Relating Bulk-Fat Properties to Emulsified Systems: Characterization of Emulsion Destabilization by Crystallizing Fats

摘要

The controlled destabilization of emulsified fats by intraglobular fat crystals plays a considerable role in the development of microstructure and sensory properties of many foods (e.g., butter, spreads, whipped toppings, and ice cream). During a cooling regime, under perikinetic or orthokinetic conditions, intraglobular fat may crystallize, and collisions between droplets may lead to flocculation. Crystals near or at the droplet interface may cause the disruption of droplets at rest, or as the result of collisions. With a disrupted interface, the available liquid oil preferentially wets protruding crystals, and a bridge is formed between the two droplets (1). Due to the structural rigidity of the crystals, the droplets are prevented from fully coalescing, a process known as partial coalescence (2,3). It has been shown that solid fat content (SFC), crystal structure, crystallization kinetics, shear, and tempering all impact the stability of emulsions containing solid fat (1,4). Fat crystallization has been extensively studied in bulk fats and, to a lesser extent, in emulsified fats. It has been shown that the crystallization behavior of a fat will proceed quite differently, depending on whether it is in bulk or emulsified form (4,5). Authors have examined the effect of the state of dispersion on the crystallization mechanisms (nucleation, crystallization rate) and polymorphic behavior (6-11) of partial- and triglycerides in bulk and emulsified form. Understanding the mechanisms of emulsion nucleation and crystallization is one of the first steps in understanding the destabilization of emulsions and partial coalescence, e.g., stabilization of liquid fat emulsions by solid particles (fat) or control of the polymorphic form of crystals during the process of partial coalescence to control the size of aggregates and textural properties. There are two approaches to nucleation kinetics that have been utilized to explain intraglobular fat crystallization―homogeneous and heterogeneous nucleation. During homogeneous nucleation, there are no impurities present to act as nucleation catalysts (6). Heterogeneous nucleation involves the presence of impu- rities that serve as nucleation sites for intradroplet crystallization. After nucleation initiation, crystals may behave as secondary nucleation sites and promote further crystallization. Although an understanding of nucleation and crystallization has been established, it is clear that further insight into the relationship of crystallization kinetics, polymorphic behavior, and rheological properties is necessary to better understand the destabilization and/or stabilization of emulsified systems. The goal of this research was to determine the effects of two different fat systems on the crystallization behavior of fats in emulsified oil-in-water and bulk systems. Two fats, of similar final SFC, but different crystallization kinetics were chosen. The kinetics, polymorphism, rheology, and microstructural behavior of two fat systems in emulsified oil-in-water and bulk form were studied.