serum albumin tannin assay also allows for the estimation of the anthocyanins content with the measurement of small and large polymeric pigments. Finally, the measurement of wine color using the CIELab space approach is also suggested as the protocol of choice as it provides good insight into the wine's color properties.

Effect of processing technologies and storage conditions on stability of black currant juices with special focus on phenolic compounds and sensory properties

Juice was pressed from black currants without enzyme treatment (NEB=Non-Enzymatic Berry) followed by re-pressing of the residue with enzymes (EPR=Enzymatic Press Residue) and the results were compared to the conventional enzyme-aided berry pressing (EB=Enzymatic Berry). EPR-juice had 9- and 5-fold higher contents of phenolic compounds compared with the NEB- and EB-juices, respectively. Effect of the low content and stability of phenolics was noticed as loss of the visual color in the NEB-juice during storage. The decrease in monomeric anthocyanins and the increase in phenolic acids were most severe in the NEB-juice, whereas the most significant decline in hydroxycinnamic acid derivatives occurred in the enzyme-treated juices. Storage in light induced less change in the phenolic composition in EPR-juice than in the two other juices. The study gave new knowledge on changes in individual metabolites, in sensory properties and in the shelf life of berry juices.

Influence of Grape Maturity on Complex Carbohydrate Composition of Red Sparkling Wines

This paper studied how grape maturity affected complex carbohydrate composition during red sparkling wine making and wine aging. Grape ripening stage (premature and mature grapes) showed a significant impact on the content, composition, and evolution of polysaccharides and oligosaccharides of sparkling wines. Polysaccharides rich in arabinose and galactose, mannoproteins, rhamnogalacturonans II, and oligosaccharides in base wines increased with maturity. For both maturity stages, polysaccharides rich in arabinose and galactose, and the glucuronic acid glycosyl residue of the oligosaccharides were the major carbohydrates detected in all vinification stages. The total glycosyl content of oligosaccharides decreased during the whole period of aging on yeast lees. The reduction of polysaccharides rich in arabinose and galactose and rhamnogalacturonans type II during the aging was more pronounced in mature samples. To our knowledge, this is the first report of the polysaccharide and oligosaccharide composition of red sparkling wines.