The stability and phase behavior of konjac glucomannan-milk systems

Abstract

Konjac glucomannan (KGM) has potential to contribute functional properties to dairy products, but mixtures containing a sufficient amount of KGM and milk may show undesirable appearance because of incompatibility between the polymers. Thus, the effects of KGM solution (with concentration of 0.1, 0.5, 1.0, 1.5, 2.0 and 2.5%) on the stability and phase behavior of KGM-milk mixtures were investigated. The phase separation diagram showed that only a low level of KGM (0.2%, w/v) was sufficient to induce phase separation in KGM-milk mixtures. KGM and milk appear to undergo segregative phase separation. The turbidity of the supernatant after centrifugation, precipitation percentages, particle size and zeta potential of the mixtures were measured to investigate the stability of the systems. The stability of the KGM-milk mixtures was related to both the concentration of KGM solution and the percentage of milk. In general, the stability of the mixtures was enhanced with increase in milk percentage and decrease in concentration of KGM solution. Confocal laser scanning microscopy was carried out to study the microstructures of the KGM-milk mixtures. When the concentration of KGM solution was higher than 0.5%, aggregate structures could be observed in the mixtures, and with increase in milk percentage, coarsening of the structures occurred. The microstructures also indicated that some KGM-milk mixtures were in metastable state even though no phase separation was observed in the mixtures after standing for 4 h at 22 °C.