June 19, 2020
June 11, 2020
The World Health Organization (WHO) has declared safe food a public priority because contaminated and spoiled food poses a significant global health risk. Hence, safety is receiving as much attention as quality in food production. It is, however, not easy to detect threats to food manually, so the WHO suggests that stakeholders consider strategies to reduce risks, including scientific estimation. Therefore, it is worth noting that the same principles that make near-infrared spectroscopy valuable for quality control can also be put to use to evaluate contamination and pest infestation.
Food safety is different from quality; it can result from contamination or microbial spoiling of food.
Sensory evaluation of food safety—by sight, touch, and smell—are still common, not just among consumers but also professionals. Though this simple method is fast, it is subjective and cannot be quantified. Moreover, no person can handle a large number of samples at a time.
There are scientific and objective chemical and microbiological methods that can be used. However, this involves sample destruction and cannot monitor all food items. The cost of analysis, especially, is also high and requires easy access to laboratories and trained personnel. Each of these methods also has its own additional problems.
There are several problems with conventional testing methods. Tests are specific for each compound, so many methods have to be used to analyze different compounds in a single sample. The range of equipment and chemicals needed to test a sample can be high to perform comprehensive tests. The need for multiple tests for a single food involves a lot of sample destruction. Also, chemical analysis produces toxic waste.
Microbial tests are suitable only to detect pathogens like bacteria and fungus and not contamination. There is a very long waiting time, extending to many days, to culture the microbes from samples before they can be identified. Valuable time is lost as defective products continue to be used in processing, packaging, transporting, and sale.
Therefore, optical technology is growing popular with replacing these methods, which, though accurate, are not convenient or pragmatic.
Near-infrared (NIR) is the part of the spectra, between 760–1400 nanometers (nm), that is next to visible light. It is used in spectroscopy as organic compounds (carbon-based compounds) respond to this spectrum. The bonds that hold the different atoms in a compound absorb, transmit, or emit this light based on their individual frequencies. Hence, the interaction of each compound with the near-infrared spectra is unique. This specific response to light or spectroscopy can be measured to identify chemicals and quantify them.
Use of NIR spectroscopy to estimate dry matter, soluble solid content, or water content is well known. Quality, maturity, and ripeness of fruits and vegetables are monitored by measuring these plant parameters.
NIR spectroscopy is also used in finding chemical composition in fish, pork, beef, poultry, milk, and dairy products. It can detect fat, protein, moisture content, carbohydrates, minerals, and vitamins.
It is possible to extend the ability of NIR spectroscopy to detect chemicals to find agents that threaten food safety, like adulterants, microbes, or toxins, as they all have their different spectral signatures.
NIR spectrometers are precise and rapid. Each reading takes only a few seconds, so many samples can be monitored. Processing, sorting, and packaging units have incorporated them in their production line so that the spectrometers can scan all the food they produce. There are also hand-held instruments, which can be equally useful.
The portable NIR is simple and requires no elaborate training or laboratory skills to use. All personnel on farms and in factories can use them to give standardized analysis results in real time.
So, spoiled or diseased materials can be immediately removed from processing lines and the market. This can curb the spread of diseases, control the quality of products, and command better prices.
This application of the technology is equally relevant to both plant and animal food products, as we will show below.
Many food products are adulterated if they are made of expensive materials. Adulteration can reduce the quality of the product and also be a health hazard.
Some of the typical industries where NIR spectroscopy is used to control adulteration is in the production of olive oil, organic food, and animal products.
Virgin olive oils are sought after around the globe for their health benefits, as they contain nutraceutical compounds. The beneficial effects are due, in particular, to the antioxidant contents. These are mainly phenolic compounds. Lipophilic phenols are characteristic in many vegetable oils. However, hydrophilic phenols are found only in olives; they not only increase the stability of virgin olive oil, but also have health benefits.
When cheap vegetable oil is added to olive oil, the concentration of hydrophilic phenols will be lower. NIR spectroscopy can successfully detect and quantify hydrophilic phenols and, thus, check for adulteration. So, suppliers and retailers can both use NIR in price fixing and to maintain the purity of their product.
Industrial agriculture uses excessive quantities of chemical fertilizers and pesticides to increase yield. Avoiding the harmful effects these chemicals have on health is one of the leading reasons for people to choose organic food. NIR detects these agri-chemicals in a wide range of foods. This prevents fraudulent practices where chemically tainted food is passed off as organic produce. Keeping food chemical-free avoids many health problems, especially for children.
Figure 1: “Example of pork meat spectra from different cuts.” (Image credits: http://www.maso-international.cz/download/39_43.pdf)
Animal products can also be adulterated. Since it is challenging to identify meat once they are cut into pieces and frozen, NIR spectrometers are used to identify meat based on their unique chemical composition of proteins, fat, carbohydrates, and moisture content. Even the different parts of an animal can have different spectral signatures based on their chemical composition, as shown in Figure 1.
Beef or lamb is more valuable than other meats, and meat cuts can vary in price. So, the new technology is handy for suppliers and retailers to identify the species and meat to avoid being cheated. There are several well-known instances of adulteration in animal products.
Plant and animal products can be attacked by pathogens and are a significant health threat. According to the World Health Organization (WHO), more than two hundred diseases, from diarrhea to cancers, can be transmitted by microbes and chemical substances they produce.
Plants, grains, and fruits can suffer bacterial and fungal infestations, which result in changes to their chemical composition. Pathogens often produce toxins, which accumulate in the plant, leading to health problems in people. The pathogen can be identified by the chemicals they produce, such as the mycotoxins. The accumulation of toxins can occur due to infestation when the crop is growing or post-harvest.
Figure 2: “HATR absorbance spectra from both fresh and spoiled meats. The box indicates where the most variance in these spectra occur and hence where spoilage signals are likely to be seen.”, Ellis et al., 2011. (Image credits: 10.1128/aem.68.6.2822-2828.2002)
When the meat is left at room temperature or even stored in fridges for days, it will begin to spoil. This results from the decomposition of tissues and the formation of metabolites by microbial enzyme action.
Consider chicken as an example. The bacteria responsible for the initial spoilage in chickens are Pseudomonas spp., Brochothrix thermosphacta, and lactic acid bacteria (LAB). Soon aerobiotic bacteria—like Moraxella spp., Acinetobacter spp., and Psychrobacter spp.—also grow on the poultry.
At a later stage, bacterial action and decomposition result in many sensory deviations. The surface of the meat becomes slimy, changes color, or produces an odor.
These changes can be absorbed in all kinds of meat.
The spectral signature of fresh chicken meat will begin to differ from spoiled meat after eight hours, as shown in Figure 2. Besides NIR, visual, and infrared (Fourier transform infrared - FT-IR) are also useful to detect spoilage of meat.
The Felix F-750 Quality Meter is an example of a NIR spectroscopy-based tool that is available on the market. The F-750 was produced to detect quality and maturity parameters in fruits and vegetables. Since then, it has been used, even by scientists, to study chemical composition in fish. Using the instructions provided, it is possible to build models and calibrate the instruments to test various other meat products. Devices like these can be used to bring scientific advances to the field and factories where they are needed to make food safe and, in the process, avoid loss and wastage of food.
Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture
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