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Abstract
Effects of ohmic pretreatment on the drying rates of seedless red grapes and adsorption isotherms of the raisins produced were investigated. The treated grape samples were heated in a medium containing 2% citric acid to a final medium temperature of 60oC using an alternating current at 14 V/cm field strength and 30 Hz, 60 Hz, and 7.5 kHz frequencies.
Results of this study reveal that the drying rate of the grapes was significantly increased by the ohmic pretreatment, especially at low electrical frequencies. The effect of the ohmic pretreatment on equilibrium moisture content of the raisins produced was evident at 0.75 or higher water activities but there was no or limited effect at low to moderate water activities.
ACKNOWLEDGMENT
Salaries and research support provided in part by the Ohio Agricultural Research and Development Center, The Ohio State University. Funding from USDA-CSREES NRICGP Grant No. 2001-35503-10035 is gratefully acknowledged. Mention of commercial products or trade names is made with the understanding that no endorsement or discrimination by The Ohio State University is implied.
Notes
a–cMeans for the same drying time with the same superscript are not significantly different at 5% level.
a,bMeans for the same water activity with the same superscript are not significantly different at 5% level.
