Oils and Fats

The peroxide value (PV)

The peroxide value (PV) is a measure of the extent to which oils and fats have undergone oxidation. It is expressed as milliequivalents of peroxide oxygen per kilogram of oil (or fat) and is an important parameter used to assess the freshness and quality of oils and fats.

When oils and fats are exposed to air, light, heat, or other factors, they undergo oxidative rancidity, resulting in the formation of peroxides. The peroxide value measures the amount of peroxides present in the sample, which is an indicator of the initial stage of lipid oxidation.

High peroxide values indicate that the oil or fat has undergone significant oxidation and may be rancid, leading to undesirable flavors, odors, and nutritional degradation. Therefore, monitoring peroxide values is crucial in the food industry to ensure the quality and shelf life of oils and fats.

Methods for determining peroxide value include titration methods, iodometric methods, and photometric methods, with titration methods being the most commonly used in food laboratories. Regulations and standards may specify permissible peroxide value limits for different types of oils and fats to ensure consumer safety and product quality.

Test methods: GSO 1218, AOAC Official Method 965.33Peroxide Value of Oils and Fats

The Anisidine value (AV)

The Anisidine value (AV) is another important parameter used to assess the quality and freshness of oils and fats, particularly in regards to their degree of oxidative deterioration and secondary oxidation products. While the peroxide value primarily measures primary oxidation products (e.g., hydroperoxides), the anisidine value is indicative of secondary oxidation products, such as aldehydes, ketones, and other volatile compounds formed during the decomposition of primary oxidation products.

The AV is determined by measuring the absorbance of a solution containing the oil or fat sample in the presence of p-anisidine, a compound that reacts with the secondary oxidation products. The higher the AV, the greater the degree of secondary oxidation and the more degraded the oil or fat is considered to be.

Similar to peroxide value, high anisidine values suggest that the oil or fat has undergone significant oxidative deterioration, which can lead to off-flavors, off-odors, and decreased nutritional quality. Therefore, monitoring anisidine values is important in assessing the quality and shelf life of oils and fats, particularly those used in food products.

Just like with peroxide value, regulatory agencies and industry standards may specify acceptable limits for anisidine values in different types of oils and fats to ensure product quality and safety. Analytical methods for determining anisidine value may involve spectrophotometric measurements or chromatographic techniques.

Rancidity

Rancidity in oils and fats refers to the development of off-flavors, off-odors, and degradation of nutritional quality due to various chemical reactions, primarily lipid oxidation. This process can occur when oils and fats are exposed to oxygen, light, heat, moisture, or enzymatic action, leading to the breakdown of the fatty acids present in the oil or fat.

Preventing rancidity in oils and fats involves proper storage and handling practices, such as storing oils in airtight containers, protecting them from light and heat, and minimizing exposure to air and moisture. Antioxidants, such as vitamin E (tocopherols) or synthetic antioxidants like BHA ( butylated hydroxy anisole ) and BHT (butylated hydroxytoluene), can also be added to oils and fats to inhibit oxidation and extend shelf life. Additionally, using oils with higher saturated fat content or refining oils to remove impurities can help improve stability and reduce susceptibility to rancidity. Regular monitoring of rancidity indicators such as peroxide value, anisidine value, and TBA value is essential to ensure the quality and freshness of oils and fats in various food products.

Free Fatty Acids (FFA)

Free Fatty Acids (FFA) in oils and fats refer to the concentration of unbound or liberated fatty acids present in the oil or fat sample. These fatty acids are released due to hydrolysis of triglycerides, which are the main constituents of oils and fats. Triglycerides consist of three fatty acid molecules attached to a glycerol backbone.

Analyzing the FFA content of oils and fats is commonly performed using acid-base titration methods, where the free fatty acids are neutralized with a standard alkali solution and the amount of alkali consumed is used to calculate the FFA content. The FFA content is often expressed as a percentage of oleic acid or another reference fatty acid.

 Unsaponifiable matter

Unsaponifiable matter refers to the portion of oils and fats that cannot be converted into soap (saponified) by treatment with alkali, typically under standard saponification conditions. It consists of components that are not fatty acids, such as sterols, tocopherols (vitamin E), hydrocarbons, pigments, and other minor constituents.

The term “unsaponifiable matter” originates from the traditional soap-making process, where oils and fats are reacted with alkali (such as sodium hydroxide or potassium hydroxide) to produce soap. During saponification, the fatty acids present in the oils and fats react with the alkali to form soap molecules, leaving behind glycerol as a byproduct.

However, not all components of oils and fats are capable of undergoing saponification. The unsaponifiable matter includes various compounds that remain unchanged during the saponification process. These components are often important for the nutritional, functional, and sensory properties of oils and fats.

The unsaponifiable matter content of oils and fats can vary depending on factors such as the source of the oil or fat, extraction methods, processing conditions, and storage conditions. Analyzing the unsaponifiable matter content provides valuable information about the composition and quality of oils and fats, particularly in terms of their nutritional and functional properties.

Test method: AOAC Official Method 933.08 Residue (Unsaponifiable) of Oils and Fats

Smoke point

Smoke point testing is a method used to determine the temperature at which an oil or fat begins to produce visible smoke when heated. The smoke point is an important indicator of the thermal stability of the oil or fat and is often used to assess its suitability for various cooking methods, particularly frying.

The smoke point is an important consideration for cooking applications because oils and fats with higher smoke points are more suitable for high-temperature cooking methods such as frying, searing, and sautéing. Oils with lower smoke points may produce unpleasant flavors and potentially harmful compounds when heated above their smoke point, so it’s important to select oils appropriate for the intended cooking method.

Flash point

Flash point testing is a method used to determine the lowest temperature at which a substance, such as an oil or fat, emits enough vapor to ignite momentarily or “flash” when exposed to an open flame under specific test conditions. This test is important for assessing the flammability and fire hazard of a substance.

It’s important to note that the flash point is not the temperature at which the substance sustains combustion but rather the temperature at which it releases enough vapor to form an ignitable mixture with air. Therefore, the flash point is a crucial safety parameter, especially in environments where flammable materials are handled or stored.

In the context of oils and fats, flash point testing may be relevant for assessing the fire risk associated with their production, storage, and transportation. While oils and fats typically have relatively high flash points compared to volatile liquids like gasoline, some oils may still pose a fire hazard under certain conditions, particularly if heated to high temperatures or exposed to an open flame.

Flash point testing is conducted following standardized methods, such as those outlined by organizations like ASTM International(ASTM D93) or the International Organization for Standardization (ISO)

Color (by Wesson Testing)

Color determination by Wesson testing is a method used to assess the color of oils and fats, particularly for evaluating the degree of refinement and potential presence of impurities or contaminants. This method is named after David Wesson, who developed it in the early 20th century.

The Wesson color test involves comparing the color of the oil or fat sample to a series of standard color discs or tiles, each representing a specific color intensity or hue. The standard color discs are arranged in a color scale, typically ranging from light to dark.

The Wesson color test provides a subjective assessment of the color of oils and fats and is commonly used in the food industry, particularly for evaluating the quality of vegetable oils and fats. The color of oils and fats can be influenced by various factors, including the type of oil or fat, processing methods, presence of impurities or contaminants, and storage conditions

Moisture insoluble impurities testing

Moisture insoluble impurities testing in oils and fats is a method used to determine the presence and quantity of solid impurities that are insoluble in water but may be present in the oil or fat. These impurities can include materials such as dirt, sand, fibers, and other solid particles that may contaminate the oil during processing, handling, or storage.

The moisture insoluble impurities content in oils and fats is an important quality parameter, as excessive levels of impurities can affect the sensory characteristics, stability, and shelf life of the oil or fat. Additionally, certain impurities may pose health or safety risks if present in significant quantities.

Regulatory agencies and industry standards may specify maximum allowable levels of moisture insoluble impurities in oils and fats for various applications to ensure product quality and safety. Testing for moisture insoluble impurities is commonly performed in food processing facilities, oil refineries, and quality control laboratories using standardized methods and equipment.

It’s worth noting that the specific procedures and techniques for moisture insoluble impurities testing may vary depending on factors such as the type of oil or fat being tested, regulatory requirements, and industry standards.

The Active Oxygen Method (AOM)

The Active Oxygen Method (AOM) test is a method used to evaluate the oxidative stability of oils and fats. It measures the resistance of oils and fats to oxidation under accelerated conditions by subjecting them to heat and oxygen. The AOM test is particularly useful for assessing the shelf life and quality of oils and fats, especially those intended for frying applications.

The AOM test is widely used in the food industry and research laboratories to assess the quality and shelf life of oils and fats. It allows manufacturers to compare the oxidative stability of different oils and fats, optimize processing and storage conditions, and develop antioxidant strategies to improve product stability.

It’s important to note that while the AOM test provides valuable insights into the oxidative stability of oils and fats under accelerated conditions, it may not fully replicate the oxidative processes that occur during actual storage or cooking. Therefore, the results of the AOM test should be interpreted in conjunction with other stability tests and real-world performance data.

The Oil Stability Index (OSI)

The Oil Stability Index (OSI) test is a method used to evaluate the oxidative stability of oils and fats under accelerated conditions. It measures the resistance of oils and fats to oxidation by subjecting them to high temperatures and continuous airflow. The OSI test is particularly useful for assessing the suitability of oils and fats for frying applications, where oxidative stability is crucial to maintain product quality and safety.

The OSI test provides valuable information about the oxidative stability of oils and fats, particularly their resistance to oxidation under frying conditions. It allows manufacturers to compare the performance of different oils and fats, optimize processing parameters, and develop strategies to improve product stability.

It’s important to note that while the OSI test provides useful insights into the oxidative stability of oils and fats, it may not fully replicate the complex oxidative processes that occur during actual frying. Therefore, the results of the OSI test should be interpreted in conjunction with other stability tests and real-world performance data.