# Evaluation of Non-_Saccharomyces_ Yeast for Low-Alcohol Beer Production
## 3 Results and Discussion
### Microbial Analyses
#### 3.1.3 Enzymatic Activities  
\(\beta\)-lyase  
Because the S-methyl-L-cysteine is the sole nitrogen source in the medium used, only yeasts which possess \(\beta\)-lyase activity should express the growth on the medium. To eliminate the influence of the possible nitrogen reserves in the cells, the yeasts were transferred three times on the medium [24].  
Except for HU2 and some _M. pulcherima_ species, all of the studied yeasts showed mostly good growth on the studied YCB medium, which proves their \(\beta\)-lyase potential (Table 1). The yeast cultures used were isolated from a winery environment. According to [PERSON] et al. [43], wine-related strains have low \(\beta\)-lyase potential. The obtained results show that this is not always the case. The _M. pulcherima_ species were characterized by high variability in the studied enzymatic activity. This variability was higher than in a study by [PERSON] et al. [44], where most of the studied yeasts showed at least some degree of growth on the YCB-SMC medium. However, [PERSON] et al. [45] found similar variability in \(\beta\)-lyase activity in the studied _M. pulcherima_ strains.  
Interestingly, the control strain studied showed a very good growth on the medium (Table 1). The \(\beta\)-lyase activity of _S. cerevisiae_ brewing yeast is corroborated by [PERSON] et al. [46] and [PERSON] et al. [47]. The \(\beta\)-lyase activity is, according to current knowledge, related to the ability of yeasts to release polyfunctional thiols from their cysteinated and glutathionylated precursors. These compounds are characterized by very low sensory threshold, and fruity, tropical aromas. The liberation of these compounds may improve the aroma of low-alcohol beers. The source of these compounds are malt and hops [48; 49].  
The highest degree of \(\beta\)-glucosidase activity was found in KL1 and TD1 (Figure 1). High potential of _T. delbrueckii_ was also found by [PERSON] et al. [50], whereas this is the first report of such high activity of this enzyme in _K. lactis_. High, but much lower activity than in two mentioned species was found in WO1. Other yeast species were found to have similar and moderate degree of this enzymatic activity (Figure 1). The moderate \(\beta\)-glucosidase potential of _S. cerevisiae_ strains is confirmed by [PERSON] et al. [22] and [PERSON] and [PERSON] [51]. All of the studied _M. pulcherima_ strains possessed this enzymatic activity, which is consistent with literature reports [52]. Some literature reports state that some strains of _M. pulcherima_ should be characterized by high enzymatic activity, which was not observed in this study [44].  
Figure 1: Results of \(\beta\)-glucosidase activity assay on pNPC. Total activity is the sum of extracellular and cellular activity.  
In all of the strains, except MP3 and US-05, the enzyme activity was mostly cell-bound (Figure 1). The occurrence of most of the \(\beta\)-glucosidase activity within the cell wall is corroborated by the other authors [22; 53]. Similarly to \(\beta\)-lysse enzyme activity, \(\beta\)-glucosidase activity may enhance the aroma of a beer. According to the current knowledge, \(\beta\)-glucosidase is at least partially responsible for the liberation of aroma-active aglycones from their glycoside-bound aroma substances. The action of this enzyme might enhance the fruity and floral aromas in a beer [54].