No abstract

Red-flesh navel orange "Cara Cara" is attractive for customers with its bright red color and has been widely planted in China. In this study, phenolic compounds in "Cara Cara" harvested from five different regions were identified and quantified by ultra high performance liquid chromatography (UPLC) coupled with Quadrupole-Time of Flight-Electrospray ionization-mass spectrometry (Q-TOF-ESI-MS n). Their antioxidant abilities were evaluated by 2,2diphenyl-1-picrylhydrazyl (DPPH) and oxygen radical absorption capacity (ORAC) assays. Twenty phenolics were detected in crude extraction, with hesperidin (29.36-44.06%) as the dominant component, followed by narirutin (13.44-17.03%) and apigenin-6,8-di-C-glucoside (8.28-12.38%). No free phenolic acid was found in crude extracts and three free phenolic acids (FPA) were determined through alkaline hydrolysis, wherein ferulic acid (86.22-90.49%) existed dominantly. Fujian "Cara Cara" showed the highest total phenolic index (TPI) and total flavonoid index (TFI) values, while the lowest TPI and TFI values were detect in Chongqing "Cara Cara". DPPH value showed positive correlation with TPC value (r 2 = 0.921), while no correlation was found between ORAC and phenolic contents.

The effects of ultrasonic-assisted extraction (UAE, 200 W, 20 min) on the yield and physicochemical properties of different walnut proteins (WNPs, including albumin, globulin, and glutelin) were investigated. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis indicated that UAE could result in protein molecular fragmentation of albumin, but did not affect the major bands of globulin and glutelin. The CD spectra demonstrated that different WNPs obtained by UAE had different changes in their secondary structure. Under UAE, there was an increase in surface hydrophobicity (H0) of albumin and gluten and no change in the fluorescence intensity, while decreases were observed in the H0 and fluorescence intensity of globulin; and the contents of total and surface free sulfhydryl in albumin dramatically decreased. UAE reduced the size of the particles and the dimension of the microstructures in albumin and gluten, indicating that ultrasound could unfold protein aggregates. In addition, UAE increased the solubility, emulsifying activity (EA), foaming capacity (FC), and foam stability (FS) of the obtained proteins. The above results indicate that ultrasound extraction is a promising approach to improve the extraction yield and properties of walnut proteins.