Abstract: Apple slices were dried in a thermostatically controlled oven at 60 ℃. Changes in eight physicochemical indices and four electrical parameters were determined at different drying times. The experimental results obtained were as follows. As the drying time was increased, moisture content and density were decreased and browning degree was increased; total soluble solid content was decreased with drying time up to 120 min, accompanied by a simultaneous increase in titratable acidity and consequently a decrease in solid/acid ratio, and remained nearly unchanged thereafter. Vitamin C content and firmness were both significantly, negatively and linearly correlated with drying time. Relative permittivity and extracellular resistivity were decreased with drying time, while intracellular resistivity and damping factor showed a wave-shaped trend. Statistical analysis showed that intracellular resistivity and damping factor were inadequate to evaluate the quality change of apples during drying and that relative permittivity and extracellular resistivity had high correlations with firmness, the ratio of total soluble solids to titratable acidity, vitamin C content, browning degree, moisture content and density but were not highly correlated with titratable acidity or total soluble solids. According to the above results, the linear equations were built with relative dielectric constant and extracellular resistivity as independent variables and six physicochemical indices as dependent variables, which would provide a rapid tool to evaluate the quality change of apple slices during drying.

Key words: apple, drying, physicochemical indices, electrical parameters, detection