[Effects of hydrocolloids on physical stability, rheological and sensory properties of milk-orange juice mixture]

ABSTRACT

One of the major defects in acidified milk-fruit juice mixtures is their physical instability due to low pH, low viscosity, and sedimentation of caseins. In the present study, the influence of some commercial and local gums on the stability, rheological, and sensory properties of milk-orange juice mixture was investigated. The effects of pectin, locust bean gum, guar gum, gum tragacanth, Persian gum, water-soluble fractions of gum tragacanth [tragacanthin] and Persian gum over a wide range of concentrations on the physical stability of milk-orange juice mixtures during storage at low temperature [4 °C, 30 days] were determined. Moreover, the stabilization mechanisms were studied using rheological [rotational and oscillatory tests], zeta potential measurements, and microstructural observations. Finally, sensory evaluation was made on the physically stabilized samples. Pectin, locust bean gum, guar gum, gum tragacanth, Persian gum, and water-soluble fractions of tragacanth and Persian gum effectively prevented phase separation for 30 days at concentrations of 0.5%, 0.5%, 0.4%, 0.3%, 2.2%, 0.175% and 1.0%, respectively. Furthermore, combinations of water-soluble fractions of gum tragacanth and Persian gum [ratios of 496 and 1981] at a concentration of 0.37% or 0.53% caused stabilization. The best fitted rheological models for the control [milk-orange juice mixture without hydrocolloids], the pectin-containing one, and rest of the samples were Bingham, Herschel-Bulkley, and Power law, respectively. In terms of sensory properties, the mixture stabilized with a combination of watersoluble fractions of gum tragacanth and Persian gum [0.53% w/w] achieved the highest scores by the taste panels [p<0.01]. Based on the findings of the present study, water-soluble fractions of gum tragacanth and Persian gum can be categorized as anionic hydrocolloids which are adsorbed on the surface of caseins which can prevent aggregation via steric and electrostatic repulsions by simulating a hairy layer. In addition, their insoluble fractions could promote physical stability of the mixtures due to making a gel-like network and increasing viscosity