Lipid formulations, structuring, and crystallization

Many commonly used food products, such as butter, margarine, chocolates and confectionery coatings, contain a significant amount of fat, of which a substantial proportion is present in the crystallized form. The macroscopic properties of these products, such as the appearance and the mouth feel, are of primary importance for the consumer's perception of the product. At the same time, these properties strongly influence the processing of the products and their application possibilities (e.g. as a moisture barrier). The ultimate goal of many studies is to be able to truly understand and eventually predict these macroscopic properties. This would allow the manufacturer to optimize the quality of the products and to maintain a good quality while making the products more favourable from a nutritional point of view (e.g. by lowering the amount of saturated fatty acids) 1. When fats are cooled, they undergo a liquid-solid transformation (i.e. the primary crystallization) to form crystals with specific shapes and sizes and with a characteristic polymorphism (i.e. the existence of several crystalline phases of the same chemical composition that differ mutually in structure). The primary crystals aggregate through van der Waals attraction and clot to form clusters, which interact further, resulting in the formation of a continuous three-dimensional fat crystal network. The number, size, shape and spatial distribution of the particles and large clusters of sizes between 1 and 200 μm define the microstructure, which has an enormous influence on the macroscopic properties of fat products 2. Each step in this structural hierarchy is influenced by the processing conditions (cooling rate, crystallization temperature, agitation speed and storage time) as well as the chemical composition. Several experimental techniques can be used to monitor the different aspects of crystallization. Differential scanning calorimetry (DSC) and pulsed nuclear magnetic resonance (pNMR) are often used to investigate the amount of primary crystallization, while X-ray diffraction gives more insight in the polymorphism of the substrate. Microscopy and rheology are used to characterize the microstructure development and texture analysis is most commonly employed to characterize the macroscopic properties 1. This special issue brings together a collection of papers further elucidating the influence of chemical composition (triglyceride composition as well as additives) on the different aspects of fat crystallization, while also warning us on the possible impact of using a certain experimental technique but also introducing some new experimental techniques. Danthine et al. 3 and Tran et al. 4 study the effect of triglyceride composition on the functionality of on the one hand blends based on shea stearin used as filling fats and on the other hand blends of cocoa butter with different SOS rich fats based on mango fat used in confectionery. Rothkopf & Danzl 5 investigate the effect of introduced filling fats on chocolate crystallization while Lopes et al. 6 show how solid lipid microparticles can modulate or optimize the fat crystallization process. Rigolle et al. 7, Daels et al. 8, Min et al. 9 and de Olivieira et al. 10 study the influence of additives on fat crystallization. The first one studies the influence of lecithin in different concentrations and matrices while the second investigates the influence of combinations of lecithin and polyglycerol esters and monoglycerides. The latter two focus on the effect of sorbitan esters whether or not in combination with fully hydrogenated canola oil. Patel & Dewettinck 11 pay attention to three different types of non fat based building blocks to structure fat without having to use saturated fatty acids. Rigolle et al. 7 also point out that the obtained results can differ depending on the experimental technique used. Gregersen et al. 12 warn for inhomogenous micro- and macrostructures formed upon crystallization and its potential effect on the evaluation of mechanical and textural properties. Franke et al. 13 introduce detrended fluctuation analysis combined with confocal laser scanning microscopy to quantify fat crystal network structures. Besides the papers dealing with crystallization phenomena, two contributions of this special issue are dedicated to lipid oxidation. The control of oxidation phenomena in fats and oils is one of the most challenging issues in the food industry 14. Indeed, product oxidation causes food deterioration because of aroma (off-flavors), texture, shelf life and color modifications. Moreover, the nutritional properties of the foods may be negatively affected. Progress in the development of foods based on lipids with desirable nutritional and physical attributes depends on the availability of improved methods of controlling their oxidative stability. Very often, lipids are in the emulsified state and in this case, oxidation is influenced by interfacial phenomena 15. The oxidation rate in emulsions can be considerably slowed down by the incorporation of phenolic compounds. The organization of these compounds within the system, as well as their interactions with other types of molecules in their immediate vicinity, has a pronounced influence on their antioxidant activity. The paper of Bravo-Díaz et al. 16 addresses the effects of pH and emulsifier concentration on the distributions of phenolic acid antioxidants between the interfacial and aqueous regions of corn oil emulsions. The paper has motivated a commentary from C. Genot 17. Imogen Foubert Guest Editor Fernando Leal-Calderon Guest Editor Access the Special Issue online at http://onlinelibrary.wiley.com/doi/10.1002/ejlt.v117.11/issuetoc Imogen Foubert Fernando Leal-Calderon