June 19, 2020
June 11, 2020
There is inherent variability in the chemical composition of fruits, vegetables, and meat, which cannot be detected by color, shape, touch, or smell. Near-Infrared technology can identify and distinguish products based on their chemical composition. Hence, it is used for the processing of both plant and animal foods in the selection of raw materials to process control, ensure quality standards, and prevent adulteration.
Near-infrared (NIR) is a portion of the light that lies next to the red color in the visible spectrum. It can detect the chemical bonds between the atoms in the organic compounds (i.e. the carbon-based compounds), which make up plants and animals. Hence, these compounds will absorb, reflect, or transmit varying amounts of NIR based on their composition. This property is called spectroscopy.
However, each compound will respond to only a particular wavelength within the NIR, so scientists have to identify this wavelength for each compound; see Figure 1.
Then, NIR spectroscopy can be used to identify chemicals within a sample and the amounts in which are present.
Figure 1: Though there are differences in the spectra of juice from 15 different regions, they all peak at the same wavelengths, Dan et al. 2015. (Image credits: http://dx.doi.org/10.1080/10798587.2015.1095474)
The ability to detect chemical composition is increasingly being used to help in the processing of food.
Modern food products meant for the market need to be of uniform quality and standard. This can be difficult if only the external parameters of fruits or meat are used.
NIR spectroscopy, which provides detailed information on the internal characteristics, has many applications. The parameters analyzed by NIR in plant- and animal-based foods are as follows:
To this end, NIR spectrometers are used in factories before, during, and after processing. In the case of fruits, the NIR examination of food needs to start at farms.
Fruits are used as fresh produce or made into products like juice, jam, wine, leather, etc. NIR is used to fix the harvest time of fruits so that they have the ideal chemical composition. NIR is also used for quality control of fruits post-harvest.
The requirements of the chemical composition will not be the same. Fruits that are processed into jams and wines are measured for sugar content.
Fruits used for juice-making need sugars, such as glucose, fructose, and sucrose, but also some acidity. The acids usually measured are ascorbic acid, citric acid, malic acid, and lactic acid.
NIR helps to fix the right time to harvest fruits and vegetables so that they have the desired levels of sugar and dry matter.
When processors get produce from multiple sources, simple portable NIR tools are useful during many steps of selection and monitoring:
Felix Instruments has a range of Quality Meters that can measure dry matter, BRIX, external and internal color, titrable acidity, and moisture content. The tools have a GPS, so they can be used with Fruit Maps and benefit from local information about crops.
The F-750 Produce Quality Meter is a universal tool that can be used for several fruits and vegetables.
Below are other tools which have been customized for use for specific fruits:
Vegetable oil is the leading food produced, and alone it accounts for 40% of all agricultural crop production. Vegetable oils are produced from soybeans, sunflower, safflower, palm, coconut, cotton, olives, and canola.
Oil production is also a significant sector that uses NIR spectroscopy to estimate oil, water content, and protein content in the seeds or flesh.
In olive oil, NIR is also used to fix harvest time. Olive oil is different from other vegetable oils as there are various grades of oils with a difference in taste. It has been found that leaving olives on trees for a longer amount of time increases the oil content in the flesh, but impacts the flavor of the oil. Moreover, the levels of phytophenols, such as hydroxytyrosol—which are also crucial for flavor and nutritional benefits—are higher in younger fruits. So, in the case of olive oil, fruits are picked earlier to make high-quality oils, and olives that are harvested later are used to make lower grades of olive oils.
Farmers use NIR to estimate dry matter, a good predictor of oil content, to fix harvest dates depending on the grade of oil that is being produced.
In the processing unit, olives are tested so that fruits of similar chemical composition can be used to get a homogeneous product.
The compounds that are analyzed the most, during milk and cheese production, are fat and water content.
Milk, usually obtained from cows, buffalos, goats, and sheep, is sold after it is pasteurized. Usually, a second process called homogenization is conducted. In raw milk, the fat, which exists as globules, tends to float and accumulate on top. In homogenized milk, the fat globules are broken so that they are more evenly distributed in the entire liquid volume.
Homogenized milk has a more extended shelf-life, a better taste, and can easily allow for mixing milk from different herds with varying fat content.
After homogenization, it is possible to skim the fat to produce milk that is low-fat or even completely fat-free.
NIR is useful in estimating fat globule size, as they have different spectral signatures, as shown in Figure 2. So, it is used before, during, and after homogenization.
Figure 2: Difference in size of fat globules in milk alters the absorption and scattering of NIR, Aeronouts, et al. 2015. (Image credits: https://doi.org/10.1016/j.colsurfb.2015.01.004)
Cheesemaking is a vast industry that is increasingly getting mechanized and larger in scale. NIR is useful in practically all of the steps involved in making an extensive range of cheese.
Figure 3: “Visible and NIR spectra of beef, pork, chicken, and lamb meat, adapted from Cozzolino and Murray 2004).” (Image credits: https://onlinelibrary.wiley.com/doi/full/10.1111/1541-4337.12295)
Similar to cheese, meat product processing also uses NIR for chemical composition estimation to help in many tasks. Some of the most common ones are discussed below:
The F-750 Produce Quality Meter can be used for analyzing meat samples, after models are built for specific meat types.
Advantages of NIR
NIR can replace conventional methods that require a lot of time, chemicals, and money. NIR spectrometers can be handy portable tools that are useful in the farm and small processing units. Others are made for use in-line, on-line, or at-line for large scale processing units. Both kinds of tools have the advantage of providing a rapid and accurate analysis that is also non-destructive. The results are available in real time, so that changes can be made immediately during processes to correct and refine them. NIR helps to make processing more precise, improves monitoring and process control, increases end yield, and, lastly, guarantees excellence in quality.
Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture
Feature image courtesy of Ajay Rai
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