Investigation on the Ultrasonic Nozzle Parameters Affecting Physical Properties of Tomato Powder

Introduction Preserving food products has been much regarded due to the population growth and food scarcity. Drying food is one of the methods of preventing the waste of food products. Spray drying for which products that are initially in the liquid phase is the most suitable method of drying the moisture. In this method, the solution is turned into particles and droplets via mechanism and synchronous collision with the hot air that enters the drying case. Moisture content is one important aspect of the food powder which is associated with an increase of adhesion. The particles size is an important feature of the product due to its effect on the product appearance, solubility, and powder fluidity. Materials and Methods In this study for producing tomato powder, 10 kg of tomato available in the market which was not good and did not have a good appearance but suitable for juicing was supplied. A meat grinder was used for juicing. Tomato juice was filtered to become pure. Tomato juice was put in the 1.5 lit bottles and was kept in the refrigerator for experiments. To spray the tomato juice, an ultrasonic nozzle with 20 kHz frequency was used. Energy sources (TOPSONICS 400W, 20 kHz) was used to provide the atomizer power with adjustable power from 0 to 400 W. In this study a hot-plate spray dryer was used to change the tomato juice into powder. An oven was used to measure the tomato powder moisture content. 0.5 g of tomato powder was weighed and was put in the oven with 70°C for 24 hours to be dried to lose moisture. To measure the size of the particles the analysis of two-dimensional images was used. The photos were taken with optical microscope OLYMPUS CX21‏equipped with a digital camera- SONY DSC-HX1. To illustrate the photos, the Digimizer software was applied. SAS software was used for further statistical analysis. Results and Discussion Analysis of variance results indicated that the effect of the studied parameters was significant on the average of the particles size except for dryer plates temperature (p < 0.01) and on the moisture content (p < 0.01). The mean comparison of these effects was done via LSD method. The effect of the temperature on the particle size was insignificant. The reason for this result is due to particles size that is an external parameter and is much related to the ultrasonic nozzle features. The reciprocal dual the flow rate in the generator power on the particles size was significant (p < 0.05). The results analysis of the mean comparison indicated that particle size average of flow rate 13 ml min-1 is smaller than the flow rate 15 and 17 ml min-1. The least particles size mean is related to the samples which have been produced with 25 watts power as it has the significant difference with 37.5 and 50 watts. The least particle size average produced with 25 watts power and the flow rate of 13 ml min-1 and 13.8 micrometers was obtained. Results of the means comparison indicated that the moisture content of the samples with 25 watts of power produced less moisture content which was significant (p < 0.01). Moisture content is strongly related to the particle size and it makes the water transfer difficult and moisture content of the samples which is produced in this power is less. Thus, when the sonication power increases, the moisture content increases too. The samples which were produced in flow rate 13 ml min-1 showed less moisture content than other flow rate levels. Results showed increasing temperature caused decreasing moisture content of the samples. This is because the exchange heat between the powders and the environment has been increased and more moisture was lost therefore, the moisture content decreases. Conclusions The results of this study indicated that the parameters such as ultrasoud power, flow rate, and the dryer plates temperature on the physical properties of tomato powder like the particles size average and moisture content were significant (p < 0.01) except for dryer plates temperature on the particle size. The results indicated that the particles size average in the samples with the flow rate 13 ml.min-1 and 25 watts’ power has been produced which has a significant difference (p < 0.01). Likewise, the least moisture content of the samples with temperature 150°C of the dryer plates and 25 watts power and flow rate 13 mL min-1 was obtained with a significant difference. It can generally be claimed that the tomato powder which has been produced with 25 watts’ power sonication and flow rate 13 ml.min-1 has the best quality regarding the size and moisture content. Considering the importance of drying the food products which are in a liquid form the effects of these parameters on the value preservation and qualitative nutritional properties can be investigated within the processes of drying, and the results can be applied before drying.