2.6. Sensory evaluation
Stock solutions of 1 mg/ml of both MNEI and Y65R were prepared
by dissolving each protein in mineral water, pH 6.8. In order to
determine the detection threshold (DT) and recognition threshold
(RT), nine concentrations of each protein obtained from stock solution,
going from 0.49 mg/l to 5.32 mg/l, were prepared. The range of
concentrations was chosen on the basis of the results from previous
research. Two different pH conditions were investigated: 6.8 and 5.1. Citric acid powder was used as an acidifying agent in both protein solutions at a concentration of 19 mg/l to reach a pH equal to 5.1. A modified version of the ‘‘difference from the
reference’’ method was used to determine DT and RT of the proteins,
as previously reported. Thirteen assessors
participated in the study; they were selected for having the same
DT and RT for the basic tastes in order to avoid errors due to different
thresholds. For each pH condition, the presentation of the samples
was carried out according to an incomplete block design: during
each session, assessors compared a reference sample of pure water
(R), with a hidden reference and four samples, two of MNEI and two
of Y65R, containing different concentrations of each stimulus.
Sensory data were analysed according to the procedure previously
illustrated.