A novel methodology independent of fermentation rate for assessment of the fructophilic character of wine yeast strains

Abstract

The yeast Saccharomyces cerevisiae has a fundamental role in fermenting grape juice to wine. During alcoholic fermentation its catabolic activity converts sugars (which in grape juice are a near equal ratio of glucose and fructose) and other grape compounds into ethanol, carbon dioxide and sensorily important metabolites. However, S. cerevisiae typically utilises glucose and fructose with different efficiency: glucose is preferred and is consumed at a higher rate than fructose. This results in an increasing difference between the concentrations of glucose and fructose during fermentation. In this study 20 commercially available strains were investigated to determine their relative abilities to utilise glucose and fructose. Parameters measured included fermentation duration and the kinetics of utilisation of fructose when supplied as sole carbon source or in an equimolar mix with glucose. The data were then analysed using mathematical calculations in an effort to identify fermentation attributes which were indicative of overall fructose utilisation and fermentation performance. Fermentation durations ranged from 74.6 to over 150 h, with clear differences in the degree to which glucose utilisation was preferential. Given this variability we sought to gain a more holistic indication of strain performance that was independent of fermentation rate and therefore utilized the area under the curve (AUC) of fermentation of individual or combined sugars. In this way it was possible to rank the 20 strains for their ability to consume fructose relative to glucose. Moreover, it was shown that fermentations performed in media containing fructose as sole carbon source did not predict the fructophilicity of strains in wine-like conditions (equimolar mixture of glucose and fructose). This work provides important information for programs which seek to generate strains that are faster or more reliable fermenters.

Occurrence of FFZ genes in yeasts and correlation with fructophilic behaviour

“…cerevisiae, both the transporter proteins Hxts and the hexokinases (Hxk) display a higher affinity for glucose than for fructose, the hexokinases involved in hexose sensing and signalling, and therefore playing an important role in this yeast's preference for glucose (Berthels et al, 2008). In addition, other factors such as response to ethanol and nitrogen availability and utilization seem to be important for sugar preference in yeasts, indicating that hexose utilization depends on several environmental and biological parameters (Liccioli et al, 2011).…”

‘TeeBot’: A High Throughput Robotic Fermentation and Sampling System

“…With the successful application of both generations of automated fermentation platforms and the publication of several reports [2,[5][6][7][8][9][10] this study achieved all the criteria defined earlier in the design and implementation of a high throughput fermentation platform. There are no other systems available that match the 'Teebots' for performance in their ability to screen large numbers of candidate fermentative organisms.…”

“…The sugar curves produced using the Generation#1 and #2 platforms were very similar (Figure 6C), although increased variation was noted for Generation#2 (Figure 6B), which is most likely a result of the number of replicates and limitations of the sugar analysis itself. Importantly, the Area Under the Curve values [6] for each strain were similar (Table 1), indicative of fermentation phenotype being reproducible when scaled up as common with screening large numbers.…”

“…Fermentations were inoculated to a density of 5 × 10 6 cells mL −1 of Saccharomyces cerevisiae grown in CDGJM starter (50 g L −1 glucose, 50 g L −1 fructose, supplemented with 10 mg L −1 ergosterol and 540 mg L −1 Tween 80). Sugar consumption (glucose, fructose) was measured during the course of the fermentation by enzyme assay [2][3][4][5][6][7][8][9][10][11][12][13][14][15].…”

Selection of Yeast Strains for Tequila Fermentation Based on Growth Dynamics in Combined Fructose and Ethanol Media

“…In particular, the presence of fructose in the raw materials used for fermented beverages such grape juice for wine production (Arroyo‐López and others ), apple juice for cider (Wang and others ) and agave juice for the production of tequila or mezcal (2 Mexican distillates with designation of origin [López‐Alvarez and others ]), has been associated with problems in fermentation. This is because glucose is preferentially consumed by yeast, which leads to high concentrations of the remaining fructose in later stages of fermentation, possibly contributing to stuck or sluggish fermentation cultures (Berthels and others ; Liccioli and others ).…”