## 4 Discussion
The antagonistic activity of _A. pullulans_ mainly includes nutrient competition and production of volatile organic compounds or glucanases, chitinases, and extracellular proteases [40; 46]. _Taplrina_ and _Cladosporium_ were the next numerous fungal microorganisms observed on unripe sea buckthorn berries in our study (Table S1, Figure 2). _Taphrina_ genus fungi are known as biotrophic plant pathogens that cause plant and fruit disease symptoms, which may be ascribed to the ability to synthesize and modulate different plant hormones [54]. _Cladosporium_ is considered as ubiquitous fungi, with some species providing numerous antifungal agents [55], while others causing plant or human diseases [56; 57]. _Cryptococcus_ encloses species producing biocontrol agents against many pathogens [16; 50], while certain species can cause infections in humans and animals [58]. During the ripening of different fruits and berries, the oxidative or weakly fermentative yeast populations--such as _Candida_, _Hanseniispora_, _Metschnikowia_, and _Pichia_--increased in frequency [42]. _Hanseniispora_ spp. have been frequently found on the surface of different fruits, e.g. apples, grapes, or strawberries [59; 60]. Numerous yeasts belonging to the _Hanseniispora_ genus display antagonistic properties against the development of fruit spoilage causing molds [40; 61]. _Metschnikowia_ spp. isolated from fruit are sugar-loving yeasts and their populations are most likely stimulated by juices diffusing from the damaged surface of mature fruit [42]. This yeast genus includes several biocontrol agents, which are very effective against fruit spoilage fungi [62]. The biocontrol abilities of _M. pulcherrima_ have been mainly assigned either to competition for nutrients or to the production of volatile organic compounds [15; 46]. The competition of _M. pulcherrima_ for iron was reported to play a substantial role in biocontrol interactions [63]. _Metschnikowia_ spp. are linked to several groups of nectarivorous insects, suggesting that this specificity could be correlated to the services provided by the yeast to the insect or vice versa [64; 65]. Yeasts produce chemo-diverse blends of volatiles comprised of aldehydes, ketones, alcohols, volatile fatty acids, esters, aromatics, heterocyclic compounds, hydrocarbons, terpenoids, and some others [66; 67]. Ethanol is probably the most known volatile metabolite of yeasts derived from carbohydrate catabolism and fermentation [66]; it is one of the major volatiles collected from the headspace of \(H\). _uvarum_, _M. pulcherrima_, and _C. wieringae_ yeasts. Amounts of ethyl acetate, another metabolite of carbohydrate catabolism, prevailed in the VOCs produced exclusively by \(H\). _uvarum and M. pulcherrima_ yeasts. It is a valuable solvent for extracting compounds with antimicrobial properties [68] and possess minor inhibitory effect for _Botrytis cinerea_[69]. In addition to ethyl acetate, 10 esters were unique for the volatile blends of \(H\). _uvarum_ yeasts; these compounds originated from amino acid synthesis and degradation pathways [66]. Prevalence of esters in volatile blends of \(H\). _uvarum_ has been reported in previous studies [70; 71]; however, ethanol being the third largest component of the blend in our experiments, has not been determined by [PERSON] et al. [71] or [PERSON] et al. [70]. High production of ethanol, 3-methylbutanol, 2-phenylethanol, ethyl acetate, and 3-methylbutyl acetate were reported for \(M\). _pulcherrima_ and \(A\). _pullulans_ yeasts [15]. The data published are comparable with the results of our study in terms of large production of alcohols by both yeast species; however, we were not able to detect ethyl acetate in the headspace of \(A\). _pullulans_. To date, there is no report on VOCs of \(C\). _wieringae_ yeast. Volatile organic compounds produced by \(A\). _pullulans_ that were found in our study (namely 2-phenylethanol, 2-methylpropanol, 2-methylbutanol, and 3-methylbutanol) had been previously shown to control postharvest fruit pathogens (\(B\).