Yeast Assimilable Nitrogen Concentrations Influence Yeast Gene Expression and Hydrogen Sulfide Production During Cider Fermentation

Flavor characteristics and formation mechanisms in spirits: A case study in whisky

Alcoholic beverages are a crucial segment of the global food industry, with water and ethanol serving as their foundational components. Trace compounds, though present in minute quantities, significantly influence the flavor complexity and sensory quality of these beverages. Understanding the flavor formation mechanisms in alcoholic beverages has emerged as a key research area. Whisky, a global esteemed spirit, is discussed thoroughly in this review with regard to its diverse flavor characters and distinctive flavor formation mechanisms. Chemical compositions and their organoleptic contributions were generalized, highlighting the intricacies of flavor development. Furthermore, flavor formation patterns and potential compound interactions were proposed based on various production processes, including raw material selection, fermentation, distillation, and aging. Additionally, non-volatile compounds were thoroughly reviewed on their gustatory and olfactory implications, emphasizing their subtle yet significant contributions to the overall sensory experience. The review also discusses sensory interactions among diverse flavor compounds, offering insights into the complex interaction and suggesting future research directions in whisky flavor analysis and other alcoholic beverages. Instrumental analysis techniques and authentication methods are reviewed, providing valuable perspectives for advancing the analytical landscape. This comprehensive overview pioneers an understanding of whisky's flavor profile and underlying flavor formation mechanisms, while proposing innovative concepts for flavor interaction investigations, serving as a pivotal reference for future research.

Effect of different nitrogen source and Saccharomyces cerevisiae strain on volatile sulfur compounds and their sensory effects in chardonnay wine

Three commercial Saccharomyces cerevisiae strains with low, medium, and high H2S-producing capacity were chosen to investigate the effect of yeast assimilable nitrogen (YAN) levels and composition on volatile compounds in a chemically defined medium, specifically high, medium, and low initial YAN levels with varying proportions of DAP or sulfur-containing amino acids (cysteine and methionine). The results revealed that the initial YAN containing a larger proportion of diammonium phosphate resulted in a higher YAN consumption rate during the early stages of fermentation. The yeast strain had a greater effect on the volatiles than the YAN level and composition. Keeping the total YAN constant, a higher proportion of sulfur-containing amino acids resulted in a considerably higher production of 3-methylthiopropanol. The sensory impact of three key volatile sulfur compounds was investigated in a Chardonnay wine matrix, indicating that 3-methylthiopropanol at subthreshold or greater concentrations was effective in enhancing the cantaloupe aroma.

QTL mapping reveals novel genes and mechanisms underlying variations in H2S production during alcoholic fermentation in Saccharomyces cerevisiae

Saccharomyces cerevisiae requirement for reduced sulfur to synthesize methionine and cysteine during alcoholic fermentation, is mainly fulfilled through the sulfur assimilation pathway. Saccharomyces cerevisiae reduces sulfate into sulfur dioxide (SO2) and sulfide (H2S), whose overproduction is a major issue in winemaking, due to its negative impact on wine aroma. The amount of H2S produced is highly strain-specific and also depends on SO2 concentration, often added to grape must. Applying a bulk segregant analysis to a 96-strain-progeny derived from two strains with different abilities to produce H2S, and comparing allelic frequencies along the genome of pools of segregants producing contrasting H2S quantities, we identified two causative regions involved in H2S production in the presence of SO2. A functional genetic analysis allowed the identification of variants in four genes able to impact H2S formation, viz; ZWF1, ZRT2, SNR2, and YLR125W, and involved in functions and pathways not associated with sulfur metabolism until now. These data point out that, in wine fermentation conditions, redox status, and zinc homeostasis are linked to H2S formation while providing new insights into the regulation of H2S production, and a new vision of the interplay between the sulfur assimilation pathway and cell metabolism.

Isolation and Characterization of Yeast with Benzenemethanethiol Synthesis Ability Isolated from Baijiu Daqu

Baijiu, a prevalent alcoholic beverage, boasts over 2000 aroma compounds, with sulfur-containing compounds being the most influential in shaping its flavor. Benzenemethanethiol, a distinctive odorant in baijiu, is known to enhance the holistic flavor profile of baijiu. Despite its importance, there is very little literature on the biotransformation mechanism of benzenemethanethiol. Thus, extensive research efforts have been made to elucidate the formation mechanism of this compound in order to improve baijiu production. In this study, 12 yeast strains capable of generating benzenemethanethiol were isolated from baijiu daqu, and the Saccharomyces cerevisiae strain J14 was selected for further investigation. The fermentation conditions were optimized, and it was found that the optimal conditions for producing benzenemethanethiol were at 28 °C for 24 h with a 4% (v/v) inoculum of 3.025 g/L L-cysteine. This is the first time that yeast has been shown to produce benzenemethanethiol isolated from the baijiu fermentation system. These findings also suggest that benzenemethanethiol can be metabolized by yeast using L-cysteine and benzaldehyde as precursor substrates.

Bioremediation of Wastewater Using Yeast Strains: An Assessment of Contaminant Removal Efficiency

The main goal of wastewater treatment is to significantly reduce organic compounds, micronutrients (nitrogen and phosphorus) and heavy metals and other contaminants (pathogens, pharmaceuticals and industrial chemicals). In this work, the efficiency of removing different contaminants (COD, NO₃^-, NO₂^-, NH₄⁺, PO₄^3-, SO₄^2-, Pb²⁺, Cd²⁺) from synthetic wastewater was tested using five different yeast strains: Kluyveromyces marxianus CMGBP16 (P1), Saccharomyces cerevisiae S228C (P2), Saccharomyces cerevisiae CM6B70 (P3), Saccharomyces cerevisiae CMGB234 (P4) and Pichia anomala CMGB88 (P5). The results showed a removal efficiency of up to 70% of COD, 97% of nitrate, 80% of nitrite, 93% of phosphate and 70% of sulfate ions for synthetic wastewater contaminated with Pb²⁺ (43 mg/L) and Cd²⁺ ions (39 mg/L). In contrast, the results showed an increase in ammonium ions, especially in the presence of Pb²⁺ ions. The yeast strains showed a high capacity to reduce Pb²⁺ (up to 96%) and Cd²⁺ (up to 40%) ions compared to the initial concentrations. In presence of a crude biosurfactant, the removal efficiency increased up to 99% for Pb²⁺ and 56% for Cd²⁺ simultaneously with an increase in yeast biomass of up to 11 times. The results, which were obtained in the absence of aeration and in neutral pH conditions, proved a high potential for practical applications in the biotreatment of the wastewater and the recovery of Pb and Cd ions, with a high benefit-cost ratio.

Screening low-methanol and high-aroma produced yeasts for cider fermentation by transcriptive characterization

The commercial active dry yeast strains used for cider production in China are far behind the requirements of the cider industry development in recent decades. In this study, eight yeasts, including Saccharomyces cerevisiae, Schizosaccharomyces pombe, Pichia bruneiensis, and Pichia kudriavzevii, were screened and assessed by growth performance, methanol production, aroma analysis, and their transcriptive characterization. Saccharomyces cerevisiae strains WFC-SC-071 and WFC-SC-072 were identified as promising alternatives for cider production. Strains WFC-SC-071 and WFC-SC-072 showed an excellent growth capacity characterized by 91.6 and 88.8% sugar utilization, respectively. Methanol production by both strains was below 200 mg/L. Key aroma compounds imparting cider appreciably characteristic aroma increased in cider fermented by strains WFC-SC-071 and WFC-SC-072. RT-qPCR analysis suggested that most genes associated with growth capacity, carbohydrate uptake, and aroma production were upregulated in WFC-SC-071 and WFC-SC-072. Overall, two Saccharomyces cerevisiae strains are the optimal starters for cider production to enable the diversification of cider, satisfy the differences in consumer demand, and promote cider industry development.

Tradition as a Stepping Stone for a Microbial Defined Water Kefir Fermentation Process: Insights in Cell Growth, Bioflavoring, and Sensory Perception

A process development from a traditional grain-based fermentation to a defined water kefir fermentation using a co-culture of one lactic acid bacterium and one yeast was elaborated as a prerequisite for an industrially scalable, controllable, and reproducible process. Further, to meet a healthy lifestyle, a low ethanol-containing product was aimed for. Five microbial strains—Hanseniaspora valbyensis, Dekkera bruxellensis, Saccharomyces cerevisiae, Liquorilactobacillus nagelii, and Leuconostoc mesenteroides—were used in pairs in order to examine their influence on the fermentation progress and the properties of the resulting water kefir products against grains as a control. Thereby, the combination of H. valbyensis and L. mesenteroides provided the best-rated water kefir beverage in terms of taste and low ethanol concentrations at the same time. As a further contribution to harmonization and reduction of complexity, the usage of dried figs in the medium was replaced by fig syrup, which could have been proven as an adequate substitute. However, nutritional limitations were faced afterward, and thus, an appropriate supplementation strategy for yeast extract was established. Finally, comparative trials in 5-L scale applying grains as well as a defined microbial consortium showed both water kefir beverages characterized by a pH of 3.14, and lactic acid and aromatic sensory properties. The product resulting from co-culturing outperformed the grain-based one, as the ethanol level was considerably lower in favor of an increased amount of lactic acid. The possibility of achieving a water kefir product by using only two species shows high potential for further detailed research of microbial interactions and thus functionality of water kefir.

Development of a New Assay for Measuring H2S Production during Alcoholic Fermentation: Application to the Evaluation of the Main Factors Impacting H2S Production by Three Saccharomycescerevisiae Wine Strains

Hydrogen sulfide (H2S) is the main volatile sulfur compound produced by Saccharomycescerevisiae during alcoholic fermentation and its overproduction leads to poor wine sensory profiles. Several factors modulate H2S production and winemakers and researchers require an easy quantitative tool to quantify their impact. In this work, we developed a new sensitive method for the evaluation of total H2S production during alcoholic fermentation using a metal trap and a fluorescent probe. With this method, we evaluated the combined impact of three major factors influencing sulfide production by wine yeast during alcoholic fermentation: assimilable nitrogen, sulfur dioxide and strain, using a full factorial experimental design. All three factors significantly impacted H2S production, with variations according to strains. This method enables large experimental designs for the better understanding of sulfide production by yeasts during fermentation.

An Overview of the Factors Influencing Apple Cider Sensory and Microbial Quality from Raw Materials to Emerging Processing Technologies

Given apple, an easily adapted culture, and a large number of apple varieties, the production of apple cider is widespread globally. Through the fermentation process, a series of chemical changes take place depending on the apple juice composition, type of microorganism involved and technology applied. Following both fermentations, alcoholic and malo-lactic, and during maturation, the sensory profile of cider changes. This review summarises the current knowledge about the influence of apple variety and microorganisms involved in cider fermentation on the sensory and volatile profiles of cider. Implications of both Saccharomyces, non-Saccharomyces yeast and lactic acid bacteria, respectively, are discussed. Also are presented the emerging technologies applied to cider processing (pulsed electric field, microwave extraction, enzymatic, ultraviolet and ultrasound treatments, high-pressure and pulsed light processing) and the latest trends for a balanced production in terms of sustainability, authenticity and consumer preferences.

The Effect of Apple Juice Concentration on Cider Fermentation and Properties of the Final Product

European legislation overall agrees that apple juice concentrate is allowed to be used to some extent in cider production. However, no comprehensive research is available to date on the differences in suitability for fermentation between fresh apple juice and that of reconstituted apple juice concentrate. This study aimed to apply freshly pressed juice and juice concentrate made from the same apple cultivar as a substrate for cider fermentation. Differences in yeast performance in terms of fermentation kinetics and consumption of nutrients have been assessed. Fermented ciders were compared according to volatile ester composition and off-flavor formation related to hydrogen sulfide. Based on the results, in the samples fermented with the concentrate, the yeasts consumed less fructose. The formation of long-chain fatty acid esters increased with the use of reconstituted juice concentrate while the differences in off-flavor formation could not be determined. Overall, the use of the concentrate can be considered efficient enough for the purpose of cider fermentation. However, some nutritional supplementation might be required to support the vitality of yeast.