RESEARCH BACKGROUND: The objective of this paper is to introduce an instrumentally simple analytical tool for determination of cocoa solid content in chocolates. This electroanalytical method is based on amperometric oxidation of all present antioxidants in chocolates at boron-doped diamond electrode (BDDE) that is integrated in a flow injection analysis (FIA) wall-jet electrode system. EXPERIMENTAL APPROACH: As part of optimisation, thirteen commonly occurring antioxidants were investigated using cyclic voltammetry at the BDDE in 0.1 mol/L phosphate buffer with different methanol (MeOH) content. Working parameters, such as MeOH volume fraction, flow rate and detection potential, were optimised. Principally, the height of the oxidation peak (current response) representing the oxidation of the sum of antioxidants (total antioxidant content; TAC) was expressed as Trolox equivalents. RESULTS AND CONCLUSIONS: For analytical purpose, a linear range from 5 to 100 mg/L described by regression equation and characterised by high correlation coefficient R2=0.9994 was achieved. Obtained high positive correlation between the determined values of Trolox equivalent antioxidant capacity (TEAC) and cocoa mass fractions characterised by correlation coefficient of 0.9187 for eight randomly selected samples (one white, two milk, and five dark chocolates) confirmed that cocoa solids represent the main source of antioxidants (reducing agents). NOVELTY AND SCIENTIFIC CONTRIBUTION: The research demonstrates that TEAC values could be considered as an additional marker of cocoa content in the chocolate analysis to the commonly used theobromine (authenticity of food products). The developed FIA could therefore serve as simple analytical tool in the food quality control.

Department of Analytical Chemistry Faculty of Chemical Technology University of Pardubice Studentská 573 532 10 Pardubice Czech Republic

Department of Chemistry Faculty of Mathematics and Natural Sciences University of Prishtina Str Mother Teresa 10 000 Prishtina Republic of Kosovo

Institute of Chemistry Analytical Chemistry Karl Franzens University Universitaetsplatz 1 8010 Graz Austria

See more in PubMed

Aprotosoaie AC, Luca SV, Miron A. Flavor chemistry of cocoa and cocoa products—An overview. Compr Rev Food Sci Food Saf. 2016;15(1):73–91. 10.1111/1541-4337.12180 PubMed DOI

Montagna MT, Diella G, Triggiano F, Caponio GR, De Giglio O, Caggiano G, et al. Chocolate, “Food of the Gods”: History, science, and human health. Int J Environ Res Public Health. 2019;16(24):4960. 10.3390/ijerph16244960 PubMed DOI PMC

Katz DL, Doughty K, Ali A. Cocoa and chocolate in human health and disease. Antioxid Redox Signal. 2011;15(10):2779–811. 10.1089/ars.2010.3697 PubMed DOI PMC

Directive 2000/36/EC of the European Parliament and of the Council relating to cocoa and chocolate products intended for human consumption. Off J Eur Comm. 2000;L197:19–25. Available from: https://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2000:197:0019:0025:EN:PDF.

Code of Federal Regulations (CFR). Title 21: Food and drugs. Part 163–Cacao products, Subpart B–Requirements for specific standardized cacao products, Paragraph 163.123 Sweet chocolate. Washington, DC, USA: US Government Publishing Office; 2019. pp. 546–7. Available from: https://www.govinfo.gov/content/pkg/CFR-2020-title21-vol2/pdf/CFR-2020-title21-vol2-part163.pdf.

Kopřiva P. As good as half of the cocoa content was missing in instant drink MalCao. Brno, Czech Republic: Czech Agriculture and Food Inspection Authority (CAFIA); 2016. Available from: https://www.szpi.gov.cz/en/article/as-good-as-half-of-the-cocoa-content-was-missing-in-instant-drink-malcao.aspx?q=JmNobnVtPTEmaGw9Y29jb2E%3d.

Risner CH. Simultaneous determination of theobromine, (+)-catechin, caffeine, and (-)-epicatechin in standard reference material baking chocolate 2384, cocoa, cocoa beans, and cocoa butter. J Chromatogr Sci. 2008;46(10):892–9. 10.1093/chromsci/46.10.892 PubMed DOI

ČSN 56 0578. Chocolate and chocolate confectionery - Determination of fat-free cocoa solids. Prague, Czech Republic: Czech technical standards (ČSN); 2017 (in Czech). Available from: https://www.technickenormy.cz/csn-56-0578-cokolada-a-cokoladove-cukrovinky-stanoveni-obsahu-tukuproste-kakaove-susiny-1/.

Steinberg FM, Bearden MM, Keen CL. Cocoa and chocolate flavonoids: Implications for cardiovascular health. J Am Diet Assoc. 2003;103(2):215–23. 10.1053/jada.2003.50028 PubMed DOI

Genovese MI, da Silva Lannes SC. Comparison of total phenolic content and antiradical capacity of powders and “chocolates” from cocoa and cupuassu. Food Sci Technol. 2009;29(4):810–4. 10.1590/S0101-20612009000400017 DOI

Švorc L, Tomčík P, Svítková J, Rievaj M, Bustin D. Voltammetric determination of caffeine in beverage samples on bare boron-doped diamond electrode. Food Chem. 2012;135(3):1198–204. 10.1016/j.foodchem.2012.05.052 PubMed DOI

Farag AS, Sýs M, Hájek T, Vytřas K. Voltammetric determination of ethylvanillin and methylvanillin sum at carbon paste electrode modified by sodium dodecyl sulfate in selected foodstuffs. Monatsh Chem. 2018;149:1945–53. 10.1007/s00706-018-2266-z DOI

Brcanović JM, Pavlović AN, Mitić SS, Stojanović GS, Manojlović DD, Kaličanin BM, et al. Cyclic voltammetric determination of antioxidant capacity of cocoa powder, dark chocolate and milk chocolate samples: Correlation with spectrophotometric assays and individual phenolic compounds. Food Technol Biotechnol. 2013;51(4):460–70.

Švorc L, Haššo M, Sarakhman O, Kianičková K, Stanković DM, Otřísal P. A progressive electrochemical sensor for food quality control: Reliable determination of theobromine in chocolate products using a miniaturized boron-doped diamond electrode. Microchem J. 2018;142:297–304. 10.1016/j.microc.2018.07.007 DOI

Dejmkova H, Scampicchio M, Zima J, Barek J, Mannino S. Determination of total phenols in foods by boron doped diamond electrode. Electroanalysis. 2009;21(9):1014–8. 10.1002/elan.200804508 DOI

Akoglu H. User’s guide to correlation coefficients. Turk J Emerg Med. 2018;18(3):91–3. 10.1016/j.tjem.2018.08.001 PubMed DOI PMC

Nova, v. 1.11.0, Metrohm Autolab B.V., Utrecht, The Netherlands; 2014. Available from: http://www.ecochemie.nl/news/NOVA_1.11.html.

Pekec B, Feketeföldi B, Ribitsch V, Ortner A, Kalcher K. Development of an electrochemical sensor for the determination of the total antioxidant capacity in berries based on boron doped diamond. J Electrochem Sci Eng. 2013;3(1):1–9. 10.5599/jese.2012.0024 DOI

Alpar N, Yardım Y, Șentürk Z. Selective and simultaneous determination of total chlorogenic acids, vanillin and caffeine in foods and beverages by adsorptive stripping voltammetry using a cathodically pretreated boron-doped diamond electrode. Sens Actuators B Chem. 2018;257:398–408. 10.1016/j.snb.2017.10.100 DOI

Jiang L, Ding Y, Jiang F, Li L, Mo F. Electrodeposited nitrogen-doped graphene/carbon nanotubes nanocomposite as enhancer for simultaneous and sensitive voltammetric determination of caffeine and vanillin. Anal Chim Acta. 2014;833:22–8. 10.1016/j.aca.2014.05.010 PubMed DOI

Miller NJ, Rice-Evans C, Davies MJ, Gopinathan V, Milner A. A novel method for measuring antioxidant capacity and its application to monitoring the antioxidant status in premature neonates. Clin Sci (Lond). 1993;84(4):407–12. 10.1042/cs0840407 PubMed DOI

Macikova P, Halouzka V, Hrbac J, Bartak P, Skopalova J. Electrochemical behaviour and determination of rutin on modified carbon paste electrodes. ‎. ScientificWorldJournal. 2012;2012:394756. 10.1100/2012/394756 PubMed DOI PMC

Chao M, Ma X. Voltammetric determination of chlorogenic acid in pharmaceutical products using poly(aminosulfonic acid) modified glassy carbon electrode. J Food Drug Anal. 2014;22(4):512–9. 10.1016/j.jfda.2013.12.006 PubMed DOI PMC

Leamsomrong K, Suttajit M, Chantiratikul P. Flow injection analysis system for the determination of total phenolic compounds by using Folin-Ciocalteu assay. Asian J Appl Sci. 2009;2(2):184–90. 10.3923/ajaps.2009.184.190 DOI

Freitas JM, da Costa Oliveira T, Munoz RAA, Richter EM. Boron doped diamond electrodes in flow-based systems. Front Chem. 2019;7:190. 10.3389/fchem.2019.00190 PubMed DOI PMC

Calixto-Cotos MR, Chire-Fajardo GC, Orihuela-Rivera CA. Antioxidants properties of chocolates sold in Peru. Acta Agron. 2018;67(4):479–85. 10.15446/acag.v67n4.71357 DOI

Godočiková L, Ivanišová E, Árvay J, Petrová J, Kačániová M. The comparison of biological activity of chocolates made by different technological procedures. Potr S J F Sci. 2016;10(1):316–22. 10.5219/628 DOI