Browning and Moisture Sorption Characteristics of Rubus coreanus Prepared by Different Drying Methods

Browning and Moisture Sorption Characteristics of Rubus coreanus Prepared by Different Drying Methods

The effects of drying methods on the browning and moisture sorption characteristics of Rubus coreanus were studied. Fruits were steamed for 5 min at 100℃, dried by sun drying, infrared drying, or freeze drying, and powdered to a size of 20 mesh. Color values were measured and equilibrium moisture contents (EMC) were determined at 20℃, over a range of water activity (aw) from 0.11 to 0.90. The browning indices L* and a* values were higher and lower, respectively, in freeze-dried Rubus coreanus compared with other samples. The b* value was greatest in freeze-dried Rubus coreanus. EMC tended to increase with increasing aw values, and a particularly sharp increment was observed above 0.75 aw. The EMC of freeze-dried Rubus coreanus was significantly higher compared with the EMC of sun-dried and infrared-dried fruit at constant aw. The moisture sorption isotherms showed a typical sigmoid shape, and the Halsey, Kuhn, and Oswin models were the best fits for the sun-dried, infrared-dried, and freeze-dried powder isotherms, respectively. With respect to monolayer moisture content, the Guggenheim-Anderson-Boer (GAB) equation showed that the various drying methods yielded very different results, with monolayer moisture contents of 0.005 g H2O/g dry solid in infrared-dried and 0.019 g H2O/g dry solid in sun- and freeze-dried powders, respectively. These results indicate that the drying method affects the browning and moisture sorption characteristics of Rubus coreanus.

The effects of drying methods on the browning and moisture sorption characteristics of Rubus coreanus were studied. Fruits were steamed for 5 min at 100℃, dried by sun drying, infrared drying, or freeze drying, and powdered to a size of 20 mesh. Color values were measured and equilibrium moisture contents (EMC) were determined at 20℃, over a range of water activity (aw) from 0.11 to 0.90. The browning indices L* and a* values were higher and lower, respectively, in freeze-dried Rubus coreanus compared with other samples. The b* value was greatest in freeze-dried Rubus coreanus. EMC tended to increase with increasing aw values, and a particularly sharp increment was observed above 0.75 aw. The EMC of freeze-dried Rubus coreanus was significantly higher compared with the EMC of sun-dried and infrared-dried fruit at constant aw. The moisture sorption isotherms showed a typical sigmoid shape, and the Halsey, Kuhn, and Oswin models were the best fits for the sun-dried, infrared-dried, and freeze-dried powder isotherms, respectively. With respect to monolayer moisture content, the Guggenheim-Anderson-Boer (GAB) equation showed that the various drying methods yielded very different results, with monolayer moisture contents of 0.005 g H2O/g dry solid in infrared-dried and 0.019 g H2O/g dry solid in sun- and freeze-dried powders, respectively. These results indicate that the drying method affects the browning and moisture sorption characteristics of Rubus coreanus.