Stabilization of black rice anthocyanins by self-assembled silk fibroin nanofibrils: Morphology, spectroscopy and thermal protection

Abstract

Nanofibrillated proteins possess diverse techno-functional properties are considered as matrices for stabilizing bioactive agents. In this study, the morphology and interaction of silk fibroin nanofibrils (SNFs) with black rice anthocyanins (ACN) were investigated through multiple microscopy and spectroscopic techniques. The impact of SNFs on the thermal stability of ACN was analyzed. Nanofibrils with diameter less than 20 nm were self-assembled from silk fibroin (SF) lyophilized powder solution at pH 6.0. A static model occurred in the interactions of cyanidin-3-O-glucoside (C3G, the major anthocyanin in black rice) with SF and SNFs. C3G binding altered the secondary structures of SF and SNFs. Moreover, the thermal retention rates of ACN combined with SF and SNFs were significantly (P < 0.05) higher than that of ACN alone followed the order of SNFs-ACN (60.87%) > SF-ACN (57.47%) > ACN alone (40.33%) after heating 120 min at 80 °C and SNFs-ACN (50.42%) > SF-ACN (32.81%) > ACN alone (23.64%) after heating 120 min at 90 °C. The half-life (t1/2) of thermal degradation of ACN was elongated in SNFs-ACN complex compared with that in SF-ACN complex. These results showed that SNFs effectively binding with C3G and exhibit better protective effects on the thermal stability of ACN than SF.