1,721,043 research outputs found
Perceived astringency in wine: A predictive model
No full textSensations perceived in the act of tasting are important determinants of consumer response to red wine. Astringency is a tactile stimulus that strongly influences wine acceptability. Astringency descriptors account for more than a half of the total terms in the mouth-feel wheel proposed for describing the sensory properties of red wine. The physiological mechanism of the astringency perception in wine is based on the reaction of phenolic compounds with salivary proteins and the consequent formation of insoluble astringent/protein complexes. The availability of in vitro assays to estimate the strength of the sensation induced by different phenolic compounds became crucial in order to optimise the processing conditions in relation to this important driver of wine acceptability and sensory quality. In this work recent advancements in predicting astringency induced by phenolic compounds are discussed and new and promising methods are presented. Critical points in collecting both sensory and chemical data are reviewed. In particular, the application of the "Astringency Mucin Index" (AMI) in predicting the astringency induced by grape and wine phenol extracts is shown. The results of the use of the AMI on commercial phenolic extract, seed phenolic extracts from 'Aglianico' grape, 18 'Sangiovese' experimental wines and 20 commercial 'Aglianico del Vulture' wines are presented. Future developments of methods capable of predicting astringency are discussed
Re-entry in cell cycle: protein metabolism and transglutaminase-like activity in Helianthus tuberosus
No full textSlices of Helianthus tuberosus L. cv OB1 tuber were activated to induce a synchronous cell cycle, during various phases of tuber dormancy. The reactivity expressed as protein content and the TGase activity are highest during deep dormancy and low during tuber formation and dormancy release. At the onset of the cycle an abrupt decrease in total protein and synthesis of several leucine- and methionine-labelled proteins occur. The solubility of the proteins also changes. After mid-G1, synthesis prevails and thus protein levels increase. The synthesis of the components of a temperature-sensitive (Ts) and -insensitive (Ti) transglutaminase-like (TGase-like) activity is cycloheximide inhibited and begins before mid-G1, but their activity is evident only later on. While the products of the Ts activity, are polyamine-protein conjugates of high molecular mass, the products of the Ti activity are not covalently bound. A possible role of endogenous proteases in this binding activity is discussed
Spectrophotometric assay using o-phtaldialdehyde for the determination of transglutaminase activity on casein
No full textIn this work, the possibility of using a simple and quick method was tested for determining transglutaminase activity on casein
using a spectrophotometric assay. The enzyme activity was estimated on the basis of the decrease of o-phthaldialdehyde reactive "-
amino groups of lysine following the formation of isopeptide bonds. The lysine residues involved in the formation of isopeptide
bonds when the reaction reaches its plateau are equal to 0.126 mmol per mg of casein. This value results as equal to 0.205 mmol per
mg of casein when N-carbobenzoxy-glutaminyl-glycine is added to the reaction medium as a small size acyl group donor. The
electrophoretic analysis of the reaction products emphasised a different kinetic formation of casein polymers with the two substrate
solutions used. This proposed method has resulted as accurate, with a mean coefficient of variation of 4.6%
The cell cycle in Helianthus tuberosus: analysis of polyamine-endogenous protein conjugates by transglutaminase-like activity
No full textParenchyma cells of dormant Helianthus tuberosus tubers were induced to enter a synchronous cell cycle with the aim of studying therein the modifications which proteins undergo when they bind to polyamines. A transglutaminase-like activity (TGase-like), which increases during the cell cycle, produces high molecular mass conjugates with [3H]- and [14C]-putrescine (PU) that can be precipitated with trichloroacetic acid or ammonium sulphate, together with complexes in which PU is not covalently bound. These pellets were subjected to acidic hydrolysis at high temperature and the amount of PU was determined by thin layer chromatography: PU decreases untill mid-G1 and then increases during the cell cycle, remaining stationary only at the beginning of cell division. Bound PU derivatives, especially compounds having a migration near zero, were also formed. Very low amounts of bound labelled spermidine, spermine or gamma aminobutyric acid were detected. The labelled conjugates that were not subjected to hydrolysis but analyzed by SDS-PAGE, were not mobile, and some of them could be separated by changing the percentage of acrylamide or by treating them with papain or cellulase and pectinase, suggesting that they are proteins linked to or entrapped by carbohydrates
Temporary Modification of Salivary Protein Profile and Individual Responses to Repeated Phenolic Astringent Stimuli
No full textThe extent of the change in salivary protein characteristics after repeated stimulations was shown to be correlated to
differences in perceived astringency. Salivary characteristics of 77 subjects were compared after masticatory (S1) and taste/
masticatory (S2) stimulations. The variations (S2 minus S1) of protein concentration and saliva haze-forming capacity (HFC)
were used to define 3 subject groups: low responding (LR, n = 20), medium responding (MR, n = 37), and high responding (HR,
n = 20). Salivary protein concentration did not change in LR subjects; decreased a little, but significantly, in MR subjects; and
strongly decreased in HR subjects. After S2, HFC increased in LR subjects, slightly decreased in MR subjects, and strongly
decreased in HR subjects. Salivary protein electrophoresis patterns for HR and LR subjects were analyzed. No significant
modifications of glycosylated proline-rich proteins (PRPs), PRPs, and amylases and a slight decrease in cystatins and histatins
were found when S2 and S1 samples were compared in LR subjects, whereas HR subjects showed a strong decrease in all the
above proteins after S2. Significant modifications of mucins were not found. Tannic acid (TA, 3 g/L) astringency ratings after S1
from HR subjects were significantly higher than those from the other 2 groups, whereas no differences were found comparing
LR and MR ratings. The ‘‘carryover’’ effect due to 4 sequential exposures to TA samples (1.4 g/L) was observed in both HR and
MR groups, whereas no significant astringency rating variation was found in the LR group. The results support the inhibiting
role of proteins with strong phenol-binding activity on astringency elicitation. Individual physiological variations of parotid
gland functionality might account for differences in sensitivity to astringent phenolic stimuli
Core Shell Functional Microspheres by Dispersion Polymerization 2: Synthesis and Characterization
No full textPrediction of perceived astringency induced by phenolic compounds II: Criteria for panel selection and preliminary application on wine samples
No full textIn the following work, subject saliva characteristics affecting panel astringency evaluation in phenolic mixtures were studied. Sixty subjects were selected on the basis of their salivary flow, haze developing capacity and protein concentration. Subjects rated the perceived astringency of tannic acid (TA), commercial procyanidin (PA) and grape seed extract (GSE) solutions with concentration values ranging from 0.42 to 1.4 g/L. Astringency intensity perception proved to be inversely related to saliva flow rate and haze developing capacity. No significant correlations were found between saliva protein concentration and intensity of astringency perception. A panel selected on the basis of subject similarity for flow rate and haze developing capacity rated the astringency intensity of set sample training solutions of TA, PA and GSE with concentrations ranging from 0.39 to 4.48 g/L. The reactivity of the same astringent solutions with mucin was measured in an in vitro assay and expressed in terms of Nephelometric Turbidity Units (NTU). Three predictive models described by a linear regression of astringency intensity vs. NTU were found. The possibility of a practical application of the proposed assay for optimization of wine production was evaluated on 18 experimental wines. A linear correlation was found between the intensity astringency ratings of wine samples and the in vitro assay response. © 2005 Elsevier Ltd. All rights reserved
Prediction of perceived astringency induced by phenolic compounds
No full textA method which can be used to estimate perceived astringency due to polyphenolic compounds is presented here. Thirty subjects were selected on the basis of them having similar salivary flows and they were trained to rate the perceived astringency of tannic acid and grape seed extract solutions. A scale of phenolic compound concentrations ranging from 0 to 3.2 g/L was selected in order to obtain an experimental curve describing the perceived intensity of the sensation. The same astringent solutions were added to a mucin solution in conditions resembling those present in the oral cavity. The formation of polyphenol-protein complexes was measured on the basis of the increasing turbidity of the reaction mixture and was expressed in terms of nephelometric turbidity units (NTU). Experimental curves describing NTU vs polyphenol concentration were obtained. Predictive models of astringency intensity vs NTU were produced. The predictive capacity of the models was checked by comparing the measured and predicted intensities of a set of samples prepared at phenolic compound concentration level varying from 0.94 to 2.13 g/L. © 2004 Elsevier Ltd. All rights reserved
Functional particles by dispersion polymerization 4 Core-shell tunable surface microspheres for selective enzyme adsorption
No full textImmobilization of an endopectinlyase on c-alumina: study of factors influencing the biocatalytic matrix stability.
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