Abstract: To enhance the color discernibility and stability of mulberry anthocyanins (MA), this study investigated the delivery efficacy of soy protein isolate (SPI) and its self-assembled fibrillated form, soy protein isolate fibrils (SPF), as nanocarriers for MA. The results demonstrated that MA was mainly loaded on the hydrophobic sites of SPI and SPF through hydrogen bonding and hydrophobic interactions, resulting in the formation of stable nanocomplexes. Fibrillation treatment significantly improved the loading efficiency (EE) of soy protein for MA (96.34% vs. 61.25%) and enhanced the color stability and naked-eye discernibility of MA. Compared with free MA, the color change of MA-loaded SPF increased from Grades 3 to 5 over the pH range of 2–8, indicating significantly improved visual discriminability (P < 0.05). Simultaneously, its thermal stability was enhanced by 32.90%, and the degradation rate of anthocyanins after 45 days of storage at 25 ℃ was decreased by 44.70%. Additionally, the color stability of MA was positively correlated with storage temperature. At 4 ℃, the degradation rate constant (k) of MA was reduced by 68.63% compared with that at 25 ℃, and the half-life (t1/2) was extended by 3.19 times. After loading onto SPI and SPF, the stability of MA was enhanced. The k values of the MA-SPI and MA-SPF complexes were only 75.00% and 41.25% of that of free MA, and the t1/2 values were 1.33 and 2.42 times higher than that of free MA, respectively. In conclusion, SPF serves as an excellent carrier for improving the color discernibility and stability of MA. The SPF-MA nanocomplex is expected to be applied as an excellent pH sensitive indicator in intelligent food packaging films.

Key words: soy protein; anthocyanins; self-assembly fibrillation; nano-delivery; indicator