Relationship between Crystallization Behavior, Microstructure, and Macroscopic Properties in trans-Containing and trans-Free Filling Fats and Fillings JEROEN VEREECKEN,* ,† IMOGEN FOUBERT, † KEVIN W. SMITH, ‡ AND KOEN DEWETTINCK † Faculty of Bioscience Engineering, Laboratory of Food Technology and Engineering, Ghent University, Coupure Links 653, B-9000 Gent, Belgium, and Consultant to Loders Croklaan, Life Science, Unilever Research Colworth, Sharnbrook, Bedfordshire, MK44 1LQ, United Kingdom The objective of this study is to investigate the architecture to feature physical functionality of filling fats. This means an investigation of the different structure levels (crystallization, microstructure, macrostructure, etc.) that lead to good technological functionality. The isothermal crystallization behavior of two filling fats (one trans-containing and one trans-free) was examined by differential scanning calorimetry and microscopy. Furthermore, the hardness of the samples was examined after cooling in a water bath at two different temperatures and at three different storage times. The trans- containing filling fat crystallized faster and in smaller crystals as compared to the trans-free filling fat. The crystallization behavior of the trans-free filling fat was more complex, with the formation of different polymorphic forms. The hardness of the fillings was not only governed by the amount of solid fat present in the network but also by the structure of this network. The filling matrix components seem to have a pronounced influence on the microstructure and thus on the macroscopic properties. KEYWORDS: Filling; crystallization; microstructure; hardness; fat INTRODUCTION Fillings are generally used in bakery applications (e.g., cream fillings) and confectionery (e.g., truffles). They are surrounded by a coating, a product that has already been studied by the same experimental setup as in this study (1). The general function of the filling fat is the same as for the coating fat: It provides the continuous matrix that holds the other ingredients and contributes to flavor, aroma, and color. The difference with the coating fats is that they need not be dry to touch at ambient temperatures. However, too low a solid fat content (SFC) can enhance fat migration with detrimental effects on the surround- ing coating (2). Upon consumption, the fat matrix should melt away quickly and completely at or near mouth temperature. Failure of the filling to melt rapidly will result in poor flavor release and, probably, a waxy aftertaste (3). Another requirement of the filling is the absence of sandiness, which mainly occurs when fat crystallizes in the wrong polymorphic form or when too large fat crystals are formed (4). Partial hydrogenation has been used as a technique to give fats the desired functionality. The problem with this process is the formation of trans fatty acids, which have received consider- able attention in recent years, both in the scientific literature and in the popular press. Reports in the scientific literature indicate that high levels of trans fatty acids in the diet, as compared to high levels of cis fatty acids, result in unfavorable effects on both low-density lipoprotein and high-density lipo- protein cholesterol. In response to these reports, many organiza- tions of health professionals have recommended reduced consumption of foods containing trans fatty acids (5). In the absence of partially hydrogenated oils—the major source of trans fatty acids—the manufacturers have to fall back to fats based on palm oil and fats based on lauric fats. As already mentioned in the previous study on coating fats (1), few studies have involved all of the structure levels that lead to good technological functionality, a factor that is determined by the macroscopic properties of the fats. The amount of solids, the polymorphism of the solid state, and the microstructure of the network of crystalline particles all play a role in the development of the macroscopic properties, and all of these factors are influenced by processing conditions (6). Brunello et al. (7) and Campos et al. (8) examined the relationship between the different structure levels in the pure fats, cocoa butter, and milk fat and lard, respectively. Humphrey and Narine (9), Narine and Humphrey (10), and deMan et al. (11) on the other hand have studied the relationships in fat blends involved in the preparation of industrial shortenings and in commercial shortenings. Braipson-Danthine and Deroanne (12) * To whom correspondence should be addressed. Tel: +32 9 264 61 68. Fax: + 32 9 264 62 18. E-mail: Jeroen.Vereecken@UGent.be. † Ghent University. ‡ Unilever Research Colworth.