## 4 Discussion
### Yeast Isolated from Apricot Fruits as Potential Starters for Beer Production  
The identification of non-_Saccharomyces_ yeasts within the epiphytes of apricot fruits suggests their possible application as starters to produce fruit beers. Indeed, it is now widely accepted that non-_Saccharomyces_ yeasts, when used in mixed fermentation with _S. cerevisiae_, positively contribute to the sensorial quality of the fermented beverage [13; 50]. In this respect, enrichment cultures of _Bisuccia_ apricot pure allowed for identifying isolates of _P. kudriavzevii_, _H. uvarum_, _H. guilliermondii_, and _H. clermontiae_ as capable of dominating the indigenous microbiota. _P. kudriavzevii_ was already associated with natural fermentation of ripped and rotten fruits, such as Indian plum (_Ziziphus mauritiana_), pineapples, and Camuu (_Myricaria dubia_) [51; 52; 53]. Previously, it has been shown that strains of _P. kudriavzevii_ isolated from fermented sugar cane led to a high degree of attenuation (up to 85%) when used as starters for beer fermentation [54]. In comparison, the isolate _P. kudriavzevii_ L1, here characterized, performed poorly (7.9% attenuation). This can be attributed to a lower capacity to assimilate the main sugars in beer wort (maltrose, maltotriose, and dextrins), as already described for this species [55]. _Hanseniispora_ spp. are mainly associated with grape surfaces. Particularly, _Hanseniispora wavum_ is the dominant yeast in the first stages of wine fermentation [39]. Grape isolates of _H. clermontiae_ contributed to the polyphenic composition of wines subjected to spontaneous fermentation [54]. In brewing, the role of _Hanseniispora_ spp. is less investigated. _Hanseniispora valbynensis_ and _Hanseniispora viene_ were evaluated for the production of alcohol-free beer [56]. A fermentative behavior similar to that here displayed by _Hanseniispora wavum_ L2 and _H. pseudoguilliermondii_ L3, which produced 0.69 and 0.77 g of CO\({}_{2}\)/100 mL of wort, respectively, was described by [PERSON] et al. [57]. Particularly, the authors showed that two _Hanseniispora uvarum_ strains, isolated from honey by-products,produced from 0.35 to 0.37 g of CO\({}_{2}\)/100 mL of wort, when used as a starter for craft beer production [57]. As a comparison, _S. cerevisiae_ US-05 released 4.077 g of CO\({}_{2}\)/100 mL of wort. The authors suggested that the low fermentation rate of _H. uvarum_ strains does not represent a limitation for beer production as these yeasts can be used in mixed fermentation with _S. cerevisiae_  
The use of non-_Saccharomyces_ yeast to produce fermented beverages has been associated with an increase in the levels of aroma-active compounds, such as higher alcohols, esters, carboxylic acids, sulfur compounds, and volatile phenols [12]. Particularly, the use of _H. guilliermondii_ in mixed fermentation increased the levels of phenylethyl acetate ('rose' aroma) in beer. [PERSON] et al. [54] found that _P. kudriavzevii_ used as a starter for beer production led to levels of 1-octanol and 1-pentanol higher than those obtained by using _S. cerevisiae_ as a single starter. The yeast \(H\). _uvarum_ used in co-inoculum with S. cerevisiae_ resulted in the production of considerable amounts of isoamyl acetate, ethyl acetate, ethyl octanoate, and ethyl exanoate in the final beer [57]. Terpenes are one of the main chemical families in the hop oil and are responsible for the fruity and floral aromas of beers ('citrus', 'floral', 'aniseed', 'lime', 'hyacinth', 'rose', etc.). The levels of terpen in beer are dependent on different factors, the yeast being used during fermentation one of the most important [58]. Particularly, geraniol and linalool could be synthesized de novo by _Hanseniaspora uvarum_[59]. In addition, yeasts can convert hop-derived monoterpene alcohols through esterification or hydrolysis [60].