Importance of micronutrients and organic nitrogen in fermentations with Torulaspora delbrueckii and Saccharomyces cerevisiae.

The current use of non-Saccharomyces yeasts in mixed fermentations increases the relevance of the interactions between yeast species. In this work, the interactions between Saccharomyces cerevisiae and Torulaspora delbrueckii were analyzed. For this purpose, fermentations with and without contact between strains of those yeast species were performed in synthetic must. Fermentation kinetics, yeast growth and dynamics were measured over time. Additionally, the effects of nitrogen and other nutrient supplementations on the mixed fermentations were determined. Our results showed that S. cerevisiae did not always dominate the sequential fermentations, and experiments without yeast contact (in which T. delbrueckii cells were removed from the medium before inoculating S. cerevisiae at 48 h) resulted in stuck fermentations except when the inoculum size was increased (from 2 × 106 to 108 cells/mL) or there was a supplementation of thiamine, zinc and amino acids at the same concentration as initially found in the synthetic must. Our findings highlight the importance of inoculum size and ensuring the availability of enough micronutrients for all yeast species, especially in sequential fermentations.

Microencapsulation by spray drying of coffee epiphytic yeasts Saccharomyces cerevisiae CCMA 0543 and Torulaspora delbrueckii CCMA 0684.

The objective of this work was to evaluate the microencapsulation feasibility of Saccharomyces cerevisiae CCMA 0543 and Torulaspora delbrueckii CCMA 0684 in three different compositions of wall material by spray-dryer. The yeasts (109 CFU mL-1) were microencapsulated separately using maltodextrin (15%), maltodextrin (15%) with sucrose (2%), or maltose (2%) as wall material. The viability was evaluated for 6 months at two different temperatures (7 and 25 °C). The yield, cell viability after spray drying, and characterization of the microcapsules were performed. Results indicate that cell viability ranged between 94.06 and 97.97%. After 6 months, both yeasts stored at 7 °C and 25 °C presented 107 and 102 CFU mL-1, respectively. Regarding Fourier-transform infrared spectroscopy analysis, all microencapsulated yeasts presented typical spectra footprints of maltodextrin. After 6 months of storage, S. cerevisiae CCMA 0543 obtained a 10.8% increase in cell viability using maltodextrin with maltose as wall material compared to maltodextrin and maltodextrin with sucrose. However, T. delbrueckii CCMA 0684 obtained a 13.5% increase in cell viability using only maltodextrin. The study showed that maltodextrin as a wall material was efficient in the microencapsulation of yeasts. It is possible to assume that maltose incorporation increased the cell viability of S. cerevisiae CCMA 0543 during storage.

Co-inoculation of yeasts starters: A strategy to improve quality of low altitude Arabica coffee.

The study aimed to improve the quality of dry-processed coffee grown at low altitudes through yeast inoculation, using three species (Saccharomyces cerevisiae CCMA 0543, Torulaspora delbrueckii CCMA 0684, and Candida parapsilosis CCMA 0544) singly and with co-inoculation for fermentation. Important chemical compounds and groups were analyzed by liquid and gas chromatography and Fourier-transform infrared spectroscopy (FTIR). The inoculated coffees with yeast populations around 106 cell/g obtained the highest scores, and the co-inoculation with C. parapsilosis CCMA 0544 and T. delbrueckii CCMA 0684 had the highest score in the sensory analysis (85). Different descriptors were observed in each treatment, and body, flavor, balance, and aftertaste are strongly related to C. parapsilosis CCMA 0544. The fermentation process improved the quality of low-altitude coffees, and the combination of non-Saccharomyces yeasts (C. parapsilosis CCMA 0544 and T. delbrueckii CCMA 0684) was the most indicated as starter cultures.

Fermentation characteristics of four non-Saccharomyces yeasts in green tea slurry.

The fermentation characteristics of non-Saccharomyces yeasts (Pichia kluyveri FrootZen, Torulaspora delbrueckii Prelude, Williopsis saturnus var. mrakii NCYC2251 and Torulaspora delbrueckii Biodiva) were evaluated in green tea slurry fermentation. Each yeast showed different fermentation performances: strains Prelude and Biodiva utilized sucrose faster than the other two yeasts; strain NCYC2251 was the only species that metabolized xylose. Strain FrootZen increased the caffeine content significantly and strain Prelude showed the opposite trend, both at a statistical level, while theanine contents in four samples were relatively stable. Biodiva and FrootZen significantly improved polyphenols content and the oxygen radical absorbance capacity of fermented teas. Some endogenous volatiles such as ketones, lactones and aldehydes decreased to lower or undetected levels, but one of the key tea aroma compounds methyl salicylate increased by 34-fold and 100-fold in P. kluyveri and W. saturnus samples respectively. Therefore, green tea fermentation by appropriate non-Saccharomyces yeasts can enhance its antioxidant capacity and alter the aroma compound profile.

Understanding the interaction of isoleucine paired with other amino acids in soy whey alcohol fermentation using Torulaspora delbrueckii.

Soy (tofu) whey is a liquid by-product generated from tofu (soybean curd) production and it is often discarded off as a waste liquid by the tofu manufacturers. Previous studies have demonstrated that soy whey can be biotransformed into a soy alcoholic beverage by using Saccharomyces and non-Saccharomyces yeasts even though soy whey is low in yeast assimilable nitrogen (YAN) content. In this study, the initial YAN of the soy whey was estimated to be 46.6 mg N/L and Torulaspora delbrueckii Biodiva was used to ferment soy whey supplemented with either isoleucine only or isoleucine paired with valine, leucine or phenylalanine (each amino acid supplemented at a dosage of 30 mg N/L). Amino acid supplementation was found to enhance sugar utilization by the yeast, which led to higher ethanol production (7.49% v/v in control versus 8.35-8.80% v/v in supplemented samples). Samples supplemented with isoleucine only experienced slower sugar utilization during the fermentation as compared to the paired amino acid samples, but the yeast was still able to utilize the sugar to low levels at the end of the fermentation. The presence of leucine supplementation counteracted the "inhibition" induced by the presence of isoleucine at the first day of the fermentation. Amino acid supplementation slowed down glutamic acid utilization and resulted in higher levels of residual glutamic acid and alanine. Amino acid supplementation increased the corresponding fusel alcohol production and the presence of other amino acids reduced the active amyl alcohol production. Therefore, interactions between amino acids can impact the metabolism of the yeast as well as the flavor modulation during soy whey fermentation.

Volatile composition of bilberry wines fermented with non-Saccharomyces and Saccharomyces yeasts in pure, sequential and simultaneous inoculations.

Bilberry (Vaccinium myrtillus L.) juice was fermented with Torulaspora delbrueckii (TD291 and TD70526) and Schizosaccharomyces pombe (SP3796 and SP70572) in pure fermentation as well as in sequential and simultaneous inoculations with Saccharomyces cerevisiae 1116 (SC1116). Altogether, 56 volatile compounds were identified and semi-quantified with HS-SPME-GC/MS in bilberry products. Yeast fermentation prominently enhanced the aroma complexity of bilberry with a sharp increase in alcohols, esters, aldehydes, and acetals. Compared to S. cerevisiae, T. delbrueckii produced less ethanol but more fusel alcohols that potentially enhance "alcohol" and "nail polish" odors in TD70526 and less "fruity" esters in TD291. SP70572 resulted in high productions of undesirable compounds of acetoin and acetaldehyde but a low content of higher alcohols and esters, SP3796 produced a high content of fatty acid ethyl esters and acetoin. In comparison with monoculture of non-Saccharomyces yeast, sequential and simultaneous cultures of S. pombe and S. cerevisiae significantly decreased the content of acetoin while increased the relative level of esters; sequential cultures of T. delbrueckii and S. cerevisiae remarkably increased the concentration of acetaldehyde; simultaneous inoculations of S. cerevisiae with TD70526 and TD291 significantly decreased the content of fusel alcohols and increased the content of esters, respectively. The findings suggested that non-Saccharomyces yeasts possess the potential to affect and modulate the aromatic profile of fermented bilberry products. Sequential and simultaneous inoculations with S. pombe strains and S. cerevisiae as well as simultaneous fermentation using T. delbrueckii strains and S. cerevisiae are optimal strategies to positively influence the aroma profile of bilberry wines.

Effect of selenium on growth and antioxidant enzyme activities of wine related yeasts.

The use of supplements in the diet is a common practice to address nutritional deficiencies. Selenium is an essential micronutrient with an antioxidant and anti-carcinogenic role in human and animal health. There is increasing interest in developing nutritional supplements such as yeast cells enriched with selenium. The possibility of producing beverages, namely wine, with selenium-enriched yeasts, led us to investigate the selenium tolerance of six wine related yeasts. The production of such cells may hamper selenium toxicity problems. Above certain concentrations selenium can be toxic inducing oxidative stress and yeast species can show different tolerance. This work aimed at studying selenium tolerance of a diversity of wine related yeasts, thus antioxidant response mechanisms with different concentrations of sodium selenite were evaluated. Viability assays demonstrated that the yeast Torulaspora delbrueckii showed the highest tolerance for the tested levels of 100 µg mL(-1) of sodium selenite. The evaluation of antioxidative enzyme activities showed the best performance for concentrations of 250 and 100 µg mL(-1), respectively for the yeast species Saccharomyces cerevisiae and Hanseniaspora guilliermondii. These results encourage future studies on the possibility to use pre-enriched yeast cells as selenium supplement in wine production.