3. Results and discussion
3.1. Colour
Based on the objective colour measurements using a chromameter,
the effect of HPP on the three colour variables progressed from strongest
to least for lightness, chroma and hue angle. Using the mixed effects
model, therewas evidence that pressure but not duration had significant
effects on tissue colour, and there was no interaction of the effects of
pressure with duration (results not shown). We examined the effect of
time between tissue preparation and HPP treatment and found that
this was not statistically significant (results not shown).
For lightness of green and yellow tissues, analysis of differences of
least squares means showed that, with the exception of the 200 MPa
treatments, all the treatment values were significantly lower than the
control values (P b 0.05) and this difference increased as the pressure
increased (Fig. 2a). There were no lightness differences (P b 0.05) between
the pressures > 300 MPa or at duration times of 3 to 10 min.
Slices became slightly darker at ≥300 MPa decreasing from 57.5 to
≅52.5 for the outside (i.e. dark green layer) of slices, and 69.5 decreasing
to ≅63–66 for the internal yellow side of the slices.
Chroma (Fig. 2b) showed a similar trend to that of lightness for
the internal side of the slices, with reduced values at the higher pressures
(>500 MPa). However, the back of the tissue slice (dark green
tissue) showed an increase in chroma only at pressures of 200 MPa
at 3 min, no significant difference at pressures of 300–500 MPa, and
a decrease at 600 MPa for 3 and 6 min