Contribution of cysteine and glutathione conjugates to the formation of the volatile thiols 3‐mercaptohexan‐1‐ol (3MH) and 3‐mercaptohexyl acetate (3MHA) during fermentation by Saccharomyces cerevisiae

Background and Aims: 3‐Mercaptohexan‐1‐ol (3MH) and its ester 3‐mercaptohexyl acetate (3MHA) are potent aromatic thiols that substantially contribute to varietal wine aroma. During fermentation, non‐volatile 3MH conjugates are converted by yeast to volatile 3MH and 3MHA. Two types of 3MH conjugates have been identified, S‐3‐(hexan‐1‐ol)‐L‐cysteine (Cys‐3MH) and S‐3‐(hexan‐1‐ol)‐glutathione (GSH‐3MH). Yeast‐driven formation of 3MH from these precursors has been previously demonstrated, while the relationship between 3MHA and GSH‐3MH remains to be established. This paper aims to investigate yeast conversion of GSH‐3MH to 3MH and 3MHA, and to assess the relative contribution of each individual conjugate to the 3MH/3MHA pool of finished wines. Methods and Results: Fermentation experiments were carried out in model grape juice containing Cys‐3MH and GSH‐3MH. We found 3MH formation from GSH‐3MH to be significantly less efficient than that of Cys‐3MH. Conversely, esterification of 3MH to 3MHA was higher when 3MH was formed from GSH‐3MH. Additional in vitro assays for measuring enzyme cleavage activity suggest the involvement of a different mechanism in 3MH conversion for the two precursors. Conclusions: These results indicate that although both 3MH conjugates can be converted by yeast, the type of precursor affects the rate of formation of 3MH and 3MHA during fermentation. Significance of the Study: Management of the pool of aromatic thiols during fermentation can depend on relative proportions of different 3MH conjugates.     

Whitening effect of α‐bisabolol in Asian women subjects

Although skin pigmentation, which results from the production and distribution of melanin in the epidermis, is the major physiological defence against solar irradiation, hyperpigmentation is a common and distressing problem caused by various inflammatory skin disorders, such as eczema, allergic contact dermatitis and irritant contact dermatitis. We evaluated the effects of a preparation containing α‐bisabolol on pigmented skin of a group of subjects. The effectiveness of the active compound, α‐bisabolol, in a base‐cream preparation for the treatment of pigmented skin was tested on 28 female subjects as follows: the cream was applied once a day to the back for 8 weeks. These same women also applied a vehicle control cream to the pigmented skin. The results were evaluated by clinical and biophysical test methods. After 8 weeks of treatment of the α‐bisabolol‐containing cream, there was significant lightening effect in the pigmented skin for the majority of the subjects who tested the cream.     

Influence of α‐amylolysis on the formation of electron density inhomogeneities on the surface of starch granules

Low‐temperature nitrogen adsorption and SAXS were used to analyze the granule surface of wheat and rice starches before and after an action of Bacillus subtilis α‐amylase. Results obtained by the first method showed that α‐amylolysis caused surface changes arising of new pores or enlarging diameters of pores already existing. According to the SAXS results, the action of enzymes caused complete sharpening of a solid skeletal boundary in the case of wheat starch granules. Partial sharpening of this boundary in the case of rice starch granules could be attributed to the relatively high content of proteins in rice starch.     

Study and quantification of monomeric flavan‐3‐ol and dimeric procyanidin quinonic forms by HPLC/ESI‐MS. Application to red wine oxidation

Monomeric flavan‐3‐ols and dimeric procyanidins of red wine were oxidised by two processes, chemical and enzymatic. Unstable quinonic forms were stabilised by sulphonation, and the resulting sulphones were quantified by coupled HPLC/ESI‐MS. The effects of temperature and UV light on the oxidation of phenolic compounds were also investigated. The concentration of quinones increased with increasing temperature, but the kinetics of the reaction was independent of temperature. Likewise, more quinones were formed in the presence of UV light than in its absence, but UV light also did not affect the kinetics of the reaction. Thus temperature and UV light affect the quantity of quinones formed but not the rate at which they appear. © 2001 Society of Chemical Industry     

A critical review of methodologies used in determination of relative bio‐availability ratio of RRR‐α‐tocopheryl acetate and all‐rac‐α‐tocopheryl acetate

Bio‐availability of different α‐tocopherol forms in livestock animals is measured by the increase in plasma or tissue concentrations of α‐tocopherol after oral administration. It is generally accepted that RRR‐α‐tocopheryl acetate (natural source vitamin E derived from vegetable oil) has a higher bio‐availability compared to all‐rac‐α‐tocopheryl acetate (synthetic vitamin E, i.e. α‐tocopherol produced by chemical synthesis). However, different bio‐availability ratios have been reported in the literature. The major reason for conflicting results in literature studies was the inability to separate the proportion of α‐tocopherol originating from test materials, from the proportion of α‐tocopherol originating from basal dietary ingredients and pre‐feeding. This causes significant variability. For bio‐availability determination, a baseline or control treatment is essential. The estimation of bio‐availability without correction for basal vitamin E status will lead to incorrect interpretation of the results. When using proper methodologies, it is possible to correct for the impact of α‐tocopherol intake from basal ingredients and α‐tocopherol originating from pre‐feeding, therefore yielding results reflecting the true relative bio‐availability of different α‐tocopherol substances. When reviewing literature data a critical evaluation of the method used in determination of relative bio‐availability is recommended. Copyright © 2010 Society of Chemical Industry     

Analysis of caffeine and flavan‐3‐ol composition in the fresh leaf of Camellia sinesis for predicting the quality of the black tea produced in Central and Southern Africa

A parameter of fresh tea leaf that correlates with black tea quality is highly desired. Twenty good and 20 poor quality tea clones were selected from the breeding programme at the Tea Research Foundation (Central Africa) (TRF(CA)). The flavan‐3‐ol profile of fresh tea leaves was analysed by capillary electrophoresis while total theaflavin (TF) content was determined in the black tea manufactured from the same leaves for each clone. The above parameters were correlated with total scores and valuation from two tea tasters with regression analysis. The significance of the differences between the 20 good and 20 poor quality tea clones was determined with the Student's t‐test. The total TF content of the black tea correlated (r = 0.63, P = 0.0001) well with the value of the tea. Of all the parameters determined in the fresh leaves, the highest correlation was obtained with (−)‐epicatechin (EC) (r = 0.65, P = 0.0001). This may facilitate early selection of good quality TRF(CA) clones in the future. © 2000 Society of Chemical Industry     

Alterations of the Profiles of Iso‐α‐Acids During Beer Ageing,Marked Instability of Trans‐Iso‐α‐Acids and Implications for Beer Bitterness Consistency in Relation to Tetrahydroiso‐α‐Acids

Age‐induced decomposition of iso‐α‐acids, the main bittering principles of beer, determines the consistency of the beer bitter taste. In this study, the profiles of iso‐α‐acids in selected high‐quality top‐fermented and lager beers were monitored by quantitative high‐performance liquid chromatography at various time intervals during ageing. The degradation of the iso‐α‐acids as a function of time is represented by the ratio, in percentage, of the sum of the concentrations of trans‐isocohumulone and trans‐isohumulone to the sum of the concentrations of cis‐isocohumulone and cis‐isohumulone. This parameter is relevant with respect to the evaluation of bitterness deterioration in aged beers. Trans‐iso‐α‐acids having a shelf half‐life of less than one year proved to be significantly less stable than cis‐iso‐α‐acids, but it appears feasible to counteract degradation if a suitable beer matrix is available. The fate of the trans‐iso‐α‐acids in particular adversely affects beer bitterness consistency. In addition to using hop products containing low amounts of trans‐iso‐α‐acids, brewers may profit of the remarkable stability of tetrahydroiso‐α‐acids, even on prolonged storage, for the production of consistently bitter beers.     

Characterization of the Supermolecular Structure of Polydatin/6‐O‐α‐Maltosyl‐β‐cyclodextrin Inclusion Complex

Polydatin is the main bioactive ingredient in many medicinal plants, such as Hu‐zhang (Polygonum cuspidatum), with many bioactivities. However, its poor aqueous solubility restricts its application in functional food. In this work, 6‐O‐α‐Maltosyl‐β‐cyclodextrin (Malt‐β‐CD), a new kind of β‐CD derivative was used to enhance the aqueous solubility and stability of polydatin by forming the inclusion complex. The phase solubility study showed that polydatin and Malt‐β‐CD could form the complex with the stoichiometric ratio of 1:1. The supermolecular structure of the polydatin/Malt‐β‐CD complex was characterized by ultraviolet–visible spectroscopy (UV), Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffractometry (XRD), thermogravimetric/differential scanning calorimetry (TG/DSC), and proton nuclear magnetic resonance (¹H‐NMR) spectroscopy. The changes of the characteristic spectral and thermal properties of polydatin suggested that polydatin could entrap inside the cavity of Malt‐β‐CD. Furthermore, to reasonably understand the complexation mode, the supermolecular structure of polydatin/Malt‐β‐CD inclusion complex was postulated by a molecular docking method based on Autodock 4.2.3. It was clearly observed that the ring B of polydatin oriented toward the narrow rim of Malt‐β‐CD with ring A and glucosyl group practically exposed to the wide rim by hydrogen bonding, which was in a good agreement with the spectral data.     

Investigation of the interaction between (−)‐epigallocatechin‐3‐gallate with trypsin and α‐chymotrypsin

Tea polyphenol (TP) inhibits digestive enzymes and reduces food digestibility. To explore the interaction between TP with digestive enzymes, bindings of ‐epigallocatechin‐3‐gallate (EGCG) to trypsin and α‐chymotrypsin were studied in detail using fluorescence, resonance light‐scattering, circular dichroism, fourier transform infrared spectroscopy methods and protein‐ligand docking. The binding parameters were calculated according to Stern–Volmer equation, and the thermodynamic parameters were determined by the van't Hoff equation. The results indicated that EGCG was capable of binding trypsin and α‐chymotrypsin with high affinity, resulting in a change of native conformation of these enzymes. EGCG had a greater influence on the structure of α‐chymotrypsin than trypsin. This study can be used to explain the binding interaction mechanism between TP and digestive enzymes.     

Ser71 of αS1‐Casein is Phosphorylated in Breast Milk—Evidence from Targeted Mass Analysis

Scope

The casein phosphoproteins in mother's milk supply calcium and phosphate ions and make them biologically available to the newborn. Human αS1‐casein is of particular interest being also an autoantigen and proinflammatory cytokine. Phosphorylation of αS1‐casein by casein kinase 2 completely abolishes binding to toll‐like receptor 4 and proinflammatory effects. It is, however, not known, which amino acids are affected. Therefore, breast milk samples were analyzed in an effort to detect the phosphorylation sites of αS1‐casein.

Methods and results

Breast milk samples were tryptically digested. Target tandem MS analysis confirmed the known phosphorylation sites S33 and S41; evidence for pS89 was found in some samples. Experimental support for the presence of pS31 and pS34 was weak. Phosphorylation of a new site in αS1‐casein, S71, was reproducibly measured in all samples, albeit at much lower intensity than pS33 and pS41.

Conclusion

Phospho‐occupancy rates varied greatly and could not be confidently correlated to other parameters within the cohort of 20 donors. The new phosphosite S71 is located in the neighborhood of the serine‐rich region and may contribute to the cluster of high charge density at normal milk pH, likely exerting an influence on protein tertiary structure and thus function.