W0069

Chocolate: Time-Resolved and High-Resolution XRD Studies of the Polymorphism of Cocoa-Butter and Triacylglyceroles. Henk Schenk, Arjen van Langevelde, Kees van Malssen and René Peschar, Laboratory for Crystallography, University of Amsterdam, Nieuwe Achtergracht 166, 1018WV Amsterdam, schenk@chem.uva.nl.

When you bite in a bar of chocolate, you are cracking cocoa-butter crystals. Cocoa butter crystallizes in six different polymorphs, but the most stable (-form wanted for quality chocolate is the most difficult to get in hands. This was our inspiration to study the crystallization behavior of cocoa butter and triacylgrlyceroles (TAGs) by means of Time-Resolved (TR), and High-Resolution (HR) XRD in the lab and with Synchrotron Radiation (ESRF). The lecture will explain this fascinating behavior by showing movies of TR-diffraction experiments.

Chocolate products are favorite confectioneries and produced at large scale. Badly processed or stored chocolate may develop fat-bloom, a grayish-white layer at the surface, giving it an aged and musty appearance, being caused by recrystallization of cocoa butter. To make chocolate free of fat-bloom, the cocoa butter of chocolate should be crystallize as ((VI). In order to realize this our research aims at a better understanding of the irreversible (’ ( ( and ((V) ( ((VI) phase transitions of cocoa butter at the molecular level and of the experimental conditions of these transitions.

Cocoa butter is a complex mixture of about thirty different TAGs. TAGs are esters of glycerol with three long-chain fatty acids and since each chain may differ in length and degree of saturation, many different TAGs exist. The hydrocarbon chains easily pack in different ways resulting in various polymorphs. The physical properties of TAG mixtures are largely determined by the properties of the individual TAGs in the mixture, e.g. the predominant polymorph in butter and margarine is (’.

With XRPD the polymorphs can be identified unambiguously, even at a one-second TR-mode in the laboratory. Moreover, the long spacings (40 to 65 Å) can be studied TR with SAXS equipment at BM26 of the ESRF. Our methodology is so much improved that sometimes even structure determinations of TAGs are feasible using HR-XRPD patterns (BM16, BM1B) or synchrotron data (ID16) of tiny poorly-diffracting single crystals.