Determination of Pomegranate Juice Powder Properties Produced by a Pilot Plant Spray Dryer with a Two-Fluid Nozzle

Abstract

The ingredients in pomegranate juice are invert sugars, citric acid, and a small amount of malic acid, all of which have low glass transition temperatures. Due to this characteristic, the particles stick to the dryer wall upon their collision with it. In order to solve the stickiness problem, maltodextrin DE12 and silicon dioxide were used as carriers to reach a suitable drying condition. A cool chamber wall spray dryer was employed in order to decrease the probability of particles stickiness on the wall. A suitable two-fluid nozzle was selected based on the feed rate of the dryer. The nozzle accessories were built in order to assemble the nozzle on top of the spray dryer. Our investigation revealed that the addition of 3% silicon dioxide and 35% maltodextrin DE12 to pomegranate juice was the optimum amount for complete and successful drying of pomegranate juice. The powder particles were amorphous and did not have a crystalline structure, so the powder solubility was high. By increasing the air temperature of the dryer, the solubility of the pomegranate powder decreased. Increasing the feed rate from 0.16 to 0.3 L/min resulted in increasing solubility from 80 to 95%. By increasing the powder storage period, color specifications (L, a, and b) decreased. Increasing the inlet air temperature caused some reduction in color specifications and decreasing the feed rate led to decreasing color specifications. Adsorption isotherms of pomegranate powder samples had a sigmoid shape, which is typical of hygroscopic materials. Kuhn's and Iglesias and Chirife's models fitted very well with the experimental moisture content data.

Keywords:

• Color specification
• Moisture sorption isotherm
• Pomegranate juice powder
• Solubility
• Spray drying
• Stickiness
• Two-fluid nozzle

ACKNOWLEDGMENTS

The authors acknowledge the very valuable comments made by Professor Mujumdar that improved this article. They also thank Mr. Sayyahi for improving the quality of the English.