Volatile compounds and protein profiles analyses of fermented cocoa beans and chocolates from different hybrids cultivated in Brazil.

Cocoa beans from different geographical and genetic origins show distinct fermentation dynamics which result in different chocolate qualities. In order to understand the effects of genetic improvement of cocoa plants, in this work volatile compounds and proteins profiles of beginning and end of the fermentation from different cocoa hybrids (CEPEC2004, PH15, PS1319, SJ02) were searched. Moreover, sensorial characterization of the produced chocolate from these hybrids was performed. According to the results obtained, different volatile compounds were identified in fermented beans and in the chocolate produced. Chocolate from CEPEC2004 was the most accepted by judges and correlated with sweet and bitter taste which can be explained by the presence of desired flavor compounds, such as 2,3-butanediol and 2-methyl-1-butanol. A higher presence of acids (undesirable compounds) was observed in chocolates samples from PS1319 hybrid, that have resulted in the low acceptance by judges. In addition, MALDI-TOF MS analysis showed that during fermentation the protein profile was different among the hybrids, which indicates this kind of compounds also contributes to the cocoa-specific flavor.

Enhanced xylose fermentation and ethanol production by engineered Saccharomyces cerevisiae strain.

We have recently demonstrated that heterologous expression of a bacterial xylose isomerase gene (xylA) of Burkholderia cenocepacia enabled a laboratorial Saccharomyces cerevisiae strain to ferment xylose anaerobically, without xylitol accumulation. However, the recombinant yeast fermented xylose slowly. In this study, an evolutionary engineering strategy was applied to improve xylose fermentation by the xylA-expressing yeast strain, which involved sequential batch cultivation on xylose. The resulting yeast strain co-fermented glucose and xylose rapidly and almost simultaneously, exhibiting improved ethanol production and productivity. It was also observed that when cells were grown in a medium containing higher glucose concentrations before being transferred to fermentation medium, higher rates of xylose consumption and ethanol production were obtained, demonstrating that xylose utilization was not regulated by catabolic repression. Results obtained by qPCR demonstrate that the efficiency in xylose fermentation showed by the evolved strain is associated, to the increase in the expression of genes HXT2 and TAL1, which code for a low-affinity hexose transporter and transaldolase, respectively. The ethanol productivity obtained after the introduction of only one genetic modification and the submission to a one-stage process of evolutionary engineering was equivalent to those of strains submitted to extensive metabolic and evolutionary engineering, providing solid basis for future applications of this strategy in industrial strains.