## 3 Results and Discussions
### Thermogravimetric Analysis (TGA)  
Thermogravimetric analysis (TGA) was performed to confirm complex formation. This was achieved by determining thermal stabilities based on mass reduction as a function of increased temperature. The thermograms of GRE, \(\beta\)-GRE, and \(\beta\)-CD are illustrated in Figure 4. The thermal degradation process of pure \(\beta\)-CD underwent two major stages, with peaks appearing at approximately between 100 and 120 \({}^{\circ}\)C and 340 and 375 \({}^{\circ}\)C. The weight loss of 11.0% occurred in the first stage, a phenomenon associated with the evaporation of water absorbed on the surface of \(\beta\)-CD, as well as the water contained in the cavities. [PERSON] et al. [22] and [PERSON] et al. [23] reported initial \(\beta\)-CD weight losses of 13% in the same region of 112 and 100 \({}^{\circ}\)C, respectively. Both these authors ascribed the weight loss to water evaporation from the \(\beta\)-CD cavities; [PERSON] et al. [23] also mentioned the evaporation of water adsorbed on the surface of the \(\beta\)-CD molecule. In the second stage, further weight loss in \(\beta\)-CD of 67% was observed from 340 to 375 \({}^{\circ}\)C, which was due to the main thermal decomposition of \(\beta\)-CD. Once more, the main degradation of \(\beta\)-CD resulting in 76% weight loss was observed at 305 and 400 \({}^{\circ}\)C [22; 23]. The result of this study lies within the ranges observed by these two authors. Regarding the GRE samples, the initial sample weight was slightly higher, which can be linked to the hygroscopicity of the sample (based on visual observation). An initial weight loss of 2%, although not significant, was observed from regions as low as 40-120 \({}^{\circ}\)C. [PERSON] et al. [18] reported similar results for aqueous extracts of green rooibos as a loss in surface moisture. The main degradation of GRE resulted in a 40% loss in weight and was seen from 180 \({}^{\circ}\)C, followed by a gradual decrease in weight as the temperature increased to 400 \({}^{\circ}\)C. This degradation pattern is synonymous with plant extract polyphenols, in particular, green rooibos. [PERSON] et al. [22] reported the degradation of Mulberry polyphenols at 138-600 \({}^{\circ}\)C, resulting in 59% mass loss. The second region of weight loss for green tea occurred at around 130 \({}^{\circ}\)C with 10-14% weight loss, which continued up to 900 \({}^{\circ}\)C.  
The broad temperature range reported for crude plant extract degradation may be due to the versatile mixture of compounds, as the decomposition of resistant aromatic structures requires higher temperatures. The thermogram of \(\beta\)-GRE possessed characteristics of both GRE and \(\beta\)-CD; [PERSON] et al. [22] referred to this phenomenon as superposition. For instance, the initial phases resembled that of \(\beta\)-CD, where approximately 4% weight loss was seen at  
Figure 3: Bar graph illustrating the mean and standard deviation (error bars) for the colour change in the GRE—green rooibos extract and \(\beta\)-GRE—betacyclodextrin-encapsulated green rooibos extract during storage (21 days at 25 \({}^{\circ}\)C) at different water activities (a\({}_{w}\)), as evaluated through the chroma (C*) value. The comparison was performed between each water activity value for GRE and \(\beta\)-GRE. 60-100 \({}^{\circ}\)C, albeit lower for the former. The structural differences between \(\beta\)-GRE and \(\beta\)-CD lie in the fact that the latter's truncated cavity was not occupied, therefore allowing more binding of water. The second-stage degradation for \(\beta\)-GRE was observed at 260 \({}^{\circ}\)C and resulted in a weight loss of 46%. [PERSON] et al. (2018) reported that green rooibos encapsulated with inulin and maltodextrin started to degrade at 190 and 220 \({}^{\circ}\)C, respectively. These results show that the thermal stability of GRE was improved by interaction with \(\beta\)-CD, thus confirming that complexation took place.