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.     

Formation of γ‐gluconolactone in a wine‐like model system

By experiments performed in wine‐like and must‐like model solutions, we have shown that intramolecular gluconic acid esterification leads to the formation of not only the well‐known δ‐gluconolactone (glucono‐5‐lactone) but also γ‐gluconolactone (glucono‐4‐lactone). To our knowledge, the presence of the latter is reported for the first time under conditions similar to those in grape musts and wines. Equilibrium between these lactones and gluconic acid was reached within 24 h of preparing a solution of gluconic acid, and in both wine‐like and must‐like model solutions the concentrations of γ‐ and δ‐gluconolactone represented the same proportions of the acid, ie about 60 and 40 mg g^?1 gluconic acid respectively. Owing to their chemical structures, not only δ‐gluconolactone but also γ‐gluconolactone could certainly contribute to sulphur dioxide binding in musts and wines containing gluconic acid. © 2002 Society of Chemical Industry     

Phenethyl isothiocyanate suppresses nitric oxide production via inhibition of phosphoinositide 3‐kinase/Akt‐induced IFN‐γ secretion in LPS‐activated peritoneal macrophages

Phenethyl isothiocyanate (PEITC), a constituent of many cruciferous vegetables, is well known to have versatile physiological activities, including chemopreventive effects. On the other hand, its anti‐inflammatory effects are poorly reported. Nitric oxide (NO) is associated with a wide variety of inflammatory diseases. In this study, we investigated the effects of PEITC on NO production in LPS‐activated peritoneal macrophages from ICR mice. The signaling pathway of LPS‐induced NO production was examined using neutralizing antibodies [anti‐interferon (IFN)‐γ and anti‐interleukin (IL‐12)] and specific protein kinase inhibitors, as well as others. The activity of PEITC toward NOx production was assessed in mice that received LPS via intraperitoneal administration. The neutralizing antibody of anti‐IFN‐γ, but not anti‐IL‐12, suppressed LPS‐induced NO production by 90%. LY294002, a specific inhibitor of phosphoinositide‐3‐kinase, suppressed Akt and IFN‐γ mRNA expression up‐regulated by LPS, whereas PEITC exhibited a similar inhibition profile. Furthermore, oral administration of PEITC significantly suppressed the serum concentration of NOx in ICR mice. Our results suggest that PEITC suppresses LPS‐induced NO production via inhibition of Akt activation and the resultant decrease in expression of IFN‐γ. This is one of the first reports to demonstrate a marked anti‐inflammatory effect of PEITC following its oral administration.     

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.     

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.