Effect of Processing on Flavour Precursors, Pyrazines and Flavour Quality of Malaysian Cocoa Beans
Studies were conducted to determine the effect of processing (fermentation, drying and roasting) on flavour precursors and pyrazines concentration of cocoa beans and its flavour quality evaluation. Fermentation was carried out in a rotary drum reactor by subjecting the mixed hybrid of cocoa beans...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English English |
| Published: |
1997
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| Online Access: | http://psasir.upm.edu.my/id/eprint/8374/1/FSMB_1997_4_A.pdf http://psasir.upm.edu.my/id/eprint/8374/ |
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| Summary: | Studies were conducted to determine the effect of processing (fermentation,
drying and roasting) on flavour precursors and pyrazines concentration of cocoa
beans and its flavour quality evaluation. Fermentation was carried out in a rotary
drum reactor by subjecting the mixed hybrid of cocoa beans to 6-day fermentation.
During fermentation, effect of mass and turning time on the concentrations of these
compounds were determined. Drying of cocoa beans was carried out in a hot air
oven at an airflow of O.7m2/sec. Similarly, during drying, effect of bean depth and
temperature were determined. Thirteen treatments of fermentation and drying were
carried out according to a central composite rotatable design configuration for two
factors. The effect of roasting on the concentrations of flavour precursors and
pyrazines was compared with air-blown and sun-dried of drum and pod-storage fermentation and a tested representative Ghanaian sample. The resultant beans were
made into cocoa liquor for flavour quality evaluation.
Fermentation significantly decreased the concentration of acidic free amino
acids in cocoa beans by 15%, whereas total, hydrophobic and other amino acids
increased significantly by 148, 280 and 127%, respectively; peptide-N and total
reducing sugars increased by 55 and 208%, respectively. The study found six types
of pyrazines, with trimethyl- and tetramethylpyrazine being the major compounds.
During cocoa fermentation, an increase in cocoa mass and turning time significantly
increased the concentrations of flavour precursors and pyrazines. Results from the
Response Surface Methodology (RSM) plots of hydrophobic free amino acids,
peptide-N and total reducing sugars recommended mass and turning time for
optimum condition of cocoa fermentation were at 60 kg and 5 min turning per day
after 48 hr of fermentation.
During drying, an increase in bean depth and temperature significantly
decreased the concentrations of flavour precursors, but significantly increased the
pyrazines concentration. In addition, total, acidic, hydrophobic and other amino
acids decreased by 43, 41, 36 and 49%, respectively; peptide-N and total reducing
sugars decreased by 56 and 71%, respectively; and trimethyl- and
tetramethylpyrazine increased by 167 and 609%, respectively. Bean depth of 8.3 cm
and temperature of 40°C were chosen as the optimum conditions for drying
treatment. Under this condition, the concentrations of hydrophobic free amino acids,peptide-N and total reducing sugars were highly significant, whereas those of
trimethyl-, tetramethyl- and total pyrazines were significantly low.
Roasting the samples at 150°C for 30 min significantly decreased the
concentrations of acidic, hydrophobic, total and other free amino acids, peptide-N
and total reducing sugars but significantly increased the pyrazines concentration.
There were no significant differences in the decrease of the concentration of
hydrophobic free amino acids, peptide-N and total reducing sugars in the air-blown
samples of different fermentation methods (drum and pod-storage); and in those of
different drying treatments (air-blown and sun-dried). Air-blown drum fermentation
samples had lower concentrations of 2,5-dimethyl-, trimethyl-, tetramethylpyrazine
and total pyrazines than those of pod-stored (air-blown and sun-dried) and drum (sun-dried) samples. |
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