Investigation of cold plasma technique as an alternative to conventional alkalization of cocoa powders

Abstract

In the production of cocoa, a crucial process called Alkalization or Dutching has been used to reduce its acidity, bitterness and astringency as well as modify its solubility and color. It is a time-and energy-consuming process. It was investigated whether it is possible to replace the conventional alkalization with the cold plasma (CP) technique. We discover that atmospheric pressure plasma jet (APPJ) CP treatment is capable of reducing the lightness values, improving the solubility, and decreasing the acidic perception of natural cocoa powders as well as protecting bioactive compounds (total phenolic and flavonoid content) of natural cocoa powders, consuming similar to 65% less time than the traditional method and without the need for external expenditures such as chemicals, high pressure, or aeration. Moreover, CP treatment did not increase the total ash content and thus water-holding capacity of powders unlike the conventional alkalization, which caused a 40% and 42% increase, respectively. The SEM micrographs demonstrated that CP treatment caused etching on the surface and removed the layer of protein-polyphenol-cell wall complex. FTIR spectra showed the incorporation of hydrophilic functional groups on the surface after CP treatment. CP treatment effectively reduced the acidic fractions of cocoa powder, but caused to the oxidation of cocoa butter and the formation of decomposition products of oleic and linoleic acid. Finally, this is a pioneering study for replacing an alkalization process step that has been used since the 19th century and has no alternative, and the results seem to be very promising for further detailed studies and pilot-and industrial-scale trials.