## 4 Discussion  
This is one of the few studies that investigate the role of terpenoid compounds on the evolution of Maillard reaction. The study highlighted a general promotion of glycation by terpenoid compounds as measured by color development and lysine depletion. However, measurement of absorbance and fluorescence intensity showed both antiglycative and proglycative capacity, depending on terpenoid compound concentration but most importantly the temperature and glucose concentration of the system. In detail, all terpenoid showed some antiglycative capacity at low glucose levels (0.1 M) and low temperatures (80 \({}^{\circ}\)C). In terms of effect sizes, thymol and aniseed oil showed stronger inhibitory capacity reducing the concentration of early glycation products by approximately 100% compared to the control, at least for the first hour of heating, while linalool showed much smaller inhibitory capacity if any. The RSM model allowed to test for the most desirable experimental condition in order to minimize the extent of the Maillard reactions and the production of AGEs in all five parameters tested. According to this model, for aniseed oil a system with 0.1 M glucose, 4 \(\upmu\)M aniseed oil heated at 80 \({}^{\circ}\)C for 1 h would be the optimal solution (Desirability = 0.845). For thymol and linalool, a system with 0.1 M glucose, 2 \(\upmu\)M aniseed oil heated at 80 \({}^{\circ}\)C for 1 h would be the optimal solution (Desirability = 0.949 and 0.713, respectively). According to the RSM analysis, the overall antiglycative capacity of the terpenoid compounds tested could be ranked Thymol > Aniseed Oil > Linalool. Such a behavior could be attributed to the high antioxidant activity of thymol and aniseed oil. Research has highlighted that not only phenols (like thymol and carvacrol) but also compounds with methylene groups show high antioxidant activity [5]. Anethole and estragole, the main compounds of the aniseed oil, possess methylene groups on their structure which may be responsible for the observed inhibition. A pro-oxidant behavior for linalool was also observed in the same research article. On the other hand, the presence of anethole and thymol in sweet cumin were positively linked with the formation of early radical intermediates on experiment where equimolar amounts of glucose and glycine with varying amounts of pure terpenoid solutions were refluxed for 1 h [25]. The dual role of terpenoid compounds to act as antioxidant and prooxidant depending on their concentration was underlined by many researchers [4]. At the same time, a dose response relationship was rarely observed and when observed the direction of the relationship was unusual. In the cases of a dose response, it was the extreme terpenoid concentrations, of 2 \(\upmu\)M and 8 \(\upmu\)M, which showed the antiglycative activity and the middle terpenoid concentrations that showed a proglycative activity. Although the increasingly stronger antiglycative capacity with increasing terpenoid concentrations could be physiologically relevant, the fact that the smallest concentration tested in this experiment (2 \(\upmu\)M) showed the same antiglycative capacity as 8 \(\upmu\)M terpenoid concentrations was an unexpected finding. Previous research on the influence of terpenoid compounds on AGEs inhibition revealed that higher concentrations are more effective for such a behavior. Particularly cynme, an aromatic monoterpene, inhibited by 56.6% the total AGEs fluorescence when used at a concentration of 100 \(\upmu\)M [24]. In the same study, the inhibitory capacity of cynme was attributed to the stabilization effect of the compound on the secondary structure of BSA. Based on our findings we could only stipulate those different mechanisms of action are responsible for the antiglycative activity at extreme terpenoid concentrations.