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Über dieses Buch

This book will review old and new methods to study emulsion stability and structure. Examples of emulsion-based foods include ice cream, yoghurt, and mayonnaise. The physicochemical properties of emulsions play an important role in food systems, as they directly contribute to the texture, sensory and nutritional properties of foods. One of the main properties is stability, which refers to the ability of an emulsion to resist physical changes over time. The development of an effective strategy to prevent undesirable changes in the properties of a particular food emulsion depends on the dominant physicochemical mechanism(s) responsible for the changes. In practice, two or more of these mechanisms may operate in concert. It is therefore important for food scientists to identify the relative importance of each mechanism, the relationship between them, and the factors that influence them, so that effective means of controlling the stability and physicochemical properties of emulsions can be established. Several techniques are used to study the physical behavior and structure of emulsions. Each technique has its advantages and disadvantages and provides different insights into the destabilization mechanisms. Among the oldest methods used to study emulsion stability is visual observation and small deformation rheometry. More recently, other techniques, such as ultrasound profiling, microscopy, droplet size distribution, and measurement of surface concentration to characterize adsorbed protein at the interface, have also been employed. Some of these techniques, such as droplet size distribution, involve some form of dilution. However, dilution disrupts some structures that play an important role in stability. The ability to study the stability of food emulsions in their undiluted form may reveal subtle nuances about their stability. Diffusing wave spectroscopy (DWS), laser scanning confocal microscopy (LSCM), nuclear magnetic resonance (NMR), and Turbiscan are among the more powerful, non-perturbing techniques used to characterized emulsions.



Chapter 1. Introduction

Water and lipids are critical for sustaining life and health, but their poor miscibility has posed a challenge for both nature and man. Emulsions are colloidal dispersions that consist of two immiscible liquids, with one of the liquids being dispersed in the other one. Oil dispersions in the form of small spherical droplets are stabilized in the aqueous phase by proteins or surfactants giving an oil-in-water (O/W) emulsion. The surface-active ingredient is adsorbed at the interface between oil and the aqueous phase to lower surface tension and prevent oil droplets from coming close enough together to aggregate.

Maria Lidia Herrera

Chapter 2. Nano and Micro Food Emulsions

Emulsions with microdroplets, sometimes called conventional emulsions, and nanodispersions, or thermodynamically stable emulsions (surprisingly called microemulsions), can be easily manufactured on an industrial scale up. Due to their satisfactory stability over a certain storage time and high bioavailability, they have attained particular interest as delivery systems for bioactive substances, such as carotenoids, phytostetol, polyunsaturated fatty acids, g-oryzanol, lipophilic vitamins, and numerous other compounds. Garti and co-workers (Amar et al. 2003; Spernath et al. 2002), for example, prepared food-grade conventional emulsions containing carotenoids with considerable success. Recently, studies have shown the successful approach of using nanoemulsions to improve stability in food applications. Tan and Nakajima (2005) and Yuan et al. (2008) prepared β-carotene nanodispersions using high-pressure homogenization and studied their physicochemical properties. Other applications include the encapsulation of limonene, lutein, omega-3 fatty acids, astaxantin, and lycopene (Chen et al. 2006), the encapsulation of α-tocopherol to reduce lipid oxidation in fish oil (Weiss et al. 2006), and the use of nanoemulsions to incorporate essential oils, oleoresins, and oil-based natural flavors into food products such as carbonated beverages and salad dressings (Ochomogo and Monsalve-Gonzalez 2009).

Maria Lidia Herrera

Chapter 3. Methods for Stability Studies

The efficient development and production of high-quality emulsion-based products depend on knowledge of their physicochemical properties and stability. A wide variety of different analytical techniques and methodologies have been developed to characterize the properties of food emulsions. Analytical instruments and experimental methodologies are needed for research and development purposes to elucidate the relationship between droplet characteristics and the bulk physicochemical and sensory properties of food emulsions, such as stability, texture, flavor, and appearance. They are also needed in quality control laboratories and in food production factories to monitor food emulsions and their components before, during, and after production so as to ensure that their properties conform to predefined quality criteria and/or to predict how the final product will behave during storage. This chapter describes the most commonly used methods for stability studies, with a focus on conventional food emulsions. Some of these techniques are also used in nanoemulsions. Several examples of applications are described in detail.

Maria Lidia Herrera


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