Effect of Thermal Treatment and Storage Conditions on the Physical and Sensory Properties of Grapefruit Juice

Physical parameters, such as particle size distribution, flow behavior, density, turbidity, and color, were measured and sensory evaluation was carried out to compare the properties of freshly squeezed grapefruit juice with those of juice that has been pasteurized by microwave or by following a conventional heating method. Samples were either frozen-stored or refrigerated. In general, the physical parameters of grapefruit juice were significantly affected by heat treatment, especially in the case of the conventional process. However, from a sensory point of view, pasteurized samples were similar to fresh ones. When frozen, turbidity, particle size distribution, density, flow behavior, and color were stable throughout the studied period, regardless of the pasteurization treatment. During refrigerated storage, the turbidity, particle size distribution, and consistency index decrease. This occurs in a more pronounced way in the case of juice which has not been submitted to a heating treatment, probably due to residual pectin methyl esterase activity. Furthermore, the association between the carboxyl groups of pectin chains and Ca²⁺ could be responsible for both the subsequent increase in the turbidity of the juice and also the decrease in its density. Throughout the period under study, the smallest color change was experienced by microwave-pasteurized juice. For these reasons, and also due to the reduction in the process time, microwave treatment can be recommended as a method for the pasteurization of grapefruit juice.