Properties of subcritical water-hydrolyzed passion fruit (Passiflora edulis) pectin

Pectin extracted from passion fruit (Passiflora edulis) using diluted nitric acid was further hydrolyzed in subcritical water to reduce its molecular weight using a batch-type reactor at different temperatures (100, 120, 140, and 160 °C) and heating rates (3.5 and 7.0 °C/min). The subcritical water-hydrolyzed pectins were investigated in their properties including viscosity, molecular mass, degree of esterification, and water adsorption isotherm. The results demonstrated that under more severe conditions the hydrolyzed pectin had lower viscosity and showed different solution characteristics. The molecular mass of pectin also decreased with the severity of subcritical water hydrolysis. The pectins dissolved in distilled water had higher intrinsic viscosities and molecular masses than those dissolved in buffer solution. Degrees of esterification of the hydrolyzed pectins only slightly changed in range of 55-60%. In addition, the moisture adsorption isotherms of the hydrolyzed pectins were evaluated and could be interpreted well with Guggenheim-Anderson-de Boer (GAB) model. The reduction of molecular mass did not significantly affect the water adsorption characteristics of the pectin.

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