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.     

High Concentration of Epigallocatechin‐3‐Gallate Increased the Incidences of Arrhythmia and Diastolic Dysfunction Via β2‐adrenoceptor

Epigallocatechin‐3‐gallate (EGCG) is the major and most potent representative in green tea, which has been proved to modulate myocardial contractility. Whether EGCG has some negative effects on cardiac function is not known. In the present study, we investigated the effects of EGCG at different doses on cardiac contraction and explored whether β₂‐adrenoceptor (β₂AR) was involved in EGCG‐induced cardiac effects. Isolated rat hearts were mounted on the Langendorff system and perfused with different concentrations of EGCG in low or normal calcium Krebs–Henseleit (KH) buffer. The contraction of hearts was measured. Ventricular myocytes were cultured with EGCG and isoprenaline (ISO, 10^?7 M) for 12 h. ICI118,551 (55 nM) was used to inhibit β₂AR. Cardiomyocyte shortening, viability, and responsiveness to ISO (10^?9 M) were measured. EGCG dose dependently enhanced contractility of perfused heart in low calcium KH buffer. In the normal calcium KH buffer, EGCG at low dose (20 μM) increased heart contraction, while at high dose (50 μM), it increased the incidences of arrhythmia and diastolic dysfunction. In isolated ventricular myocytes, EGCG at the concentration of 0.001 to 1.0 μΜ did not affect their contraction. However, the responsiveness to ISO and the survival of myocytes were increased by EGCG (0.01 μM). The increased responsiveness was partially abolished by ICI118,551. The data obtained in this study demonstrated that EGCG at low dose conferred cardioprotection, yet at high dose increased the incidences of arrhythmia and diastolic dysfunction. β₂AR was involved in EGCG‐induced cardiac effects.     

Adsorption of Shiga Toxin to Poly‐γ‐Glutamate Precipitated

We screened foods containing indigestible ingredients in the ability to adsorb Shiga toxin (Stx). When 5 mg of foods and dietary fibers such as dry vegetables and inulin were mixed and incubated with 0.5 mL of Stx solution (100 ng/mL) containing 0.5% bovine serum albumin, both Stx1 and Stx2 seemed to be adsorbed by only a fermented food, natto (a traditional Japanese food prepared from steamed soybeans by the biological action of Bacillus subtilis). We purified the Stx‐adsorbing substance from natto by extraction with H₂O, acid treatment, Proteinase K treatment, and an ion exchange chromatography. The purified substance showed an average molecular mass of about 600 kDa. We identified it as poly‐γ‐glutamate (PGA) by amino acid analysis of its hydrolysate and peptide analysis after its treatment with Proteinase K. Purified PGA (MW: molecular weight = about 600 kDa) was considered to adsorb both Stx1 and Stx2 when we separated adsorbed and unadsorbed Stxs (MW = about 72 kDa) by an ultrafiltration method with a centrifugal filter unit (MWCO: molecular weight cut‐off = 100 K). However, PGA with the ability to adsorb Stx was an insoluble form precipitated in the filter unit during centrifugation. PGA precipitated beyond the saturated density was also confirmed to well adsorb both Stx1 and Stx2 by an equilibrated dialysis method. To the best of our knowledge, this is the 1st report on food‐adsorbing Stx.     

Effects of poly‐γ‐glutamic acid on the physicochemical characteristics of skim milk yoghurt

The physicochemical and sensory properties of skim milk yoghurts containing poly‐γ‐glutamic acid (PGA) at different levels (0.0025, 0.005 and 0.01%) were evaluated. Addition of PGA up to 0.01% to reconstituted skim milk (11%, w/v) did not affect the growth of lactic acid bacteria or the development of titratable acidity in yoghurt, whereas full‐fat control yoghurt had reduced acid production. No changes were found in viable cell counts of PGA yoghurts during storage (4 weeks at 4 °C). The addition of PGA (0.005%) significantly decreased syneresis in skim milk yoghurt and did not cause any undesirable effects in sensory acceptability.     

Screening of β‐Glucosidase and β‐Xylosidase Activities in Four Non‐Saccharomyces Yeast Isolates

The finding of new isolates of non‐Saccharomyces yeasts, showing beneficial enzymes (such as β‐glucosidase and β‐xylosidase), can contribute to the production of quality wines. In a selection and characterization program, we have studied 114 isolates of non‐Saccharomyces yeasts. Four isolates were selected because of their both high β‐glucosidase and β‐xylosidase activities. The ribosomal D1/D2 regions were sequenced to identify them as Pichia membranifaciens Pm7, Hanseniaspora vineae Hv3, H. uvarum Hu8, and Wickerhamomyces anomalus Wa1. The induction process was optimized to be carried on YNB‐medium supplemented with 4% xylan, inoculated with 106 cfu/mL and incubated 48 h at 28 °C without agitation. Most of the strains had a pH optimum of 5.0 to 6.0 for both the β‐glucosidase and β‐xylosidase activities. The effect of sugars was different for each isolate and activity. Each isolate showed a characteristic set of inhibition, enhancement or null effect for β‐glucosidase and β‐xylosidase. The volatile compounds liberated from wine incubated with each of the 4 yeasts were also studied, showing an overall terpene increase (1.1 to 1.3‐folds) when wines were treated with non‐Saccharomyces isolates. In detail, terpineol, 4‐vinyl‐phenol and 2‐methoxy‐4‐vinylphenol increased after the addition of Hanseniaspora isolates. Wines treated with Hanseniaspora, Wickerhamomyces, or Pichia produced more 2‐phenyl ethanol than those inoculated with other yeasts.     

Glycyrrhetic Acid 3‐O‐Mono‐β‐d‐glucuronide (GAMG): An Innovative High‐Potency Sweetener with Improved Biological Activities

Glycyrrhetic acid 3‐O‐mono‐β‐d ‐glucuronide (GAMG) is an important derivative of glycyrrhizin (GL) and has attracted considerable attention, especially in the food and pharmaceutical industries, due to its natural high sweetness and strong biological activities. The biotransformation process is becoming an efficient route for GAMG production with the advantages of mild reaction conditions, environmentally friendly process, and high production efficiency. Recent studies showed that several β‐glucuronidases (β‐GUS) are key GAMG‐producing enzymes, displaying a high potential to convert GL directly into the more valuable GAMG and providing new insights into the generation of high‐value compounds. This review provides details of the structural properties, health benefits, and potential applications of GAMG. The progress in the development of the biotransformation processes and fermentation strategies to improve the yield of GAMG is also discussed. This work further summarizes recent advances in the enzymatic synthesis of GAMG using β‐GUS with emphasis on the physicochemical and biological properties, molecular modifications, and enzymatic strategies to improve β‐GUS biocatalytic efficiencies. This information contributes to a better framework to explore production and application of bioactive GAMG.     

Preferential extractability of γ‐oryzanol from dried soapstock using different solvents

BACKGROUND: γ‐Oryzanol from rice bran has lately gained potential importance because of its proven health benefits. Thus the extractability of γ‐oryzanol from the soapstock of crude rice bran oil is important from the perspective of future large‐scale production, which would give value addition to this by‐product obtained from the rice bran oil industry. The aim of the present study was to investigate the extraction of γ‐oryzanol from the drum‐dried soapstock of rice bran oil using various solvents. RESULTS: It was found that γ‐oryzanol could be extracted most effectively using ethyl acetate, followed by dichloromethane and ethyl methyl ketone. All components of γ‐oryzanol have an alcohol group in the ferulate portion giving rise to relatively high polarity, thereby increasing the extraction in more polar solvents efficiently. Ethyl acetate showed maximum extractability of γ‐oryzanol by the Soxhlet method. To quantify γ‐oryzanol, reverse phase high‐performance liquid chromatography (RP‐HPLC) was used for fingerprinting the γ‐oryzanol analogues with respect to standard γ‐oryzanol. CONCLUSION: A new RP‐HPLC method for determining the individual components of γ‐oryzanol has been reported that can be used for performing an online characterisation of γ‐oryzanol analogues by liquid chromatography/mass spectrometry. Copyright © 2008 Society of Chemical Industry     

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.