Oxidation in Foods: Causes, Effects, and Prevention

Oxidation is a series of chemical reactions yielding undesirable products such as off odors, colors, and flavors. This process often occurs in fruits, vegetables, and foods high in fats and oils during exposure to air, light, heat, heavy metals, certain pigments, or alkaline conditions.

Enzymatic browning is a specific type of oxidation that occurs in some fruits and vegetables, particularly apples, bananas, peaches, pears, and potatoes, which contain phenolase enzymes. When these fruits and vegetables are cut or sliced and exposed to air, phenolases catalyze the oxidation of phenolic compounds to ortho-quinone compounds. These compounds then polymerize, forming brown pigments. This browning not only affects the aesthetic quality of the produce but can also alter its taste and nutritional value.

In foods high in fats and oils, oxidation occurs in the form of autoxidation. This process is the result of the susceptibility of fatty acids, the building blocks of fats and oils, to oxidation and the subsequent formation of reactive compounds known as free radicals. These free radicals promote a series of chemical reactions leading to the production of off-flavors, colors, odors, and rancidity. While both saturated and unsaturated fatty acids are prone to oxidation, unsaturated fatty acids are significantly more susceptible, especially at room temperature and elevated temperatures.

To combat these undesirable effects, antioxidants are commonly used. The Food and Drug Administration (FDA) defines antioxidants as substances used to preserve food by retarding deterioration, rancidity, or discoloration due to oxidation. Antioxidants can function in multiple ways. For example, ascorbic acid (vitamin C) may act as a free-radical chain terminator, oxygen scavenger, or metal chelator. However, under certain conditions, ascorbic acid can also act as a promoter of oxidation, highlighting the complex nature of oxidation reactions in food.

Understanding the mechanisms of oxidation and the role of antioxidants is crucial in food preservation. By controlling exposure to air, light, and heat, and by using antioxidants, the shelf life and quality of food products can be significantly improved, ensuring better taste, appearance, and nutritional value for consumers.
Oxidation in Foods: Causes, Effects, and Prevention

Effective Use of Antioxidants in Food Preservation

Antioxidants play a crucial role in food preservation by preventing oxidation, which leads to spoilage and rancidity. However, their effectiveness can be compromised when they interact with oxygen. Therefore, using oxygen-sensitive antioxidants is beneficial only if the food is enclosed in an oxygen-free system or if air can be effectively excluded.

When employing antioxidants, it is essential to consider additional precautions to minimize oxidation. Factors such as heat, light, and metals act as prooxidants, accelerating oxidative reactions. Hence, it is vital to protect foods from these elements to maintain antioxidant efficacy.

Many commercial antioxidants are naturally present in foods, including vitamin C, citric acid, amines, and certain phenolic compounds. Despite their natural occurrence, amines and phenolic compounds can be toxic to humans even at low concentrations. Consequently, both natural and synthetic antioxidants are subject to stringent regulations to ensure their safe use in foods.

While natural antioxidants offer benefits, their potency often falls short compared to synthetic antioxidants. The most effective and widely used synthetic antioxidants are butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and propyl gallate. These compounds are typically used in formulations that combine two or all three, often with an additional component like citric acid. Citric acid serves primarily as a chelator, binding metal ions that could otherwise catalyze oxidative reactions.

Fats and shortenings, particularly those used in bakery goods and fried foods, are highly susceptible to oxidation and the development of rancidity post-cooking. To prevent this, chemical antioxidants are added in concentrations up to 0.02% of the fat content. This small amount is effective in significantly extending the shelf life and maintaining the quality of the food products.

In conclusion, the strategic use of antioxidants in food preservation involves careful selection and combination of compounds, adherence to regulatory guidelines, and protection from prooxidant factors. By understanding and applying these principles, the food industry can effectively combat oxidation, ensuring the safety, taste, and longevity of food products.
Effective Use of Antioxidants in Food Preservation

Antioxidants: Essential Additives for Food Preservation

Since their introduction as food additives around 1947, antioxidants have been essential in stabilizing foods that would otherwise degrade in quality due to oxygen exposure. Oxidative deterioration manifests in various forms, such as rancidity from the oxidation of unsaturated fats, leading to unpleasant odors and flavors, and discoloration from the oxidation of pigments or other food components.

Although preventing food oxidation might seem simple through proper packaging and handling, the reality is more complex. Oxygen is pervasive and difficult to completely eliminate from food systems. Even trace amounts can cause significant degradation, underscoring the necessity of using antioxidants in food preservation.

A wide array of antioxidants exists, each uniquely functioning to achieve the common goal of preventing, delaying, or minimizing food oxidation. Some antioxidants directly combine with oxygen, effectively removing it from the food environment. For example, compounds like ascorbic acid (vitamin C) and tocopherols (vitamin E) react with oxygen, preventing it from interacting with other food components. This method is particularly effective in hermetically sealed containers, where the limited oxygen present can be entirely consumed by the antioxidants due to their high affinity for it.

Other antioxidants work by interrupting the chemical reactions that lead to oxidative damage. Synthetic antioxidants such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) are commonly used in the food industry. They function by donating hydrogen atoms to free radicals, neutralizing these reactive molecules before they can damage food components.

Recent advancements in food science have led to the development of natural antioxidants, which are gaining popularity due to consumer preference for natural additives. Extracts from rosemary, green tea, and grape seeds are examples of natural antioxidants that have proven effective in preserving food quality.

In summary, antioxidants are indispensable in the food industry for maintaining the quality and shelf life of various products. They work by either reacting with oxygen to remove it or by preventing oxygen from interacting with food components, ensuring that foods remain appealing and safe for consumption.
Antioxidants: Essential Additives for Food Preservation

Balancing Tradition and Innovation: The Role of Antimicrobial Agents in Food Preservation

Salt, an ancient and widely used preservative, excels as a microbial inhibitor primarily by reducing the water activity in foods to which it is added. Microorganisms require water to grow, and by binding water molecules, salt effectively reduces the available moisture, thereby inhibiting microbial growth. This method of preservation is further enhanced when combined with drying or smoking processes. Drying reduces moisture content, and smoking introduces compounds that have antimicrobial properties, thereby providing a partial preservative effect.

The effectiveness of salt is complemented by other preservative methods involving weak acids and their salts, such as sorbic acid, benzoates, and propionates. These compounds create an environment that is inhospitable to microbial growth. Additionally, nitrites and nitrates are used in cured meats to inhibit Clostridium botulinum, the bacteria responsible for botulism. These compounds not only prevent the growth of this deadly bacterium but also maintain the meat's desirable color and enhance its flavor.

Natural spices like garlic, cinnamon, and cloves also possess antimicrobial properties, making them effective natural preservatives. In recent years, there has been a renewed interest in these natural preservatives due to consumer demand for clean labels and natural ingredients. Antibiotics, although effective as antimicrobial agents, are increasingly regulated. Their use as food additives has been banned in many countries, including the United States, due to concerns about antibiotic resistance and toxicity.

Regulation of antimicrobial agents is crucial, as many of these substances can be toxic to humans if consumed in excessive amounts. Regulatory bodies, such as the FDA in the United States, establish maximum allowable levels for these additives to ensure food safety. Nitrites, for instance, while effective in preventing botulism, must be carefully regulated due to their potential health risks.

In summary, the use of salt, weak acids, natural spices, and regulated chemical additives remains essential in food preservation. These methods, when used within established safety guidelines, effectively inhibit microbial growth, ensuring the safety and longevity of food products. The combination of traditional and modern preservation techniques continues to evolve, balancing efficacy and consumer health concerns.
Balancing Tradition and Innovation: The Role of Antimicrobial Agents in Food Preservation

Essential oils

Driven by the growing interest of consumers for natural ingredients and their concern about potentially harmful synthetic additives, the global demand for essential oils is increasing nowadays.

Essential oils (also called volatile or ethereal oils) are aromatic oily liquids obtained from plant material (buds, flowers, leaves, bark, twigs, seeds, herbs, wood, fruits and roots) and possess radical scavenging characteristics.

The significance of essential oils in food industry applications is attributed to their antimicrobial, antioxidant, antiviral, antimutagenic and anticarcinogenic characteristics. Their main active components are: thymol, carvacrol, eugenol, cinnamaldehyde and linalool, although their mechanism of action is still poorly understood.

Radicals involved in lipid peroxidation can be scavenged by antioxidants. Because of health protective role of antioxidants, essential oils can be used as food additives. Since ancient times, spices in different types of food to improve flavors are well known for their antioxidant capacities.

The essential oils effectiveness is attributed to the presence of phenolic natural compounds and they are an important and healthy alternative to synthetic preservatives and chemical additives. The FDA treats antimicrobial agents of natural origin as GRAS type products, including plant products and their essential oils.
Essential oils

Free radicals and food quality

Oxygen is an element indispensable for life. When cells use oxygen to generate energy, free radicals are created as a consequence of ATP (adenosine triphosphate) production by the mitochondria.

A free radical can be defined as an atom or molecule containing one or more unpaired electrons in valency shell or outer orbit and is capable of independent existence.

The presence of an unpaired electron results in certain common properties that are shared by most radicals. Many radicals are unstable and highly reactive. They can either donate an electron to or accept an electron from other molecules, therefore behaving as oxidants or reductants.

If free radicals overwhelm the body’s ability to regulate them, a condition known as oxidative stress ensues. Oxidative stress plays a major part in the development of chronic and degenerative ailments such as cancer, arthritis, aging, autoimmune disorders, cardiovascular and neurodegenerative diseases.

In food, free radicals are derived from major food components or their reactive constituents, such as proteins, lipids, and carbohydrates. The formation and decay of free radicals lead to chemical changes in food and thus affect food quality during processing and storage.

The free radicals promote the development of a series of chemical reactions which lead to the production of off-flavors, colors, odors, and rancidity. While both saturated and unsaturated fatty acids are susceptible to oxidation, unsaturated fatty acids are significantly more susceptible than their saturated counterparts at room temperatures and at elevated temperatures.

Synthetic and natural food antioxidants are used routinely in foods and medicine especially those containing oils and fats to protect the food against oxidation. There are a number of synthetic phenolic antioxidants, butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) being prominent examples.

Tea and rosemary extracts are known as efficient natural antioxidants to prevent lipid oxidation in the food industry. The antioxidant activities of tea and rosemary are associated with the presence of phenolic compounds, which can break the lipid radical chain reaction and thus inhibit lipid oxidation.
Free radicals and food quality

Autoxidation of lipids

Products that contain fats and oils turn rancid and deteriorate in other ways when they are exposed to air. The action known as autoxidation. Oxidation in lipids (autoxidation) and in fat and oil containing foods, on the other hand, occurs as a result of the susceptibility of fatty acids to oxidations and subsequent formation of reactive compounds referred to as “free radicals”.

One of the most important problems of lipid oxidation is the generation of harmful compounds that implicate several human pathologies, including atherosclerosis, cancer, inflammation and aging processes, among others.

Autoxidation reaction leads to lipids breakdown and formation of wide range of oxidation products. The reaction happens between oxygen and the unsaturated lipids to form a lipid hydro-peroxide, which then undergoes further reaction with or without the participation of other compounds. This reaction is enhanced by light and metal ions.

Oxidation affects many interactions among food constituents, leading to both desirable and undesirable products.

Oxidation reactions not only reduce the nutritional value of products due to the loss of essential fatty acids and vitamins. Generally, the first change observed results in a gradual reduction of sensory quality. The oil, meat, fishery, dairy, and bakery industries suffer serious losses from autoxidation of their products.

The most common antioxidant is vitamin E, or tocopherol. Fats and oils generally contain phosphatidcs, complex substances that sometimes act as an antioxidant and sometimes also enhance the activity of other antioxidants present.
Autoxidation of lipids

Food additive of vitamin C

Vitamin C or ascorbic acid is the most commercially important vitamin use as a food additive in terms of volume. Vitamin C is used as an antimicrobial and antioxidant in foods. It is preferentially oxidized in place or other substrates and complements very well as a synergist to other antioxidants, such as BHA and BHT in polyphase food system.

The addition of vitamin C to meat is to improve color, flavour and odor as well as lowering the amount of nitrite which has to be used in curing.

Ascorbic acid

Vitamin C occurs naturally in citrus fruits, berries and most other fruits. It is commercially produce exclusively from glucose to sorbitol.

The most important applications for vitamin C include fruit juices, fruit flavored drinks, juice added sodas and dry cocktail or beverage power mixes. Vitamin C is very widely used in bread baking, where it is present as a ‘flour improver’.
Food additive of vitamin C

Tocotrienols in food

Vitamin E is represented by eight different isomers of varying biological potency: four tocopherols and four tocotrienols differ in that the tocopherols have a saturated C16 isoprenoid side chain whereas the tocotrienols have a similar isoprenoid with an unsaturated side chain.

Tocotrienols as a group or as specific isomers have in recent decades been added to the food supply, either as ingredients added to foods or in dietary supplements.

Three major sources of tocotrienols are rice, palm, annatto. One of the biggest challenges in the food industry is keeping food fresh for extended periods of time. This is of particular concern when food contains monounsaturated or polyunsaturated vegetable oils and it is easily oxidized.

Therefore, antioxidants are added to prevent oxidation and preserve freshness. Palm oil and palm tocotrienols are being added to foods for this purpose. Tocotrienols are as efficient as tocopherols in quenching peroxyl radicals in solution whereas in membranes, tocotrienols seem to be more active.

Tocotrienols and tocopherols are powerful antioxidants – known as early as 1937 – for improving food protection and are shown today to potentially protection from cognitive decline. Tocotrienols can help human minds healthy by protecting the blood vessels going to the brain and maintaining proper circulation.
Tocotrienols in food

What are the reasons antioxidants added to foods?

Antioxidants are food additives used since about 1947, to stabilize foods that by their composition would otherwise undergo significant loss in quality in the presence of oxygen.

The uses of antioxidant have a positive effect relative to nutrition. For example, without added antioxidant, essential unsaturated fatty acids, and certain vitamins can be degraded with processing and storage thereby lowering the overall nutritional value of certain foods.

Vitamin C

Oxidative quality changes in foods inlcdue:
*The development of rancidity from the oxidation of unsaturated fats resulting in off-odors and off-flavors
*Discoloration from oxidation of pigments or other components of the food

Antioxidants play an important role in the deceleration of lipid oxidation reactions in foodstuff. According to FDA they are defined as: substances used as preservatives, with the aim to reduce spoilage, rancidity or food discoloration, which are derived from oxidations.

These are some examples of antioxidant food additives:
*Ascorbic acid
*Butylated hydroxyanisole
*Butylated hydroxytoluene
*Propyl gallate
*Tocopherols
What are the reasons antioxidants added to foods?

Vitamins as Food Additive

Vitamins as Food Additive
Oxidation, a series of chemical reactions yielding undesirable and products (off odors, colors, and flavors), may occur in many fruits and vegetables and foods high in fat and oil during exposure to air, light, heat, heavy metals, certain pigments or alkaline conditions. Enzymatic browning may occur in some fruits and vegetables, particularly apples, banana, peaches, pear, and potatoes, which contain phenolase enzymes. When these fruits and vegetables are cut or sliced and exposed to air, the phenolases catalyze oxidation of phenolics compounds to ortho-quinone compounds, which then polymerize, forming brown pigments.

Oxidation in lipids (autoxidation) and in fat and oil containing foods, on the other hand, occurs as a result of the susceptibility of fatty acids (building blocks of fats and oils) to oxidations and subsequent formation of reactive compounds referred to as “free radicals”.

The free radicals promote the development of a series of chemical reactions which lead to the production of off-flavors, colors, odors, and rancidity. While both saturated and unsaturated fatty acids are susceptible to oxidation, unsaturated fatty acids are significantly more susceptible than their saturated counterparts at room temperatures and at elevated temperatures.

Antioxidants, as defined by Food and Drug Administration are “substances used to preserve food by retarding deterioration, rancidity or discoloration due to oxidation.” Some oxidations have more than one function. For example, Ascorbic acids may function as a free-radical chain terminator, and oxygen scavenger, or a metal chelator. Under certain conditions, it may act as a promoter for oxidation.
Vitamins as Food Additive

The Effectiveness of Antioxidants

The Effectiveness of Antioxidants
Some antioxidants lose their effectiveness when they combine with oxygen; therefore, there is no advantages to using this type of antioxidant unless the food is enclosed in a system from oxygen or air can be excluded. In the use of antioxidants, it should be kept in mind that other precautions are necessary to minimize oxidation since heat, light, and metals are prooxidants, that is, their presence favors oxidative reactions.

Many of the antioxidants used in commerce occur naturally in foods (e.g., vitamin C, citric acid, amines, and certain phenolics compounds). However, the amines and the phenolics compounds can be toxic to human in low concentrations; therefore, they and the synthetic antioxidants require strict regulations of their use in foods.

It should be pointed that the potency of the naturally occurring antioxidants is not as great as that of the commonly used synthetic antioxidants. The antioxidants that are considered to be the most effective and therefore are most widely used are butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and propylgallate.

These are usually used in formulations that contain combinations of two or all three of them, and often in combination with even fourth component, very often citric acid. The main purpose in adding citric acid is for its action as a chelator.

Fats and shortening, especially those used in bakery goods and fried foods, are subject to oxidation and the development of rancidity after cooking. To prevent this, chemical antioxidants in concentrations up to 0.02% of the fat components may be added.
The Effectiveness of Antioxidants

Antioxidants as food additive

Antioxidants as food additive
Antioxidants are food additives used, since about 1947, to stabilize foods that by their composition would otherwise undergo significant loss in quality in the presence of oxygen. Oxidative quality changes in foods include the development of rancidity from oxidation of unsaturated fats resulting in off-odors and off-flavors and discoloration from oxidation of pigments or other components of the food.

Although it would seem relatively simple to prevent oxidation of foods by proper packaging and precaution during handling, the facts are that oxygen is difficult to exclude from food systems, especially since it is often closely associated with the food and that only minute amounts of oxygen are sufficient to degrade the food.

There are a large number of antioxidants, and although they may function in different ways, the net effect of each is to prevent, delay, or minimize the oxidation of foods to which they are added. One other ways by which some antioxidants function involves their combination with oxygen.

Others prevent oxygen from reacting with components of the food. When only a limited amount of oxygen is present, as in a hermetically sealed container, it is possible for some antioxidants to use up all of the available free oxygen, because they have a relatively great affinity for it.
Antioxidants as food additive