## 1 Introduction  
Cacao beans are the most important raw material for chocolate production [1], and the demand for fine-flavor cacao beans has increased over the years [2]. Most of the world's cacao production is considered as bulk-grade, but other genetic groups are regarded as fine-flavor cacao and can be sold at premium prices [3]. Fine-flavor cacao groups are usually characterized by floral and fruity aromas, while bulk cacao shows fewer desirable traits when compared to fine-flavor cacao [4]. Amongst all the cacao groups, Trininario, Forastero, Criollo and Nacional are the most commercialized worldwide [5]. Nacional cacao is mostly produced in Ecuador and has been categorized as fine-flavor, but few materials of this genetic group are currently available [5, 6], as hybrids between Nacional and Trininario have become predominant in Ecuador. Nacional \(\times\) Trininario cacao beans are also regarded as fine-flavor because of their distinctive organoleptic characteristics [4, 6]. From a global market perspective, huge opportunities and more monetary benefits are offered for fine-flavor cacao beans compared to those proffered in the bulk cacao market [7; 8].  
Even though there are numerous processes that take place throughout the manufacturing of chocolate, the fermentation of the cacao beans is considered an essential step for the development of the chocolate flavor [9]. The fermentation of Nacional cacao beans is a spontaneous process carried out in short fermentation times (approximately 96 h) and performed in heaps or boxes [10; 11].  
During the different stages of the fermentation process, several changes in the components of the pulp occur, as some act as a substrate for the growth of different microorganisms [12]. Numerous researchers have characterized the microbial diversity of cacao bean fermentation processes by culture-dependent and next-generation sequencing (NGS) methods, such as metabarcoding sequencing. NGS stands out because of its sensitivity in community analysis and throughput [13], and was able to reveal a defined succession of yeasts, lactic acid bacteria (LAB) and acetic acid bacteria (AAB) [7; 14; 15; 16; 17; 18; 19] during the cacao fermentation process. The microbiota of cacao bean fermentation and their metabolic activities can influence the production of volatile compounds that are related to fruity and floral aromas, as well as the removal of undesirable characteristics, such as astringency and bitterness [3; 20; 21]. However, the role of each microorganism in the formation of volatile-aroma compounds during fine-flavor cacao fermentation is still unclear.  
Recent studies have evaluated the use of starter cultures for fine-flavor coca bean fermentation, including the use of _Candida parapsilosis_, _Torulaspora delbrueckii_ and _Pichia kluyveri_ in Scavina cacao from Brazil [22], as well as the inoculation of _Pichia kudriavezvi_ and _Saccharomyces cerevisiae_ in Criollo cacao from Colombia [23]. The results obtained in both studies showed the capability of yeast-based starter cultures to improve the quality of fine-flavor cacao. However, the role of microorganisms such as LAB and AAB in the production of aroma compounds during fine-flavor cacao fermentation is still poorly understood.  
The objective of this research was to characterize the microbial diversity of fine-flavor cacao (Nacional \(\times\) Triinitario) using culture-dependent and NGS methods. Additionally, lab-scale fermentations were performed to assess the production of volatile compounds by each microbial isolate under controlled conditions.