Polyphenols are phytochemicals responsible for the astringency, bitterness, green
flavours and antioxidant activities in
Theobroma cacao
beans. Polyphenols degradation
in cocoa beans during roasting is crucial to the flavour outcome and it is influenced by
factors such as temperature, time and pod storage. Antioxidants are compounds that
help to inhibit oxidation reactions caused by free radicals such as singlet oxygen,
superoxide, peroxyl radicals, hydroxyl radicals and peroxynitrite thereby preventing
damage to the cells and tissues. Their mechanisms of action include scavenging reactive
oxygen and decreasing localised oxygen concentration thereby reducing molecular
oxygen’s oxidation potential, metabolising lipid peroxides to non-radical products and
chelating metal ions to prevent generation of free radicals in humans. The study aimed
at investigating changes in total polyphenols, anthocyanins,
o-diphenols and
antioxidant activity (free-radical scavenging activities) after roasting of pulp preconditioned
and fermented cocoa beans using standard analytical methods. A 4×4 full
factorial design with the principal experimental factors as pod storage time (0, 3, 7 and
10 days) and roasting duration (0, 15, 30 and 45 minutes) at 120°C were used to study
the changes in the total polyphenols, anthocyanins,
o-diphenols and % free-radical
scavenging activities of the cocoa beans. Variable decrease in total polyphenols, odiphenols
and anthocyanins were observed with increase in pre-conditioning (pod
storage time) and roasting duration. However, variable trends were observed for the %
free-radical scavenging activities. The total polyphenols, anthocyanins and
o-diphenols
in the cocoa beans after 45 minutes roasting decreased in the range 132.24 to 57.17
mg/g, 6.71 to 1.07 mg/kg and 15.94 to 8.25 mg/g respectively at all pod storage
treatments. The total polyphenols of the fermented, dried and unstored (freshly
harvested) cocoa beans was 132.25 mg/g which reduced to 122.14 mg/g (7.6%
degradation), 116.721 mg/g (11.7% degradation) and 92.22 mg/g (30.3% degradation)
after storage for 3, 7 and 10 days, respectively. The optimum decrease in the % freeradical
scavenging activity was 7 days and above of pods storage. Increasing roasting
time caused a continuous decrease in the % free-radical scavenging activity from
89.10% to 74.31% after 45 minutes for beans from the unstored (freshly harvested)
pods. However, pod storage caused an increase in the % free radical scavenging
activities during roasting. Pulp pre-conditioning (pod storage) and roasting duration
could be used to reduce the astringency and bitterness caused by polyphenols,
o-diphenols
and anthocyanins in cocoa beans as well as increase the antioxidant activity
imparted by cocoa.
