Rheological Characteristics of Fresh and Freeze-Dried Reconstituted Juices Obtained from Some Non-Traditional Fruits

Abstract

This study aimed to evaluate the rheological characteristics of fresh and reconstituted juices obtained from acerola, annona and cactus fruits at 25°C. The relationship between the applied shear rates and the corresponding shear stress response was not linear indicating the non-Newtonian behavior of the juices obtained from acerola, annona, and cactus fruits. The magnitude of the obtained shear stress values varied according to the type of fruit and its composition. Maximum shear stress responses at shear rate of 145.8s-1were122.97 and 59.87 Dynes/cm2for juices obtained from acerola and annona, respectively. On other side, the juices of yellow and red cactus fruit recorded lower shear stress values at the same shear rate (145. 8s-1), being 27.68 and 30.75 Dynes/cm2, respectively. According to power law equation, the n-value (behavior index) of tested juices was in the range of 0.222 to 0.5203 indicating the pseudoplastic behavior of the tested fruit juices. The highest values of consistency coefficient (K-value) was recorded for acerola juice (14.70 Dynes.sn /cm2), while the lowest values was recorded for the enzyme treatment of red cactus juice (4.766 Dynes.sn /cm2). The highest values of R2 were recorded for enzyme treated yellow cactus juice (0.998), while the lowest values were recorded for annona juice (0.868).The rheological parameters of the reconstituted freeze dried juices showed that the n-values were in the range of 0.562 to 0.695, being higher than their corresponding n-values of the fresh juices. The lowest values were recorded for red cactus reconstituted juice. The highest values of R2 were recorded for yellow cactus juice (0.991), while the lowest values were recorded for reconstituted freeze-dried red cactus juice (0.974). The highest values of consistency coefficient (K-value) of the reconstituted juices were recorded for yellow cactus (2.733 Dynes.sn /cm2), while the lowest values were recorded for Annona (1.030 Dynes.sn /cm2).