## 2 Non Destructive Sensing
### Non Destructive Measurements  
Ultrasound technology is used in a limited range in the food industry. Ultrasonic waves can be transmitted, reflected, refracted or diffracted as they can interact with the material. Wave propagation velocity, attenuation and reflection are the important ultrasonic parameters used to evaluate the tissue properties of horticultural products. Ultrasonic measurements could be used for firmness determination in some fruits but that a more powerful ultrasonic source is required to penetrate them [34]. Acoustic tomography quantified red oak decay and the tomograms could not distinguish between large internal cracks and heartwood decay [35]. Ultrasonic transmission through potatoes was used for hollow heart detection [36]. Three X-ray techniques are used to measure the interior quality of fruits and vegetables: two-dimensional radiography, line scan radiography and X-ray computerized tomography (CT). The application of X-ray CT for quantifying physical properties of fleshy fruits requires appropriate correlations between the physical property and X-ray absorption have been demonstrated by many researchers [37-39], X-ray techniques has been applied for detecting watercore in apple, split pit in peach, the presence of pits in processed olives and cherries, freeze damage in citrus, bruises, and the presence or feeding of insects on fruits [38,40-42]. Internal changes during peach ripening and different maturity can be clearly monitored through X-ray imaging [43]. X-ray spectrometry combined with chemometrics presents high potential to discriminate conventional from organic grown tomatoes and coffee beans [44]. In the nuclear magnetic resonance (NMR) imaging technique, water in the material is subjected to both static and oscillating magnetic fields at right angles to each other and areas with greater free water appear brighter (MRI). Disorders involving water distribution as watercore, chilling injury, bruising, decay and presence of insects can be visualized [45-49]. MRI has been used to show ripening [50], seeds or pits [51], pathogen invasion [52], bruises [53], and ripening changes due to freezing and chilling [48,54]. A study of red cherries correlated firmness, dry matter, soluble solid content, total acidity and bir acid ratios [55]. However, NMR imaging has a number of disadvantages: the high cost of the instruments, radiation hazard, insensitivity near the surface, variation in readings due to density changes, which may cause error rates up to 15%. Actually those equipments are of no practical use as they are expensive and difficult to operate, but have a great potential for evaluating the internal quality of fruits and vegetables. Imaging techniques have been developed as an inspection tool for quality and safety assessment of agricultural food products. Imaging is generally non-destructive, reliable, and rapid depending on the specific technique used [56]. Inspection of tomatoes, apples, peaches with respect to size, color and shape by machine vision is already automated in the industry [57-59]. Studies with different fruits indicated that the decay of chlorophyll parallels the ripening process [60,61]. Hyperspectral imaging systems combine conventional imaging techniques and spectroscopy to acquire both spatial and spectral information from fruits and vegetables for determining important quality parameters [56,62-65]. However, the technology thus far is very slow and cannot be implemented in a real time detection system. Starch or soluble solids [66,67] contents can be determined in intact fruit (apple, citrus, kiwifruit, mango, melons, peach, potato and tomato). Oil content in seeds, nuts and avocado can be determined using near infrared (NIR), while differences between healthy and damaged tissues in visible and NIR diffuse reflectance are useful for detecting bruises [68,69] chilling injury [70], scalp [71], decay lesions and numerous other defects.