## 3 Results
### Non-Specific Markers of Maillard Reaction
#### 3.1.2 Assessment of the Maillard Reaction Evolution by Ultraviolet-Visible  
(UV-Vis) Spectroscopy  
The measurement of the absorbance in specific wavelengths associated with different stages of the Maillard reactions, however, highlighted differences among the terpenoid compounds behavior. As shown in Figure 2, the terpenoid compounds tested have different effects on the absorbance measurements at 280 nm, both among them and in different incubation conditions. In 80 \({}^{\circ}\)C systems, aniseed oil (median--77.7%) and thymol (median--80.5%) were associated with 100% lower concentrations of early glycation products in 0.1 M glucose in the first hour of incubation (Supplementary Table S1) which were reduced over time. Linalool (median--39.6%) showed a constant association with reduced levels of early glycation products throughout the 3 h of incubation. In 1 M glucose at 80 \({}^{\circ}\)C, aniseed oil (median--9.35%) and thymol (median--5.35%) showed reduced inhibitory activity, if  
Figure 1: The effect of terpenoid compounds on color development in heated glucose/lysine solutions at 0.1 M and 1 M glucose at pH 7.2 and (**A**) 80 \({}^{\circ}\)C and (**B**) 100 \({}^{\circ}\)C. Symbols (\({}^{\star}\), \({}^{\circ}\)) outside the boxplots indicate outliers. any, while linalool (median 10.25%) was associated with promotion of the early glycation product formation as early as the first hour of incubation (Supplementary Table S1). For incubations at 100 \({}^{\circ}\)C the effects of terpenoid compounds on early glycation products formation indicated almost no effect at 1 M glucose (for aniseed median--1.0%, for thymol median--0.15% and for linalool median--0.6%) whereas at 0.1 M glucose, thymol (median--8.7%) and aniseed oil (median--1.8%) showed small inhibitory activity. In addition, the inhibitory activity of aniseed oil and thymol was seen after 3 h of incubation at all glucose concentration (Supplementary Table S1). At 100 \({}^{\circ}\)C, all systems showed a much smaller variability in absorbance values at 280 nm compared to the incubations at 80 \({}^{\circ}\)C. At 80 \({}^{\circ}\)C and low glucose concentration the variability was larger as indicated by the interquartile range which was more pronounced for aniseed oil and thymol than linalool. Interestingly at 80 \({}^{\circ}\)C and 0.1 M glucose the net effect of all terpenoid compounds was towards reduced absorbance (inhibitory effect) (Figure 2). The RSM model confirmed that, the choice of terpenoid compound (\(p\) = 0.001), glucose concentration (\(p\) < 0.001), temperature (\(p\) < 0.001) and time (\(p\) = 0.02) were associated with different effects on absorbance at 280 nm. Significant effects were also seen for the interactions between glucose concentration and temperature (\(p\) < 0.001), temperature and terpenoid compound (\(p\) = 0.004), glucose concentration and terpenoid compound concentration (\(p\) = 0.004) and terpenoid compound and its concentration (\(p\) = 0.046). At both temperatures, in low glucose levels (0.1 M) higher terpenoid compound concentrations were associated with reduced inhibitory capacity overtime, while the opposite effect was seen in high glucose levels (1 M) (Figure 3). These were specifically true for linalool and aniseed oil. On the contrary overtime higher thymol concentrations were associated with higher inhibitory capacity in all temperatures and glucose levels (data not shown). In terms of their effect on intermediate glycation products measured at 360 nm unlike what was seen at 280 nm, all systems showed a smaller variability in absorbance measurements at 360 nm at 80 \({}^{\circ}\)C compared to 100 \({}^{\circ}\)C, with the greatest variability (interquartile ranges) seen at 100 \({}^{\circ}\)C and 1 M glucose (Figure 4). Aniseed oil and thymol showed 8-14% inhibitory capacity on average at 80 \({}^{\circ}\)C (Supplementary Table S2), with greater inhibition in lower glucose concentration (Figure 4A).