Biochemical Differentiation of Cocoa Cotyledon Proteins from Various Genetic Origins
Previous studies have reported that differences in the cocoa flavour of roasted beans from various genetic origins do exist; however, the findings were mainly based on sensory evaluation. In addition, the cocoa flavours differences were also claimed to be solely due to the maternal plants and not...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English English |
| Published: |
2000
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/8424/1/FSMB_2000_14_IR.pdf |
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| Summary: | Previous studies have reported that differences in the cocoa flavour of roasted
beans from various genetic origins do exist; however, the findings were mainly
based on sensory evaluation. In addition, the cocoa flavours differences were also
claimed to be solely due to the maternal plants and not to other factors such as
physiological factors. Cocoa cotyledon contains vicilin (7S)-class globulin (VCG), a
major storage protein. It is a native source of oligopeptides and free amino acids,
both of which have been identified as precursors of specific-cocoa aroma. These
precursors are formed by proteolysis during fermentation. The VCG and the
splitting specificity of proteases from cocoa cotyledons have been known to be
responsible in the production of cocoa-specific aroma precursors during
fermentation. The separation patterns of VCG which were separately isolated from
cocoa cotyledons of various genotypes namely Forastero, Criollo, Trinitario, PBC
140, SCA 12 and UITI are shown. Comparative studies of VCG patterns and its
multiple forms were conducted by means of SDS-PAGE and two-dimensional
electrophoresis (2-DIEF/SDS-PAGE), whereas oligopeptide profiles were detected using a high performance liquid chromatography. SDS-PAGE analysis of the
molecular weights of the predominant polypeptides of VCG subunits (47 and 31
kDa) from various genotypes did not show qualitative differences. The 2-D
IEF/SDS-PAGE analysis of the VCG subunits revealed at least 10 multiple forms
with pIs in the range of 6.1 to 6.8. The additional polypeptides with their multiple
forms which had pIs in the range of VCG subunits were also detected on 2-D
IEF/SDS-PAGE. These polypeptides were most probably the resultant degradation
proteolytic products from the action of aspartic endoprotease on VCG subunits.
There were very strong similarities in the VCG subunits and their degradation
products at the level of their polypeptide constituents from the standpoint of number,
molecular weight and isoelectric point. The oligopeptide profiles of autolysis
products of the acetone dry powder prepared from various genotypes did not
revealed differences. It indicates that the action of aspartic endoprotease of the
various cocoa genotypes on VCG during autolysis was similar. There was no
analytical identity difference of VCG subunits and their degradation proteolytic
products for all the genotypes. Thus, VCG seems not to be responsible for cocoa
aroma differences in cotyledons of the various genotypes within methodical limits.
The VCG was almost completely degraded as compared to the storage albumin at the
end of fermentation. In conclusion, aroma differences in raw cocoa harvested from
various genotypes are the result of other genotypes, physiological or curing related
factors but are not due to genetic differences of aroma precursors derived from
storage proteins. |
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