| Total polar material(TPM) in frying oil is a complex mixture generated at high temperature, which increases with oil deterioration. According to national food safety standard, TPM should not exceed 27% by column chromatography method. However, due to the method limitation of long detection period and massive organic solvent as well as the instrument limitation of anti-environment disturbance ability and standard operation procedure, an accurate and effective rapid detection technology is demanded. The research is based on dielectric and rheological property and the main contents are as follows:1. Analysis on 420 samples from 47 restaurants and 1 laboratory. Samples exceeding TPM 27% accounts for 12.50% and oil degradation from meat and fish frying is the main factor. The samples present TPM values from 0 to 35%, which indicates a normal distribution deflecting to right with a peak of TPM 23.0% during commercial deep-frying. Testo 270 results were correlated with that from conventional method(Y=0.7625X+3.6818,R2=0.8737). The result is underestimated beside TPM 27%, which may be attributed to instrument system and human operation errors.2. Correlation between dielectric constant, complex dielectric constant, dynamic viscosity, viscosity-temperature change rate and TPM. Dielectric constant, with relative standard deviation(RSD) 0.39~2.10% and good correlation(Y=0.0137X+3.1297, R2=0.8867), can be used for immersion-type rapid instrument development based on the temperature compensation. Complex dielectric constant, with RSD 7.02~79.49% and bad correlation(Y=(9×10-6)X+3×10-5, R2=0.7549), cannot be applied in the research. Dynamic viscosity, with RSD 0.40~1.67% and bad correlation(Y=0.3677X+25.2033, R2=0.7317), is significantly affected by oil type and can only be used for evaluation of single oil. Viscosity-temperature change rate, with RSD 0.06~1.76% and bad correlation(Y=-0.0011X-0.1892, R2=0.6689), can only be used for theoretical research on activation energy due to the limitation of oil type and apparatus.3. Evaluation on rapid detection instrument based on dielectric constant and relevant standard operation procedure. The instrument resolution is 0.1% with good repeatability of relative deviation 1.08~4.61% and good accuracy of correlation coefficient of 0.9601 and slope of 0.9074, which is correlated well with conventional method. Induction heating device should be switched off for a stable reading. With temperature range of 50~180oC, the temperature influence is well compensated within ±0.5%. With water content lower than 0.1%, the interference is minimized.4. Model between the frying conditions and the chemical composition via oil rheological parameter. TPM=3.881-2.935×10-3tp2-2.852F*tp+1.788×10-2tp*Tave-2.410 tp, R2=0.9463, in which Tave represents average oil temperature, tp represents frying time, F represents frying load(ratio of food weight and oil volume). |
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