Introduction
Any food (fruits, vegetables, meat, egg, cereals, pulses, etc) which is either in a raw form or processed and packed are highly spoilable, have a shorter shelf life and can readily degrade during the various stages of post-harvesting such as handling, processing, transiting and storage. The spoilage and deterioration taking place leading to loss of quality can be attributed to various factors, being physiological, microbiological, biochemical and biological factors. Moreover, pests, insects and microbial growth significantly contribute heavily towards spoilage of various food products. Quality evaluation is required to be performed, before food products are dispensed with in retail shops and arrive at the customer’s desk. Traditional methods of detecting food quality are devastating, as they require chemicals, are time-consuming and also have high analysis costs. As a result, in the food industry, an optical method for quality analysis is a fundamental one.
Biospeckle Laser Imaging
Biospeckle is a non-devastative, optical method used in the study of biological materials. Biospeckle phenomena occurs when a biological material is illuminated by coherent light. When any material is illuminated by coherent light, the light is backscattered from an optically coarse surface. On the observation plane, bright and dark areas are displayed due to the interferation. By using laser light when the objects are illuminated, the optical intervention effect can be observed which is granular in appearance, with light and dark “speckles” which are formed due to constructive and destructive interference, discretely of scattered laser light. When the investigated object is stable in time, the pattern is also frozen.
For biological materials like food products, light can invade through the plant cell walls and can be backscattered, unless from the external surface or by internal irregularity. The material, while alive, is not stable in both physical and chemical states in space and time. This results in the speckle design pattern comprising of a vital component. The occurrence of a dynamic speckle pattern has been known as the biospeckle. The distinct activity of bio-speckles is formed by the particles with physical movement interior to the cells and is pretentious, due to the changes in the absorption of light by cellular tissue pigments. Hence, the bio-speckles movement supplies information regarding many living operations arising inside a cell. The biotic motion of materials is altered as a result of adulteration, injury, growth development and other elements. Therefore, these parameters might be examined non-destructively using the biospeckle approach in conjunction with a few numerical processing techniques.
Principles and components of Biospeckle Laser Imaging
Laser light from the source is passed through the mirror to reflect the light and is passed through the spatial filter. This spatial filter has three major functions which are as under:
1. To diverge the laser beam;
2. To eliminate noise;
3. To partially annihilate internal noise.
The light from the filter is then passed through the mirror to the sample. The camera captures the image and is processed by a computer to produce a speckle pattern.
Applications of Biospeckle Laser Imaging
Biospeckle Laser Imaging can be used for the detection of damages, ageing of foods, ripening of fruits, respiration rate, water activity, total soluble solids, contamination detection, microbial growth, etc. It has also been used for pre-harvest monitoring of fruits and vegetables. Biospeckle Imaging helps in online monitoring of the quality of food products.
Challenges to applying Biospeckle
The main constraints of the Biospeckle Laser Technology are the inadequacy of a standard as well as the unavailability of the mercantile agricultural instrument to build a universal methodology for activity assessment. The biospeckle laser’s penetration depth on biological samples (about 632.8 nm wavelength) also restricts their applicability. For instance, the penetration depth in apple skin is just 2 mm and 7–10 mm in apple cellular tissue.
The limits of dynamic biospeckle methods may be split into two categories. There are hardware and software constraints.
a) Laser Stability
The He–Ne laser is often used for interferometric measurement, yet its main drawback is troublesome in transporting it from ocular laboratories to further locations. Diode-type lasers have a wide range of highest wavelengths. The usage of low-quality and unstable power sources in the operation of the laser instrument may result in inaccuracies in measurements and results.
b) Camera Modifications
The cameras on the retail shops include several characteristics such as focusing, white light balance, speed and so on. These parameters can be self-operated and set as the default, ensuring that cameras are always functioning in response to changes in lighted substance. This may cause variations in lasers’ dynamic speckle generation. As a result, the solution to this problem is to turn off the camera’s automatic features before entering the data. This will also assist users in analyzing with low-cost cameras.
c) Portability
The external use of the device should be made feasible by fortifying the characteristic attributes to prevail over the interferences caused by machine-like sounds and light from outside sources. The instrument must be built to have an unconventional power source, high stability, longevity and the ability to avoid ripple.
d) Standardization
There should be a well-systematized procedure for standardizing the methodologies employed in the investigation and comparison of biospeckle phenomena. Currently, two sorts of procedures are employed for analysis: offline approaches and online ways. Laser Speckle Contrast Analysis (LASCA) and Motion History Image (MHI) are used in the online technique and the findings are displayed in graphical representations.
e) Light Reference
The impact of light throughout the biospeckle phenomena should be regarded, because the intensity of light might cause changes in the ultimate output.
Future trends and conclusions
The Biospeckle is a non-devastative instrument for evaluating livelihood materials. Biospeckle has a vast range of applications in agriculture, microbiology and medicine. Lately, in the sphere of agriculture, the approach has seen widespread application in evaluating the safety and quality parameters of food items. It is a simple and low-cost technology that has the potential to be used in the food sector, since it enables the quality of samples to be determined without ever encountering them.
The main application is to monitor the ageing and growth development process in the fresh product as well as to identify illness and flaws. Biochemical changes occur in biotic material as well as other intracellular activities, such as cytoplasmic streaming, organelle movement, cell division and growth and so on. Brownian motion is discovered to be the source of biospeckle activity.
References:
1. Braga Júnior, R. A. (2017). When noise became information: State-of-the-art in biospeckle laser. Ciência e Agrotecnologia, 41(4), 359–366. https://doi.org/10.1590/1413-70542017414000317
2. Braga, R. A. (2017). Challenges to apply the biospeckle laser technique in the field. Chemical Engineering Transactions, 58, 577–582. https://doi.org/10.3303/CET1758097
3. Braga, R. A. J., Pujaico Rivera, F., & Moreira, J. (2016). A Practical Guide to Biospeckle Laser Analysis. Theory and Software. 160. https://doi.org/http://dx.doi.org/10.1016/j.omega.2014.12.006
4. Pandiselvam, R., Mayookha, V. P., Kothakota, A., Ramesh, S. V., Thirumdas, R., & Juvvi, P. (2020). Biospeckle laser technique – A novel non-destructive approach for food quality and safety detection. Trends in Food Science and Technology, 97(January), 1–13. https://doi.org/10.1016/j.tifs.2019.12.028
About the Authors:
Suka Thangaraju a, Monica Shankar a & Venkatachalapathy Natarajan a*
a – Research Scholar, Department of Food Engineering, NIFTEM, Thanjavur
a* – HoD, Department of Food Engineering, NIFTEM, Thanjavur
Corresponding Author Email ID: venkat@iifpt.edu.in
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