Temperature, concentration, and frequency dependent dielectric properties of pineapple juice relevant to its concentration by microwave energy

Microwave heating concentration of raspberry pulp: Evaluation of processing variables on concentration characteristics and quality attributes

Concentration of fruit pulp is an important unit operation in food processing and has a wide range of applications. In this study, the microwave heating concentration (MHC) of raspberry pulp at different microwave powers, heating times and sample masses were investigated considering concentration characteristics and quality attributes. The results showed that increasing microwave power/heating time or decreasing sample mass significantly decreased the moisture content but had no significant effect on the temperature of raspberry pulp, while these conditions resulted in loss of total anthocyanin content and deterioration of total color difference. LF-NMR and SEM results revealed that the changes in temperature and moisture content caused by MHC significantly affected the total anthocyanin content and total color difference of the final product. Microwave power of 800 W, heating time of 3 min and sample mass of 90 g are selected as suitable parameters for MHC of raspberry pulp. This study may provide guidance for the development of appropriate technology for MHC of berry pulp.