High temperature and nib acidification during cacao-controlled fermentation improve cadmium transfer from nibs to testa and the liquor’s flavor

Migration of nib Cd to the testa during fermentation can be achieved with high temperatures (> 45 °C) and low nib pH values (< 5.0) using spontaneous fermentation. However, this low pH can lead to low flavor quality. This study used three controlled temperature fermentation treatments on three cacao genotypes (CCN 51, ICS 95, and TCS 01) to test its effects on the nib pH, the migration of nib Cd to the testa, and the liquor flavor quality. All treatments were effective in reducing the total nib Cd concentration. Nevertheless, the treatment with the higher mean temperature (44.25 °C) and acidification (pH 4.66) reached the highest mean nib Cd reductions throughout fermentation, a 1.37 factor in TCS 01, promoting the development of fine-flavor cocoa sensorial notes. In unfermented beans, the Cd concentration of nibs was higher than that of the testa, and the Cd migration proceeded down the total concentration gradient. However, Cd migration was observed against the concentration gradient (testa Cd > nib Cd) from the fourth day. Cd migration could increase by extensive fermentation until the sixth day in high temperatures and probably by the adsorbent capacity of the testa. Genotype-by-treatment interactions were present for the nib Cd reduction, and a universal percentage of decrease of Cd for each genotype with fermentation cannot be expected. Selecting genotypes with highly adsorbent testa combined with controlled temperatures would help reduce the Cd concentration in the cacao raw material, improving its safety and quality.


Rationality behind temperature profiles (treatments)
Three temperature profiles were established to obtain variations in the fermentation pH (Table 1).Thus, a temperature gradient was used for the death of the embryo to achieve a differential decrease in the pH of the nib, which will simulate the most favorable conditions reported in the literature for spontaneous fermentations: • Embryo death occurs in the first 48 hours between 36-44 °C1 .
• There are two main fermentation temperature phases.The exothermic phase (from day 0 to 4) with a higher metabolic activity increased from approx.27 to 49 °C, while the isothermic phase (from day four on) with a lower variation in temperature remains constant between 45 and 50 °C5 .
• After the death of the embryo, temperature increments higher than the range of 45-48 C are not favorable to produce acetic acid due to the death of acetic bacteria 2,3 .
• Try reaching phases below 35 °C for long periods has not resulted or has resulted in grain germination 2,6 .
• Depending on the observed flavor, Small-scale fermentation can achieve good fermentation with a maximum temperature of 46 °C and 38-46 °C after the thirtieth hour 7 .

Figure S1 .
Figure S1.Time course for the pH of cacao bean tissues of three genotypes (CCN 51, ICS 95, TCS 01) fermented under three temperature profiles (T) for six days.Three sample units (14, 25, 36) per genotype are plotted.

Figure S3 .
Figure S3.Time course for the relative decrease of Cd concentration (RDCd, estimated on days 2, 5, and 6) of the cacao nib of three genotypes (CCN 51, ICS 95, TCS 01) fermented under three temperature profiles (T) for six days.Three sample units (14, 25, 36) per genotype are plotted.

Figure S4 .
Figure S4.Time course for the relative increase of Cd concentration (RICd, estimated on days 2, 5, and 6) of the cacao testa of three genotypes (CCN 51, ICS 95, TCS 01) fermented under three temperature profiles (T) for six days.Three sample units (14, 25, 36) per genotype are plotted.

Figure S5 .
Figure S5.Time course for the internal translocation factor (ITF, estimated on days 2, 5, and 6) of cacao bean tissues of three genotypes (CCN 51, ICS 95, TCS 01) fermented under three temperature profiles (T) for six days.Three sample units (14, 25, 36) per genotype are plotted.An ITF higher than 1.0 indicates that testa Cd is higher than nib Cd concentration (horizontal reference line).

Table S1 .
Abbreviations used in this paper.