Two Main Biosynthesis Pathways Involved in the Synthesis of the Floral Aroma of the Nacional Cocoa Variety

Abstract

Theobroma cacao is the only source that allows the production of chocolate. It is of major economic importance for producing countries such as Ecuador, which is the third-largest cocoa producer in the world. Cocoa is classified into two groups: bulk cocoa and aromatic fine flavour cocoa. In contrast to bulk cocoa, fine flavour cocoa is characterised by fruity and floral notes. One of the characteristics of Nacional cocoa, the emblematic cocoa of Ecuador, is its aromatic ARRIBA flavour. This aroma is mainly composed of floral notes whose genetic and biochemical origin is not well-known. This research objective is to study the genetic and biochemical determinism of the floral aroma of modern Nacional cocoa variety from Ecuador. Genome-Wide Association Study (GWAS) was conducted on a population of 152 genotypes of cocoa trees belonging to the population variety of modern Nacional. Genome-Wide Association Study was conducted by combining SSR and SNP genotyping, assaying biochemical compounds (in roasted and unroasted beans), and sensory evaluations from various tastings. This analysis highlighted different areas of association for all types of traits. In a second step, a search for candidate genes in these association zones was undertaken, which made it possible to find genes potentially involved in the biosynthesis pathway of the biochemical compound identified in associations. Our results show that two biosynthesis pathways seem to be mainly related to the floral note of Nacional cocoa: the monoterpene biosynthesis pathway and the L-phenylalanine degradation pathway. As already suggested, the genetic background would therefore appear as largely explaining the floral note of cocoa.

Variability and genetic determinants of cocoa aromas in trees native to South Ecuadorian Amazonia

“…During fermentation, cocoa beans may react to biotic stress, as previously suggested (Colonges, Jimenez, Saltos, Seguine, Loor Solorzano, Fouet, Argout, Assemat, Davrieux, Cros, et al, 2021a;Sabau et al, 2006), and synthesise volatile compounds for defence against micro-organisms involved in fermentation, as previously shown for example in maize, plants synthesise volatile compounds to defend themselves (Block et al, 2019). The genomic areas associated to volatile compounds identified in our study included a large number of genes involved in plant defence pathways.…”

“…Of the candidate genes detected, 53 are in common with previous GWAS studies on the aroma traits of the modern Nacional population (Dataset S6) (Colonges, Jimenez, Saltos, Seguine, Loor Solorzano, Fouet, Argout, Assemat, Davrieux, Cros, et al, 2021a;Colonges, Jimenez, Saltos, Seguine, Solorzano, Fouet, Argout, Assemat, Davrieux, Cros, & Lanaud, 2021b). The repetition of detection of these candidate genes between two studies on two different populations brings additional weight to the role of these candidate genes.…”

“…The cocoa trees studied in this paper, widespread in the South of Ecuadorian Amazonia, have a different genetic background than the modern Nacional variety. They are the result of natural evolution from thousands of years giving to this population a low LD favourable to a better precision of localization of associations than the study carried out on the modern Nacional population (for which the hybridizations between the three contrasting ancestors are recent) (Bartley, 2005;Colonges, Jimenez, Saltos, Seguine, Loor Solorzano, Fouet, Argout, Assemat, Davrieux, Cros, et al, 2021a;Loor, 2007). The associations detected are therefore more precise and reliable.…”

“…Previous recent studies aimed to decipher the genetic determinant of aromatic flavours of cocoa from the modern Nacional variety. In a study focusing on floral aromas, Colonges, Jimenez, Saltos, Seguine, Loor Solorzano, Fouet, Argout, Assemat, Davrieux, Cros, et al (2021a) was able to identify two main biosynthetic pathways involved in the synthesis of floral aromas: the monoterpene biosynthetic pathway and the L‐phenylalanine degradation pathway. Then investigating the genetic determinism of fruity aromas, Colonges, Jimenez, Saltos, Seguine, Solorzano, Fouet, Argout, Assemat, Davrieux, Morillo, et al (2021c) identify five main biosynthetic pathways involved: the monoterpene biosynthetic pathway, the L‐phenylalanine, the fatty and sugar degradation pathways and the synthesis of Maillard precursors (for the production of pyrazines).…”

Diversity and determinants of bitterness, astringency, and fat content in cultivated Nacional and native Amazonian cocoa accessions from Ecuador

“…The fine (floral and fruity) flavors of modern Nacional have started to be studied for their volatile compound composition (Cevallos-Cevallos et al, 2018;Colonges et al, 2021aColonges et al, , 2021bLuna et al, 2002;Rottiers et al, 2019;Ziegleder, 1990). Nacional cocoa, like all cocoa, also contains nonvolatile compounds, such as polyphenols, caffeine, or theobromine (Wollgast & Anklam, 2000;Zheng et al, 2004), which are known to provide bitterness and astringency to cocoa products (Lesschaeve & Noble, 2005).…”