Research Paper Crystallization of model fat blends containing symmetric and asymmetric monounsaturated triacylglycerols Jeroen Vereecken 1 , Imogen Foubert 1 , Kevin W. Smith 2 , Gary J. Sassano 2 and Koen Dewettinck 1 1 Department of Food Safety and Food Quality, Laboratory of Food Technology and Engineering, Faculty of Bioscience Engineering, Ghent University, Gent, Belgium 2 Consultant to Loders Croklaan, Unilever Research Colworth, Sharnbrook, Bedfordshire, UK In this study, the crystallization and melting properties of four different fat blends with the same saturated fat content (30%) but with different ratios of symmetric and asymmetric monounsaturated triacylglycerols were investigated using pNMR, DSC and polarized light microscopy. Blends were either palmitic (P) or stearic (S) based, and were combinations of SatOSat-rich (Sat = saturated, O = oleic) and SatSatO-rich vegetable oils with high-oleic sunflower oil. The DSC results demonstrate that there was almost no dif- ference in crystallization mechanism and crystallization rate between the two P-based blends. Both blends showed a two-step crystallization, which can be explained by polymorphism. Stop-and-return DSC results suggested an initial crystallization into an unstable polymorph followed by polymorphic transition during the crystallization. For the S-based blends there was a clear difference between the SOS-rich and the SSO-rich blend, with a slower crystallization for the SSO-rich blend. Possibly, this can be explained by fractional crystallization. The microstructure did not differ greatly between the blends. Directly after crystallization, the crystals of the SSO-rich blend were slightly larger than the crystals of the SOS-rich blend. Keywords: Asymmetric / Microstructure / Solid fat profile / Stop-and-return DSC / Symmetric / Triacylglycerols Received: April 25, 2009; accepted: July 28, 2009 DOI 10.1002/ejlt.200900037 Eur. J. Lipid Sci. Technol. 2010, 112, 233–245 233 1 Introduction Fats are the main structural components in many food prod- ucts such as margarine, chocolate, butter and spreads. They are mixtures of different types of triacylglycerols (TAG) and minor components. The complicated behavior of melting, crystallization, polymorphic transition, crystal morphology and aggregation of a fat is due in part to the physical proper- ties of each TAG and in part to the phase behavior of the mixture of different TAG. These TAG form the basis for the development of a fat crystal network that is directly related to the macroscopic properties of the end products such as spreadability, hardness and mouth feel. This means that the TAG composition of a fat system is of primary importance for the consumers’ perception of the end products [1–3]. Previous research from the authors’ group has demon- strated the importance of the structural hierarchy in fat crys- tallization, with the chemical composition of the fats being one of the important factors for the final structural development [4, 5]. Nowadays, a wide range of modification techniques has been used in different studies to combine the properties of totally different fats in order to get a new product with the desired physicochemical and technological properties. This route is investigated particularly in answer to the trend of re- ducing trans fatty acids in the diet [6, 7]. Blending of natural oils and fats is the easiest modification technique, and thus it has been frequently used to combine the properties of differ- ent fats. For example, Jeyarani and Reddy [8] studied the preparation of plastic fats with zero trans fatty acids by blend- ing different palm oil fractions. They found that the plastic range of palm stearins could further be improved by blending them with suitable oleins and with other vegetable oils. Also Jirasubkunakorn et al. [9] made use of different palm oil frac- Correspondence: Jeroen Vereecken, Ghent University, Faculty of Bio- science Engineering, Department of Food Safety and Food Quality, Lab- oratory of Food Technology and Engineering, Coupure Links 653, 9000 Gent, Belgium. E-mail: Jeroen.Vereecken@UGent.be Fax: 132-9-2646218  2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ejlst.com