Abstract
Appearance is an important quality determinant of cocoa beans and it is used as standard criteria to establish the degree of fermentation and drying of the beans. Changes in browning index and colour (L*a* b*) during roasting of pulp pre-conditioned and fermented cocoa beans were studied using standard analytical methods. Increasing pod storage and roasting time at 120oC led to variable increases in browning index (BI) and b*-values of the beans with decreases in the L* and a* values. Cocoa pod stored for 10 days showed the highest BI (1.144) with the least L* value (24.15) whilst beans from the unstored pods showed the least BI (1.007) with the highest L* value (25.55). The rates of change in BI and colour (L*, a*, b*) were however more pronounced during roasting than pod storage. Brown pigment formation (BI) and the L* value were more pronounced after 30 minutes of roasting in beans from pods stored for 3 to 7 days. The colour changes in beans from 10 days pod storage was significant (p<0.05) after 45 minutes of roasting. The beans from the pods stored for 3 to 7 days showed consistent decrease in L* and a* values with increasing roasting time whiles the beans from the 10 days of pod storage were observed to produce lower L* value (darker beans) after 45 minutes of roasting. Pod storage between 3 to 7 days could be used to improve the brownness and appearance of roasted cocoa nibs. Beans from cocoa pod stored between 3 to 7 days produced the most acceptable BI and L* value after roasting for 30 minutes at 120oC.
Highlights
Roasting is critical to the flavour and appearance qualities of cocoa beans during industrial processing
Several physical and chemical changes occur in the cocoa beans such as evaporation of volatile acids, causing reduction in the acidity reducing the sourness as well as bitterness of the cocoa beans
Roasting temperature is the main factor affecting colour development, flavour, and texture. These changes are mainly related to Maillard reactions during roasting
Summary
Roasting is critical to the flavour and appearance qualities of cocoa beans during industrial processing. Several physical and chemical changes occur in the cocoa beans such as evaporation of volatile acids, causing reduction in the acidity reducing the sourness as well as bitterness of the cocoa beans. These changes lead to the production of desirable chocolate flavours and colour [2] by maillard reaction. The quality of the flavours produced is dependent on several factors, such as the origin of the beans, period of harvesting, postharvest treatment, variety and the roasting conditions [4,9,10,11,12,13,14]
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