**4. Conclusions**

An effective ultrasound-assisted solid–liquid process for extracting polyphenols from cocoa beans was optimized using an experimental design. The 2<sup>4</sup> factorial design showed that all parameters studied were significant factors in affecting the polyphenolic content as well as enabling us to determine the optimal values for the extraction process. This optimization showed that the best conditions to obtain high polyphenol yield were 50% of ethanol, solid/solvent ratio of 1:120 *w*/*v*, pH 6 at 70 ◦C for a maximum equilibrium time of 45 min. Operating conditions to avoid degreasing and freeze-drying steps were also established, thus leading to a more cost-effective strategy. Overall, the process extraction allowed to increase on 59.7% and 12.8% of cocoa polyphenols amount and extraction yield, respectively. The extract rich in polyphenols could replace the synthetic antioxidants and could be used in the food and cosmetic industries. Our results suggest that ultrasound-assisted solid–liquid extraction is a suitable method for the recovery of cocoa polyphenols and could be used for the scaleup procedure for further research.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2076-3921/9/5/364/s1, Table S1: ANOVA for TP, TF, and TF3 through 24 surface design + central points+ start points.

**Author Contributions:** Formal analysis, E.I., E.A.D. and L.J.L.-G.; Investigation, S.T.-U.; Methodology, S.T.-U.; Supervision, E.I., E.A.D., A.R.V.-J. and L.J.L.-G.; Writing—original draft, S.T.-U.; Writing—review & editing, L.J.L.-G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Universidad Industrial de Santander, grant number 2511. In addition, to Department of Science, Technology and Innovation (COLCIENCIAS-Colombia), grant number 567 of 2012.

**Acknowledgments:** Said Toro wants to thank Colciencias (Colombia) for my financial scholarship, University of Massachusetts, Foodomics Laboratory. Also, the authors want to thank Vicerrectoría de Investigación y Extensión from Universidad Industrial de Santander for their financial support that made this work possible.

**Conflicts of Interest:** The authors declare no conflict of interest.
