Identification by HPLC-MS of anthocyanin derivatives in raisins.
Marquez, A., Dueñas, M., Serratosa, M. P. & Merida, J. (2012). Journal of Chemistry, 2013, Article ID 274893.
The anthocyanin composition in red grapes dried under controlled conditions has been studied. Pyranoanthocyanins and condensed anthocyanins with flavanols by a methylmethine bridge have been identified. Typically, these compounds appear in wine after the fermentation process, as they require compounds such as pyruvic acid, acetoacetic acid, and acetaldehyde for their formation. During the chamber-drying process a stress situation is originated, inducing significant changes in the grape metabolism from aerobic to anaerobic, and as a result it produces the activation of the alcohol dehydrogenase enzyme (ADH) and others that would cause the formation of these compounds. These derivatives are very interesting because they give greater stability to the color of red wine.
Fractionation of sulfur isotopes by Desulfovibrio vulgaris mutants lacking hydrogenases or type I tetraheme cytochrome C3.
Sim, M. S., Wang, D. T., Zane, G. M., Wall, J. D., Bosak, T. & Ono, S. (2013). Frontiers in microbiology, 4(171), 1-10.
The sulfur isotope effect produced by sulfate reducing microbes is commonly used to trace biogeochemical cycles of sulfur and carbon in aquatic and sedimentary environments. To test the contribution of intracellular coupling between carbon and sulfur metabolisms to the overall magnitude of the sulfur isotope effect, this study compared sulfur isotope fractionations by mutants of Desulfovibrio vulgaris Hildenborough. We tested mutant strains lacking one or two periplasmic (Hyd, Hyn-1, Hyn-2, and Hys) or cytoplasmic hydrogenases (Ech and CooL), and a mutant lacking type I tetraheme cytochrome (TpI-c3). In batch culture, wild-type D. vulgaris and its hydrogenase mutants had comparable growth kinetics and produced the same sulfur isotope effects. This is consistent with the reported redundancy of hydrogenases in D. vulgaris. However, the TpI-c3 mutant (ΔcycA) exhibited slower growth and sulfate reduction rates in batch culture, and produced more H2 and an approximately 50% larger sulfur isotope effect, compared to the wild type. The magnitude of sulfur isotope fractionation in the CycA deletion strain, thus, increased due to the disrupted coupling of the carbon oxidation and sulfate reduction pathways. In continuous culture, wild-type D. vulgaris and the CycA mutant produced similar sulfur isotope effects, underscoring the influence of environmental conditions on the relative contribution of hydrogen cycling to the electron transport. The large sulfur isotope effects associated with the non-ideal stoichiometry of sulfate reduction in this study imply that simultaneous fermentation and sulfate reduction may be responsible for some of the large naturally-occurring sulfur isotope effects. Overall, mutant strains provide a powerful tool to test the effect of specific redox proteins and pathways on sulfur isotope fractionation.
New applications for Schizosaccharomyces pombe in the alcoholic fermentation of red wines.
Benito, S., Palomero, F., Morata, A., Calderón, F. & Suárez‐Lepe, J. A. (2012). International Journal of Food Science & Technology, 47(10), 2101-2108.
The fermentation of grape must using non-Saccharomyces yeasts with particular metabolic and biochemical properties is of growing interest. In the present work, red grape must was fermented using four strains of Schizosaccharomyces pombe (935, 936, 938 and 2139), Saccharomyces cerevisiae 7VA and Saccharomyces uvarum S6U, and comparisons were made over the fermentation period in terms of must sugar (glucose + fructose), malic acid, acetic acid, ammonia, primary amino nitrogen, lactic acid, urea (a possible fermentation activator or precursor of other metabolites) and pyruvic acid (a molecule affecting vitisin formation and therefore colour stability) concentration. The colour intensity of the fermenting musts was also recorded. The Schizosaccharomyces strains consumed less primary amino nitrogen and produced less urea and more pyruvic acid than other Saccharomyces species. Further, three of the four Schizosaccharomyces strains completed the breakdown of malic acid by day 4 of fermentation. The main negative effect of the use of Schizosaccharomyces was strong acetic acid production. The Schizosaccharomyces strains that produced most pyruvic acid (938 and 936) were associated with better ‘wine’ colour than the remaining yeasts. The studied Schizosaccharomyces could therefore be of oenological interest.
Selection of appropriate Schizosaccharomyces strains for winemaking.
Benito, S., Palomero, F., Calderón, F., Palmero, D. & Suárez-Lepe, J. A. (2014). Food Microbiology, 42, 218-224.
This paper describes the selection of Schizosaccharomyces yeasts with adequate oenological suitability and high capacity for the degradation of malic acid. Despite the almost non-existent number of commercial strains, the use of this yeast genus has recently been recommended by the International Organisation of Vine and Wine (OIV, in French). Thus, in the present study, a large number of Schizosaccharomyces strains were isolated using a selective differential medium. Initially, classic parameters of oenological interest for the use of fermentative strains of Saccharomyces cerevisiae (the most frequently used type of yeast) were assessed. Only five strains of moderate acetic acid production lower than 0.4 g/L were obtained at the end of fermentation. Other, more specific features of this yeast genus' physiology were also studied, including urease activity and the production of pyruvic acid and glycerol. Finally, oenological suitability was determined by comparing selected strains with other Schizosaccharomyces reference and S cerevisiae control strains. Schizosaccharomyces strains produced 80% less urea content, four times higher pyruvic acid levels and 1 g higher glycerol contents than the Saccharomyces reference strains. The results confirmed that it is possible to perform selective processes on microorganisms from the genus Schizosaccharomyces using methodology developed in this work to obtain strains of industrial interest.
Physiological features of Schizosaccharomyces pombe of interest in making of white wines.
Benito, S., Palomero, F., Morata, A., Calderón, F., Palmero, D. & Suárez-Lepe, J. A. (2013). European Food Research and Technology, 236(1), 29-36.
This work studies the physiology of Schizosaccharomyces pombe strain 938 in the production of white wine with high malic acid levels as the sole fermentative yeast, as well as in mixed and sequential fermentations with Saccharomyces cerevisiae Cru Blanc. The induction of controlled maloalcoholic fermentation through the use of Schizosaccharomyces spp. is now being viewed with much interest. The acetic, malic and pyruvic acid concentrations, relative density and pH of the musts were measured over the entire fermentation period. In all fermentations in which Schizo. pombe 938 was involved, nearly all the malic acid was consumed and moderate acetic concentrations produced. The urea content and alcohol level of these wines were notably lower than in those made with Sacch. cerevisiae Cru Blanc alone. The pyruvic acid concentration was significantly higher in Schizo. pombe fermentations. The sensorial properties of the different final wines varied widely.
The influence of the primary and secondary xanthan structure on the enzymatic hydrolysis of the xanthan backbone.
Kool, M. M., Schols, H. A., Delahaije, R. J. B. M., Sworn, G., Wierenga, P. A. & Gruppen, H. (2013). Carbohydrate Polymers, 97(2), 368-375.
Differently modified xanthans, varying in degree of acetylation and/or pyruvylation were incubated with the experimental cellulase mixture C1-G1 from Myceliophthora thermophila C1. The ionic strength and/or temperature of the xanthan solutions were varied, to obtain different xanthan conformations. The exact conformation at the selected incubation conditions was determined by circular dichroism. The xanthan degradation was analyzed by size exclusion chromatography. It was shown that at a fixed xanthan conformation, the backbone degradation by cellulases is equal for each type of xanthan. Complete backbone degradation is only obtained at a fully disordered conformation, indicating that only the secondary xanthan structure influences the final degree of hydrolysis by cellulases. It is thereby shown that, independently on the degree of substitution, xanthan can be completely hydrolyzed to oligosaccharides. These oligosaccharides can be used to further investigate the primary structure of different xanthans and to correlate the molecular structure to the xanthan functionalities.
Formation of pyranoanthocyanins by Schizosaccharomyces pombe during the fermentation of red must.
Morata, A., Benito, S., Loira, I., Palomero, F., Gonzalez, M. C. & Suarez-Lepe, J. A. (2012). International Journal of Food Microbiology, 159(1), 47-53.
Schizosaccharomyces pombe is a non-Saccharomyces yeast strain that can ferment grape musts with high sugar contents — but it also has other metabolic and physiological properties that render it of great interest to wine biotechnologists. This work compares the production of pyranoanthocyanins by S. pombe, Saccharomyces cerevisiae and Saccharomyces uvarum during fermentation. Total pyranoanthocyanins ranged from 11.9 to 19.4 mg/l depending on the strain of S. pombe used. On average, S. pombe produced more pyruvic acid than did either Saccharomyces species; as a consequence it also formed more vitisin A-type pigments. S. pombe 938 produced the largest quantity of vitisin A (11.03 ± 0.82 mg/l). The formation of large amounts of pyranoanthocyanins intensifies the post-fermentation colour of wines somewhat, a phenomenon that helps them maintain their colour over ageing as the natural grape anthocyanins become degraded. Some of the S. pombe strains showed hydroxycinnamate decarboxylase activity, which favours the formation of vinylphenolic pyranoanthocyanins. Fermentation with S. pombe therefore provides an interesting way of increasing the overall pyranoanthocyanin content of red wines, and of stabilising their colour during ageing.
Formation of vitisins and anthocyanin–flavanol adducts during red grape drying.
Marquez, A., Dueñas, M., Serratosa, M. P. & Merida, J. (2012). Journal of Agricultural and Food Chemistry, 60(27), 6866-6874.
This study evaluated the formation of anthocyanin-derived compounds during the production of sweet red wines from Merlot and Syrah grapes previously chamber-dried under controlled-temperature conditions. The musts from both grape varieties were found to contain pelargonidin-3-glucoside throughout the vinification process. Besides, HPLC-DAD-MS revealed the presence of pyranoanthocyanins in unfermented musts from the raisins. These compounds are adducts resulting from the cycloaddition of pyruvic acid (type A vitisins) and acetaldehyde (type B vitisins) to anthocyanin molecules. The analyses additionally revealed the presence of products of the condensation via a methylmethine bridge between anthocyanins and (epi)catechin, which requires the presence of acetaldehyde. The absence of pyruvic acid, acetaldehyde, and ethanol in the musts from fresh grapes and their presence in those from dried grapes support the idea that these compounds result from enzymatic transformations because the vinification of the musts involves no alcoholic fermentation. The drying process alters the permeability of grape membranes by the lipoxygenase activation effect (LOX), a switch to an anaerobic metabolism and the resulting triggering of the alcohol dehydrogenase enzyme (ADH). The activation of these and several other enzymes confirmed the occurrence of enzymatic transformations and the formation of vitisin A, acetylvitisin A, and the B vitisins of malvidin-3-glucoside, peonidin-3-glucoside, peonidin-3-acetylglucoside, and malvidin-3-acetylglucoside, as well as the adducts Pn-3-glc-methylmethine(epi)catechin, Mv-3-glc-methylmethine(epi) catechin, and Mv-3-acetylmethylmethine(epi)catechin.