Kinetics of Cadmium Bioaccumulation in Beans of Five Cocoa Varieties

Cadmium (Cd) is a non-essential heavy metal for cocoa that in high concentrations in chocolate is harmful to health; however, there are hypoaccumulative varieties which can guarantee its innocuousness. The aim was to study the kinetics of Cd accumulation in the beans of five cocoa varieties identifying those of lowest bioaccumulation at the Tulumayo station. As genetic material, five cocoa genotypes S-08 (ICS-95 x UF-296), S-12 (ICS-1 x SCA-6), S-23 (IMC-67 x U-68), S-28 (ICS-39 x U-45) and C-60 (farmer's selection) of different genetic origin were tested. Chemical analyzes of Cd in beans were carried out by atomic absorption spectrophotometry. The dispersion data were fitted to a curvilinear polynomial regression model and were analyzed using univariate statistics, Pearson's correlation and biplot analysis. The accumulation of Cd in the cocoa beans showed a reductional trend from June to September (summer) characterized by low rains, with a slight increase from October to November (beginning of winter) in which ones are more frequent, accumulating 0,894 ppm of Cd on average. Also, there was a differential response between genotypes, having S-8 and C-60 varieties the lowest accumulation with 0,650 and 0,815 ppm of Cd, respectively, turning out to be less than or equal to the maximum allowable limit established by the European Commission for chocolates with dry cocoa solids ≥ 50 %, respectively. Positive and highly significant correlations between Cu / Zn (r = 0,869), Mn / Fe (r = 0,755), Fe / Zn (r = 0,655), while negative correlations highly significant for Cd / Zn (r = - 0,667) and Cd / Cu (r = - 0,531) and significant between Cd/Mn (r = 0,365), were found. The biplot analysis showed positive values for Cu and Zn in PC1, that are closer to S-08 than to S-28, while Mn and Cd with negative values in PC2, are closer to S-23 variety. The very distant positions of Zn and Cd with positive values in PC1 and negative in PC2, would show dissimilarity or antagonism between them. The soil chemical analysis (initial and final) did not show substantial differences. 

Keywords: Biplot analysis, cacao varieties, correlation analysis, cadmium in beans.