Beyond the familiar names of salt and sugar listed on the labels of our food products, there is a whole other world of other ingredients working to preserve the quality and safety of our food. In today's article, we will be looking at an ingredient that is not given the recognition it deserves. Embark of this journey to know about the ingredient in question which is known as sequester.
Sequesters: What are they?
Sequesters also known as sequestrants are compounds which play important roles in food by interacting with various components in food systems. They are generally added to food for the primary purpose of controlling the reactivity and availability of metal ions in food. They enhance food quality, stability and safety through their diverse functions which will be discussed later on in the article. Now that we have an idea of what sequesters are, let's look at some of the sequesters added to food.
Coming in at first place is the ever humble citric acid found in citrus fruits. Citric acid does not only add a tangy zing to our food, but they also play the crucial role of chelating or binding metal ions. They yield their power by forming stable complexes with metal ions in food and preventing them from forming complexes with other components in the food.
Another player in the group of sequesters is the polyphosphate. This polyphosphate is derived from phosphoric acid and have the ability to manage the water behaviour in food. This ability of polyphosphates prevents the soggy texture that is associated with frozen foods and baked goods.
Ethylenediaminetetraacetic acid commonly known as EDTA belong to the high-tech sequesters. EDTA is a synthetic sequester with a remarkable ability to bind a wide range of metal ions present in food. They form stable complexes with these wide range of metal ions making them a great ally when it comes to preserving food integrity.
Naturally occurring in grains, legumes and seeds, phytic acid is another ally in the group of sequesters. This acid binds minerals like zinc, calcium and iron and reduce their bioavailability. They prevent oxidation and discolouration in whole grain foods and legume-based products.
Functions of sequesters in food
Metal binding ability: Sequesters are commonly used to bind metal ions in food such as calcium, magnesium and iron. By chelating or binding with these ions, undesired reactions which lead to flavour deterioration and nutrient loss are prevented (Vardhanabhuti, 2018).
Antioxidant activity: Some sequesters like citric acid exhibit antioxidant properties by scavenging free radicals and inhibiting oxidative reactions in food. This helps to extend the shelf life of food and maintain their fresh quality.
Texture maintenance: Sequesters contribute to texture maintenance in food by interacting with proteins and polysaccharides. They enhance textural properties like viscosity, stability and mouthfeel which brings about an improved sensory experience (Tang, 2019). Also sequesters such as polyphosphates control the moisture levels in food by binding with metal ions like calcium and magnesium and this prevents the soggy texture sometimes associated with frozen foods and baked goods. This explains why your bread stays fresh and your favourite ice-cream maintains its smooth, creamy texture.
Preventing enzymatic browning: The process of enzymatic browning requires the action of copper ions to catalyze the browning process. Introducing sequesters into food prevent this action from taking place since the copper ions needed to catalyze the process is bound by the sequesters. This preserves the appealing appearance of fresh products.
Prevent contamination of processed foods: Apart from their role in preservation, sequesters also ensure the safety of food like processed meats and canned foods. Some heavy metals like cadmium and lead can make their way into acidic foods in trace amount during processing or storage. Now with sequesters like EDTA present in such foods, they perform the action of binding and immobilizing these harmful ions and prevent them from being absorbed into the body.
Mechanism of action of sequesters
Chelation of metal ions is the basic mechanism of action when it comes to sequesters. Chelation is basically the process where a chelator forms a stable, water soluble complex with metal ions, effectively removing them from the food matrix. The major aspect of the chelating process include:
Approach: The sequestrant molecule approaches the metal ion, facilitated by factors such as pH, ionic strength, and the presence of competing ions or compounds.
Coordination: The donor atoms such as oxygen or nitrogen
present in the sequestrant form coordinate covalent bonds with the metal ion, leading to the formation of a metal-ligand complex (Aaseth et al., 2004).
Ring formation: As more donor atoms from the sequestrant bind to the metal ion, a cyclic, ring-like structure known as a chelate complex is formed. This ring structure is more stable than individual metal-ligand bonds due to the chelate effect.
Equilibrium: The chelation process is an equilibrium reaction, where the formation of the chelate complex is governed by the stability constant (or equilibrium constant) of the complex. Factors such as pH, temperature, and the presence of competing ions can influence the stability and formation of the chelate complex.
Applications of sequesters in the food industry
Applied in the beverage industry: Although citric and phosphoric acids are employed as acidulants in soft drink beverages, they also chelate metals that otherwise could promote oxidation of flavor compounds, such as terpenes, and catalyze discoloration reactions. Sequesters also stabilize fermented malt beverages by complexing copper. Free copper catalyzes oxidation of polyphenolic compounds that subsequently interact with proteins to form permanent hazes or turbidity.
Used in making baked goods and dairy products: Sequesters are used to improve the texture and stability of dairy products such as processed cheese and ice cream. They are also used in baked goods to control moisture levels and maintain freshness and texture.
Employed in canned seafood and vegetables: They are used in canned seafoods to prevent reactions, particularly with sulfides, that lead to product discoloration. EDTA and citric acid bind to copper ions, which are cofactors for enzymes that cause browning in vegetables. By chelating these copper ions, sequestrants inhibit enzymatic browning and maintain the natural color and appearance of canned vegetables.
Used in processed meat: They prevent lipid oxidation and rancidity in processed meat. They also maintain its texture and water-binding capacity.
Conclusion
As the food industry continues to evolve and consumer demands for freshness, quality, and safety remain paramount, the role of sequestrants will only become more crucial. They work tirelessly behind the scenes to ensure that the foods we love maintain their vibrant colors, tantalizing flavors, and optimal textures, from farm to fork. So, the next time you glance at a food label and see an unfamiliar ingredient like sodium polyphosphate or EDTA, remember the vital role these compounds play in preserving the integrity and safety of our culinary delights.
References
Aaseth, J., Crisponi, G. and Anderson, O., 2016. Chelation therapy in the treatment of metal intoxication. Academic Press.
Vardhanabhuti, B., 2018. Metal Ion Binding Properties of Sequesters in Food Systems. Food Chemistry, 264, 108–115
Tang, L., 2019. Texture Modification by Sequesters in Food Products. Trends in Food Science & Technology, 86, 37–45
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