Recent Advances in Chemistry and Technology of Fats and Oils
Since we produced Fats and Oils: Chemistry and Technology in 1980, the trend we anticipated to up-date the classical texts of oils and fats has manifested itself. Bailey's famous textbook has been completely revised and a second edition of Bernardini's wo
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and F. B. PADLEY V nilever Research, Sharnbrook, UK
1.1 INTRODUCTION
The physical properties of fats and oils have been the subject of longstanding research efforts both in the academic world and in industrial research. Academic research has mainly been involved with fundamental studies often on pure triacylglycerols or simple mixtures of known composition. The edible fats industry, on the other hand, is often involved in the study of complex fat blends with the aim of tailoring their properties to suit specific applications in food products, and to control stability and shelf-life. Fractionation, hardening, interesterification, emulsification, crystallization and creaming are the most important processes for the production of a variety of fat based products such as margarines, halvarines, mayonnaise, creams, chocolate, speciality fats and table oils. In many cases, the triacylglycerol composition of the fat blend used is not known in detail. Successful manufacture of these commodities relies on the manipulation of the fat blend in order to arrive at suitable physical properties, preventing undesirable changes in product properties during or after production. Well-known examples of such changes leading to product defects are the development of graininess in margarines and of bloom on chocolate. An essential requirement for achieving control over production processes and product properties is a thorough understanding of the physical properties of oils and fats. Some important properties like melting and crystallization behaviour, polymorphism and crystal structure are discussed. Relevant physical analytical methods such as Differential
R. J. Hamilton et al. (eds.), Recent Advances in Chemistry and Technology of Fats and Oils © Elsevier Applied Science Publishers Ltd 1987
P. J. M. W. L. Birker and F. B. Padley
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Scanning Calorimetry (DSC), X-ray diffraction (XRD), NMR, dilatometry and the use of phase diagrams in various forms are also described.
1.2 MELTING AND CRYSTALLIZATION BEHAVIOUR 1.2.1 Polymorphism
Melting and crystallization temperatures of triacylglycerols depend on two major factors: chemical structure and polymorphic behaviour. The chemical composition of triacylglycerol mixtures can be modified by blending, interesterification, fractionation and by partial or complete hydrogenation. The way in which crystallization is controlled in the subsequent processes needed to manufacture products like margarines or chocolate largely determines the ultimate product properties. One of the most striking features of triacylglycerol crystallization is the occurrence of a variety of crystal modifications (polymorphism). Polymorphism is in fact deliberately used in the manufacture of fat products as one of the ways of controlling crystal shape and size and crystal-crystal interactions in products. After a great deal of controversy in the early literature on fat polymorphism it is now generally accepted that triacylglycerols can crystallize in four major types of modification, known as sub-a,a, W and ~. The ~ mod
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