Intermittent microwave drying and heated air drying of fresh and isomaltulose (Palatinose) impregnated strawberry

Abstract

Fresh and osmotically pretreated (using a 35% isomaltulose solution) strawberries are highly perishable. This work aimed to dry them by intermittent microwave drying (IMD) and heated air drying (HAD) and evaluate their qualitative parameters. The sample temperature was monitored during IMD, adopting a setpoint temperature of 60 °C and continuous airflow, at room temperature. The HAD was performed by exposing the samples to air at 60 °C. IMD stood out for being faster (up to 64.91%) and consuming less energy (up to 73.16%) than HAD. During IMD, the magnetron was off for most of the time (up to 74.13%). The isomaltulose impregnation reduced drying rates in both methods, increasing drying time. Dried samples showed water activity (aw) within the safe range (aw<0.6). The impregnation process was carried out to a reduced shrinkage product besides the enrichment with isomaltulose. Non-pretreated strawberries had lower aw, hardness, and total color difference, and higher levels of bioactive compounds and antioxidants, especially with the IMD method. Retentions of up to 47.46%, 70.26%, and 81.18% of anthocyanins, phenolic compounds, and antioxidant capacity were obtained by IMD, respectively, concerning fresh strawberries. Therefore, IMD was an interesting alternative for fresh and impregnated with isomaltulose strawberries drying.