DRYING OF SPINACH WITH A HIGH ELECTRIC FIELD

Abstract

An alternating current high electric field (HEF) of 430 kV/m generated by multiple point-to-plate-electrodes was used to dry spinach (Spinacia oleracea L). Point electrodes distributed above a layer of fresh spinach were effective in removing moisture. Drying continuously for 7 h removed 80.1% of the total moisture compared with 79.8% and 19.3% when dried in an oven (60°C) and in ambient air (25°C), respectively. The Hunter ‘a’ value for HEF-dried samples maintained most of the original green color compared with oven-drying, during which the spinach turned brown. Total chlorophyll (Chl), Chl a and Chl b contents in spinach were substantially higher after HEF-drying than oven-drying. The ascorbic acid content after six weeks of storage of the dried material was almost three times higher in HEF-dried samples than those oven-dried. HPLC determinations of organic acids and sugars indicated no formation of by-products in post-HEF-dried spinach.

Keywords:

• HPLC
• Non-thermal drying
• Organic acids
• Sugars
• Ascorbic acid
• Chlorophyll

Acknowledgments