## 3 Results and Discussion
### The Maillard Reaction: An Overview  
The Maillard reaction involves the condensation of carbonyl groups from reducing sugars, such as glucose or fructose, with amino groups present in amino acids, peptides, and proteins (Figure 3). This condensation initially produces imines, referred to as Schiff bases, bearing a hydrocarbonlyl group on the nitrogen atom. These are aldosylamines or ketosylamines when the reducing sugar involved in the reaction is an aldose or a ketose, respectively. The Schiff bases are unstable and can rearrange into more stable compounds called Amadori compounds (Figure 3) or Heyns compounds via a 1,2-enaminol [12]. Amadori compounds are N-substituted 1-amino-1-deoxyketoses, while Heyns compounds are N-substituted 2-amino-2-deoxyaldoses. Amadori and Heys compounds are more stable than imines since they can be converted into cyclic molecular structures [13]; however, they are partially stable. They can undergo enolization to 1,2-enaminol or 2,3-enaminol; then, \(\alpha\)-dicarbonyl compounds such as deoxyosomes can form [5] (Figure 3). At pH \(\leq\) 7, the Amadori compounds undergo 1,2-enolization, and 3-deoxyosome is generated. The cyclization and dehydration of 3-deoxyosome produces 5-hydroxymethylfurfural from hexose and furfural from pentose. When the pH is higher than 7, the Amadori compound is subjected to 2,3-enolization to form 1-deoxyosome, which can formuranones following cyclization [14; 15] (Figure 4). Deoxyosomes can also degrade into \(\alpha\)-dicarbonyl compounds, such as glyoxal (GO) and methylglyoxal (MGO) [14], or react with the \(\alpha\)-amino group of amino acids and form Strecker aldehydes (Figure 4), which impart a pleasant flavor to some foods, such as bread, coffee, cocoa and roasted meats. The production of Strecker aldehydes commonly occurs in food with higher concentrations of free amino acids and under more drastic conditions such as higher temperatures [13]. Nucleophilic and electrophilic intermediates of the MR can react via condensation reactions, and colored compounds, referred to as melanoidins, can be obtained (Figure 4). They are responsible for the brown color of processed foods, such as in bread crusts and meat [16]. In the advanced phase of the MR, dicarbonyl compounds react with the arginine and lysine residues of proteins and form AGEs (Figure 4) such as 3-deoxyglucose, 3-deoxyglucose lysine dimers, glyoxal, glyoxal-lysine dimers, methylglyoxal-derived hydroimidazalone, and methylglyoxal-lysine dimers [12]. AGEs are classified into three groups: (i) fluorescent crosslinking AGEs, namely crossline and pentosidine; (ii) non-fluorescent crosslinking AGEs, such as imidazolium dilysine crosslinks, and (iii) non-fluorescent non-crosslinking AGEs, including N 3-carboxyethyl-lysine and N 3-carboxymethyl-lysine. Figure 2: PRISMA flow diagram. Figure 3: Simplified scheme of the formation of \(\alpha\)-dicarbonyl compounds during the Maillard reaction. The formation of melanoidins and AGEs increases due to the high temperatures reached during sterilization, cooking, and roasting. These processes result in significant changes in color and taste, as well as digestibility and protein functionality [17; 18]. Describing the Maillard reaction chain in foods is challenging due to the different dynamic conditions found in various food matrices. Additionally, the presence of multiple reactants and the varied processing and storage conditions further contribute to the complexity of this chemical landscape [5]. The determination of the rate of the Maillard reaction is also difficult because it is affected by various factors, including pH, temperature, humidity, and the food matrix. For instance, an increase in pH and temperature promotes the progression of the reaction; high pH values enhance protein solubility, and temperatures higher than 55 \({}^{\circ}\)C induce protein denaturation, resulting in more abundant amino acid residues [2].