Differential interaction of seed polyphenols from grapes collected at different maturity stages with the protein fraction of saliva

Grape seed and skin proanthocyanidins undergo significant changes during grape maturation. Those changes have been associated with a decreased astringency of grapes collected at later maturation stages. We have now compared the ability of proanthocyanidin‐rich extracts from Carménère grape seeds collected at two stages of berry development (veraison vs. harvest) both to interact with salivary proteins and to produce astringency. Interaction of proanthocyanidins with the salivary protein was assessed by analysing the concentration‐dependent effect of seed extracts both on inducing salivary protein precipitation and on restricting diffusion of the salivary protein on cellulose membranes. Seed extracts from grapes collected at veraison compared with those of grapes collected at harvest displayed a higher ability both to interact with the salivary protein fraction and to produce astringency. As a whole, our observations show that astringency is closely dependent on the magnitude of the interactions between proanthocyanidins and the salivary protein fraction.     

Precipitation of low molecular weight phenolic compounds of grape seeds cv. Carménère (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L.) by whole saliva

Low molecular weight phenolic compounds (LMWP) contribute to astringency and bitterness, two important sensory attributes. This work aimed to study the interactions between human saliva and a group of LMWP from a grape seed extract, namely, monomers, dimers and trimers of flavan-3-ol plus gallic acid. LMWP in the sediment that was produced by mixing whole saliva with the grape seed extract were identified by high-performance liquid chromatography analysis (HPLC–DAD). Two assays to produce LMWP-salivary protein sediments were carried out. An indirect assay consisted of in vitro mixing aliquots of saliva with a constant volume of the grape seed extract followed by centrifugation and sediment analysis. In a direct assay, aliquots of the grape seed extract were mixed in-mouth with saliva, returned to a vessel and centrifuged. In each assay, polyphenol composition of the sediments varied according to the tannin/saliva vol/vol ratio although in both cases monomeric LMWP were the most abundant polyphenol components of the sediments. The study also suggested the need for a strict control of the in vitro experimental conditions used to mimic the in vivo conditions in which tannin–protein interactions do occur and produce astringency perception.     

Inhibition studies in sweet corrosion systems by a quaternary ammonium compound

Benzyl dimethyl-n-hexadecylammonium chloride (BHDC) was investigated for its effectiveness as a corrosion inhibitor of pure iron in carbon dioxide saturated 3% sodium chloride solutions. Both a.c. impedance and d.c. electrochemical techniques were used. The compound inhibited the anodic reaction and was effective at low temperatures. Data obtained fitted the Frumkin adsorption isotherm. The inhibition characteristics are interpreted in terms of thermodynamics and the structure of the compound.     

Interactions of enological tannins with the protein fraction of saliva and astringency perception are affected by pH

The effects of pH on both tannin-induced astringency and tannin–salivary protein interactions were investigated. A trained sensory panel evaluated astringency perception. Tannin–salivary protein interactions were assessed in vitro by examining the effects of either a condensed enological tannin or an hydrolyzable enological tannin on two physicochemical properties of the protein fraction of saliva, namely, its mode of diffusion on cellulose membranes and its precipitation. Comparative assays mimicking the degree of dilution experienced by saliva during a tasting assay were performed at pH 3.5 and pH 7.0. Results indicated that both enological tannins were perceived as clearly more astringent at pH 3.5 compared with pH 7.0. In addition, the effects of tannins on protein diffusion and protein precipitation were markedly exacerbated at pH 3.5.     

Tannin–protein interaction is more closely associated with astringency than tannin–protein precipitation: experience with two oenological tannins and a gelatin

Relative abilities of two commercial oenological tannins to interact with a single oenological gelatin were compared with their relative abilities to elicit astringency. A trained sensory panel assessed astringency, whereas the interaction between tannins and gelatin was estimated by observing the ability of tannins both to interfere with gelatin diffusion on a cellulose membrane and to form tannin–gelatin precipitates. HPLC‐DAD chromatography and spectroscopic analysis showed that one of the commercial tannins was a hydrolysable tannin, while the other one was a condensed. The majority of the sensory panelists recognised the hydrolysable tannin as far more astringent than the condensed. The more astringent oenological tannin was found to interfere markedly with gelatin diffusion on a cellulose membrane, but it failed to produce tannin–gelatin precipitation. The condensed oenological tannin both interfered with gelatin diffusion and was a powerful gelatin‐precipitant. This study supports the hypothesis that astringency correlates better with tannin–gelatin interaction than tannin–gelatin precipitation.     

Evaluation of pathogenesis-related protein content and protein instability of seven white grape (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L.) clones from Casablanca Valley,Chile

Thaumatin-like proteins and chitinases are the main pathogenesis-related (PR) proteins found in grapes, grape juice and wine and are responsible for protein haze formation in bottled white wine during storage and transport. We have studied the effect of the content of both thaumatin-like proteins and chitinases on protein instability of Sauvignon blanc (clones 1, 107 and 242) and Chardonnay (clones 4, 5, 75 and Mendoza) grape juices from both a warm and a cold production zone in the Casablanca Valley, Chile. The PR proteins were identified and quantified by reversed-phase liquid chromatography (RP-HPLC). Protein instability was determined using a heat test and was expressed in nephelometric turbidity units (NTUs). Thaumatin-like (TL) proteins were identified as the major PR proteins present in all grape juices studied. Three TL proteins were identified and named Vitis vinifera thaumatin-like proteins 1, 2 and 3 (VVTL1, VVTL2 and VVTL3). Chitinase A (ChitA) was identified in the Sauvignon blanc and Chardonnay grape juices, and chitinase B (ChitB) was found only in Chardonnay grape juices. Significant differences in the protein content and in the type of protein were observed between grapes from different production zones and between grapes of different varieties, respectively.     

A study on biological clogging of nonwoven geotextiles under leachate flow

This paper presents results of long-term permittivity tests using leachate to evaluate biological clogging of nonwoven geotextiles. Three types of geotextiles with varying masses per unit area were used in the tests. The identification and quantification of microorganisms in the geotextile were carried out as well as microscopic investigations. The accuracies of semi-empirical models to evaluate the kinetics of bacteria growth and to correlate hydraulic properties and microbiological parameters were examined. Permittivity tests under increasing water heads were also performed on the geotextile samples already subjected to long-term leachate flow in order to evaluate the values of water heads required to wash the biofilms out of the geotextile pores. The results of the tests showed the marked reduction of geotextile permeability due to biological clogging and that the results of the predictions by semi-empirical methods were consistent with the biological mechanisms observed.     

Phenolic characterization of commercial enological tannins

Enological tannins are widely used in winemaking process to improve different characteristics of wines. A wide spectrum of enological tannins is now available on the market; however, the tannins’ chemical nature and botanical origin are not always clearly defined in the commercial products. The aim of this work was the chemical characterization of ten commercial plant-derived tanning agents of enological use. Enological tannins were analyzed by spectrophotometry (total phenols, total tannins and gelatin index) and high performance liquid chromatography (HPLC–DAD) (low molecular weight phenolic compounds). In general it was possible to observe important differences in the concentration of total phenols, total tannins and gelatin index values among the commercial products studied. By using HPLC–DAD it was possible to classify different types of tannins (mainly hydrolyzable (gallotannins and ellagitannins), condensed or proanthocyanidic tannins and blends of these groups). Clear differences were evident between the study results and the information on the type of tannin indicated on some of the commercial tannin labels. These discrepancies could lead to technological problems in the winery industry because of the different aims that guide the use of different types of these enological products.