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Bio-Imaging and its Applications in Food Processing
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Monday, 09 December, 2019, 08 : 00 AM [IST]
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Dhanavath Srinu and D Baskaran
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Food safety has become one of the top priorities around the world and the importance is well understood by everyone involved in the food supply chain including producers, processors, transporters, retailers and consumers. Food safety standards are periodically reviewed worldwide to increase the safety and maintain the quality of agricultural products and processed foods supplied to the consumers. As safety standards are raised, conservative technologies cannot sustain the needs and hence pave the way for new technologies such as bio-imaging in the food industry.
1. Introduction
Digital image processing began in the 1960s for space applications and the early 1970s for medical applications, remote sensing, and astronomy. Research interest in image processing for the food and agriculture industry began in the late 1970s and a few real-time applications were developed in the years of 1980s and 1990s. Researchers understood the potential of image processing and began to focus on research in the food industry.
2. What is bio-imaging?
Biological imaging or bio-imaging is a computer vision technology that uses artificial vision rather than human vision to observe, capture, process and present an object of interest. Researchers in the food and agriculture industry have explored the possibilities of using X-ray, MRI, infrared and thermal imaging.
3. Components of bio-imaging
Bio-imaging systems comprise the basic components such as camera, illumination, frame grabber, and image processing hardware and software.
A camera is a primary component that captures the image of the material of interest. There are a wide variety of sensors used, of these sensors, a charge-coupled device camera is the most commonly used for evaluating external characteristics such as colour, shape, size, and surface texture. For evaluating internal quality characteristics, advanced image acquisition sensors, such as X-ray and MRI are used. Illumination is the lighting source and is very important in capturing good quality images. The frame grabber is a device that aids in the conversion of the analog video signal from the camera into a digital signal. Image processing hardware performs arithmetic and logical operations, and software enables users to write codes to analyse the captured images.
4. Steps involved in bio-image processing
Bio-image processing involves basic steps such as image acquisition, pre-processing, enhancement, segmentation, representation, description and recognition. Image acquisition is the process of acquiring the raw binary data from the image of interest. Pre-processing is the process of reducing the unwanted features in the images. Enhancement is the technique of making the image clearer and highlighting the area of interest.
Segmentation is the process of dividing the image into many parts. Segmentation is followed by representation in which data are represented as a boundary or whole region depending on whether the objective is to focus on the external shape characteristics or the internal features. The description is the process of obtaining useful quantitative information from the image features. Image recognition is the process of identifying an object based on its description.
5. Need for bio-imaging
Quality is the most important aspect of the food industry since the final product is directly related to the health and well-being of the consumer. The need for bio-imaging became significant as awareness and expectation among consumers increased regarding the safety aspects of food products. Many of the quality monitoring operations in the food industry are performed by human inspection, which is labour-intensive, tedious, inconsistent, and subjective, and sometimes produces less accurate results. Image processing techniques are rapid, consistent, and non-destructive for the quality assessment of various foods.
6. Imaging techniques
a. X-ray Imaging replaced metal detectors due to the ability to detect metal or thin products in the range of 0.5 to 0.7 mm and glass contaminants in the range of 1.5 to 3 mm. Since it is based on the density of the products, it is possible to detect many contaminants in food. Metal detectors cannot be used for products packaged in metalised films, foils, or aluminium trays, whereas X-ray systems can be used for all types of product packaging. X-ray imaging is not only used to detect product contamination, but it can also find missing or broken products, monitor fill levels, and detect improperly sealed packages.
b. Magnetic Resonance Imaging provides useful information on internal processes such as oil and moisture distribution, crystallisation of frozen food, fermentation monitoring in beer and dairy products. MRI is useful to monitor and provide internal characteristics of fruits and vegetables such as bruising, cracks in apples, tomatoes, and potatoes.
c. Infrared Imaging is a non-contact, non-destructive technique that allows on-line testing during production and gives valuable information without impeding productivity and consuming time.
d. Thermal Imaging is used in the food industry for non-contact temperature measurement of foods. Temperature is an important parameter and an increase or decrease in it may decrease the shelf-life of products or even result in the growth of microorganisms, which makes the product unsafe for consumption. Thermal imaging has various applications such as monitoring the temperature of various products and proper filling of frozen meals.
7. Biological imaging in various food applications
i. Grains
X-ray imaging is used for the detection of insect infestation, classification of vitreousness, detection of fungal infection in wheat. MRI could be used for the measurement of the change of moisture profile and to study the structural changes in rice during cooking by monitoring the water distribution. Thermal imaging was used for the detection of insect infestation in grain and sprout damage in wheat.
ii. Fruits and vegetables
X-ray imaging is used for classification of split-pit and normal peaches and detection of insect damage in mangoes, bruises and water core in apples, defects in onions. MRI could be used for the detection of core breakdown in pears, sensory analysis of potatoes and measurement of tomato maturity. Thermal imaging can be used to monitor and assess the surface drying time of citrus fruits. Optical imaging is used for grading fruits and vegetables such as peaches, apples, mandarins, strawberries, potatoes, tomatoes, and onions.
iii. Nuts
X-ray imaging is used for the detection of foreign bodies in hazelnuts. The presence of unwanted foreign materials such as stones, metal chips, and cardboard in almonds, chestnuts, and raisins was detected using thermal imaging.
iv. Confectionery
The three-dimensional cellular microstructure of foods such as chocolate, marshmallows, and muffins was analysed using X-ray imaging. MRI could be used to observe moisture migration in confectioneries and to study the rehydration properties of extruded pasta.
v. Meat and poultry
The applications of MRI in the meat industry are the estimation of poultry breast meat yield, determination of various food components such as water and fat content in ground beef, high-fat deboned chicken, and fresh pork, measurement of the lean meat percentage of a pig carcass. Thermal imaging is used for determining the fat content of pork and ham. MRI is used to determine the quality of eggs to detect defects such as blood spots, dirt stains, and cracks in eggs.
vi. Packaged foods
Detecting spoilage in packaged food is a major challenge for the food industry because they require destructive testing of the sample and time-consuming procedures. MRI could be used to inspect food quality because the main indicator of food spoilage is a lowered pH. MRI is used for detecting bacterial contamination in soy sauce, milk and cheese. Optical coherence tomography could be used for on-line analysis and quality control of multi-layered foils used in food packaging.
Conclusion
X-ray imaging has replaced metal detectors for determination of physical contamination in fresh fruits and vegetables, processed and packaged foods, grains, meat, fish, and dairy products. Thermal imaging found applications in the temperature mapping of foods to detect spoilage and contamination. MRI is used for the determination of moisture migration and water distribution in the foods. It is evident that soon bio-imaging will play an important role in the food industries.
(Srinu is Ph D scholar, College of Food and Dairy Technology [TANUVAS], Chennai and Baskaran is professor, Dept of Livestock Products Technology, Madras Veterinary College [TANUVAS], Chennai)
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