Study of the Stability of Wine Samples for 1H-NMR Metabolomic Profile Analysis through Chemometrics Methods.

Wine is a temperature, light, and oxygen-sensitive product, so its physicochemical characteristics can be modified by variations in temperature and time when samples are either sampled, transported, and/or analyzed. These changes can alter its metabolomic fingerprinting, impacting further classification tasks and quality/quantitative analyses. For these reasons, the aim of this work is to compare and analyze the information obtained by different chemometric methods used in a complementary form (PCA, ASCA, and PARAFAC) to study 1H-NMR spectra variations of four red wine samples kept at different temperatures and time lapses. In conjunction, distinctive changes in the spectra are satisfactorily tracked with each chemometric method. The chemometric analyses reveal variations related to the wine sample, temperature, and time, as well as the interactions among these factors. Moreover, the magnitude and statistical significance of the effects are satisfactorily accounted for by ASCA, while the time-related effects variations are encountered by PARAFAC modeling. Acetaldehyde, formic acid, polyphenols, carbohydrates, lactic acid, ethyl lactate, methanol, choline, succinic acid, proline, acetoin, acetic acid, 1,3-propanediol, isopentanol, and some amino acids are identified as some of the metabolites which present the most important variations.

Understanding the Biosynthetic Changes that Give Origin to the Distinctive Flavor of Sotol: Microbial Identification and Analysis of the Volatile Metabolites Profiles During Sotol (Dasylirion sp.) Must Fermentation.

In northern Mexico, the distilled spirit sotol with a denomination of origin is made from species of Dasylirion. The configuration of the volatile metabolites produced during the spontaneous fermentation of Dasylirion sp. must is insufficiently understood. In this study, the aim was to investigate the composition of the microbial consortia, describe the variation of volatile metabolites, and relate such profiles with their particular flavor attributes during the fermentation of sotol (Dasylirion sp.) must. Ascomycota was the phylum of most strains identified with 75% of total abundance. The genus of fermenting yeasts constituted of 101 Pichia strains and 13 Saccharomyces strains. A total of 57 volatile metabolites were identified and grouped into ten classes. The first stage of fermentation was composed of diesel, green, fruity, and cheesy attributes due to butyl 2-methylpropanoate, octan-1-ol, ethyl octanoate, and butanal, respectively, followed by a variation to pungent and sweet descriptors due to 3-methylbutan-1-ol and butyl 2-methylpropanoate. The final stage was described by floral, ethereal-winey, and vinegar attributes related to ethyl ethanimidate, 2-methylpropan-1-ol, and 2-hydroxyacetic acid. Our results improve the knowledge of the variations of volatile metabolites during the fermentation of sotol must and their contribution to its distinctive flavor.

Mezcal: indigenous Saccharomyces cerevisiae strains and their potential as starter cultures.

In this study, 19 indigenous mezcal Saccharomyces cerevisiae strains were screened for their tolerance to grow under different stress conditions and their potential use in fermentation. All strains were able to tolerate pH value of 3, significant levels of glucose (30%), ethanol (12% v/v), and temperature of 37 °C. Eleven of them were able to grow in presence of 15% of ethanol, but only CH7 and PA18 strains grew at 42 °C. Both were selected for evaluation of their fermentative abilities in maguey juice and in a synthetic medium incubated at 30 and 40 °C. Temperature of 40 °C had a positive effect on the ethanol production, increasing the productivity and efficiency in maguey fermentation. Ethyl acetate, isobutanol and isoamyl alcohols production was favored at 30 °C. Both evaluated strains presented a good fermentative capacity and production of volatile compounds, suggesting their potential use as starter cultures in mezcal fermentation.

Predominant Yeasts During Artisanal Mezcal Fermentation and Their Capacity to Ferment Maguey Juice.

Artisanal mezcal is produced by the natural fermentation of maguey juice, which frequently results in a process that becomes stuck or is sluggish. Using selected indigenous starter inoculums of Saccharomyces and non-Saccharomyces yeasts is considered beneficial in overcoming these problems and thereby preserving the essence of the artisanal process. In this work, three hundred and four yeast isolates were recovered from 17 distilleries and then grouped by the ARDRA analysis, their restriction profiles were clustered in 15 groups. Four of them included 90% of all isolates, and these were identified using the sequence of the D1/D2 domain of the large-subunit rDNA. Pichia kudriavzevii, Pichia manshurica, Saccharomyces cerevisiae, and Kluyveromyces marxianus were detected as predominant species. Both species belonging to the Pichia genus were detected in 88% of the distilleries, followed by S. cerevisiae (70%) and K. marxianus (50%). In order to evaluate the fermentative capacity, one strain of each species was assessed in a pure and mixed culture in two culture media, filtered maguey juice (MJ) and maguey juice including its bagasse (MJB). Findings demonstrated that non-Saccharomyces yeast presented better growth than that of S. cerevisiae. K. marxianus PA16 was more efficient for ethanol production than S. cerevisiae DI14. It produced 32 g/L of ethanol with a yield of 0.47 g/g and efficient of 90%. While, P. kudriavzevii produced more ethyl acetate (280 mg/L) than the others species. All fermentations were characterized by the presence of isobutyl and isoamyl alcohol. The presence of K. marxianus in a mixed culture, improved the ethanol production and volatile compounds increased using co-cultures.

Oxoester oxidoreductase activities in new isolates of Pichia anomala from apple, grape and cane juices.

Thirty-nine yeasts isolated from apple, grape and cane juices were screened for their oxidoreductase activity. The two strains of Pichia, one isolated from apple and one from cane juices, appear to be promising strains for oxidoreductase activity on alpha-oxoesters. They showed similar high yields in converting ethyl pyruvate to ethyl lactate as Saccharomyces spp. (86.6% and 85.3% versus 86.6%), and higher yields in the reduction of alpha-oxocarboxylic esters (ketopantolactone to pantolactone: 74% and 73.3%, respectively) compared to Saccharomyces spp. (yield 60%).