The rheology of chocolate plays several important roles in
determining the nature of the end product. It helps determine the
efficiency of mixing and pumping during processing, and also has a
consequential effect on the textural properties of both molten and
molded finished products.
However, the extent to which the rheology of dark chocolate is
influenced by particle size distribution, as well as its fat and
lecithin content during processing, is not fully understood. Nor is the
interrelationship that exists between these factors and the textural
properties of the finished chocolate.
Scientists in Scotland wanted to evaluate the relationship between
the rheological and textural properties of dark chocolate systems as
influenced by the particle size distribution of their inherent solids
and composition under processing conditions. The investigators conducted
a factorial experiment that incorporated varying particle size
distributions, fat and lecithin.
Using a commercial shear rate-controlled rheometer and a commercial
texture analyzer, the researchers measured dark chocolate rheological
properties (yield stress and apparent viscosity) and textural properties
(firmness, viscosity index and hardness). They found that particle size
distribution, fat and lecithin content significantly affected all
rheological and textural properties.
Increasing the particle size led to significant reductions in the
yield stress, apparent viscosity, viscosity index, firmness and hardness
of the chocolates. Increases in the particle size had the greatest
impact on products containing 25% fat and 0.3% lecithin. The extent of
yield stress, apparent viscosity, firmness, viscosity index and hardness
was reduced further as fat and lecithin content increased.
Correlation and regression analysis--statistical techniques--showed
high correlation coefficients and regression coefficients among the
rheological and textural properties, which indicated the existence of
interrelationships. An analysis of the data showed that the rheological
and textural properties of the dark chocolates were highly related.
Particle size distribution, fat and lecithin accounted for 95.4% of the
variability in the data.
Further information. Dr. Alistair Paterson, Strathclyde Institute
of Pharmacy and Biomedical Sciences, University of Strathclyde, The John
Arbuthnott Building, 27 Taylor St., Glasgow G4 0NR Scotland, U.K.;
phone: +44 141 548 2125; fax: +44 141 552 2562; email:
alistair.paterson@strath.ac.uk.
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