Chemical composition and some rheological properties of Mesona blumes gum.

摘要

Liangfen cao (Mesona blumes) is an annual herb used in China for medicinal purposes and in the preparation of teas or a jelly-like dessert. In this study, a gum was extracted from the leaves of liangfen cao and its physicochemical properties were analysed. The extraction yield was 29.36%. The crude gum contained 9.74% protein, 30.89% ash, 2.98% crude fibre and 42.19% total sugar (w/w). Monosaccharide components of the gum were mainly galactose, glucose, arabinose and uronic acid at molar ratios of 3.1:2.3:2.3:1.4. Minerals in the ash included 40.26 mg/g Na, 10.57 mg/g K, 1.42 mg/g Mg and 2.81 mg/g Ca. Mol/ wt. of the 2 fractions of the gum were 16 264 and 7372 Da, respectively. The intrinsic viscosity of the gum was 91.01 ml/g in distilled water at 25 degrees C. Its rheological properties were dependent on shear rate, gum concn., sugar content, temp., pH and salt content. The gum exhibited pseudoplastic behaviour with increases in shear rate. Apparent viscosity increased with increases in gum concn. and sugar addition and varied according to pH, with the highest viscosity being reached at pH 10.0 and the lowest at pH 6.0. Decreases in apparent viscosity were observed with increases in temp. The activation energy of 10% (w/w) gum was 17.58 kJ/mol. Apparent viscosity decreased with Na+ addition and also with addition of <1% Ca2+, whereas it increased with addition of >1% Ca2+.