4. ConclusionResults from this study indicated that colour degradation was
influenced by storage temperature and time. Browning was clearly
detected and became more evident at elevated storage temperatures
and at prolonged storage. In view of predicting the colour
degradation, a zero-order model was chosen as the best fitting
model for all colour parameters. With respect to the carotenoid
profile, several carotenoids showed important changes and
appeared to have different susceptibilities to storage. Due to the
relatively limited decrease of carotenoids, isomerisation could be
more important than oxidation reactions. Amongst the carotenoids
studied, f-carotene showed an important increase in concentration
under all storage conditions. Additionally, more carotenoids displayed
important decreases as temperature and time increased,
which implies differences in individual carotenoids due to storage.
These changes correlated to changes in orange juice colour. As
visual colour degradation is rather complex, the rise of redness
and darkness which may be perceived as brown colour could be
attributed to a decrease in some major carotenoids (e.g., a-carotene
and b-carotene). Besides the contribution of carotenoid degradation,
it is likely that the generation of the brown colour upon
storage is caused by additional formation of brown pigments.
Other reactions such as non-enzymatic browning reactions could
play an important role in the perceived colour changes. Since
orange juice contains an appreciable amount of ascorbic acid, its
degradation may contribute to browning. Also, interaction
between different pathways or compounds may occur. Therefore,
further research is needed to understand the mechanisms responsible
for the colour instability in orange juice, not just focusing on
the influence of carotenoids.
Acknowledgements
This research was financially supported by the Seventh Framework
Programme (FP7) of the European Union under the Marie
Curie Initial Training Network ‘HST FoodTrain’ (Grant agreement
264470). Tara Grauwet is a postdoctoral researcher funded by
the Research Foundation Flanders (FWO).