Synergistic rheological behaviour of mixed HM/LM pectin gels

The objective of this study was to investigate the rheological behaviour of mixed gels of high methoxyl (HM) and low methoxyl (LM) pectins with the purpose of designing gels with reduced sucrose content but unaltered rheological properties. The gelation behaviour of mixed HM/LM pectin gels was compared to that of HM and LM pectin gels in the presence of 30%, 45% and 60% sucrose. The gels were investigated in the presence of 0.1% CaCl2·2H2O and pH 3.5, conditions that favour the gel formation of both HM and LM pectins. Strong synergistic effects occurred in the rheological behaviour for three mixed 0.8% HM/0.4% LM pectin gels under conditions where LM pectin formed microgels instead of coherent gels. The addition of LM pectin strongly increased the storage modulus in mixed HM/LM pectin gels based on 60% and 45% sucrose compared to HM pectin gels of the same sucrose concentration. The kinetic behaviour of the mixed HM/LM pectin gels during gel formation varied depending on the kinetic behaviour of the HM pectins differing in degrees of blockiness. Transmission electron microscopy (TEM) showed that the gel microstructure of the mixed gel with 60% sucrose was inhomogeneous. The addition of HM pectin in mixed gels with only 30% sucrose increased the storage modulus two to five times compared to that of 0.4% LM pectin gels under the same conditions. The phase angle for the mixed gel with 30% sucrose was also higher than for the corresponding 0.4% LM pectin gel.