Detection of coating waxes on apples by differential scanning calorimetry
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In the European Union, beeswax, candelilla wax, carnauba wax and shellac are approved as coating agents for apple surfaces, provided that the coating is clearly stated. For detecting such coatings on apples, differential scanning calorimetry (DSC) was successfully applied. From the thermograms, the temperature at the peak maximum and the phase transition enthalpy were obtained as the main criteria. For the genuine surface wax of ten apple cultivars, the means were 64.4°C [standard deviation (SD), 1.5°C] for the maximum temperature and 82 J/g (SD, 9 J/g) for the enthalpy. The four coating agents resulted in divergent peak maxima and in enthalpies above 100 J/g in all cases. For beeswax, means of 68°C and 136–165 J/g were found, for candelilla wax 77°C and 116–161 J/g, for carnauba wax 89°C and 127–162 J/g and for shellac (two samples only) 76–89°C and 141–208 J/g. Studies with mixtures of the coating agents and apple wax and analyses of commercial apple samples marked as waxed confirm that DSC suits very well as a screening method for detecting an unstated treatment. In some cases it is even possible to characterize the coating agent used. First results indicate that paraffins, montanic acid esters and polyethylene wax oxides which are not approved for coating apples can be detected in the same way.
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