Abstract:Partially hydrolyzed guar gum (PHGG) with different relative molecular mass was prepared using controlled enzymatic hydrolysis technology, and the mass fraction of galactomannan in PHGG was calculated by ion chromatography. The molecular structure of PHGG was characterized by infrared spectroscopy, nuclear magnetic resonance and X-ray diffraction. Thermodynamic properties of PHGG were investigated by differential scanning calorimetry and thermogravimetric analysis. The results showed that the critical factors influencing the enzymatic hydrolysis of PHGG were substrate mass concentration, enzyme addition amount, and enzymatic hydrolysis time. By manipulating these factors, medium and high relative molecular mass PHGG (molar mass 8.92×105 g/mol), medium relative molecular mass PHGG (molar mass 5.07×105 g/mol) and low relative molecular mass PHGG (molar mass 0.62×105 g/mol) were prepared. Among them, the mass fraction of galactomannan in medium relative molecular mass alcohol-precipitated PHGG reached 84.09%. In PHGG with different relative molecular mass, the mass fraction ratio of mannose to galactose decreased, and the main chemical structure remained unchanged, but there were minor disruptions to the crystalline region structure, indicating that PHGG exhibited good thermal stability even at elevated temperatures. Overall, PHGG with different relative molecular mass, prepared by controlled enzymatic hydrolysis, has good stability in thermally processed foods, which provides a theoretical basis for the application of guar gum.
