Effect of enzyme-assisted acid extraction on citrus high-methoxyl pectin riched in RG-I: preparation, structure characterisation and physico-chemical properties

Summary The properties of pectin extracted by enzyme-assisted nitric acid (EAE-N) and pectin extracted by enzyme-assisted oxalic acid (EAE-O) were analysed and compared with pectin extracted by nitric acid (AE-N) and pectin extracted by oxalic acid (AE-O) systematically. The yield of pectin obtained by the enzyme-assisted acid method (23.73% ~ 25.60%) was significantly higher than that by acid extraction method (19.75% ~ 20.60%). Monosaccharide analyses demonstrated that the enzyme-assisted acid method was able to attain more branched rhamnogalacturonan I (RG-I) regions (36.59% ~ 42.06%) than using acid solely (31.01% ~ 34.58%). Fourier transform infrared spectroscopy (FT–IR) and nuclear magnetic resonance ( 1 H NMR) analyses indicated that there was no obvious difference in the characteristic structure of pectin. The atomic force microscopy (AFM) images revealed that EAE-N and EAE-O had more short side chains and cross-link compared with AE-N and AE-O. Thermogravimetric analysis (TGA) shows that EAE-N and EAE-O have good thermal stability. All pectin samples showed a shear-thinning fluid flow behaviour and an elastic gel-like behaviour. The results suggested that enzyme-assisted acid provided a viable alternative method for the extraction of pectin.