## 4 Role of Maillard Reaction on Production of Volatile Organic Compounds (VOCs)  
The Maillard reaction (MR) is a complex, non-enzymatic browning reaction that occurs between the amino groups of amino acids, peptides, or proteins and the carbonyl groups of reducing sugars, such as glucose, fructose, and lactose or other carbonyl-containing compounds, including lipid degradation products. This reaction is induced when the food matrix reaches high temperatures. Also, the reaction products and final flavor and taste profiles are influenced by multiple factors, including water activity, pH, lipid degradation products, and the specific types of amines and carbohydrates involved [48]. The MR is typically divided into three stages:  
The first stage involves a condensation reaction between an amino group and a reducing sugar [49]. The nucleophilic addition reaction occurs between these two chemical compounds, resulting in the formation of a Schiff base [50]. The formation of Schiff bases can also occur at room temperature [51]. Shift bases can be aldosylamine if derived from an aldose sugar, or ketosylamine if derived from a ketose sugar [52]. Subsequently, if the reducing sugar is an aldose, an N-glycoslamine is formed, which subsequently rearranges into an Amadori compound. However, if the amino group reacts with a ketose sugar, Heyns rearrangement products are formed [49]. However, after undergoing several reactions, including isomerization, dehydration, hydrolysis, elimination, and condensation, the first stage ultimately yields 5-hydroxymethylfurfural (HMF) [51]. The intermediate stage starts when the food matrix is heated [52], then starts from Amadori or Heyns products, leading to sugar fragmentation and the release of the amino group [49]. This reaction can lead to various reactions, including fragmentation, cyclization, and Strecker degradation, resulting in the formation of aldehydes, ketones, dicarbonyls, and heterocyclic compounds. Amadori and Heyns products are the first stable products of the MR, and their subsequent degradation products determine the development of flavor, aroma, color, and taste in food products [50]. In this stage, lipids play a fundamental role in the release of aroma molecules. It is well known that the type and quality of lipids can generate aroma through the production of organic volatile compounds. These compounds are released during the breakdown of fatty acid macromolecules. For example, aldehydes generated from lipid oxidation can interact with MR products at various stages of the roasting process, leading to the formation of pyrazines, thiophenes, pyridines, oxazoles, and thiazoles. Another example of aroma formation involves the Strecker degradation of amino acids, phenolic compounds, and lipid oxidation, which can lead to the production of aldehydes. These aldehydes can then react with MR products to form intermediates that subsequently break down, releasing flavor compounds [53]. During the baking process of malt, in the intermediate phase of the MR, various volatile organic compounds such as maltol, phenylacetaldehyde, 2-furan methanol, HMF, and acetic acid are generated. If the temperature exceeds 200 \({}^{\circ}\)C, pyrazines and other nitrogen-containing heterocyclic compounds are released [51]. For example, pyrazines are among the most important volatile organic compounds that contribute to the aroma of products. They are monocyclic aromatic rings containing two nitrogen atoms in the para position. These compounds are formed from nitrogen atoms originating in amino acids and carbon atoms derived primarily from fructose rather than glucose [54]. It is well reported that pyrazines are key aroma compounds in roasted almonds. Furthermore, [PERSON] et al. (2012) reported high concentrations of dimethylpyrazine, trimethylpyrazine, and 2-methylpyrazine in roasted almonds [55]. The third stage involves several reactions, such as dehydration, fragmentation, cyclization, and polymerization.