Protection and delivery of mandarin (Citrus reticulata Blanco) peel extracts by encapsulation of whey protein concentrate nanoparticles

Abstract Flavonoids rich in citrus peels have poor stability and bioavailability, which limits their commercial applications. In present study, citrus peel extracts were obtained from four citrus types and their stability and antioxidant activity were investigated in terms of pH conditions. Then, the extracts were encapsulated and protected by whey protein concentrate nanoparticles (WPC NPs). The results showed that the degradation rate of extracts decreased with higher pH values. At pH 2–3, the antioxidant activity of extracts was relatively lower than that at pH 4–7. Fourier transform infrared spectroscopy results indicated that extracts were encapsulated by WPC NPs via hydrophobic interaction or H-bond. Encapsulation efficiency (EE) and loading efficiency (LE) of extracts in WPC NPs ranged from 14.4 ± 0.7% to 27.9 ± 0.9% and from 11.0 ± 0.6% to 18.6 ± 0.9%, respectively, depending on the citrus types. Transmission electron microscope showed that all nanoparticles had spherical morphology. WPC NPs controlled the release of encapsulated flavonoids and kept their antioxidant activity under in vitro simulated gastrointestinal conditions. After 4 h, DPPH• scavenging activity of extracts from Guangxi red orange in simulated intestinal fluids was 34.8 ± 1.5% and 66.4 ± 2.4%, respectively. The obtained knowledge will be helpful to develop food protein-based carriers for flavonoids.