Effect of Calcium Ion and Microwave Power on Structural and Quality Changes in Drying of Apple Slices

Abstract

Effects of impregnated calcium ion and microwave (MW) power on texture, rehydration, shrinkage, color, and other selected indexes of freeze-dried apple slices were investigated. Apple slices were dried by freeze drying and microwave freeze drying (MFD) separately. Vacuum impregnated (VI) and non-vacuum-impregnated apple slices were dried at various microwave power levels. Non-vacuum-impregnated apple slices were found to preserve their mechanical structure better than the VI-treated ones. Microwave application resulted in decreased protopectin fraction as well as total pectin content. As microwave power varied from 1.2 to 2.0 W/g, the total pectin content decreased from 0.810 to 0.521 (expressed as g galacturonic acid/100 g fresh sample). The effect of microwave power in decreasing the drying time was significant. The color of MFD apple slices varied to a minor extent with MW power level over the range of parameters studied.

Keywords:

• Calcium ion
• Color
• Drying time
• Microwave freeze drying
• Pretreatment

ACKNOWLEDGMENTS

The authors express their appreciation to Frito-Lay, Inc., Plano, Texas, for their financial support. Discussions with Dr. Ted Farrington were very valuable during the course of this work. His support and contribution is gratefully acknowledged. The authors also thank the National Natural Science Foundation of China (No. 20776062) and 863-HI-TECH Research and Development Program of China (No. 2007AA100406) for financial support of the equipment and part of research.

Notes

Note: Samples in same column with different letter differ significantly at p ≤ 0.05.