The effect of ultrasound and microencapsulation on characteristics of bioactive compounds of extracted from grape pomace Rashe Sardasht cultivar

In this research, the effects of ultrasound and microencapsulation on quantitative and qualitative characteristics of bioactive compounds extracted from red grape of Roshe Sardasht cultivar were investigated. Response surface method was used to study the effects of intensity and process time of ultrasound. Independent variables included ultrasound intensity at three levels 20, 60 and 100% and process time also at three levels 5, 10, and 15 minutes. The results showed that with increasing ultrasound intensity, total phenolic compounds, Ferric reducing activity of plasma (RRAP) and DPPH free radical-scavenging assay increased, but then decreased (p < 0.05). Also with increasing the process time, the RRAP and DPPH assay decreased (P <0.05). , Ultrasound intensity at level of 60% and process time at level of 8.78 minutes were determined as optimum conditions for extraction of aqueous grape pomace. In this condition, the extraction efficiency, total phenolic compounds, the RRAP and DPPH assay were obtained 14.99%, 55.56 mg/g, 1608.94 μmole Fe2+/L and 78.80% respectively.  Using the mixture of calcium alginate (0.1%) and maltodextrin with three concentration (5, 10 and 15%), the optimal extract of red grape pomace was microencapsulated by freeze drying method.  The results of statistical analysis of the data showed that encapsulation yield, moisture, bulk density and particle size of the microencapsulated powders increased (P <0.05) with increasing the concentration of wall materials. The glass transition temperature of all microcapsules was higher than the ambient temperature. Microencapsulated powder with 15% maltodextrin had the highest phenolic content, FRAP, DPPH assay and glass transition temperature.