Changes in instrumental color of a pumpkin purée
Table 2 shows instrumental color changes after HPTP of pumpkin
purée. Apart from HPTP, changes in color could be also
caused by the preheating time inside the vessel (impossible to
avoid in each experimental run), and because color measurements
were carried out in the presence of oxygen. Although
these factors affected all samples it is possible that final color
of purées would be better avoiding these conditions.
Significant differences were found for L*, a* and Hue values
while b* and C were not affected by treatments. Lightness (CIE
L*) was significantly higher in processed purées than in control
samples. Purées treated at 600 MPa/60 ◦C had the highest value
of L*, while other treatments had intermediate values respect
to the control. Within the same pressure of treatment, the
lightness was not significantly affected by the temperature.
The CIE a* value was significantly highest in untreated
purées and HPTP at lower temperatures and pressure
(300 MPa/60 ◦C). Within the same pressure level, CIE a* value
tended to decrease with increasing temperature, so purée
treated at 900 MPa/80 ◦C had the lowest CIE a* value. Hue angle
was significantly higher in purées treated at 300 MPa/80 ◦C
than in control and those processed at the same pressure
level and lower temperature. Contador et al. (2012)
did not find differences between untreated pumpkin purée
and 400 MPa/5min treated purée (refrigerated temperature)
for CIE L*a*b* parameters, while more intense pressures at
600 MPa/5min decreased the parametersCIE L*, a* and b* value.
The differences in the values of CIE L* and a* which undergoes
pumpkin purée in our study may be due to the increase of
pressure, rather than to the increase of temperature within
the same pressure intensity.
The significant differences in individual color parameters
cannot indicate whether a difference in color is perceptible by
humans or not. For that reason, total color differences (E)
were calculated (Table 2). Differences in perceivable color can
be classified analytically as not noticeable (0 to 0.5), slightly