Crystallization Dynamics of Shear Worked Cocoa Butter

Abstract

Control of heat and mass transfer conditions during chocolate manufacture is a critical factor influencing product quality and performance. The molecular basis for specific tempering protocols developed by the chocolatiers, and used widely by the food industry, is poorly understood. Here we show that cooling and shear rates applied during cocoa butter crystallization affect the incorporation of specific triacylglycerol (TAG) molecular species onto the surface of growing seed crystals, thus affecting the different structural levels in a cocoa butter crystal network. In this work, the effects of shear work on the different structural levels in cocoa butter are determined. Results from this research show different compositions during the early stages of static crystallization at different cooling rates. In other words, there is selective attachment of TAG species onto growing crystal surfaces, leading to fractional crystallization. With the application of shear, differences between cooling rates became negligible. Shear appears to enhance the formation of mixed crystal in the growing crystals, leading to faster crystallization kinetics, the formation of a higher number of smaller crystals, and a mechanically stronger crystal network. ■ INTRODUCTIONIn the manufacturing of chocolate products, the molten chocolate mass is processed under specific shear and cooling conditions with the aim of crystallizing cocoa butter into an ordered crystalline structure. Cocoa butter is chocolate's main fat component; therefore, its structure will directly affect the product's final physical properties such as contraction, snap, gloss, melting properties, and bloom resistance. This controlled crystallization is known as tempering. The purpose of tempering is to produce 1−3% of the desired highly ordered β V seed crystals, which will subsequently serve as nuclei for the rest of the mass to crystallize. 1−4 If molten chocolate mass were to be cooled directly at cooling tunnel or ambient temperatures, cocoa butter would crystallize in the metastable α II and β′ III−IV forms. 5−8 This results in a dull, soft, low melting point chocolate, prone to bloom.During tempering, the chocolate mass is cooled to 27−29°C to induce nucleation of both stable and unstable crystals. The temperature is then raised to 30−33°C to promote transformation of seed crystals to the stable β V form and melt unstable crystals. The temperature set points used vary by recipe. The tempered chocolate mass is then rapidly cooled to complete crystallization of the fat phase, yielding chocolate with desired quality attributes. 1−4 All methods of tempering, from small-hand tempering to large industrial scales, involve controlled cooling and some element of shear. Shear improves heat and mass transfer of molten cocoa butter, helping overcome kinetic barriers for nucleation and growth. 9 Shorter induction times for crystallization in cocoa butter 10 and chocolate 11,12 when processed under shear suggest that shear affects nucleation. The effect of shear on secondary nucleati...

Thermal Transitions of Cocoa Butter: A Novel Characterization Method by Temperature Modulation

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Protein-Stabilized Palm-Oil-in-Water Emulsification Using Microchannel Array Devices under Controlled Temperature

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Sonocrystallization of a Palm‐Based Fat with Low Level of Saturation in a Scraped Surface Heat Exchanger

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