Термический анализ в исследовании качества шоколада и кондитерских изделий

Abstract

High and unstable prices on such cocoa products as cocoa butter have triggered a search for substitutes. Thus, it is necessary to develop identification methods for chocolate authenticity, since chocolate is one of the most popular confectionery products. The present research employed the methods of thermal and thermomechanical analysis to study samples of chocolate produced in the countries of the Eurasian Economic Community (the Russian Federation, the Republic of Kazakhstan, and the Republic of Belarus) and chocolate bars with cocoa butter substitutes. An analysis of the sucrose – cocoa butter (CB) system revealed that samples with CB = 10–30%, 60%, and 90% demonstrated a single polymorphic modification of glycerides CB α-form with a melting point of 21–23°C. The samples with CB = 0%, 50%, 70%, and 80% showed a more heat-resistant modification (β’-modification) with a maximum melting point of 27.0–27.5°C. In addition, the melting peaks of glycerides were found not constant, which may indicate a eutectic effect in the sucrose – CB system. The samples of chocolate produced in the Russian Federation and the Republic of Kazakhstan passed the tempering stage and demonstrated the most heat-resistant β-modification of CB. However, the samples differed in the melting temperature: T max = 33.9°C for the Russian chocolate and T = 34.8°C for 
 the samples from Kazakhstan (the Rakhat brand). The samples from Belarus did not pass the tempering and were found to contain a thermodynamically unstable CB α-phase (the Kommunarka factory). The samples produced by the Spartak factory (Gomel, the republic of Belarus) contained an additional CB β’-phase. The differential scanning calorimetry (DSC) curves for chocolate bars with CB substitutes differed from the DSC curves for cocoa butter and chocolate samples. The fact can be used for identification. The DSC method can be used to identify the individual characteristics of the producer of chocolate and its analogues since the parameters of the melting curve of the fat phase and the shape of the curve are individual. The thermomagnetic analysis (TMA) method complemented the identification by determining the mass fraction of the liquid phase. Joint application of DSC and TMA methods allowed the authors to evaluate the quality of chocolate, its formulation, as well as to reveal the presence of cocoa products substitutes in the samples as compared to the reference sample.