# Antimicrobial and Odour Qualities of Alkylpyrazines Occurring in Chocolate and Cocoa Products
## 2 Pyrazines in Chocolate and Cocoa
### The Way of Formation of Pyrazine in Cocoa and Cocoa Products
#### 2.1.2 Roasting Stage of Cocoa Manufacturing  
The oxidation reactions, which started during fermentation, continue at a dry heat processing stage. Incompetent drying may lead to an inability to produce compounds that are important for the odour of cocoa, such as pyrazines, and high levels of off-odour carbonyl compounds [8,10]. It is known that varying the temperature and roasting duration have a major impact on the overall aroma produced [7,10,18]. The Maillard process, also known as the nonenzymatic browning reaction, is primarily a reaction between the reducing sugars and free amino groups of amino acids. Leucine, alanine, phenylalanine and tyrosine, which are hydrophobic amino acids produced by proteinase reactions during fermentation, as well as the reducing sugars fructose and glucose obtained from sucrose hydrolysis, were observed as contributing significantly to the Maillard process. The roasting procedure typically results in the formation of heterocyclic aromatic compounds such as pyrazines (with the exception of tetramethylpyrazine, which is biosynthesized during cocoa fermentation), the efficient inhibition of polyphenol oxidase activity and a decrease in free acetic acidity, and thereby eliminates some unpleasant volatile constituents of cocoa. A considerably higher pH is required for the Maillard process to produce maltol as well as several nitrogen-containing molecules like pyrazines, the concentration of which in fermented cocoa beans may be reduced by a low pH and depends on the roasting treatment's temperature and duration. The majority of pyrazine formation occurs once amino ketones react, frequently with the addition of a Strecker aldehyde as a substituent on the pyrazine ring. The breakdown of glucose, which is initiated through an amino acid mostly in the Maillard reaction, results in the production of highly reactive dicarbonyl molecules such glyoxal and methylglyoxal, which are converted into amino ketones. They could be made only from glucose and glycine, and in this case, the main byproducts are pyrazine and methylpyrazine. Nonetheless, side chains could also be added to the pyrazine ring by the inclusion of an aldehyde that can also react with a dihydropyrazine in a process known as the \"a + a + b\" mechanism, where \"a\" is the dicarbonyl or hydroxycarbonyl and \"b\" is an aldehyde. By incorporating valine into a glucose/glycine structure, the Strecker aldehyde 2-methylproposal will be produced, which when added to the pyrazine molecule will result in pyrazines with a 2-methylpropyl substituent. This aldehyde can be produced by the Maillard reaction from the Strecker degradation of the specific amino acid. Additionally, the relationship between the alkylpyrazines 2,3-dimethyllyrazine, tetramethylpyrazine and trimethylpyrazine is utilized to gauge the extent of cocoa roasting [13,14,16,17,19,20,21]. 2,5-diketopierazines, another type of heterocyclic molecule that contributes to the choolate flavour by adding pleasant bitterness, were discovered to be possible identifiers of cocoa bean variety as well as indications of postharvest heat processing [22]. Additionally, a crucial function for alanine and/or its Strecker aldehyde, acetaldehyde, in the creation of chocolate odour is suggested by the presence of an ethyl group in several pyrazine compounds present in cocoa and chocolate [20]. It was determined that the side groups on dioxo-compounds control the precise pyrazine structure. For instance, pyruvatedehyde and valine produce the nutty-tasting 2-methyl-propanol and 2,5-dimethyl pyrazine as their final products [13]. It was discovered that temperatures over 130 \({}^{\circ}\)C and a roasting time over 25 min had a positive impact on the concentration of all methylpyrazines [17; 23]. The rapid drying of cocoa beans, on the other hand, traps volatile acids inside the beans, which is undesirable because the high acid concentration can result in an off-putting aroma of both cocoa and chocolate [15].