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The near infrared spectrum is a region between visible and middle infrared light. The wavelength and wavenumber range are 780 ~ 2526 and 12500 ~ 4000 cm-1, respectively, which belong to the molecular vibration spectrum, and mainly reflects the double frequency and combined frequency information of molecular hydrogen group (C-H, O-H and N-H). Due to the different vibration forms and environments of different hydrogen containing groups, their spectra are different in the intensity and location of absorption peaks. Based on different near-infrared spectral information, the required data can be obtained for qualitative and quantitative analysis of samples. It has the advantages of rich information in infrared region and easy to obtain spectral data in visible region, which has been widely used in food and agricultural crop processing and inspection, environmental pollution analysis, scientific medicine, biomedicine, petrochemical and other fields.
Aquatic products are rich in water, protein, unsaturated fatty acids and free amino acids, etc., and are one of the foods consumers like. However, because of its high water content, it accelerates the reproduction of microorganisms and reduces their freshness, which eventually leads to corruption and even endangers the lives of consumers. The rapid and safe detection of aquatic products has become a core issue of concern. At present, the rapid detection methods of aquatic products include near-infrared spectroscopy, Raman spectroscopy, hyperspectral imaging, electronic nose, electronic tongue, and low-field nuclear magnetic resonance. Compared with other detection techniques, near infrared spectroscopy has the following advantages: (1) good reproducibility, high efficiency and low cost. (2) the test is simple, rapid and non-destructive to the sample. (3) the analysis process has the advantages of no pollution, low requirement for testers, on-line detection and so on. Because of this, near infrared spectroscopy has become one of the widely used nondestructive and rapid testing techniques, and has been applied in the fields of product composition analysis, quality detection, adulteration identification and grade evaluation, so as to realize the shelf-life prediction of aquatic products and extend its shelf life.
Freshness evaluation is of great significance to aquatic product quality, safe transportation, storage, etc. The evaluation of freshness of aquatic products using near-infrared spectroscopy has been partially studied. The content of water, protein and fat in aquatic products is closely related to their freshness. The change information of moisture, protein and fat content can be obtained by near-infrared spectrometer, which provides a basis for the identification of freshness of aquatic products. For example:
a. the contents of crude protein, crude fat and water in grass carp meat were determined by near infrared spectroscopy combined with stoichiometry;
b. the correction model was established by near infrared spectroscopy combined with partial least square method to predict the content of water and protein in surimi and fish meal respectively;
c. the contents of water and protein in fish sauce were determined;
d. to evaluate the nutritional status of three species of Dao shrimp;
e. to evaluate the lipid composition and degradation of haddock and long-tailed cod.
At present, there are many kinds of aquatic products in the market, and the phenomenon of adulteration of aquatic products occurs from time to time. The adulteration identification of aquatic products mainly includes variety, origin and foreign matter and so on. Traditional adulteration identification is evaluated by sensory indicators, but the results are too subjective, so it is necessary to perform adulteration analysis of aquatic products in combination with near infrared spectroscopy. The relevant researches are as follows:
Using near-infrared spectroscopy and stoichiometry to identify salmon, cod and seven freshwater fish species.
|Adulteration of meat products||1. In the aspect of surimi detection, visible-near infrared spectroscopy was used to identify two kinds of crab meat with known adulteration;|
2. Qualitative detection of melamine in fish meal and quantitative prediction of its content;
3. Qualitative and quantitative identification of cod liver oil mixed with mutton fat.
|Origin analysis||1. Chemical composition and traceability analysis of tilapia fillets exported from China;|
2. Identify reared and wild sea bass.
As one of the main methods of adulteration identification of aquatic products, near infrared spectroscopy (NIRS) will become a promising detection technology in the future due to its fast, nondestructive and no pretreatment of samples.
The purpose of aquatic product quality classification is to promote the development of fishery, improve the quality of aquatic products and enhance people's consumer trust in aquatic products. Its quality classification is usually based on its color, odor, and texture. In recent years, research scholars have used near-infrared spectroscopy to perform aquatic product rating studies, which are mainly manifested in product freezing and thawing and freshness evaluation. After repeated freezing and thawing, the protein, lipid and moisture in fresh meat will change, affecting its absorption and scattering coefficient, which can be reflected by near infrared spectroscopy. Cold fresh meat and frozen meat can be quickly identified by principal component analysis (PCA).
Shelf life is an important research direction in the field of food. Food shelf life refers to the period of time when food reaches consumers from the perspective of sensory and food safety analysis. Prediction of food shelf life is to use food quality change kinetics and deterioration mechanism to reflect the change of food quality. By studying the freshness and shelf life prediction models of aquatic products, the quality of aquatic products can be better controlled. At present, the shelf life model prediction of aquatic products mainly includes chemical kinetic models (physical and chemical indicators), predictive microbiology (specific decay bacteria), and BP neural network method (multi-index comprehensive), etc. There are few studies on the prediction of shelf life of aquatic products by near infrared spectroscopy, and the establishment of shelf life model is still not perfect.
Near-infrared spectroscopy also has related research in the detection of heavy metal pollution in aquatic products, such as rapid detection of loach contaminated by heavy metals. Organic compounds such as petroleum hydrocarbons are the main pollutants in fish, which can be enriched and harmful to the human body through the food chain. The development of a rapid detection method for petroleum hydrocarbon residues in fish meat is one of the most important research topics at present. Researchers use near infrared spectroscopy to quickly detect petroleum hydrocarbon pollution in silver carp meat. Endosulfan is widely used in agriculture for pest control, resulting in endosulfan residues in water environment or aquatic products, and there is a risk of food safety. It is found that near infrared spectroscopy can also be used as a rapid and convenient method to detect endosulfan residues in aquatic products. In addition, near infrared spectroscopy is also used to determine the age of deep-sea sharks.
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