Introduction

Ideally, a food manufacturer would like to take a combination of raw materials and convert them into a high quality product at the lowest possible cost. This conversion is achieved by subjecting the raw materials to a number of processing conditions, e.g., heating, cooling, pressure, shearing or mixing. Inherent variations in the raw materials and of the processing conditions mean that the properties of the final product vary in an unpredictable manner. To control and minimize these variations food manufacturers need to characterize the properties of the raw materials, and to monitor the food at each stage of processing. Food processing operations are becoming increasingly sophisticated and are often computer controlled. Traditional chemical and gravimetric techniques are time consuming and laborious to carry out, and so there has been considerable motivation for the development of rapid analytical sensors for monitoring the properties of foods.

Ultrasound utilizes interactions between high-frequency sound waves and matter to obtain information about the composition, structure and dimensions of materials through which it propagates. The power levels used in ultrasonic testing are so low that the properties of the material are not altered, thus the technique is non-destructive. This is in contrast to high energy ultrasonic applications which are sometimes used in the food industry for cleaning, cell disruption, heating, sterilization or emulsification purposes [1],

A wide variety of different applications of ultrasound to foods have been developed over the past 50 years or so, reflecting the diversity and complexity of food materials, and the versatility of the ultrasonic technique [2-6]. Even so, ultrasound has still not found wide spread use in monitoring food processing operations. This situation will almost certainly change in the near future. Advances in microelectronics have made available sophisticated electronic instrumentation capable of making accurate ultrasonic measurements at relatively low-cost. The interaction between ultrasound and many microheterogeneous materials is fairly well understood, and there are mathematical formulae available for interpreting ultrasonic measurements in a number of systems relevant to the food industry. Finally, ultrasound offers a number of advantages over alternative techniques used to monitor food processing operations: it is capable of rapid and precise measurements, it is non-intrusive and noninvasive, it can be applied to systems which are concentrated and optically opaque, it is relatively inexpensive and it can easily be adapted for on-line measurements.

The basic concepts of ultrasonic propagation in materials, and methods used to carry out and interpret measurements in food systems have been reviewed elsewhere [2-6]. In this chapter applications of ultrasound relevant to food processing are discussed.

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