Applications of Stable Isotopes in the Food Industry
Stable Isotopes in Food Industry
The stable isotopes 20Ne and 22Ne were the first isotopes to be discovered, followed by stable isotopes of Ar, Kr, Xe, Cl, O, C, N, H and other elements. Molecules containing stable isotopes possess the same chemical and biological properties as compared to normal molecules. However, due to the existence of mass differences, the content of isotopes changes in some processes, which is the isotope fractionation effect. Stable isotope techniques have been widely used in the fields of medicine, agriculture and environmental science, ecology, physiology and food safety. In the food industry, isotopes can be applied mainly in the following directions:
- Identification of food adulteration
- Identification of food origin sources
- Product original traceability
- Pesticide and veterinary drug residue monitoring
Stable Isotopes in Food Traceability Techniques
Food traceability is the process of identifying the origin of a particular product or batch of products from downstream to upstream in the supply chain. Food origin traceability is the process of identifying the origin of a food product and clarifying where the food product being marketed comes from. In nature, different species of plants grown in different geographical areas have different stable isotope ratios. This difference is affected by a variety of factors such as the plant's own qualities, the soil in which it grows, and the atmospheric environment. But the most essential reason is the fractionation of isotopes. Organisms are constantly exchanging substances with the external environment, and there are differences in the natural abundance of their isotopes such as 13C/12C, 15N/14N, 2H/1H, 18O/16O, and 34S/32S. This information, which carries environmental factors, reflects the environmental conditions in which the organisms live, and becomes a kind of "natural fingerprint", which can be used to distinguish substances of different geographical origins. Isotope fingerprint is a natural label of all organisms, which is closely related to the growth environment of organisms, and does not change with the change of chemical additives, and as a characteristic label, it provides food traceability with a kind of scientific, independent, unchangeable, and accompanying the flow of the entire food chain identification information. In terms of food origin traceability, the measurement and analysis of the isotope ratios of the elements C, N, H and O are commonly used.
Carbon Isotope
Carbon isotope composition in plants is closely related to the photosynthetic carbon metabolism pathway of plants, and also affected by environmental factors, 13C value in plants is the result of the joint action of biological factors and environmental factors. Temperature is an important climatic factor affecting carbon isotope fractionation in plants, and the results of its influence on 13C values are more complicated. Therefore, 13C value is mainly used for the traceability of crops and plant products.
Nitrogen Isotope
The 15N/14N ratio is not only related to the plant's own nitrogen source, but also influenced by environmental factors such as climate and soil conditions. By calculating the 15N value, it is possible to distinguish between products of different agricultural production methods and different geographical origins.
Hydrogen and Oxygen Isotope
Hydrogen and oxygen are components of the water molecule, and they are the most desirable isotopes for tracing the water cycle. Stable hydrogen isotope compositions are usually expressed as 2H/1H and stable oxygen isotope compositions as 18O/16O. The ratio of stable isotopes in water is subject to regular changes in the water cycle mainly due to mixing and isotope fractionation caused by changes in physical conditions such as condensation and evaporation of rainwater. Plants and animals obtain water from the environment when they exchange substances, and the isotope ratios in their tissues are directly related to the environment of their growing regions, thus providing a theoretical basis for food traceability.
Issues such as additive residues in food and beverages and pesticide residues in fruits have always been a common concern. In addition to food safety, food authenticity also has an important impact on human health, and the means of counterfeiting and adulteration will greatly reduce the quality of food. For the time being, food authenticity has gradually become an important part of food testing research. The traditional determination of the content of the main components can no longer meet the needs of food authenticity identification, such as the addition of sucrose in honey, the addition of corn syrup in fruit juice, the use of edible alcohol to blend grain wine and other adulteration behavior. General physical and chemical analysis means have become increasingly unsuitable for the detection needs. Stable isotope technology is used to identify the real properties of food by detecting 13C, 15N, 18O and 2H values in food. Stable isotope technique is gradually favored by researchers because of its high sensitivity, high accuracy and low detection limit.
13C Isotope
The stable carbon isotope technique is widely used in the identification of the true properties of food. The technique was first used in the 1970s by Dr. White, an American scientist, to detect carbon isotope ratios in honey to identify adulteration of high-fructose corn syrup. The United States and the European Union have recognized the use of this technique for adulteration and traceability of products such as fruit juices and honey.
2H, 18O Isotope
Stable isotope techniques are mainly based on 13C and are widely used especially in the identification of fruit juice adulteration. However, 18O and 2H values can also support the identification of food authenticity. For sugar adulteration in fruit juices, 13C values are often used, but if C-3 plant sugars such as beet sugar are added, they cannot be identified by 13C values. However, the 2H value of beet sugar is more different from that of sugar in fruit juices, so it is more suitable for discriminating the presence of beet sugar adulteration. In addition, through the simultaneous determination of hydrogen and oxygen stable isotope ratio values, the authenticity of fruit juices can be more comprehensively analyzed, which provides multiple support for authenticity determination and origin traceability.
15N Isotope
Nutrients in food, such as proteins, amino acids, and vitamins, contain nitrogen (N). Classical Kjeldahl nitrogen determination is not applicable for the quantitative analysis of N-containing nutrients. Isotope Dilution Mass Spectrometry (IDMS) allows for the specific detection of various substances. For instance, pantothenic acid, also known as vitamin B5, is widely present in living organisms. It is a constituent of coenzyme A, participating in the physiological metabolism of proteins and carbohydrates. Its crucial role in the synthesis and metabolism of fats is particularly significant.
Isotope Dilution Mass Spectrometry (IDMS) is a sensitive and accurate quantitative analytical method that uses a certain concentrated isotope substance with the same molecular structure as the substance to be measured as diluent, and obtains the absolute amount of the substance to be measured in the sample after mathematical calculation by accurate mass spectrometry measurements of isotope abundance and accurate weighing of the added diluent. Since the 1970s, isotope dilution mass spectrometry has been widely used in agricultural, environmental, biological and medical fields, and in recent years, its application in food analysis has been developing rapidly, including the detection of pesticide and veterinary drug residues, illegal and abusive additives, migratory pollutants and toxins in food.
