Effect of cream cooling rate and water content on butter microstructure during four weeks of storage S. Rønholt a, * , J.J.K. Kirkensgaard b , K. Mortensen b , J.C. Knudsen a a Department of Food Science, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark b Niels Bohr Institute, University of Copenhagen, Denmark article info Article history: Received 31 May 2012 Accepted 23 October 2012 Keywords: Butter Fat crystallization Rheology Solid fat content Stability Water content Emulsions Milk fat abstract Crystallization, rheological properties and microstructure of butter with varying water content and sub- jected to different cooling rate were studied during four weeks of storage at 5  C. Using small and large deformation rheology, the elastic modulus (G 0 ) and Hencky strain at fracture was followed. When comparing samples with an equal water content, samples produced from fast cooled cream (7.5  C/min) have a higher G 0 compared to butter produced from slow cooled cream (0.4  C/min), at day 1e7. However, no difference in G 0 is observed as a function of time, even though the solid fat content increases. Increasing the water content from 20% to 32% decreases G 0 at day 1e14, yet X-ray scattering and differential scanning calorimetry shows no difference in crystal polymorphism or crystallinity. After 21 days of storage, no difference in G 0 is observed as a function of cream cooling rate or water content. For all samples, small angle X-ray scattering shows formation of 2L (41  A) and 3L (57  A) lamellar organization, while the wide angle spectra shows mainly b 0 -crystals (4.2 Å & 3.81  A) together with traces of b (4.6  A). Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction In recent years one of the major challenges in food research has been to develop and create products covering the essential nutri- tional needs, being low fat based while maintaining an appealing texture and taste (Wassell, Bonwick, Smith, Almiron-Roig, & Young, 2010). In commercial butter-like products and spreads, vegetable oils, such as canola oil, have been added in order to obtain a soft and spreadable product (Kaufmann, Andersen, & Wiking, 2012). One way to lower the amount of fat per serving is to increase the water content in the products. The water percentage is closely related to the quality of the final product. Therefore, it has been discussed that presence of water might influence crystallization behavior, which in turn could influence the texture of the product (Vanhoutte, Dewettinck, Foubert, & Huyghebaert, 2002; Vereecken, Foubert, Meeussen, Lesaffer, & Dewettinck, 2009). Butter, spreads and margarines are all multiphase water-in-oil emulsions, consisting of fat globules, crystalline fat and water droplets dispersed within a continuous oil phase (Juriaanse & Heertje, 1988). The fat crystal network strongly contributes to the product stability by physical stabilization of the water droplets dispersed within the fat phase, hence preventing microstructural changes (Rousseau, Zilnik, Khan, & Hodge, 2003). The organization of the fat crystals is in lamellar planes near the water and oil inter- faces, almost parallel to the interface plane (Wassel et al., 2012). Both the properties of the fat crystals and the size of water droplets are crucial for the strength of the fat crystal network (Juriaanse & Heertje, 1988; Rousseau, Gosh, & Park, 2009). When the water content is increased, more interactions between the water droplets can occur and they might become deformed with a bimodal size distribution (van Dalen, 2002). Still, more knowledge is needed on how water impacts milk fat crystallization together with the colloidal stability of butter, butter-like products and spreads. Other factors, such as thermal history and storage conditions, also affect the properties of a fat crystal network (Kellens, Meeussen, & Reynaers, 1992; Rousseau, Marangoni, & Jeffreys, 1998) together with microstructure of the fat crystals (Litwinenko, Singh, & Marangoni, 2004; Narine & Humphrey, 2004). In milk fat, the crystals primarily form three different poly- morphs: a, b 0 and b (Fig. 1)(Lopez, Bourgaux, Lesieur, & Ollivon, 2002). The triacylglycerol chains pack hexagonally in the a-crys- tals, orthorhombic in the b 0 -crystals and triclinic in the b-form (Chapman, 1962), in increasing order of stability. The crystalline structure formed in concentrated cream (40% fat) and anhydrous milk fat quenched from 60  C to 4  C has been studied during 6 days storage at 4  C(Lopez et al., 2002). After 15 min of storage, a (4.14 Å & 4.17  A) and b 0 -form (3.84, 4.26 & 4.28  A) are formed in cream and anhydrous milk fat. In addition, traces of b-crystals (4.65  A) were observed in the anhydrous milk fat. For long spacings, Lopez et al. * Corresponding author. Tel.: þ45 2398 3044; fax: þ45 3533 3190. E-mail address: roenholt@life.ku.dk (S. Rønholt). Contents lists available at SciVerse ScienceDirect Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd 0268-005X/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodhyd.2012.10.018 Food Hydrocolloids 34 (2014) 169e176