Samples for threshold tests were prepared by spiking a neutral
lipid base of rice bran oil with
the required concentration of either indole or skatole .
Samples of 20 mL were prepared in 50 mL amber
glass screw-top bottles that were heated to 60–65 °C and held for
20 min before evaluation by panellists to ensure that sufficient of the
compounds volatilised within the headspace for sniffing. For sensory
threshold tests, six ascending concentrations of skatole and indole in
binary steps were used (0.0125, 0.025, 0.05, 0.10, 0.20, 0.40 ìg/g). The
concentrations were selected based on the range of ‘First Approximation’
thresholds obtained from the trained panel following earlier
tests.