Leo Gracin

Characterization of seed and skin polyphenolic extracts of two red grape cultivars grown in Croatia and their sensory perception in a wine model medium.

A study of proanthocyanidin and anthocyanin composition and concentrations in seed and skin extracts of two Croatian native red grape cultivars (Plavac mali and Babić) by HPLC-UV-Fluo/MS analysis was conducted in this work. A sensory analysis of extracts astringency and bitterness intensity was also performed. In the seeds, Babić showed generally higher concentrations of proanthocyanidins, while in the skins, Plavac mali showed higher concentrations of proanthocyanidins and anthocyanins. Babić proanthocyanidin seed fractions, greater in polymer size and percentage of galloylation, were perceived to be significantly more astringent. Babić proanthocyanidin skin fractions, greater in polymer size and lower in percentage of galloylation and prodelphinidins, were perceived to be significantly bitterer, but only in polymeric fractions. A positive correlation was found between the degree of polymerization, the percentage of galloylation and astringency intensity in the seeds. A negative correlation was found between the percentage of prodelphinidins and bitterness intensity in the skins.

Extraction of Proanthocyanidins and Anthocyanins from Grape Skin by Using Ionic Liquids

In this study, eight different types of imidazolium-based ionic liquids (ILs) were applied as new solvents in the extraction of flavonoids from grape skin, and compared to the conventional organic solvent extraction that was not reported earlier. The structure of anions, cations and concentration of ILs significantly affected extraction yields. The highest mass fractions of proanthocyanidins and anthocyanins were obtained with 2.5 mol/L of 1-butyl-3-methylimidazolium bromide [C4mim][Br] and 2.5 mol/L of 1-ethyl-3-methylimidazolium bromide [C2mim][Br], respectively. The studied ILs provided an excellent preliminary result in the extraction of anthocyanins. Significantly higher mass fractions of total and all free anthocyanins were extracted with 2.5 mol/L of [C2mim][Br] and 2.5 mol/L of 1-methylimidazolium hydrogen sulfate [mim][HSO4] than with conventional solvent with the exception of anthocyanin-3-O-acetylmonoglucosides in the latter. On the other hand, 2.5 mol/L of [C4mim][Br] and 2.5 mol/L of 1-(4-sulfobutyl)-3-methylimidazolium hydrogen sulfate [sC4mim][HSO4] showed significantly higher selectivity towards anthocyanin-3-O-acetylmonoglucosides and anthocyanin-3-(6-O-p-coumaroyl)monoglucosides.

Application of the shifted excitation Raman difference spectroscopy (SERDS) to the analysis of trace amounts of methanol in red wines

Shifted Excitation Raman Difference Spectroscopy (SERDS) has proven an effective method for performing Raman analysis of fluorescent samples. This technique allows achieving excellent signal to noise performance with shorter excitation wavelengths, thus taking full advantage of the superior signal strength afforded by shorter excitation wavelengths and the superior performance, also combined with lower cost, delivered by silicon CCDs. The technique is enabled by use of two closely space fixed-wavelength laser diode sources stabilized with the Volume Bragg gratings (VBGs). A side by side comparison reveals that SERDS technique delivers superior signal to noise ratio and better detection limits in most situations, even when a longer excitation wavelength is employed for the purpose of elimination of the fluorescence. We have applied the SERDS technique to the quantitative analysis of the presence of trace amounts of methanol in red wines, which is an important task in quality control operations within wine industry and is currently difficult to perform in the field. So far conventional Raman spectroscopy analysis of red wines has been impractical due to the high degree of fluorescence.

Comparison of Proteomic, Metabolic, and Growth Profiles for Brettanomyces bruxellensis Isolates from Croatian Wines

Brettanomyces bruxellensis is one of the most important spoilage yeasts in red wine production. The aim of this paper was to investigate the diversity of B. bruxellensis isolates in regard to their proteomic, growth, and metabolic profiles. Ten isolates were obtained from several wineries in Croatian winegrowing regions during different phases of wine production. Proteomic analysis revealed 12 proteins that were expressed by all tested isolates and the reference strain. These proteins could be used as biomarkers in Dekkera/B. bruxellensis yeast identification. Five of these proteins were involved in carbohydrate metabolism (enolase, hxk2p, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, and pyruvate decarboxylase), and four were involved in protein biosynthesis (elongation factor 1-alpha, eukaryotic translation initiation factor 5a, 60s ribosomal protein 13, and putative cytosolic ribosomal protein s24). One each was involved in cellular stress responses to glucose starvation (heat shock protein ssb1); ubiquitin conjugation pathways such as transcription, proteolysis trafficking, and kinase activation (ubiquitin); or nitrogen metabolism (peptidyl-prolyl cis-trans isomerase). Isolates identified as B. bruxellensis and taken during malolactic fermentation expressed 18 similar proteins, and isolates from aging in steel vessels/wood barrels or bottled wine expressed 23 and 24 similar proteins, respectively. Growth and metabolic profiles of these isolates were evaluated in two growth media (glucose complex and wine-mimicking media). The growth profiles of the tested isolates and conversion of hydroxycinnamic acids varied among the investigated media in that the use of glucose complex medium resulted in faster growth and consumption of hydroxycinnamic acids and in higher production of volatile phenols and esters. The results obtained suggest the possibility of applying proteomic fingerprinting for the identification and differentiation of B. bruxellensis wine isolates and reveal different spoilage capacities, such as growth and metabolic profiles, of the tested isolates.

The effect of high power ultrasound on phenolic composition, chromatic characteristics, and aroma compounds of red wines

High power ultrasound (HPU) is a novel, non-thermal technology the application of which has been primarily evaluated in managing food quality. The application of high power ultrasound in wine technology is therefore directed at modulating microbial activity during fermentation, extraction of phenolic and aroma compounds from grapes to must, as well as at accelerating aging reactions in wine. The main aim of this article was to evaluate the effect of different HPU process parameters on sustaining the phenolic and aroma composition of red wine and its colour characteristics. Three different red wines, including Cabernet Sauvignon, Merlot, and Plavac mali, were treated with high power ultrasound (20kHz), considering the variations in ultrasound probe diameter size (12.7 and 19 mm), amplitude level (20, 30, and 40 %), and processing time (2, 4, and 6 minutes). Total polyphenol content, total anthocyanin concentration, and chromatic characteristics were analyzed by spectrophotometry, free anthocyanins were analysed by high performance liquid chromatography, and wine aroma compounds were analyzed by gas chromatography combined with solid-phase microextraction. The obtained results show that ultrasonic irradiation induces chemical changes in phenolic composition, chromatic characteristics, and aroma compounds concentration, and accelerates chemical reactions responsible for wine aging. The intensity of the mentioned chemical changes depends on the selected processing parameters and on the treated variety. Among three different parameters, the selection of the probe diameter was showed to be most significant factor influencing chemical composition, followed by the amplitude level and processing time. The smaller diameter probe size (12.7 mm), lowest amplitude (20%), and a shorter processing time (2 minutes) showed a more favourable and lighter effect on the chemical composition of the treated red wines.