Despite the increasing demand for natural colourants, their sensitivity to light is a major
disadvantage and could pose restrictions to their utilization as food colourants in industry.
Turmeric (Curcuma longa L.) is a tropical plant native to southern and south eastern tropical
Asia. The most active colour components in turmeric roots are curcuminoids, which are used in
many food and pharmaceutical preparations. However, curcuminoids are unstable and have been
replaced by stable synthetic dyes such as sunset yellow. Hence, the purpose of this study was to
evaluate the effect of storage of turmeric oleoresin with and without protection from external
environmental conditions, including sunlight during daytime, on the stability of curcuminoid
pigments, measured by high-performance liquid chromatography and correlated with L*a*b*
colour space values and colour evaluation by a trained sensory panel.
Turmeric oleoresin powders were placed in labelled, clear plastic jars and exposed to external
environmental conditions during the day for a period of 10 weeks. Control samples were stored
in a refrigerator at 4 °C. To determine the effect of protection of turmeric oleoresin powders from
external environmental conditions on curcuminoid stability, jars were covered with aluminium
foil and stored outside and exposed to external environmental conditions for a period of 10 weeks.
Control samples were refrigerated at 4 °C.
Over time of exposure to external environmental conditions, curcuminoid pigment degradation
was evidenced, with 100% degradation observed after 9 weeks of storage, relative to the control.
Curcuminoids were less sensitive to degradation when shielded from external environmental
conditions, with a 22% reduction in degradation observed relative to turmeric oleoresin powders without aluminium foil protection after 10 weeks of exposure to external environmental
conditions. Significant sensory differences were observed between turmeric oleoresin powders
with and without protection from external environmental conditions compared to the control
In an attempt to enhance curcuminoid stability in the presence of external environmental
conditions, the effect of antioxidants, tertiary butylhydroquinone (TBHQ) and ascorbic acid on
the stability of curcuminoid pigments in turmeric oleoresin, was studied. The effect of divalent
ion-curcuminoid complexation on the stability of curcuminoid pigments in turmeric oleoresin
when exposed to external environmental conditions, was also investigated.
Antioxidants were homogenously distributed onto the powdered turmeric oleoresin base at
0.02% (m/m). Samples were exposed to external environmental conditions for a period of 10
weeks. According to the total colour difference results (L*, a* and b* values), the addition of both
TBHQ and ascorbic acid did not improve the colour stability of the curcuminoid powders after
10 weeks of exposure to external environmental conditions. The presence of ascorbic acid had
no significant influence on curcuminoid stability, with the degradation trend following that of
the control, which did not contain antioxidants.
The effect of complexation of curcumin with divalent ion (Mg2+) by mechanical mixing was also
investigated. After 10 weeks of exposure to external environmental conditions, no significant
improvement in curcuminoid stability was observed after the addition of magnesium ions to
turmeric oleoresin powders when compared to the control which did not contain magnesium ions.
Correlation analysis was conducted to determine the relationship between percentage
curcuminoid degradation, sensory scores and colour ratings of turmeric oleoresin powders that
were exposed to external environmental conditions. A strong negative linear relationship was
observed between percentage curcuminoid degradation and rating of colour. A perfect positive
relationship was observed between chroma and b* values. Chroma also had a strong positive
relationship with L*. Percentage curcuminoid degradation showed a weak positive relationship
with both a* and hue angle values.
Exposure to external environmental conditions negatively affected the colour stability of
curcuminoid pigments in turmeric oleoresin powders and the level of pigment degradation was dependent on time of storage. Stabilization strategies investigated in this study, such as Mg2+-
curcuminoid complexation as well as the addition of antioxidants (TBHQ and ascorbic acid) did
not significantly improve curcuminoid stability in turmeric oleoresin powders.
Constant storage of ingredients and products containing turmeric oleoresin at low temperature
(<5 °C), together with light protection is vital to retard colour degradation.