Title : Expression of tc-mybpa gene involved in the regulation of the biosynthesis of proanthocyanidins in some cocoa beans (Theobroma cacao l.)
Abstract:
Proanthocyanidins (PAs) are known as flavor precursors of a chocolate. In the course postharvest processes (fermentation and drying), PAs impart astringency and bitterness to many cocoa bean genotypes. The goal of this work was therefore to see if there was a relationship between expression level of Tc-MybPA gene and PAs content in cocoa bean (fermentation and drying). Five cocoa hybrid genotypes and one commercial cocoa were used to assess physicochemical parameters (pH, fermentation index and cut-test score). Later, spectrophotometric method was used to assess PAs content, while epicatechin and procyanidin C1 were identified in cocoa beans using Ultra Performance Liquid Chromatography-Diode array detector- Electrospry Ionization –Mass spectrometry (UPLC-DAD-ESI(+)-MS). Tc- MybPA gene expression [by semi-quantitative Reverse Transcription and Polymerase Chain Reaction (semi qRT-PCR)] in each genotype was evaluated. Following cut-test, commercial cocoa cotyledon color is shown weak success fermentation (14% of brown beans) and is positively correlated at small PA accumulation level (9.71±1.27 mg CEq/g defatted cocoa powder) (P?0.05). Four genotypes SCA12×ICS40, ICS40×SCA12, ICS40×UPA134 and SNK16×T60/887 have exhibited more than 60% fully brown colored beans formed during fermentation and drying and vary directly with highest PAs content in cocoa (P?0.05). (-)- epicatechin (in all genotypes) and procyanidin C1 (only SNK10×IMC67 and SNK16×T60/887) were identified in genotype beans. After post-harvest processes, cocoa beans from the SCA12×ICS40 (1.75) and ICS40×UPA134 (1.79) genotypes had the highest levels of Tc- MybPA gene expression. However, weak positive correlation (r= 0.311) was displayed between expression of Tc-MyAbPA gene and PAs content of the cocoa hybrids studied. Thus, the indicators for identifying well-fermented cocoa beans rich in polyphenols such PAs is still the use of physicochemical parameters. Moreover, a set of genes that act as co-factors in PA biosynthesis have to be combined with the Tc-MyAbPA gene.
Keywords: Cocoa bean, physicochemical parameters, proanthocyanidin, Tc-MybPA gene, Semi qRT-PCR, UPLC-DAD-ESI(+)-MS
