Reconstitution potentials and moisture sorption isotherms of selected freeze dried Nigerian soups

Selected Nigerian soups were freeze dried with the aim of establishing their storage stabilities and reconstitution potentials. Freshly prepared soups were freeze-dried under vacuum for 12–14 hr. Sorption isotherms were determined at 27 °C using gravimetric method at water activities (aw) of 0.1 − 0.8. Reconstitution potentials were determined at 30 and 100 °C using gravimetric methods. Data were analyzed using SPSS for the best fit model equations (Peleg, GAB, Oswin, and Langmuir). The rehydration ratios of the freeze dried soups ranged from 1.00 to 9.11 g absorbed water/g dry matter. Soups were optimally reconstituted at 30 °C for 30 min and at 100 °C for 5 min. The equilibrium moisture contents of freeze dried soups ranged from 8.84 to 27.50%. The GAB model was the best estimator for predicting the monolayer moisture contents of the soups, which ranged from 7.87 to 9.82% (dry basis), and were within the acceptable limit of 10% dry basis for good storage stability. Practical applications Traditionally, soups are generally reheated several times in the day to prevent spoilage, while in modern homes, most soups are kept under frozen condition to preserve them and to avoid nutritional loses which can arise as a result of periodical heating once used, but these methods of soup preservation had been shown to lead to losses of nutrients. Development of shelf stable soups that requires little energy to preserve them for considerable length of time is desirable. Freeze drying (FD) is a gentle technique, which retains the nutritional and sensory properties of food products and their final products can be reconstituted easily by simple addition of liquid. The moisture sorption isotherms, which describe water activity food products are of special interest in the design of Nigerian soups FD process and are also required for the prediction of soups storage stability, shelf life, and calculation of drying time.