Chocolate is defined as a homogeneous product made from cocoa liquor (cocoa mass or paste) and cocoa butter, with or without additions of sugar, sweeteners, dry milk (except whey), vegetable fats up to 5%, and permitted food additives. It is a complex mixture of approximately 70% fine solid particles (from sugar and cocoa) in a continuous fat phase. It is prepared from cocoa beans grown on the cocoa tree (Theobroma cacao) that need to be technologically processed before consumption. First, they are fermented to remove bitterness, then dried, roasted and finally ground and mixed with various ingredients. At room temperature (around 25°C), chocolate is solid and melts at body temperature (37°C), forming a smooth mixture of solid particles in cocoa butter. Depending on its composition we distinguish between dark, milk, and white chocolate. As the demand for liquid and solid chocolate increases in global markets, understanding the factors affecting its quality is beneficial for both producers and consumers. A serious problem related to production parameters, distribution, and storage conditions of chocolate products is the development of fat bloom, which is associated with fat crystallization. Understanding the crystallization behaviour of cocoa butter is important in the development of chocolate products. In experimental work, we developed various methods for differential scanning calorimetry (DSC) and simple chemical experiments suitable for students. With various measurement conditions, the cyclic DSC method for measuring cocoa butter and various chocolate samples were optimized, samples were compared with each other and their polymorphic modifications were determined. We also compared the oxidative stability of cocoa butter and dark chocolate, which contains a lot of antioxidants, by determining the oxidation induction time (OIT); for these samples we also calculated the activation energy of oxidative degradation. With DSC measurements up to 600°C in nitrogen and air atmospheres, we took a closer look at the composition of chocolate and the decomposition of its individual components. The effect of lecithin and some other factors affecting the viscosity of different mixtures that can be associated with chocolate were studied with a simple educational experiment. We showed why proper tempering of chocolate is so important using a problem-based experiment. Samples of cocoa butter and dark chocolate were recorded with a digital optical microscope during cyclic DSC measurement to help students visually understand what happens to the sample during the measurement itself. For all school experiments, we prepared worksheets for students with solutions and instructions for teachers.
|
