Structural and rheological characterization of pectin from passion fruit (Passiflora edulis f. flavicarpa) peel extracted by high-speed shearing

In this study, the structural and rheological properties of pectin extracted by high-speed shearing (HSS–P) at 50 °C ultrapure water and conventional heating methods (CE50-P and CE90-P) from passion fruit ( Passiflora edulis f. flavicarpa ) peel were evaluated and compared. The HSS-P has loose, honeycomb-like surface morphology, lower molecular weight and higher polydispersity index compared to CE50-P and CE90-P. Monosaccharide composition indicated that HSS-P had more side chains, which were caused by its highly branched molecular structure, short main chains and a high molar ratio of RG-I in the molecular configuration. FTIR spectra showed that high-speed shearing led to a decrease in the linearity of the main chain of the pectin molecule. NMR spectra indicated that the molecular structure of HSS-P was a linear chain of homogalacturonan (HG) inserted into rhamnogalacturonan I (RG-I) possibly with arabinans and galactans as the principal side chains. Furthermore, the effects of pectin concentration, sucrose , CaCl 2 and pH on the rheological properties of different pectins were investigated. All pectin exhibited pseudoplastic fluid behavior at different environmental conditions. The HSS-P samples showed the greatest increase in the apparent viscosity and viscoelasticity in the presence of sucrose (60%–100%) and CaCl 2 (0.1–0.2 g/100 mL), pH changes and increased pectin concentration. The HSS-P was easily combined with the co-solutes and its viscoelasticity showed stronger stability under temperature changes. In conclusion, the high-speed shearing results in a unique molecular structure that contributed to the excellent rheological properties of pectin. Thus providing theoretical guidance for further application of high-speed shearing in extracting pectin.