## 3 Contribution of Selected Yeasts to Emerging Winemaking Demands
### Reduction of Sulfur Dioxide  
Sulfur dioxide (SO\({}_{2}\)) is widely applied in winemaking at specific stages since it can inhibit the Maillard process and regulate oxidative activities, such as polyphenol oxidase, that affect the nutritional and sensory qualities of wine [129; 130]. SO\({}_{2}\) is mainly used for its antibacterial properties against spoilage microorganisms, to reduce the growth of molds during the initial stages of fermentation or deleterious bacteria and yeasts throughout fermentation, minimizing undesirable secondary fermentations. Furthermore, when SO\({}_{2}\) is added before bottling, it can prolong shelf life and reduce the chance of undesirable aroma production [131]. On the other hand, sulphite exposure has been related to bronchoconstriction, urtic, headaches, dermatitis, diarrhea, or worsening of asthmatic symptoms [132; 133]. Therefore, it is necessary to take into account the long-term effect on consumers. In Europe, the International Organization of Vine and Wine (OIV) recommends the following limit for SO\({}_{2}\) to be added during winemaking: 150 mg/L for red wines, 200 mg/L for white wines, 300 mg/L for wines with a sugar content over 4 g/L, and 400 mg/L for sweet and special wines [134]. Bioprotection has been widely proposed as an effective approach to replacing SO\({}_{2}\) in winemaking [135]. Specifically, selected yeast strains can inhibit the growth of unwanted microorganisms since they can overtake spoilage fungi for space and nutrientsas well as synthesize biocontrol compounds as killer toxins [136]. Among wine spoilage microorganisms prevented by SO2, _Bretanomyces bruxellensis_ is the most important since, as reported before, its presence is related to undesirable traits such as the typical \"horse sweat\" odor [62; 137]. In this context, the use of NS yeasts as biocontrol has already been established, in particular by employing them both at harvest and during fermentation, limiting the development of spoilage microorganisms and preventing chemical and enzymatic oxidation [102]. The NS _Torulaspora delbruveckii_ and _M. pulcherrima_ species have been widely used to drive industrial fermentations without reduced-added sulfites. The ability of _T. delbruveckii_ to bioprotect is attributable to the killer toxin TdKT, which exhibits a broad spectrum against wine spoilage yeasts without altering _S. cerevisiae_ growth [138]. [PERSON] et al. [139] showed that _T. delbruveckii_ was found to have efficacy in bioprotection under sulfite-free conditions without altering the complex flavor profile of Merlot red wines. Similar results were obtained by [PERSON] et al. [140], although native yeasts are still less effective than sulphites at preventing oxidation of the must. On the other hand, the antibacterial activity of _M. pulcherrima_ seems to be related to the pulcherriminic acid (precursor of pulcherrimin), which immobilizes the iron in the growth medium; in this case, it has already been proven that _M. pulcherrima_ is efficacious in inhibiting _B. bruxellensis_[141] as well as fungal species, such as _Botrytis cinerea_[142]. A recent study verified that, under experimental conditions, _M. pulcherrima_ reduced the growth of spoilage microbiota in Pinot Noir grapes in pre-fermentation stages without any change in aroma profile [135]. However, due to the amensalism of _M. pulcherrima_ to _S. cerevisiae_ through iron depletion, adverse effects on fermentation kinetics could be observed when mixed cultures are used [143]. Among the non-conventional yeasts, the use of _W. anomalous_ against _Bretanomyces_ additionally stands out due to the presence of the killer toxin KTCf20 in some specific strains [144]. Similarly, [PERSON] et al. [145] demonstrated the efficiency of selected strains of _W. anomalous_, isolated from dairy environments, as a biocontrol agent against _B. bruxellensis_. Furthermore, strains of _Candida pyrralidae_ showed production of two killer toxins, CpKT1 and CpKT2, capable of suppressing the proliferation of _B.