No abstract

Osmotic dehydration is an intermediate stage in drying processes in which water is extracted using a hypertonic solution, but it is a slow process, especially in hard foods such as coconut. Microwaves use an electromagnetic field which can raise the temperature in the depth of samples as a result of friction, which facilitates mass transfer due to molecular expansion and increased porosity. The aim of this study was to investigate the effect of a microwave pre-treatment on the quality of the osmotic drying of coconut and optimize the whole process by response surface methodology (RSM). The independent variables were the microwave power (X1), the sugar solution concentration (X2) and the duration of the process (X3.). The responses (dependent variables) were the moisture content difference (MD), weight reduction (WR), water loss (WL) and solids gain (SG). The results showed that the linear terms of X2and X3 had significant effects on all the dependent variables but the linear term of X1 only significantly affected WL, SG and WR (p< 0.05). The interaction of X1X2 significantly affected WL and WR and the interaction of X2X3 significantly affected all the dependent variables, but the interaction of X1X3 only significantly affected MD (p < 0.05). On the other hand, X22 significantly affected SG and WR (p < 0.05). The two-factor model (2FI) was able to express the changes in MD and WL, but only the quadratic model adequately fitted SG and WR, the determination coefficients being 0.98, 0.99, 0.99 and 0.99 respectively. Finally, the optimized condition was obtained with a power of 900 watts, concentration of 47.80% and duration of 5 hours.

In this investigation, four biopolymers were mixed with Maltodextrin (MDX) and used as emulsion stabilizers and wall materials to encapsulate lycopene natural pigment. These biopolymers were whey protein concentrate (WPC), soy protein concentrate (SPC), Gelatin (GEL) and Arabic Gum (AG). Some parameters such as droplet size, viscosity and creaming index of emulsions were investigated and then, to produce lycopene microcapsules, emulsions were transferred to spray dryer to be dried. Inlet air temperature (150 and 200 °C) and pressure of nozzle (1 and 2 bar) were considered as drying variables. Results showed that WPC emulsions had the smallest droplet size and lowest viscosity among other samples. The highest Encapsulation Efficiency (EE) belonged to WPC emulsions which were dried at 150 °C and 2 bar, also these samples had the highest bulk density. Results showed that samples which were atomized by using 2bar pressure at nozzle during spray drying, needed a significant longer time to be rehydrated (P<0.05).

In this study an artificial neural network, multi-layer perceptron (MLP), and Peleg's mathematical model were used to find the best model for the prediction of rehydration kinetic of air dried potato cubes. For rehydration, samples were immersed in water during different periods of time and temperatures (23±2 °C and 100±2 °C). Rehydration kinetic was monitored by measuring samples weights at regular intervals. In MLP neural network, water temperature, soaking time and potato varieties (Agria, Satina and Kenebek) were used as input parameters and the moisture content was used as output parameter. The results were compared with experimental data. Both Peleg's model and MLP had a proper correlation coefficient for each variety and water temperature but the correlation coefficient of the generalized Peleg's model was lower than of MLP.

The Peleg model was used to determine effect of drying conditions and rehydration water temperature on kinetic of moisture content and rehydration ration changes of celery. Celery cubes (1×1×1 cm) were dried at 65ºC in hot air oven. Samples were rehydrated by immersion in water during different periods of time and temperatures (25±2ºC and 100±2ºC). Rehydration kinetic was monitored by measuring samples' weights at regular intervals. Results showed that the highest final moisture content which was observed belonged to the samples which were dried at 70 °C and reydrated at 25°C water temperature, also, dried celeries which were rehydrated at a water temperature of 25°C, had higher levels of RR as a function of physical properties. The Peleg’s e constant (K1), decreased significantly while water temperature increased and in case of the Peleg capacity constant (K2), it increased slightly while water temperature increased. Decreasing of K2 values is a sign of more water absorption capacity. Finally, it was observed that the predicted and experimental values had a good correlation which indicates that the Peleg model is adequate to describe rehydration kinetics of celery cubes.