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. 2016 Jul 5;113(27):7399-402.
doi: 10.1073/pnas.1605416113. Epub 2016 Jun 20.

Electrorheology Leads to Healthier and Tastier Chocolate

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Free PMC article

Electrorheology Leads to Healthier and Tastier Chocolate

Rongjia Tao et al. Proc Natl Acad Sci U S A. .
Free PMC article

Abstract

Chocolate is one of the most popular food types and flavors in the world. Unfortunately, at present, chocolate products contain too much fat, leading to obesity. Although this issue was called into attention decades ago, no actual solution was found. To bypass this critical outstanding problem, two manufacturers introduced some low-calorie fats to substitute for cocoa butter. Somehow, their products are not allowed in most countries. Here we show that this issue is deeply related to the basic science of soft matter, especially to the viscosity of liquid suspension and maximally random jammed (MRJ) density. When the concentration of cocoa solid is high, close to the MRJ density, removing a small amount of fat will jam the chocolate flow. Applying unconventional electrorheology to liquid chocolate with applied field in the flow direction, we aggregate the cocoa particles into prolate spheroids in micrometers. This microstructure change breaks the rotational symmetry, reduces liquid chocolate's viscosity along the flow direction, and increases its MRJ density significantly. Hence the fat level in chocolate can be effectively reduced. We are expecting a new class of healthier and tastier chocolate soon.

Keywords: electrorheology; fat in chocolate; liquid chocolate; maximum random jammed density; viscosity.

Conflict of interest statement

Conflict of interest statement: Temple University holds patents on a methodology to alter the viscosity of liquid chocolate through the application of an electric field. R.T. and H.T. are the inventor of the patents. The authors received funding from Mars Chocolate, Inc.

Figures

Fig. 1.
Fig. 1.
Under microscope, (A) the original cocoa solids in liquid chocolate are spherical around 2 µm; (B) the electric field aggregates these particles into short chains, which are similar to prolate spheroids.
Fig. 2.
Fig. 2.
Viscosity of original liquid chocolate and the viscosity of ER-treated liquid chocolate along the flow direction. Point A represents the original state at ϕ = 0.6. Without the ER treatment, removing a small amount of fat leads to dramatically increased viscosity (point B). With the ER treatment, the fat can be reduced by 20% and the viscosity remains the same (point C).
Fig. 3.
Fig. 3.
As the liquid chocolate flow passes a strong local electric field, the solid particles aggregate along the field direction to form streamline aggregates and the viscosity along the flow direction is significantly reduced.
Fig. 4.
Fig. 4.
Sketch of the device.
Fig. 5.
Fig. 5.
(A) Application of 1,600-V/cm electric field significantly increases the flow rate. (B) The flow rate was increased by 74.3%. (C) The viscosity was reduced by 43.5%.

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