The determination of cocoa solids in chocolate products
With certain exceptions, the Cocoa and Chocolate Products Regulations (England)
2002 require designated products to be labelled with a declaration of the dry cocoa
solids content expressed as a minimum percentage. Other edible ingredients present
that need to be included in, or excluded from, the calculation are specified.
Various cocoa products are used in chocolate manufacture e.g. cocoa nib, cocoa mass,
cocoa powder and cocoa butter. All of these products are derived from fermented and
dried cocoa beans after roasting and removal of the cocoa shell.
Cocoa butter and non-fat cocoa solids constitute cocoa solids. The amounts of these
two components in cocoa products will vary according to the recipe of the products
and the manufacturing specification applied.
Laboratory analysis as a means of checking declarations of dry cocoa solids requires
the dry non-fat cocoa solids and cocoa butter contents to be determined and the results
summated for comparison with the stated values.
Dry non-fat cocoa solids.
Estimation of the amount of a natural foodstuff in a food product requires the natural
ingredient to be constitutionally unique in some respect when compared to other
ingredients likely to be present. For estimations to be acceptably accurate any such
constitutional uniqueness needs to be relatively unvarying quantitatively.
The methyl xanthine alkaloids caffeine and theobromine occur naturally in tea, coffee,
cocoa and cola nuts. In cocoa beans, theobromine is the main alkaloid present, along
with minor amounts of caffeine. These alkaloids, given suitable analytical
methodology, thus provide a basis for estimating the amount of cocoa solids in a
chocolate product providing that, for example, coffee is not present. Since the
alkaloids are non-fat soluble, they provide a measure of non-fat cocoa solids.
Since Kunze1 in 1894, various methods for determining theobromine, or theobromine
+ caffeine, in cocoa products have been published. Refinements in analytical
techniques and in speed of analysis have been made in parallel with instrumental
developments.
The results of a collaborative trial testing a method for the determination of
theobromine in chocolate and chocolate products were reported by Brereton et al 2 in
1994. 24 public analysts’ laboratories and the Government Chemist’s laboratory took
part in the trial. The method tested consisted of a water extraction, addition of a
clearing agent and filtration, followed by separation and quantification using HPLC
with UV detection. The method demonstrated satisfactory precision for five samples
containing levels of theobromine in the range 1200-5900 mg/kg.
The stumbling block to deriving non-fat cocoa solids from the alkaloids present is not
analytical. Rather, it is the extent to which the alkaloids in cocoa are subject to natural
variation. The appended table sets out some, but not all, published data. It sufficiently
illustrates the extent to which theobromine and total alkaloid levels vary. As well as
differing between varieties of cocoa, the levels are influenced by geographic and
climatic conditions.
To convert determined amounts of theobromine (TD) to percentages of dry fat-free
cocoa solids requires a conversion factor (TF) to be used i.e.
% Dry fat-free cocoa solids = 100TD / TF
Conversion factors proposed by different workers vary according to whether
theobromine or the total alkaloids have been determined. The factors range between 3
and 3.5. However, the wide natural variation in the amounts of theobromine and
caffeine occurring in dry fat-free cocoa solids cannot be ignored. Based on the
analysis of 45 differing samples of cocoa mass, Pusey reported 95% limits of ± 1.224
round a mean theobromine level of 3.48 % in the dry fat-free cocoa solids.
It is clear that, whatever analytical method and arbitrary factor is chosen, the outcome
can only be a rough guide to levels of dry fat-free cocoa solids in a chocolate product.
Reasonable accuracy requires prior knowledge of the levels of the alkaloids in the
cocoa ingredients used to make the chocolate product, and its recipe, so that a
weighted factor can be derived and applied.
Total dry cocoa solids
Analytical derivation of the total dry cocoa solids present in a chocolate product
requires summation of the determined values for cocoa butter and dry non-fat cocoa
solids.
If no fat other than cocoa butter is present, then the amount of solvent extracted fat
will indicate how much cocoa butter there is. However, this circumstance is the
exception rather than the rule. Vegetable fat and milk fat are likely to be present, as
well as lecithin. These other solvent extractable ingredients need to be determined and
subtracted from the total fat in order to estimate how much cocoa butter is present.
The determination of milk fat is prone to the same problem as is found with dry cocoa
solids. A conversion factor is called for since determinations are based on the butyric
or orotic acids present in milk fat and each of these constituents is subject to natural
variation.
The determination of vegetable fats other than cocoa butter is based on triglyceride
analysis. The types of triglycerides that constitute each of the fats present, and their
natural variation, significantly affect the accuracy of this determination.
Because of these cumulative analytical problems, the estimation by difference of the
proportion of cocoa butter in the total fat present can only provide a rough
approximation.
CONCLUSION
Laboratory analysis of chocolate products is unsuitable for checking the correctness
of declared percentages of dry cocoa solids. This is because interpretation of the
analytical results is considerably influenced by natural variations in the constituents of
the chocolate on which the analysis is based.
REFERENCES
1.
2.
3
4
5
6
7
8
9
W.E. Kunze, Z.anal.Chem., 1894, 33, 1.
P. Brereton, M. Hague and R. Wood, J. Assoc. Public Analysts 1994, 30, 49.
M. S. Pusey, Analyst, 1977, 102 (1219), 697.
R. V. Wadsworth, Analyst, 1921, 46, 32.
K. E. Holmes, Analyst, 1950, 75, 457.
M.J. Ellis, LRSC Dissertation, Royal Society of Chemistry, 1981.
D. D. Moir & E. Hinks, Analyst, 1935, 60, 439.
K. W. Gerritsma & J. Koers, Analyst, 1953, 78, 201.
H. Hadorn & J. Kleinert, Rev. Int. Choc. 1967, 22, 310.
Alan Turner
January 2003
DRY NON-FAT COCOA SOLIDS – THEOBROMINE AND TOTAL
ALKALOID LEVELS
Analysts
Samples tested
% Theobromine
Range & (Mean)
M S Pusey3
Cocoa mass*
2.57 – 5.26 (3.48)
R V Wadsworth4
Cocoa nib
Cocoa powder
2.2 – 3.9
3.0 – 3.6
K E Holmes5
Cocoa nib
2.58 – 3.10 (2.99)
M. J. Ellis6
Cocoa nib**
2.02 – 3.31 (2.57)
D D Moir & E
Hinks7
Criollo: Java
Samoa
Forestero: Accra
Bahia
Trinidad
Grenada
K W Gerritsma & J
Koers8
Cocoa powder
residues
H Hadorn & J
Kleinert9
Blend of:
Venezuela
Arriba
Accra
% Total alkaloids
Range & (Mean)
2.57 – 3.54 (3.09)
3.37
3.16
3.07
3.17
3.16
2.70 (3.11)
1.50 – 3.12 (2.54)
3.05
Blend of:
Trinidad
Accra
3.22
Blend of:
Java
Trinidad
Accra
2.95
(3.07)
*Samples included beans from: Accra, Bahia, Ecuador, Ghana, Ivory Coast, Malaya,
New Guinea, Nigeria, Trinidad and Venezuela.
**Samples included beans from: Grenada, Jamaica, New Guinea, Nigeria and
Trinidad