TLC separation combined with an FID for detecting paraffin and wax coatings on apples

TLC separation with silica gel on a quartz rod combined with an FID detecto r is a useful tool to detect wax and paraffin coatings on apple surfaces. I t separates the natural cuticular wax into four fractions, containing hydro carbons (A), wax esters (B), long chain alcohols (C) and a polar fraction ( D) which is the main component (mean 86.4% from 16 apple varieties). The pe ak area ratio AID was fairly constant (0.11-0.16, mean 0.13) for apple cuti cular wax, whereas a ratio of 0.03 was found for shellac, of 0.06 for carna uba wax, of 0.25 for beeswax and of 0.45 for candelilla wax. For this reaso n, any A/D ratio analyzed which differs more than 0.03 from 0.13 proves the presence of a wax coating. The ratios A/B and A/C provide additional evide nce on the wax type present. Only 10% of paraffin, which is not approved fo r coating apples, are easily detected due to a large increase of the A/D ra tio.