6.3 Lipid oxidation and antioxidants
3 min read•august 7, 2024
Lipid oxidation can turn your favorite foods rancid, ruining their taste and smell. It's a chain reaction triggered by free radicals, causing unsaturated fats to break down into stinky compounds. But don't worry, there's hope!
Enter antioxidants, the superheroes of food preservation. These compounds, both natural and synthetic, fight off free radicals and stop oxidation in its tracks. They keep your food fresh and tasty for longer, making them essential in food science and production.
Lipid Oxidation
Rancidity and Free Radicals
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- occurs when lipids undergo oxidative deterioration resulting in and odors
- Caused by the formation of free radicals, highly reactive molecules with an unpaired electron
- Free radicals are generated through exposure to light, heat, or metal ions (iron, copper)
- React with in lipids to initiate a chain reaction of lipid oxidation
- Leads to the formation of various aldehydes, ketones, and other compounds responsible for rancid flavors and odors (hexanal, pentanal)
Autooxidation Process
- is a spontaneous reaction between atmospheric oxygen and unsaturated fatty acids
- Occurs in three stages: initiation, propagation, and termination
- Initiation involves the formation of lipid free radicals through the abstraction of a hydrogen atom from an unsaturated fatty acid
- Propagation involves the reaction of lipid free radicals with oxygen to form peroxy radicals, which then abstract hydrogen from another unsaturated fatty acid, creating a new lipid free radical and a lipid hydroperoxide
- Termination occurs when two radicals react with each other to form non-radical products or when antioxidants donate hydrogen atoms to neutralize the radicals
Hydroperoxides and Decomposition Products
- Lipid hydroperoxides are the primary products of autooxidation
- Unstable and readily decompose into various secondary oxidation products (aldehydes, ketones, alcohols, hydrocarbons)
- Decomposition is accelerated by heat, light, and metal ions
- Secondary oxidation products contribute to the off-flavors and odors associated with rancidity
- Measuring the concentration of hydroperoxides and secondary oxidation products is used to assess the extent of lipid oxidation in foods (, thiobarbituric acid reactive substances)
Antioxidants
Natural Antioxidants
- Compounds naturally present in foods that can delay or prevent lipid oxidation
- Act by donating hydrogen atoms to neutralize free radicals or by chelating metal ions that promote oxidation
- Examples of include tocopherols (vitamin E), ascorbic acid (vitamin C), carotenoids (beta-carotene, lycopene), and phenolic compounds (flavonoids, phenolic acids)
- Tocopherols are the most widely used natural antioxidants in foods, particularly in vegetable oils and nuts
- Ascorbic acid is commonly used in meat products to prevent oxidation and maintain color stability
Synthetic Antioxidants
- Chemically synthesized compounds added to foods to prevent or delay lipid oxidation
- Commonly used include butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tertiary butylhydroquinone (TBHQ), and propyl gallate (PG)
- These antioxidants are effective at low concentrations and are often used in combination to achieve synergistic effects
- BHA and BHT are widely used in cereals, baked goods, and processed meats, while TBHQ is commonly used in vegetable oils and fried foods
- The use of synthetic antioxidants is regulated by food safety authorities, with maximum permitted levels established for each antioxidant
Chelating Agents
- Compounds that can bind metal ions (iron, copper) and prevent them from promoting lipid oxidation
- Work by forming stable complexes with metal ions, rendering them inactive and unable to catalyze oxidation reactions
- Common chelating agents used in foods include citric acid, ethylenediaminetetraacetic acid (EDTA), and phosphates
- Citric acid is widely used in beverages, jams, and canned fruits and vegetables to prevent oxidation and maintain color stability
- EDTA is often used in salad dressings, mayonnaise, and other emulsified products to prevent oxidation and extend shelf life
Key Terms to Review (18)
Autooxidation: Autooxidation is a chemical reaction that occurs when unsaturated lipids react with oxygen, leading to the formation of free radicals and ultimately resulting in the degradation of fats and oils. This process can cause rancidity, affecting the flavor, color, and nutritional quality of food products, and it often occurs spontaneously without the need for external catalysts.
Chelation: Chelation is a chemical process where a molecule binds to a metal ion, forming a stable complex that can enhance solubility and prevent the metal from participating in unwanted reactions. This process is crucial in various biological and chemical systems, especially in food science, where it plays a significant role in lipid oxidation and the action of antioxidants.
Food fortification: Food fortification is the process of adding essential nutrients to food products to enhance their nutritional value and prevent deficiencies in the population. This practice addresses specific dietary gaps and health issues by introducing vitamins, minerals, or other beneficial substances into commonly consumed foods, ensuring that individuals receive the necessary nutrients even when their diets may be lacking. It plays a critical role in public health strategies aimed at improving overall nutrition and reducing the incidence of diet-related diseases.
Hydrolysis: Hydrolysis is a chemical process that involves the breaking down of compounds by the reaction with water. This reaction is essential in food science as it can lead to the breakdown of larger molecules like starches and lipids into smaller, more manageable units, which can then be utilized in various food applications. The process plays a crucial role in modifying starches for better functionality and impacts lipid stability, particularly in the context of oxidation reactions.
Light exposure: Light exposure refers to the amount of light, particularly ultraviolet (UV) and visible light, that a substance is subjected to over a certain period of time. This exposure can significantly influence various chemical reactions, especially lipid oxidation in food products, leading to changes in flavor, aroma, and nutritional quality. Understanding light exposure is crucial for managing the stability and shelf life of food products containing lipids.
Natural antioxidants: Natural antioxidants are compounds found in various foods that help prevent or slow down oxidative damage in cells by neutralizing free radicals. These substances play a crucial role in maintaining food quality and safety, as well as offering potential health benefits by protecting the body from oxidative stress and related diseases.
Off-flavors: Off-flavors refer to undesirable tastes and odors in food products that deviate from the expected sensory qualities. These flavors can arise from various sources, including chemical reactions, microbial activity, or exposure to environmental factors. The presence of off-flavors can greatly affect consumer acceptance and food quality, making it essential to understand their origins and how to prevent them, particularly in relation to lipid oxidation and the role of antioxidants.
Oxidative Stability: Oxidative stability refers to the ability of lipids to resist oxidative degradation over time, maintaining their quality and nutritional value. This stability is crucial in food science as it impacts flavor, color, and nutrient retention, while also determining the shelf-life of food products. Understanding oxidative stability helps in identifying effective antioxidants and predicting product longevity under various storage conditions.
Packaging technologies: Packaging technologies refer to the various methods and materials used to protect, preserve, and present food products during storage, transportation, and sale. These technologies play a crucial role in extending the shelf life of food items by minimizing exposure to environmental factors like oxygen, light, and moisture, which can lead to spoilage. Effective packaging not only maintains food quality but also serves as a marketing tool and provides information about the product.
Peroxide Value: Peroxide value is a measure of the extent to which lipid oxidation has occurred in fats and oils, indicating the presence of peroxides and hydroperoxides formed during oxidative deterioration. This value is crucial in evaluating the freshness and quality of fats, as high peroxide levels can lead to off-flavors, odors, and potential health risks. Understanding peroxide value helps in assessing the effectiveness of antioxidants in preventing lipid oxidation and maintaining the stability of food products.
Rancidity: Rancidity is the process through which fats and oils undergo decomposition, leading to unpleasant flavors and odors. This deterioration can occur due to lipid oxidation or hydrolysis, which can be accelerated by exposure to heat, light, and oxygen. Rancidity is a significant concern in food science as it affects the safety, quality, and shelf-life of food products.
Scavenging of free radicals: Scavenging of free radicals refers to the process by which certain compounds, known as antioxidants, neutralize or eliminate free radicals from the body. Free radicals are unstable molecules that can cause oxidative damage to cells, lipids, and DNA, leading to various health issues. Antioxidants donate electrons to stabilize free radicals, effectively preventing cellular damage and maintaining overall health.
Shelf-life: Shelf-life refers to the length of time that a food product remains safe to consume and maintains its desired quality, including taste, texture, and nutritional value. Understanding shelf-life is crucial in the context of food science because it helps in determining how long products can be stored before they start to deteriorate or become unsafe. Factors such as lipid oxidation can significantly affect the shelf-life of food products, making it essential to study ways to prevent spoilage through the use of antioxidants and proper storage techniques.
Synthetic antioxidants: Synthetic antioxidants are chemical compounds that are artificially created to prevent the oxidation of lipids and other substances in food products. These additives play a crucial role in preserving the quality, safety, and shelf-life of foods by slowing down or inhibiting the oxidative reactions that can lead to rancidity and nutrient loss. They are particularly important in processed foods, where lipid oxidation can significantly affect flavor, color, and nutritional value.
Temperature: Temperature is a measure of the average kinetic energy of the molecules in a substance, which influences various physical and chemical processes. In food science, temperature plays a crucial role in lipid oxidation, thermal processing, and the shelf-life of products, as it affects reaction rates, nutrient stability, and microbial growth.
Thiobarbituric acid reactive substances (TBARS): Thiobarbituric acid reactive substances (TBARS) are a group of compounds formed during the oxidative degradation of lipids, particularly unsaturated fatty acids. These substances are often measured as an indicator of lipid peroxidation, which is a significant reaction that can lead to the deterioration of food quality and safety. Understanding TBARS helps in evaluating the extent of lipid oxidation and the effectiveness of antioxidants in food systems.
Triglycerides: Triglycerides are a type of fat (lipid) found in the blood, composed of three fatty acid molecules attached to a glycerol backbone. They are the most common form of fat in the body and serve as a significant energy source, while also playing a role in various physiological functions and being important for the structure of cell membranes.
Unsaturated fatty acids: Unsaturated fatty acids are fatty acids that contain one or more double bonds in their hydrocarbon chain, which causes kinks that prevent them from packing tightly together. This structural feature makes them typically liquid at room temperature and contributes to their health benefits, as they are known to lower bad cholesterol levels and provide essential fatty acids that the body cannot produce. Their presence in lipids is crucial for understanding processes like lipid oxidation and the role of antioxidants.