Optimization of ultrasound‐assisted osmotic dehydration of pomegranate seeds ( Punica granatum L.) using response surface methodology

Abstract

The main objective was to investigate the effect of ultrasound‐assisted osmotic dehydration (UOD) pretreatment on the dehydration kinetics and the physicochemical properties of pomegranate seeds using a response surface methodology, in order to optimize the process. Quality attributes of seeds were estimated through the assessment of physical and thermal characteristics. Results showed a good correlation of experimental values with the model. The optimum conditions used for UOD and osmotic dehydration (OD) were found to be 240 min, 60°Brix, 41°C, and 240 min, 29°Brix, 50°C, respectively. UOD pretreatment led to a higher mass transfer rate than the OD process. UOD‐treated seeds reached the optimal moisture content (10%) and water activity (aw < 0.650) faster than both fresh seeds and OD‐treated seeds. Differential scanning calorimetry revealed that UOD pretreatment induced the loss of an important amount of water. X‐ray diffraction analysis showed that ultrasound pretreatment did not affect the amorphous characteristics of pomegranate seed powder during drying. Practical applications Ultrasound‐assisted osmotic dehydration could be a novel approach for food preservation and processing, due to the combined effect of osmotic pressure gradient and ultrasonic effect on the surface of the food material. Ultrasound pretreatment can be implemented as an alternative pretreatment to reduce drying time and, consequently, processing costs. Ultrasound‐assisted osmotic dehydration is gradually gaining attention as a pretreatment method due to its advantages which include preservation of antioxidant properties and bioactive compounds. This study provides information on the application of response surface methodology for the optimization of ultrasound‐assisted osmotic dehydration of pomegranate seeds.

Current Applications of Ultrasound in Fruit and Vegetables Osmotic Dehydration Processes

“…Due to sonication, the OD was more intense, hence the loss of turgor pressure and shrinkage of the protoplast along with its separation from the cell wall [113] probably resulted in a decrease in the maximum compression force and an increase of work required to deform the sample. On the contrary, the hardness was not significantly changed in UOD pomegranate arils [24] and pomegranate seeds [100] when compared with OD. The studies carried out on kiwifruits [108] revealed that US pretreatment significantly enhanced the firmness after 120 min of OD, resulting in similar value for samples treated by 20 and 30 min of US+OD than for fresh kiwifruit.…”

“…However, for osmotic solution with a concentration of 70% NaCl and US pretreatment in water, diffusivity increased up to 130%. In addition, Bchir et al [100] noticed higher mass transfer rate for UOD of pomegranate seeds in comparison to OD process. On the basis of surface methodology response, the optimum conditions for a higher mass transfer rate were established at 240 min, 60 • Brix and 41 • C for UOD and 240 min, 29 • Brix and 50 • C for OD process.…”

“…Amami et al [114] observed a higher shrinkage and rehydration ratio of UOD strawberries than dried without pretreatment. On the other hand, sometimes the UOD caused such damage to the structure that did not allow absorbing the same water content as in the case of dried sample without treatment [100].…”

Effect of Osmotic Dehydration Pretreatment on the Drying Characteristics and Quality Properties of Semi-Dried (Intermediate) Kumquat (Citrus japonica) Slices by Vacuum Dryer

“…Our results are close to those observed by Sakooei-Vayghan et al [ 14 ] where OD pretreatment before hot-air drying for 30 and 45 min decreased drying time to 8 and 7 h, respectively for apricot cubes. Moreover, Bchir et al [ 42 ] emphasized that ultrasound-assisted OD reduced the drying time of pomegranate seeds by over 40%. These results showed parallelism with our research.…”

Application of ultrasound in combination with other technologies in food processing: A review

“…Recently, Bchir et al [20] reported the effect of ultrasound assisted osmotic dehydration on the pomegranate seeds. The result showed that the ultrasound pretreatment involves a reduction in the osmotic solution temperature and favoring a reduction in the process cost.…”