Microwave–vacuum drying of pomegranate arils ( Punica granatum L. cv. Hicaznar): Effect on quality and nutrient content

Abstract

In this study, microwave–vacuum drying of pomegranate arils (Punica granatum L. cv. Hicaznar) was investigated and the effect of microwave power and vacuum level on some quality and nutritional characteristics was determined by the response surface methodology. The drying experiments were conducted at three levels of microwave power (50, 100, and 150 W) and three levels of vacuum level (40, 75, and 110 mbar (abs)) employing a face-centered composite design. Dried arils were analyzed for some physical (hue angle, hardness, and shrinkage) and chemical (total phenolics, total monomeric anthocyanins, gallotannins, and antioxidant capacity) attributes. The results showed that the effect of vacuum level on the dried product characteristics was generally more significant than the microwave power. Second-order polynomial equations were suggested with generally high R2 values to predict the responses. The optimum drying conditions recommended by the response surface analyzer (150 W and 58 mbar (abs)) were validated experimentally. Practical applications Effect of microwave–vacuum drying process parameters (microwave power and pressure) on the nutritional value of pomegranate arils was investigated for the first time with this study. The optimum conditions within the studied ranges of parameters were identified by taking into account both quality attributes and bioactive compounds and experimentally validated. Temperature measurements with an infrared camera revealed that excessively high temperatures were reached toward the end of drying under the optimum conditions. This suggests that there is an opportunity to further reduce the quality and nutrient degradation if the temperature increase can be limited. Applying high power in the initial stage and low power in the final stage of drying were proposed as a potential approach to carry out. The study also showed that further investigation is needed to better understand the relationship between the temperature history during drying and the final product's quality attributes and nutritional value.