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Physical & Chemical properties

Partition coefficient

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Description of key information

Key value for chemical safety assessment

Additional information

The logKOWof cocoa powder was measured using the HPLC method carried out in accordance with EC Method A.8.

This method was used to determine the partition coefficient of the methanol/water soluble portion of cocoa powder, however, a

definitive result could not be estimated from the standard graph and the results for these peaks have been stated as less than the log P for the lowest standard used (acetophenone, log P = 1.70). It is, however, possible to extrapolate Log P values forthe methanol/water soluble portion of cocoa powder from the linear regression line and these values have been included in the data table for reference.

 During sample preparation, it was noted that most of the substance did not dissolve in the mobile phase (50 % MeOH in water), so the experimental data only describes the partition co-efficient of those components soluble in the mobile phase.

Assessment of the components of the cocoa powders indicate that the compounds likely not to have dissolved in the mobile phase are “protein, cocoa”, lignin, cellulose, pectin and “glycerides, cocoa”. Of these components the first four are polymeric and are unlikely to show any solubility in either octanol or water, so partition co-efficient is not an appropriate variable to calculate. However, the partition co-efficients of glycerides are well known and should be included in the calculation of the partition co-efficient of cocoa powder. There are two possible reasons for the log Kowof these components not being measured in the experiment;

1. The glycerides did not dissolve in the diluent.

2. The high log Kowof the glycerides meant that they were never released from the HPLC column.

It is difficult to experimentally measure the partition co-efficient of substances with high log Kow. In these situations the partition co-efficient can be calculated using modelling software.

Calculation of log KOWusing modeling software

Cocoa, glycerides

For the purposes of the calculation the composition of “Glycerides, cocoa” has been simplified to 33 wt% C16 saturated (palmitic), 33% C18 saturated (stearic) and 33% C18 mon-unsaturated (oleic). The degree of esterification of the glycerides is not defined, so the log Kowof mono-, di- and tri-glycerides are given. [Please see CSR 1.3.3 for details of the results]

Conclusions

The experimental data is supported by the literature values of the individual components. However it is important to include the calculated logKOWof the glyceride components of cocoa powder. From the experimental analyses, logKow of the methanol/water soluble portion of cocoa powder was determined to be <1.70, whereas the logKow of the lipid portion not soluble in methanol/water is expected to be in the range6.53 – 24.62 (theoretical calculation). However, the lipid and methanol/water soluble components of cocoa powder are minor contributors to the total composition, much of which is polymeric (ca 70% by weight) and these components are not included in the determination of partition coefficient.

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