The oxidative stability of fat in three dark chocolates at different stages of manufacturing process.

The process of making chocolate, like many other technological processes, is highly temperature-dependent. One of the unfavorable changes that may take place during the process of making dark chocolate is the oxidation of cocoa butter, which may prevent the process of appropriate crystallization leading to the most desirable polymorphic form V. The parameter that allows predicting the sensitivity of the sample to oxidation is the activation energy of the oxidation process. The study aimed to compare three dark chocolates and preceding cocoa masses at different stages of production, produced by three different manufacturers using different production methods, based on thermal analysis of fats extracted from mentioned cocoa masses and statistical analysis of the results to assess the impact of production conditions on the oxidative stability of the fat phase. The Ozawa-Flynn-Wall method based on the Arrhenius equation was used to estimate the activation energy (E_a) and the pre-exponential factor (Z). A DSC apparatus (Q20, TA Instruments), calibrated with pure indium, was used for the tests. The measurements were carried out using non-isothermal mode with the following sample heating rates: 2.5 K/min, 4 K/min, 6 K/min, 7.5 K/min, 10 K/min, 12.5 K/min, 15 K/min. The mass of the samples used for the test was about 3 - 4 mg. An increase in the activation energy corresponding to the increase in fat oxidative stability was observed in the case of raw dark chocolate from a small company and classic dark chocolate from a large company. Moreover, in the case of classic dark chocolate produced by a small manufacturer, the stability of fat in the final product was much lower (65.36 kJ/mol) than that of the starting material such as cocoa butter (123.89 kJ/mol) or cocoa liquor (104.68 kJ/mol). In most of cases, the activation energy values calculated from the maximum oxidation temperature/peak maximum (T_max) were significantly lower than the values calculated from the extrapolated oxidation onset temperature (T_on) with just two exceptions: cocoa butter used by a large manufacturer (Ea_(Ton) = 82.43 kJ/mol, Ea_(Tmax) = 105.10 kJ/mol) and the final product (chocolate bar) of a small manufacturer of classic dark chocolate (Ea_(Ton) = 65.36 kJ/mol, Ea_(Tmax) = 94.05 kJ/mol), both showed the opposite trend.