Effects of cola nut extract and powder on fungal growth, mycotoxins production, physico-chemical properties and fat quality during drying of fermented cocoa beans

Abstract

Cocoa beans are the main ingredient for making chocolate and in Ghana, it is a major contributor to the economy as it generates an annual foreign exchange of about US $2 billion. The ability to produce high quality cocoa beans free from moulds and mycotoxin contamination has therefore become critical due to the impact mycotoxins have on health of consumers and global trade. This study investigated changes in fungal growth, mycotoxin concentrations, physico-chemical properties and cocoa butter qualities as affected by cola nut raw powder and cola nut powdered extract using a 2 x 4 full factorial experimental design with treatment type (cola nut raw powder and cola nut powdered extract) and treatment levels (0 g/5 kg, 50 g/5 kg, 100 g/ 5kg and 150 g/5 kg) as the principal factors. Changes in pH, titratable acidity, fermentation index, cut test scores, free fatty acids, peroxide value, iodine value, mould colony forming unit (Aspergillus spp, Penicillium spp, Rhizopus and Mucor spp) and mycotoxins concentrations (Aflatoxins and Ochratoxin A) of cocoa beans as affected by cola nut powder and extract were studied using standard analytical methods. There was a general decrease in acidity of cola nut treated cocoa beans as treatment concentrations increased. The measured pH ranged from 5.39 for control to 5.71 for 150 g/5 kg cola powder treated beans while the titratable acidity ranged from 0.112 (mole of NaOH/g) for 150 g/5 kg cola powder treated beans to 0.122 (mole of NaOH/g) for the control. The cocoa butter qualities of cola nut treated cocoa beans were better than that of the control which had no cola nut treatment. The 150 g/5 kg cola treated beans recorded the least FFA content of 0.71 % and 0.61 % for cola extract and cola powder treatments, respectively. These were significantly different (p < 0.05) from the control which recorded 2.34% free fatty acid content. Peroxide value of 21.6 Meq/kg was recorded for the control which was significantly higher than 15.8 Meq/kg and 14.2 Meq/kg for 150 g/5 kg cola extract and cola powder treated beans, respectively at 95% confidence level. The untreated cocoa beans had the highest iodine value of 35.96 g I/100 g which was significantly different (p < 0.05) from 33.63 g I/100 g and 33.21 g I/100 g for the 150 g/5 kg treated beans for cola nut powder and extract, respectively. Penicillium spp., Aspergillus spp., Rhizopus and Mucor spp. of moulds were identified in the dried fermented cola nut extract and powder treated cocoa beans. Concentration of 150 g/5 kg cola extract significantly (p < 0.05) inhibited growth of Penicillium spp from 6.13 log cfu/g to 4.18 log cfu/g which represented 98.9% inhibition while 150 g/5 kg cola powder inhibited growth from 6.13 log cfu/g to 4.7 log cfu/g representing 96.3% inhibition. Aspergillus spp had a 100% inhibition for both cola nut extract and powder for the highest treatment concentration of 150 g/5 kg which significantly (p < 0.05) reduced growth from 4.88 log cfu/g for control (0 g/5 kg) to no visible growth on OGYEA plate. Rhizopus and Mucor spp in contrast showed no significant reduction for all cola nut treatment concentrations except for 150 g/5 kg cola extract which significantly (p < 0.05) reduced growth of Rhizopus and Mucor from 4.95 log cfu/g for control to 4.3 log cfu/g. Aflatoxin levels for all treatment concentrations including the control were below the instrument’s limit of detection (0.13 μg/kg for aflatoxins B1 and B2 and 0.15 μg/kg for aflatoxins G1 and G2). With respect to the control (0 g/5 kg), there was significant reduction of OTA (p < 0.05) from 8.32 μg/kg to 2.85 μg/kg and 3.02 μg/kg, respectively for the 150 g/5 kg extract and 150 g/5 kg powder concentrations. These represented 65.7% and 63.7% reduction for 150 g/5 kg cola extract and powder, respectively. Generally, cola nut powder and extract at concentrations of 150 g/5 kg of cocoa beans led to a considerable reduction of mouldiness and associated mycotoxin production in dried cocoa as well as improved the cocoa butter qualities