Introduction of Oxidative Enzymes
Oxidative enzymes control oxidation in living systems and food processing through the transfer of electrons and hydrogen atoms, and utilizing oxygen at some stage of the process. They are found in plants, grains, fruits, vegetables, and microorganisms. They influence the chemical and physical attributes of food.
In the flour and food industry, oxidative enzymes matter because they impact the quality of the finished food product. These include the strength of the dough, the texture of the dough, the color, the stability of the product, and the overall quality of the product. Some examples of oxidative enzymes are oxidases, peroxidases, polyphenol oxidase, and lipoxygenase. These enzymes can be classified as having either a positive or negative effect on the food they are processed with, as well as the processing conditions and the concentration of the enzyme.
Dough strength can be positively affected by some oxidative enzymes because they can interact with and connect protein and other dough components. This can improve the handling of the dough, gas retention, volume, and result in a better crumb structure. Using oxidative enzymes can positively affect processing of bakery products; however, issues with unregulated oxidation include both color and flavor changes, as well as the loss of nutrients and a decrease in the overall quality of the product.
The activity of oxidative enzymes is pH dependent, as is moisture content, temperature, the amount of oxygen, processing time, and the presence of substrates. Enzyme activity must be regulated for the improved outcome of the end product.
Knowing about oxidative enzymes is vital for milling and baking since their activity happens at the beginning from the raw materials, and can continue through the storage, mixing, fermentation and baking processes. Proper management of beneficial oxidative processes can provide food manufacturers better quality flour and bakery products. Therefore, oxidative enzymes are a vital part of modern food technology and development of better-quality flour and bakery products.
Types of Oxidative Enzymes
Oxidative enzymes are enzymes which play a role in the transfer of electrons or hydrogen atoms to other compounds during reactions. Oxygen, hydrogen peroxide, or other compounds which are oxidizing in nature, may take part in the reactions. In food processing, oxidative enzymes are key and unique because they can affect the quality attributes of foods including color, taste, texture, the strength of the dough, the properties of gluten, nutritional value of foods, and the stability of stored foods. The effects can be either positive or negative, in a given enzyme, substrate, concentration, and processing conditions.
Lipoxygenase
Lipoxygenase is one of the most important naturally occurring oxidative enzymes in wheat, soybean, legumes, and other plants. It acts on polyunsaturated fatty acids like linoleic and linolenic acids in the presence of oxygen and forms lipid hydroperoxides. These lipid hydroperoxides can take part in other oxidation reactions.
Lipoxygenase
In flour processing, when lipoxygenase reacts with lipids it can oxidatively generate a color change in flour, affect dough characteristics, modify flavor, as well as impact pigment oxidation. In a controlled setting, its oxidative activity can produce a slightly refined appearance in flour and positively impact some dough characteristics. While lipid oxidation can affect the desirability and the shelf-life of the food it is used in, so it must be controlled to achieve desired quality in flour and in the bakery.
Polyphenol Oxidase (PPO)
PPO or polyphenol oxidase is predominantly found in wheat, fruits, vegetables and other plants. It oxidizes phenolic compounds into quinones. Quinones react with proteins and other compounds to develop complex pigmentation and dark coloration.
In the context of bakery products, PPO has a great deal of importance. Excessive PPO activity can result in discoloration and browning, which can have adverse effects on appearance. This can also impact the marketability of noodles and pasta, wholegrain baked goods, and other similar cereal based food products. Better raw material selection along with appropriate control of processing parameters can positively impact appearance.
Peroxidase
It oxidizes compounds in the presence of hydrogen peroxide. It is found in cereals, fruits, and other plants and in microorganisms. Peroxidase participates in the oxidation of a number of compounds including pigmented compounds and other food constituents.
Peroxidase plays an important role as it is relatively heat resistant and food processors decide whether food has been adequately thermally processed based on peroxidase activity. Significant activity of peroxidase following thermal processing may suggest that other quality related enzymes could also be active.
Glucose Oxidase
Glucose oxidase is the name of an enzyme which converts glucose to gluconic acid and produces hydrogen peroxide in the process. Glucose oxidase is capable of providing dough with an oxidizing environment.
During the process of dough strengthening and dough conditioning, glucose oxidase can cross-link the amino acids within the gluten network and thus improve the elasticity and stability of the dough in addition to improving the ability of the dough to retain gas and ease in handling.
Laccase
Laccase, along with other phenolic compounds, is found in fungi and some plants and microorganisms. Laccase is an oxidative enzyme which contains copper and oxidizes phenolic compounds.
In biotechnology, especially in food biotechnology, laccase has an important role to play in the phenolic compounds and thus the structure of food ingredients. Laccase has the potential of modifying the phenolic compounds in cereal and bakery applications. Laccase may also affect the texture and structure of the dough in a controlled manner. Laccase works best with the available substrate and is influenced by the type of flour.
Ascorbate Oxidase
Ascorbate oxidase converts ascorbic acid or vitamin C to its oxidized form. Ascorbic acid, in its unoxidized state, does not serve as an oxidizing agent in the gluten network during dough processing and is converted to an oxidizing agent to strengthen the gluten network.
The oxidative system is essential for breadmaking. Controlled oxidation improves dough strength and elasticity while increasing gas retention and volume of the final loaf. The final effects of the oxidation are dependent on the system processing and formulation. For these reasons, the use of the enzyme should be viewed within the context of the broader oxidative system and not simply as a dough improver.
Catalase
Catalase is the name of an enzyme that breaks hydrogen peroxide into water and oxygen. The main role of catalase is to manage hydrogen peroxide within biological and food systems.
Catalase is necessary to control unregulated oxidation of hydrogen peroxide. By removing excess hydrogen peroxide, it averts the oxidation of food components. It is used in both biotechnology and food processing to control oxidation and manage the residual hydrogen peroxide.
Tyrosinase
Tyrosinase is the name of an oxidative enzyme that acts on phenolic compounds of which tyrosine is one. It catalyzes the formation of quinones and colored polymers.
Tyrosinase is a strongly known component of enzymatic browning in most of the plant-based foodstuffs. oxidation of phenolic substances in the enzymes and substrates (which occur during cutting/milling and processing) along with Oxygen, catalyzes the browning reaction (even though it is unwanted). Control of the aforementioned factors (oxygen, temperature, pH, enzyme activity) may minimize the browning reaction.
Phenol Oxidases
Phenol oxidases are a group of enzymes that oxidize phenolic compounds. This group of enzymes can generate quinones that are reactive towards proteins and food components.
There are many ways these reactions can influence the color, flavor, and the nutritional properties of foods, as well as how long they are stable after being processed. When appearance and color are critical quality factors for a cereal product, controlling phenol oxidase activity is vital in cereal processing.
Aldehyde Oxidase
Aldehyde oxidase converts aldehydes into the corresponding acid. Although it receives less attention than lipoxygenase or polyphenol oxidase in the field of flour technology, aldehyde oxidase groups with the other oxidative enzymes.
It’s worth noting that aldehyde oxidase substrates undergo reactions that convert reactive aldehyde compounds and May contribute indirectly to the changes in food systems that affect flavor, aroma, and chemical stability.
Alcohol Oxidase
Alcohol oxidase converts alcohol to an aldehyde, or in certain cases, to a ketone. It is found in many microorganisms and biological systems.
In food biotechnology, there are enzymes that oxidize alcohol, which can assist in the conversion of unstable volatile substrates. Because flavor and aroma of food products are primarily due to volatile compounds, it is critical to control alcohol oxidase activity in order to avoid rapid flavor development and uncoordinated changes.
Amino Acid Oxidase
Amino acid oxidase is an oxidase that converts amino acids to a keto acid and ammonia as well as hydrogen peroxide. It occurs in microorganisms and biological systems.
These oxidases can affect the levels and conversion of amino acids in food systems that can contribute to changes in the food flavor. Oxidation, however, can be detrimental to food systems, and thus, it is critical to control the activity of these enzymes.
Uricase and Other Specific Oxidases
Some oxidative enzymes act on highly specific substrates. An example of this type of enzyme is uricase, which oxidizes uric acid and forms hydrogen peroxide in the process. While enzymes like uricase might not be considered major enzymes in traditional flour processing, they demonstrate the vast potential of oxidative enzymes on their substrates.
There are many applications in food biotechnology, laboratory scenarios, fermentation, and waste-handling with the understanding of these specialized enzymes.
Role of Oxidative Enzymes in Flour and Baking
The food flour milling and processing industries have a unique role for oxidative enzymes. Particularly in wheat, there are naturally occurring enzymes that can impact the flour’s characteristics from the milling phase to dough mixing and fermentation. Some oxidative reactions can facilitate the formation of protein and component cross-linkages and thus strengthen the structure of the dough.
There are beneficial effects to controlled oxidation of the dough on elasticity and stability and on the volume and structure of the crumb. Excessive oxidation may cause color changes and undesirable flavor and/or nutrient and storage quality changes. Thus, the goal in such processes is not to maximize oxidative enzymes, but to achieve just the right level of oxidation.
Factors Affecting Oxidative Enzyme Activity
There are various factors involved in the activity of oxidative enzymes, mainly temperature and pH, though oxidases are affected by other molecules and movements as well.
Other factors include the concentration of the substrate as well as the chosen combination of enzyme, time, and other flour components. Food manufacturers manage these factors in order to achieve the optimal oxidation of their products.
Control of Oxidative Enzymes
The amount of oxidation that occurs is the largest concern when dealing with oxidative enzymes. Not enough oxidation can result in little improvement of dough or product characteristics, and too much oxidation can result in off-flavors, discolorations, or excessive oxidation, and therefore, a loss in quality of the product.
Because of this, the main priority of food manufacturers is the choice of enzyme and the dosage and control of processing conditions. The optimal use of oxidative enzymes will result in an attractive and better performing food product that is safe and stable.
Oxidative Fungal Enzymes
Oxidative fungal enzymes are fungal enzymes that aid in the decomposition of complex organic compounds via oxidation. These enzymes are mainly secreted by filamentous fungi, usually wood-decaying fungi, and play a vital part in natural decomposition of plant biomass. Fungal oxidative enzymes attack even recalcitrant compounds such as lignin, phenolic compounds, dyes and other aromatic compounds. Given their effective oxidation potentials and broad substances they act on, fungal oxidative enzymes play an important role in biotechnology, agriculture, food, pulp and paper industry and environmental applications.
The main oxidative enzymes produced by fungi include laccase, lignin peroxidase (LiP), manganese peroxidase (MnP) and versatile peroxidase (VP). Laccase is a phenol oxidizing enzyme that contains copper. Lignin peroxidase is an oxidizing enzyme that is able to degrade complex lignin structures. Manganese peroxidase oxidizes manganese and can be used to attack lignin and other compounds. Versatile peroxidase has the property of both lignin peroxidase and manganese peroxidase. These enzymes are extracellular, thus allowing fungi to degrade large and insoluble materials outside their cells.
There are numerous applications for oxidative fungal enzymes in industry. For one, these enzymes can function in a range of conditions bordering on mild, unlike most other enzymes. This property makes oxidative fungal enzymes very useful in many industries. In the pulp and paper industry, oxidative enzymes can degrade and alter lignin and help to decrease the amount of severe lignin removal chemicals needed for the paper-bleaching process.
In other industries such as textiles, these enzymes are used to degrade and reduce the color of synthetic dyes. There are many other industrial applications, for example, employing these enzymes in the food industry to change and alter the phenolic content of food products to improve the product quality. Oxidative enzymes from fungi also play an important part in biotechnology to convert agricultural waste into useful substances.
Oxidative enzymes from fungi are also valuable for use in many environmental technologies. Whereas oxidative fungal enzymes can degrade pollutants such as synthetic dyes and some pesticides and pharmaceuticals, oxidative enzymes can be used in bioremediation and to treat wastewater. There are many fungal species that can be used to develop these enzymes, as well as control the activity to be alleviated. These species also grow best under certain conditions including moisture, pH, various nutrients, and the presence of inducers, including oxygen. Knowing and controlling these factors can help improve fungal growth and enzyme production. Altogether, oxidative fungal enzymes are powerful tools for industry, waste processing, and pollution control.
Oxidative Enzymes in Human Cells
Oxidative enzymes in human cells play an important role in oxidation and reduction reactions that occur during the conversion of nutrients into usable cellular energy. Oxidation and reduction processes are channeled by oxidases, oxygenase’s, dehydrogenases, catalases, and peroxidases, among others. Cellular respiration and the metabolism of carbohydrates, fats, and proteins as well as the removal of harmful products from the cell are some of the processes involving oxidative enzymes. The mitochondrial enzymes, along with other metabolic enzymes, facilitate the transfer of electrons in the process of energy generation. At the late stages of cellular respiration, the enzyme cytochrome oxidase participates in the process.
Oxidative enzymes in the human cell also protect the cell from reactive oxygen species (ROS) that can cause damage to the cellular systems. Substrates of oxidation, in the presence of molecular oxygen, are converted to hydrogen peroxide when catalyzed by oxidative enzymes. Catalase converts hydrogen peroxide to water and oxygen while glutathione peroxidase converts hydrogen peroxide and lipid peroxides to water. The conversion of ROS requires a maintenance of balance between oxidation and the antioxidant response. Oxidative enzymes, therefore, participate in the cellular metabolism and the detoxification of harmful substances while their activity must be controlled to avoid the oxidation of cellular components.
Oxidative Enzymes in Peroxisomes
Oxidative enzymes in peroxisomes mainly play a role in the breakdown of fatty acids and the detoxification of harmful substances. Key enzymes in this process are acyl-CoA oxidase, urate oxidase, and D-amino acid oxidase. These enzymes transfer a hydrogen atom to molecular oxygen to form hydrogen peroxide as a by-product. The process of peroxisomal oxidation is critical in the breakdown of very long chain fatty acids, which cannot be effectively processed by the mitochondria on their own. The end products of this breakdown can be further processed by other cellular pathways.
Catalase, like peroxisomes, protects cells from oxidative damage by hydrogen peroxide, which is a byproduct of oxidative reactions. By aiding the conversion of hydrogen peroxide to water and oxygen, catalase helps to avoid oxidative damage of the components of the cell. The role of peroxisomal enzymes in lipid metabolism, detoxification, and the maintenance of the cellular redox balance is attributed to their oxidative nature. Peroxisomal enzyme metabolism is imperative to the normal functioning of a cell, while an absence of peroxisomal enzymes results in the accumulation of harmful material and metabolic disorders.
Mitochondrial Oxidative Enzymes
Mitochondrial oxidative enzymes play a critical role in oxidative phosphorylation and the subsequent production of energy. Most of these enzymes are involved in the electron transport chain (ETC) and the citric acid cycle (TCA cycle). These enzymes include NADH dehydrogenase (Complex I), succinate dehydrogenase (Complex II), cytochrome bc₁ complex (Complex III), and cytochrome c oxidase (Complex IV). During the process of cellular respiration, these enzymes help to transport electrons obtained from nutrients to various components of the chain, and in the process, a proton electrochemical gradient is developed across the mitochondrial inner membrane.
The proton gradient drives the ATP synthase complex. In the final step of the process, cytochrome c oxidase helps to complete the reduction of oxygen to water. Therefore, the role of mitochondrial oxidative enzymes is to convert the potential energy obtained from carbohydrates, fats and proteins to the usable energy of the cell. Even under normal operating conditions, the leakage of electrons during the process produces some reactive oxygen species (ROS). Therefore, the system of antioxidants is vital to avoid oxidative damage.