Moisture Adsorption Characteristics of Freeze-Dried Composite Tropical Fruit Purees and Application to Shelf Life Prediction in Flexible Packages

The moisture adsorption characteristics of freeze-dried watermelon, orange, and mango composite fruit purees were determined using the standard gravimetric method at 20, 25, 30, 40 and 50°C respectively over a water activity range of 0.11-0.95 and the data analyzed using the BET, GAB and Oswin sorption models. The data obtained and moisture permeability characteristics of commercial aluminium pouches, low density polyethylene (LDPE), Melinex 813, and Propafilm C flexible materials were used for shelf life prediction at various ambient storage temperatures. Sorption data exhibited type III isotherms, typical of foods rich in soluble components. The GAB model provided the best fit for the experimental data compared to the other tested models. BET monolayer moisture contents (4.72 – 8.80 g H2O/100g solids) decreased with increasing temperature indicating reduced water binding sites at higher temperatures. Net isosteric heats (0.00012 to 0.0052 kJ/mol) decreased while the entropy of adsorption (-0.1343 to -0.0312 kJ/mol.oC) increased with moisture content. The predicted shelf life was highest for Aluminum pouch followed by, Propafilm C, LDPE and Melinex 813 in that order. This study provides valuable insights for optimizing storage conditions and packaging selection for freeze-dried composite fruit products, with practical implications for commercial applications in the food industry.