Abstract:The effects of four extraction methods such as hot acid-water extraction, enzymolysis, ultrasound, and enzymolysis-ultrasound treatment on the content and structural characteristics of the pectins from okra were studied, and the hot acid-water extraction and enzymolysis-ultrasound methods were found more effective. At the ratio of dried okra to the HCl aqueous solution (pH 3) of 1:20, the extraction at 70 ℃ for 1 h (the hot acid-water extraction method) or with addition of 3‰ of pectinase, and the digestion at 50 ℃ for 90 min followed by an ultrasound treatment at 200 W for 10 min (the enzymolysis-ultrasound method), led to a pectin content (as the galacturonic acid mass in okra) of 43.61 and 32.59 g/kg, respectively. All the pectins produced by the four extraction methods was in the pyranose configuration, but the ester bond in the pectins prepared via the hot acid-water extraction or the enzymolysis method tended to degrade, causing the infra-red adsorption peak at 1725 cm-1 to be weakened or even disappear. Whereas, the ultrasound methods or enzymolysis-ultrasound treatment promoted the breakage of the pectin molecular chain, making its average molecular weight decrease from 533 ku (by the hot acid-water method) to 420~467 ku and 319 ku. The results showed that the okra pectin prepared via the hot acid-water extraction method had a higher extraction yield and narrow molecular weight distribution with a flake-like and densely arranged appearance. The results of this research has laid the foundation for the preparation of high quality okra pectin.
