Cambios en la viscoelasticidad de pitahaya amarilla (Selenicereus megalanthus) liofilizada durante el almacenamiento a diferentes temperaturas

Background: Yellow pitahaya has nutritional qualities of great acceptance. Pitahaya freeze-dried is highly hygroscopic and to has a fragile texture. To define a critical point of quality during storage, (that considers the influence of the above weaknesses), to understand some physical properties of the constituent materials is necesary. The relaxation time and Deborah number (N_De) are determined through the relaxation test. They are the most important parameters in viscoelastic characterization of agricultural product. Objective: To evaluate the effect of storage temperature on viscoelastic properties of the freeze-dried pithaya, and to define the time of N_De critical value. Methods: Yellow pitahaya pulp was sliced to 40 mm of diameter and 5 mm of thickness. The slices were freeze dried using 5 Pa and 25°C. The samples were packed in low density bagsof polyamide-polythene, and these were stored to 30, 40, 50°C, and 70% HR. Every week, relaxation tests were performed (8% strain, test 600 s and 200 mm / min compression rate). The data were adjusted to the model of Maxwell of degree two. To determinate the relaxation time and N_De, A 2-way completely randomized design was used. Results: The increase of the temperature presented a significant effect in the diminution of the relaxation time and therefore in the N_De. All samples showed a behavior like a viscoelastic liquid which increased with storage time. The critical conditions on the viscoelastic properties were measured in the flexion point of the N_De. The flexion point was observed at 4 and 24 days of storage, 50 and 40 °C respectively. Conclusions: The changes in the viscoelastic behavior indicate the presence of two phases in the structure of freeze-dried pitahaya. The pitahaya has a highest physical stability when storage temperature 30°C is used.