3.6. Color
Changes in color parameter L* of dark chocolate with hazelnuts as
a function of active and modified atmosphere packaging, packaging
material oxygen permeability and time of storage in the dark at 20 °C
are shown in Fig. 3. After 12 months of storage, chocolate packaged
under vacuum, irrespective of packaging material permeability,
showed the lowest increase in L* parameter (from 32.89 to 49.00)
(pb0.05) while in case of commercially packaged product the highest
increase in L* values was determined (from 32.89 to 56.12). Samples
packaged under N2 or with the oxygen absorber irrespective of
packaging material permeability showed an intermediate increase in
L* values (from 32.89 to 53.45) (pb0.05). Color parameters a* (red to
green) and b* (yellow to blue) showed a small but statistically
insignificant (pb0.05) change during storage (data not shown). The
observed increase in color parameter L* can be directly related to the
formation of large white spots on the surface of chocolate. This is
known in the literature as “fat bloom”. It is interesting to note that
chocolate samples packaged under vacuum retained their initial dark
brown color better than all the rest. As the phenomenon of fat bloom
is still not clearly understood (Briones & Aguilera, 2005) it is difficult
to provide a satisfactory explanation as to why vacuum packaging
retarded this phenomenon. Pressure being applied to the surface of
chocolate by the packaging film may be related to “fat bloom”
retardation. In any case this postulation requires further study.
Khan and Rousseau (2006) studied the effect of three storage
temperatures (11, 20 and 26 °C) on the migration kinetics and
equilibrium of a model confectionery product consisting of dark
chocolate and a hazelnut based filling during storage for 8 weeks.
Similar to findings in this study they reported whitening of surface of
chocolate during storage. The rate of migration and the diffusion
coefficient increased by 20 and 400 times respectively, when the
storage temperature was raised from 11 to 26 °C, respectively. Also,
Briones and Aguilera (2005) studied changes in surface color of milk
chocolate stored at 28 °C for 52 days. Similar to findings in this study
they reported an increase in L* value after 52 days of storage resulting
in surface whitening of the product. It must be noted that these
authors reported a lag period before the onset of bloom was observed
(36 days of storage) which was not observed in the present study
probably due to longer sampling periods as compared to those applied
by the above workers (sampling every 2 months vs. sampling every
3 days). Also, Ali, Selamat, Man, and Suria (2001) studied the effect of
storage temperature on bloom formation of dark chocolate filled with
desiccated coconut during storage at 18 and 30 °C for 2 months. They
reported no bloom for samples stored at 18 °C while for samples
stored at 30 °C, the onset of bloom was observed after 1 week of
storage. Similarly, Jinap et al. (2000) reported no bloom during
storage at 18 °C for 8 weeks, while in case of storage at 30 and 35 °C
the onset of bloom was observed after 4 and 1 week, respectively,
resulting to whitening of the surface of product