Content area
Full text
Abstract
The influence of gellan gum on the flow behavior, particle size distribution, microstructure, surface tension and phase separation of a fat-free fermented dairy drink, as a suspension of protein particles, was studied. Proteins were present as large aggregated particles produced by mixing, diluting and homogenising a milk protein gel. In the absence of gellan, sedimentation occurred. Gellan caused a significant decrease in sedimentation but the phase behavior was altered and a syneresis process was observed. The size of the protein particles increased and their size distribution was affected by the gellan. Microstructure observations along with particle size analysis indicated that the associative phase behavior of gellan and caseins occurred due to aggregative interactions between gellan and protein particles. Also, flow behavior measurements indicated that a weak gel structure was created in the solution due to the presence of gellan gum. The temperature used for hydration of the hydrocolloid changed the shape and rheological behavior of the proteins and the consistency index of the gellan-free solution decreased as the temperature was increased. However, the opposite trend was observed at low concentration (0.01%) of gellan. At higher concentrations (0.03% and 0.05%), the consistency index was highest for the hydration temperature of 80°C.
Aust. J. Dairy Technol. 63, 87-92
Introduction
Technologically, the proteins of milk are its most important constituents. The acidification of milk, a widespread process, results in dissociation of micellar caseins. Lowering the pH reduces the repulsive forces and promotes hydrophobic interactions causing the casein micelles to coagulate (van Hooydonk et al. 1986). Low-fat fermented dairy drinks (such as Doogh) are produced by mixing, diluting and homogenising yogurt with water and salt. Such drinks can be described as acidified protein suspensions containing modified particles of milk proteins. Homogenisation disperses the gel, producing casein gel fragments (Laurent and Boulenguer 2003).
Stabilisers are important to control the physical properties such as texture, viscosity or mouthfeel, and are commonly used to prevent the phase separation phenomenon (Laurent and Boulenguer 2003; Koksoy and Kilic 2004). Hydrocolloids have been widely used as stabilisers to improve the textural properties of fermented milk products (Kravtchenko et al. 1995; Koksoy and Kilic 2004). Gellan gum, a bacterial polysaccharide, is a multi-functional hydrocolloid with actual and potential uses in a wide variety...