ABSTRACT
With regard to produce, the term “quality” encompasses sensory properties, nutritive values, chemical constituents, mechanical properties, functional properties, and freedom from defects, each of which has been the subject of many studies (Abbott, 1999; Shewfelt and Bruckner, 2000). Increasing awareness of quality and enhanced perspicacity on the part of consumers are stimulating a strong drive for improved quality of fruit and vegetables, in both the fresh produce market and
Introduction .................................................................................................................................... 129 Fundamentals of Ultrasound Technology ...................................................................................... 131
Utilization of Ultrasound Technology for Agricultural Purposes ............................................. 131 Ultrasound Wave Propagation through Fresh Agricultural Tissue ............................................ 132
Wave Modes and Velocities .................................................................................................. 133 Wave Attenuation and Amplitude ......................................................................................... 133 Directivity Distribution of Ultrasound Waves ...................................................................... 134
Basic Ultrasound Hardware ...................................................................................................... 138 Quality-Related Parameters Correlated with Ultrasound............................................................... 138
Mechanical Parameters ............................................................................................................. 139 Physicochemical Indices ........................................................................................................... 139
Ultrasonic Measurement Techniques Developed for Fruits and Vegetables .................................. 140 Measurements of Tissue Segments ........................................................................................... 140 Measurements of Cut Half Fruit Specimens ............................................................................. 141 Measurements of Whole Fruits ................................................................................................. 145 Portable Systems ....................................................................................................................... 147
Fixed-Load System Operating in the Time Domain ............................................................ 147 Fixed-Load System Operating in the Frequency Domain .................................................... 148 Variable-Load System Operating in the Time Domain ........................................................ 148
Ultrasound Implementations and Quality Assessment of Selected Fruits and Vegetables ............ 150 Avocado ..................................................................................................................................... 150 Apple ......................................................................................................................................... 154 Mango ....................................................................................................................................... 154 Melon ........................................................................................................................................ 156 Olive .......................................................................................................................................... 156 Plum .......................................................................................................................................... 157 Potato......................................................................................................................................... 157 Tomato ....................................................................................................................................... 158
Conclusions .................................................................................................................................... 158 References ...................................................................................................................................... 159
the food-processing industry. There is strong demand to evaluate fruit and vegetable quality during growth and maturation and in the course of the harvest period, storage, and shelf life, and this is an important issue for the growers as well as the distributors and consumers. Generally, people base their quality evaluation of fruits on combined inputs from several senses and, since human judgments are, in general, subjective, these evaluations are liable to be inconsistent and to lead to erroneous quality assessment of the fruit. Thus, there is an increasing need for better quality monitoring. Over the years, many methods and associated instrumentation, based on mimicking human sensory perceptions, have been developed to measure quality-and quality-related attributes; they have been accompanied by a vast array of instrumental sensors for real-time and nondestructive testing (Upchurch et al., 1994; Abbott, 1999). There have been numerous studies of technologies for nondestructive quality measurement of fruits and vegetables-visual, spectroscopic, acoustic, etc.—but Butz et al. (2005) surveyed the literature and found that, in the context of food, about 20% of nondestructive or noninvasive techniques used acoustic methods. This multitude of techniques encompasses an enormous range, from traditional human sensory evaluation by trained inspectors to sophisticated mechanical and electronic devices equipped with state-of-the-art sensors to measure and classify many different quality parameters of fruits and vegetables. The use of ultrasound obviously belongs among the acoustic methods, and Butz et al. (2005) included some examples from this research ›eld in their survey. Ultrasonics is a rather recent addition to the acoustic technologies and methods used in agriculture, especially in fruit quality (Mizrach, 2000a,b). One of the major advantages of ultrasonic waves is their capability to penetrate the produce and nondestructively extract the material characteristic that might be correlated with quality indices of the fruits and vegetables (Mizrach et al., 1989; McClements et al., 1990).
