基于电特性的苹果干燥品质检测

Quality Evaluation of Apple Slices during Drying Based on Electrical Properties

对苹果片进行60℃恒温干燥,选取不同干燥时间点测定其8项理化指标和4个电参数的变化情况。结果表明:随干燥时间延长,苹果含水率、质量密度降低,褐变度增大;可溶性固形物质量分数下降的同时其可滴定酸质量分数升高,固酸比减小,可溶性固形物质量分数在干燥120 min后基本保持不变;VC含量、硬度与干燥时间呈显著线性负相关。随干燥时间的延长,苹果相对介电常数和胞外电阻率下降,胞内电阻率和损耗因数呈波浪式变化。对理化指标与电参数间的差异显著性分析发现,胞内电阻率和损耗因数不能用于干燥过程中苹果品质变化的检测;相对介电常数、胞外电阻率与硬度、固酸比、VC含量、褐变度、含水率和质量密度间的相关性较高,与可滴定酸、可溶性固形物质量分数无明显相关性。据此,建立以相对介电常数和胞外电阻率为自变量,6个生理指标为因变量的线性方程,建立苹果电参数和理化指标间的关系,对快速评价其干燥加工过程中的品质变化具有指导意义。

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 ？rmness were both signi？cantly, 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 ？rmness, 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.