3.5.3. DSC

Thermal properties of individual components and composite nanoparticles were studied via DSC. As shown in (Figure 4D), the embedded thermograms of 7,8-DHF displayed a narrow and sharp peak at 246.24 ◦C. This temperature peak was probably caused by the melting of 7,8-DHF crystals [46]. Furthermore, the representative endothermal peak of CMC and ALG was at approximately 96.33 and 113.33◦C, respectively. These findings confirmed that ALG had a higher thermostability than CMC because of its specific carbohydrate structure. However, the endothermic peak of S/Z was at approximately 60.33 ◦C, showing a low thermostability. After 7,8-DHF was encapsulated, no endothermic peaks of 7,8-DHF were found in DHF-S/Z, DHF-CMC/S/Z, and DHF-ALG/S/Z. The lack of endothermic peaks verified that 7,8-DHF was defined as an amorphous form rather than a crystalline form. Similar literature has reported in recent study on curcumin [47] and hyperoside [48]. In addition, the endothermic peak of DHF-S/Z nanoparticles was increased from 60.33 ◦C to 64.66 ◦C compared to S/Z. This increase in melting temperatures could be attributed to intermolecular interactions among 7,8-DHF, zein and sophorolipids [29]. Most importantly, after adding CMC and ALG, the endothermic peak of DHF-CMC/S/Z and DHF-ALG/S/Z rose to 70.01 and 76.33 ◦C in comparison to DHF-S/Z, respectively. The higher endothermic peak of DHF-CMC/S/Z and DHF-ALG/S/Z manifested that they possessed better thermal stability than DHF-S/Z. This new peak might be the result of CMC and ALG interaction enhancements for hydrophobic, electrostatic, or hydrogen bond interactions among different components in nanoparticles, which ultimately leads to a higher endothermic peak temperature.
