Effects of High Sugar Content on Fermentation Dynamics and Some Metabolites of Wine-Related Yeast Species Saccharomyces cerevisiae, S. uvarum and Starmerella bacillaris.

Starmerella bacillaris (synonym Candida zemplinina) is an important non-Saccharomyces yeast in winemaking with valuable oenological properties, accompanying Saccharomyces species in sweet wine fermentation, and has been suggested also for application as combined starter culture in dry or sweet wines. In this study, the major metabolites and nitrogen utilization of these yeasts are evaluated in the musts with high or extremely high sugar concentration. The change in the metabolic footprint of Saccharomyces cerevisiae, Saccharomyces uvarum and Starmerella bacillaris strains was compared when they were present as pure cultures in chemically defined grape juice medium with 220 and 320 g/L of sugar, to represent a fully matured and an overripe grape. Surprisingly, the extreme sugar concentration did not result in a considerable change in the rate of sugar consumption; only a shift of the sugar consumption curves could be noticed for all species, especially for Starmerella bacillaris. At the extreme sugar concentration, Starmerella bacillaris showed excellent glycerol production, moderate nitrogen demand together with a noticeable proline utilisation. The change in the overall metabolite pattern of Starmerella bacillaris allowed clear discrimination from the change of the Saccharomyces species. In this experiment, the adequacy of this non-Saccharomyces yeast for co-fermentation in juices with high sugar concentration is highlighted. Moreover, the results suggest that Starmerella bacillaris has a more active adaptation mechanism to extremely high sugar concentration.

Authentication of Tokaj Wine (Hungaricum) with the Electronic Tongue and Near Infrared Spectroscopy.

Tokaj wines (Hungaricum) are botrytized wines acknowledged for the unique organoleptic properties bestowed by botrytized grape berries during production. Excluding these berries during wine production or manipulating the sugar content of low-grade wines to imitate high-grade wines are some recent suspicious activities that threaten the wine quality. Advanced methods such as spectroscopy and sensor-based devices have been lauded for rapid, reliable, and cost-effective analysis, but there has been no report of their application to monitor grape must concentrate adulteration in botrytized wines. The study aimed to develop models to rapidly discriminate lower grade Tokaj wines, "Forditas I" and "Forditas II," that were artificially adulterated with grape must concentrate to match the sugar content of high-grade Tokaj wines using an electronic tongue (e-tongue) and two near infrared spectrometers (NIRS). Data were evaluated with the following chemometrics: principal component analysis (PCA), discriminant analysis (LDA), partial least square regression (PLSR), and aquaphotomics (a novel approach). There was a noticeable pattern of separation in PCA for all three instruments and 100% classification of adulterated and nonadulterated wines in LDA using the e-tongue. Aquagrams from the aquaphotomics approach showed important water absorption bands capable of being markers of Tokaj wine quality. PLSR models showed coefficient of determination (R2 CV) of 0.98 (e-tongue), 0.97 (benchtop NIRS), 0.87 (handheld NIRS), and low root mean squared errors of cross-validation. All three instruments could discriminate, classify, and predict grape must concentrate adulteration in Tokaj with a high accuracy and low error. The methods can be applied for routine quality checks of botrytized wines. PRACTICAL APPLICATION: Tokaj wines (Hungaricum) are botrytized wines acknowledged for the unique organoleptic properties bestowed by botrytized grape berries during production. Excluding these berries during wine production or manipulating the sugar content of low-grade wines to imitate high-grade wines are some recent suspicious activities that threaten the wine quality. Using advanced instruments, the electronic tongue, benchtop near infrared spectroscopy, and a handheld near infrared spectroscopy, we could discriminate, classify, and predict grape must concentrate adulteration in Tokaj with a high accuracy and low error. The models in our study can be applied for routine quality checks of botrytized wines.

Anaerobic organic acid metabolism of Candida zemplinina in comparison with Saccharomyces wine yeasts.

Organic acid production under oxygen-limited conditions has been thoroughly studied in the Saccharomyces species, but practically never investigated in Candida zemplinina, which seems to be an acidogenic species under oxidative laboratory conditions. In this study, several strains of C. zemplinina were tested for organic acid metabolism, in comparison with Saccharomyces cerevisiae, Saccharomyces uvarum and Candida stellata, under fermentative conditions. Only C. stellata produced significantly higher acidity in simple minimal media (SM) with low sugar content and two different nitrogen sources (ammonia or glutamic acid) at low level. However, the acid profile differed largely between the Saccharomyces and Candida species and showed inverse types of N-dependence in some cases. Succinic acid production was strongly enhanced on glutamic acid in Saccharomyces species, but not in Candida species. 2-oxoglutarate production was strongly supported on ammonium nitrogen in Candida species, but remained low in Saccharomyces. Candida species, C. stellata in particular, produced more pyruvic acid regardless of N-sources. From the results, we concluded that the anaerobic organic acid metabolisms of C. zemplinina and C. stellata are different from each other and also from that of the Saccharomyces species. In the formation of succinic acid, the oxidative pathway from glutamic acid seems to play little or no role in C. zemplinina. The reductive branch of the TCA cycle, however, produces acidic intermediates (malic, fumaric, and succinic acid) in a level comparable with the production of the Saccharomyces species. An unidentified organic acid, which was produced on glutamic acid only by the Candida species, needs further investigation.

Botrytized wines.

Botrytized wines are natural sweet wines, produced from grapes that are affected by Botrytis cinerea under particular conditions. This rare and special form of fungal infection, called noble rot, includes complex enzymatic conversions and concurrent dehydration of the grape berry and results in a highly concentrated final product. The main characteristics of the noble rotted grapes involve high sugar, acid, glycerol and mineral contents, special polysaccharides, and particular aroma composition, which are thoroughly studied. The saprophytic microbiota of the grapes is also affected. Harvest and vinification of the noble rotted grapes are difficult, having special requirements. Microbiology and biochemistry of the alcoholic fermentation in these wines have been recently studied more deeply. Depending on the grape varieties as well as vinification and ageing technologies, botrytized wines show large diversity in style. Most of them are rich in polyphenols, possessing high antioxidant capacity. Biogenic amine and micotoxine contents of these wines are no public health concerns. This chapter presents the microbiological, biochemical, and technological aspects of noble rot and botrytized wines and discusses the recent findings on these fields.

Comparative evaluation of some oenological properties in wine strains of Candida stellata, Candida zemplinina, Saccharomyces uvarum and Saccharomyces cerevisiae.

Due to the recent changes in yeast taxonomy, a novel wine-related species Candida zemplinina as well as a "reinstated" species Saccharomyces uvarum have been accepted in addition to Candida stellata, Saccharomyces bayanus and Saccharomyces cerevisiae, and the use of the different taxon names has been inconsistent in the literature of food microbiology. The aim of this work is to make an exact comparison of genetically identified strains of these species, under oenological conditions. Dynamics and some important products of alcoholic fermentation were investigated in laboratory fermentations. The results show that C. zemplinina and C. stellata are similar in their strong fructophilic character. C. stellata produces more glycerol and fare more ethanol, which is comparable with that produced by S. uvarum. Strains of the latter species differed from S. cerevisiae mainly in low acetic acid production and lower ethanol yield. Revision of the oenological traits of these yeasts provides new data for consideration in the control of fermentation, with special regard to botrytized sweet wines, where they are frequently found in mixed population.