Characterization of food texture: application of Microscopic technology M. Fazaeli, M. Tahmasebi and Z. Emam.Djomeh Transfer Properties Lab (TPL), Department of Food Science and Technology, Faculty of Agricultural Engineering and Technology, University of Tehran, 31587-11167 Karadj, Iran. This review is a survey on the latest and more recent applications of microscopy to study the morphological changes that food components or microorganisms undergo during processing. Apart from a brief discussion on the fundamentals of microscopic techniques, examples have been set out on the physical effects of different processes such as drying (hot air drying, spray drying, microwave, osmotic drying, freeze drying and superheated steam drying), freezing, high hydrostatic pressure, pulsed electric fields, and ultrasound on the microstructure and three-dimensional surface morphology of a wide range of different food materials. Selected examples of microscopic studies of food structure are presented to illustrate the potential of this technique to reveal detailed and specific information. Understanding the relation between processing conditions and food structure, by the use of microscopy, can be helpful for improving food processes or defining the proper conditions that help to retain the quality of the product. Keywords microscopy technique; scanning electron microscopy; microstructure; food processing 1. Introduction Microscopy is being increasingly used to study the influence of processing conditions and ingredients on food structure and only in the last few decades the full potential of electron microscopy (EM) has been recognized. [1] Recent developments in these fields have changed our understanding not only about food structures but also about the types of information which can be now expected to glean regarding structure. Three dimensional imaging, minimal sample intervention and in situ microscopy for dynamic studies, coupled with a greater appreciation of the power of image analysis to derive quantitative information from microscopic images are becoming more common. [2, 3] Scanning electron microscopy (SEM) is a very useful tool to visualize food structure because; it combines in many ways the best features of light microscopy (LM) and transmission electron microscopy (TEM). [4] Several excellent reviews of applications of SEM to food studies exist, including books by Holcomb and Kalab, [5] and a section of Aguilera and Stanley [4] . In addition to these, papers summarizing the applications of SEM [6, 7] and cryo-SEM [8] provide a valuable introduction to the aspects of food structure that can be revealed by these techniques. The history of electron microscopy began with the development of electron optics. In 1926, Busch studied the trajectories of charged particles in axially symmetric electric and magnetic fields, and laying the foundations of geometrical electron optics showed that such fields could act as particle lenses. [9] Nearly at the same time, French physicist de Broglie introduced the concept of corpuscule waves. A frequency and hence a wavelength was associated with charged particles: wave electron optics began. Following these two discoveries in electron optics, the idea of an electron microscope began to take shape. The first true SEM was described and developed in 1942 by Zworykin, who showed that secondary electrons provided topographic contrast by biasing the collector positively relative to the specimen. [10] Compared to light microscopy, SEM has been very attractive for food scientists because both surface and internal features can be studied, a wide range of magnification is possible and the SEM can achieve a depth of field roughly 500 times greater than that of light microscopy. In recent years, the study of the microstructure of food has taken on increasing significance since; the structure of foods can have a profound influence on its nutritional value, rheology and textural attributes. Food processing, such as thermal and nonthermal processes, can be thought of as altering the natural structure and the composition of food materials. [11] However, heat processing, particularly under severe conditions, may give rise to chemical and physical changes that impair the organoleptic properties and reduce the content or bioavailability of some nutrients. Therefore, the food industry is constantly searching for emergent mild processing technologies such as high hydrostatic pressure (HHP), pulsed electric fields (PEF), ultrasound (US), and irradiation, among others, not only to obtain high-quality food with “fresh-like” characteristics, but also food with improved or even novel functionalities. [12] All of these technologies are considered as nonthermal technologies, because the main preservation factor is different from heat (i.e. pressure, electricity, sound waves, light or radiation) and most of them conducted at room temperature. [13] This review article covers uses of microscopy in the study of food structure and highlights the effect of different processes on the microstructure of food ingredients. Different common microscopic techniques are briefly summarized for analysis of food structure. Numerous examples and images are included to demonstrate the richness of information that can be obtained by the discussed techniques. The effects of different processes such as different kinds of drying, freezing, high hydrostatic pressure, pulsed electric fields, and ultrasound on the microstructure of food ingredients or microorganisms have been reported in this study. Current Microscopy Contributions to Advances in Science and Technology (A. Méndez-Vilas, Ed.) © 2012 FORMATEX 855