Paper No. : 11 Paper Title: Food Analysis and Quality Control Module-32: Quality control of fats and oils

Paper No. : 11 Paper Title: Food Analysis and Quality Control Module-32: Quality control of fats and oils INTRODUCTION: Fats and oils are recognized as essential nutrients in both human and animal diets. Nutritionally, they are concentrated sources of energy (9 calories/gram); provide essential fatty acids which are the building blocks for the hormones needed to regulate bodily systems; and are a carrier for the oil soluble vitamins A, D, E, and K. They also enhance the foods we eat by providing texture and mouth feel, imparting flavor, and contributing to the feeling of satiety after eating. Fats and oils are also important functionally in the preparation of many food products. They act as tenderizing agents, facilitate aeration, carry flavors and colors, and provide a heating medium for food preparation. Fats and oils are present naturally in many foods, such as meats, dairy products, poultry, fish, and nuts, and in prepared foods, such as baked goods, margarines, and dressings and sauces. IMPORTANCE OF FATS AND OILS Fats and oils are constructed of building blocks called triglycerides resulting from the combination of one unit of glycerol and three units of fatty acids. They are insoluble in water but soluble in most organic solvents. They have lower densities than water, and may have consistencies at ambient temperature of solid, semisolid, or clear liquid. When they are solidappearing at a normal room temperature, they are referred to as fats, and when they are liquid at that temperature, they are called oils. Fats and oils are classified as lipids which is a category that embraces a broad variety of chemical substances. In addition to triglycerides, it also includes mono- and diglycerides, phosphatides, cerebrosides, sterols, terpenes, fatty alcohols, fatty acids, fat-soluble vitamins, and other substances. CHEMICAL COMPOSITION OF FATS The main components of edible fats and oils are triglycerides. The minor components include mono- and diglycerides, free fatty acids, phosphatides, sterols, fat soluble vitamins, tocopherols, pigments, waxes, and fatty alcohols. The free fatty acid content of crude oil varies widely based on the source. Other than the free fatty acids, crude vegetable oils contain approximately two percent of these minor components. Animal fats contain smaller amounts. The Major Component Triglycerides A triglyceride consists of three fatty acids attached to one glycerol molecule. If all three fatty acids are identical, it is a simple triglyceride. The more common forms, however, are the

mixed triglycerides in which two or three kinds of fatty acids are present in the molecule. Typical simple and mixed triglyceride molecular structures are shown in the figure 1. Figure1. Structures of simple and mixed triglycerides. The Minor Components 1. Mono- and Diglycerides - Mono- and diglycerides are mono- and diesters of fatty acids and glycerol. They are used frequently in foods as emulsifiers. They are prepared commercially by the reaction of glycerol and triglycerides or by the esterification of glycerol and fatty acids. Mono- and diglycerides are formed in the intestinal tract as a result of the normal digestion of triglycerides. They occur naturally in very minor amounts in both animal fatsand vegetable oils. Oil composed mainly of diglycerides has also been used as a replacement for oil composed of triglycerides. Illustrations of mono- and diglyceride molecular structures are provided below:

Figure 2. Structures of mono- and diglycerides. 2. Free Fatty Acids - As the name suggests, free fatty acids are the unattached fatty acids present in a fat. Some unrefined oils may contain as much as several percent free fatty acids. The levels of free fatty acids are reduced in the refining process. Fully refined fats and oils usually have a free fatty acid content of less than 0.1%. 3. Phosphatides - Phosphatides, also known as phospholipids, consist of an alcohol (usually glycerol) combined with fatty acids, and a phosphate ester. The majority of the phosphatides are removed from oil during refining. Phosphatides are an important source of natural emulsifiers marketed as lecithin. 4. Sterols - Sterols are found in both animal fats and vegetable oils, but there are substantial biological differences. Cholesterol is the primary animal fat sterol and is found in vegetable oils in only trace amounts. Vegetable oil sterols are collectively called phytosterols. Stigmasterol and sitosterol are the best-known vegetable oil sterols. Sitosterol has been shown to reduce both serum and LDL cholesterol when incorporated into margarines and/or salad dressings. The type and amount of vegetable oil sterols vary with the source of the oil. 5. Tocopherols and Tocotrienols - Tocopherols and tocotrienols are important minor constituents of most vegetable fats. They serve as antioxidants to retard rancidity and as sources of the essential nutrient vitamin E. The common types of tocopherols and tocotrienols are alpha (α), beta (β), gamma (γ), and delta (δ). They vary in antioxidation and vitamin E activity. Among tocopherols, alpha-tocopherol has the highest vitamin E activity and the lowest antioxidant activity. Delta tocopherol has the highest antioxidant activity. Tocopherols which occur naturally in most vegetable oils are partially removed during processing. Corn and soybean oils contain

the highest levels. Tocopherols are not present in appreciable amounts in animal fats. Tocotrienols are mainly present in palm oil, but can also be found in rice bran and wheat germ oils. 6. Pigments - Carotenoids are yellow to deep red color materials that occur naturally in fats and oils. They consist mainly of carotenes such as lycopene, and xanthophylls such as lutein. Palm oil contains the highest concentration of carotene. Chlorophyll is the green coloring matter of plants which plays an essential role in photosynthesis. Canola oil contains the highest levels of chlorophyll among common vegetable oils. At times, the naturally occurring level of chlorophyll in oils may cause the oils to have a green tinge. Gossypol is a pigment found only in cottonseed oil. The levels of most of these color bodies are reduced during the normal processing of oils to give them acceptable color, flavor, and stability. 7. Fatty Alcohols - Long chain alcohols are of little importance in most edible fats. A small amount esterified with fatty acids is present in waxes found in some vegetable oils. Larger quantities are found in some marine oils. Tocotrienols are mainly present in palm oil, and can also be found in rice bran and wheat germ oils. Quality assurance of Fats and Oils: Regardless of the source of fat, the amount of fat, or the product composition, predicting and monitoring fat and oil quality is an important component of developing and manufacturing high quality products. The quality of fats and oils is dictated by several physical and chemical parameters that are dependent on the source of oil; geographic, climatic, and agronomic variables of growth in the case of plant oils as well as processing and storage conditions. Thus, quality assurance criteria may depend partly on the type of oil under investigation as well as on other factors that may vary depending on the intended use and regulations that vary from country to country. The parameters evaluated for quality assurance of edible oils are those related to the makeup of the oil or their properties. Table 1 summarizes a list of parameters usually employed to assess quality of edible fats and oil. However, not all parameters listed may be evaluated for each oil. Table 1. Quality parameters of oils and fats. Parameter Detail Fatty acid composition and distribution Percentage of total; depends on the type of fat or oil. Relative density At 20 C or 40 C relative to water at 20 C (<1) Refractive index At 40 C

Viscosity At 20 C Color Visual, Lovibond or Colormet Turbidity Visual or instrumental Odor and taste Sensory evaluation Saponification value Mg KOH/g Iodine value (IV) g iodine/100-g sample (WIJS method) Unsaponifiable matter g/kg Acid value (AV) mg KOH/g Smoke, flash and fire points C Peroxide value (PV) meq oxygen/100-g sample Thiobarbituric acid reactive substances (TBARS) μmol/g para-anisidine value (p-anv) mg/kg Volatile mater (%) At 105 C Metal ions mg/kg Trans-fatty acids Percentage Carotenoids and chlorophylls mg/kg Synthetic antioxidants BHA, BHT, TBHQ, PG Adulterants Fingerprinting using sterols or other minor components Oxidation of lipids is one common and frequently undesirable chemical change that may impact flavor, aroma, nutritional quality, and, in some cases, even the texture of a product. The chemicals produced from oxidation of lipids are responsible for rancid flavors and aromas. Vitamins and other nutrients may be partially or entirely destroyed by highly reactive intermediates in the lipid oxidation process. Oxidized fats can interact with proteins and carbohydrates causing changes in texture. Of course, not all lipid oxidation is undesirable. Enzymes, for example, promote oxidation of lipid membranes during ripening of fruit. For most products, though, predicting and understanding oxidation of lipids is necessary to minimize objectionable flavors and aromas arising from fat rancidity. Two Types of Rancidity: Selecting an optimum test for lipid oxidation is difficult due to the complexity of the chemical processes involved. In fact, many of the oxidation pathways are not entirely understood. Two types of lipid oxidation cause the most concern. These are oxidative rancidity and hydrolytic rancidity. Hydrolytic Rancidity - Hydrolytic rancidity results in the formation of free fatty acids and soaps (salts of free fatty acids) and is caused by either the reaction of lipid and water in the presence of a catalyst or by the action of lipase enzymes. Low levels of free fatty acids are not necessarily objectionable, particularly if they are sixteen or eighteen carbon fatty acids as commonly found

in soybeans, corn or animal fat. However, for other fats like coconut oil or butter fat, low levels of shorter carbon chain fatty acids may be quite objectionable. Oxidative Rancidity - Oxidative rancidity results from more complex lipid oxidation processes. The processes are generally considered to occur in three phases: an initiation or induction phase, a propagation phase, and a termination phase. In complex systems, the products of each of these phases will increase and decrease over time, making it difficult to quantitatively measure lipid oxidation. During the initiation phase, molecular oxygen combines with unsaturated fatty acids to produce hydro peroxides and free radicals, both of which are very reactive. For this phase to occur at any meaningful rate, some type of oxidative initiators must also be present, such as chemical oxidizers, transition metals (i.e., iron or copper), or enzymes (i.e., lipoxygenases). Heat and light also increase the rate of this and other phases of lipid oxidation. The reactive products of this initiation phase will, in turn, react with additional lipid molecules to form other reactive chemical species. The propagation of further oxidation by lipid oxidation products gives rise to the term auto-oxidation that is often used to refer to this process. In the final, termination phase of lipid oxidation, relatively unreactive compounds are formed including hydrocarbons, aldehydes, and ketones. A variety of tests for lipid oxidation have been developed since these mechanisms were first proposed in the mid-1940 s. These tests measure either: products of hydrolytic rancidity, products of the initiation and propagation phases, products of the termination phase, depletion of oxygen or substrate. Lipid Oxidation Tests Tests for lipid oxidation are either predictive tests or indicator tests. Predictive tests use accelerated conditions to measure the stability of a fat or finished product. These tests may be used to determine ingredient quality, measure effectiveness of preservatives, or estimate product shelf life. Indicator tests are intended to quantify product or ingredient rancidity. Predictive Tests AOM (Active Oxygen Method) - This method predicts the stability of a fat by bubbling air through a solution of the fat using specific conditions of flow rate, temperature, and concentration. At intervals, peroxides and hydroperoxides produced by this treatment are determined by titration with iodine. The AOM value is defined as the number of hours required for the peroxide concentration to reach 100 meq/kg of fat. The more stable the fat, the longer it will take to reach that level. For products other than fats and oils, the fats must first be gently extracted with solvents. The method is very time-consuming since a stable fat may require 48 hours or more before reaching the required peroxide concentration. While still used today, the AOM method is being supplanted by faster automated techniques.

OSI (Oxidative Stability Index) - The method is similar in principle to the AOM method, but it is faster and more automated. Air is passed through a sample held at constant temperature. After the air passes through the sample, it is bubbled through a reservoir of deionized water. Volatile acids produced by lipid oxidation are dissolved in the water increasing its conductivity. Conductivity of the water is monitored continuously and the OSI value is defined as the hours required for the rate of conductivity change to reach a predetermined value. Multiple samples can be tested simultaneously and software controls instrument parameters and data collection. The method has been collaboratively studied and accepted by AOCS. Iodine Number - While not a specific measure of fat stability, iodine number measures can indicate the potential of a fat to be oxidized. The method measures the reaction of iodine with double bonds of unsaturated fatty acids. Fats with a greater number of double bonds provide more sites for oxidation. Because other factors can influence fat stability, iodine number is not useful by itself for predicting fat stability. Oxygen Bomb Test - This method is used to predict stability and evaluate antioxidant systems in fats and finished products. Oxygen uptake of the sample is measured in a closed system. The rate at which oxygen is consumed indicates the oxidative stability of the tested product. An advantage of this technique is its ability to measure stability of the complete product without prior extraction of the fat. Because other components of a product, like transition metals or chemical oxidants, can promote oxidation, extracted fat may not be a suitable predictor of product stability. Oxidation Indicator Tests Peroxide value - One of the most widely used tests for oxidative rancidity, peroxide value is a measure of the concentration of peroxides and hydroperoxides formed in the initial stages of lipid oxidation. Milliequivalents of peroxide per kg of fat are measured by titration with iodide ion. Peroxide values are not static and care must be taken in handling and testing samples. It is difficult to provide a specific guideline relating peroxide value to rancidity. High peroxide values are a definite indication of a rancid fat, but moderate values may be the result of depletion of peroxides after reaching high concentrations. TBA test - Saturated aldehydes, 2-enals, and 2-dienals, produced in the termination phase of lipid oxidation, can be detected by reaction with 2- thiobarbituric acid. The reaction produces a red color which can be measured using a spectrophotometer. While originally developed to detect malonaldehyde, TBA has been shown to react with other aldehydes, as well as possible interfering substances like phenols in smoke flavors. As with peroxide value, a low TBA value is not an absolute indicator of fat quality. Aldehydes may have not yet formed or volatile aldehydes may have been lost during processing and storage. Anisidine value - When hydroperoxides break down, they produce volatile aldehydes like hexanal, leaving behind a non-volatile portion of the fatty acid that remains a part of the

glyceride molecule. This non-volatile reaction product can be measured by reaction with anisidine. High anisidine values may be an indication that a fat has been oxidized even when TBA and other aldehyde tests give low results because volatile aldehydes may incidentally or intentionally be removed during processing. Anisidine value is defined as 100 times the absorbance (at 350 nm) of a solution resulting from reaction of 1 g of fat in 100 ml of solvent. Hexanal value - Hexanal, produced during the termination phase of lipid oxidation, can be measured by gas chromatographic analysis of the headspace over a sample. Methods vary, but generally a portion of sample is moderately heated in a sealed septum bottle. A gas syringe is used to withdraw a small portion of the headspace over the sample. The headspace sample is then injected onto a GC column to separate hexanal from other volatile components. Hexanal concentrations can vary widely depending on a number of factors including sample history, fat content, and fat composition. Generally, data is needed on a variety of samples of the same product to establish a correlation between hexanal concentration and product quality. Once that correlation is established, hexanal measurement can be a rapid and useful tool for lipid oxidation measurement. Headspace Profile - Using techniques similar to those used for hexanal analysis, it is possible to measure the total volatile profile of the headspace over a product. Lipid oxidation produces a variety of volatile compounds including hydrocarbons, aldehydes, enals, dienals, ketones, and organic acids. As oxidation increases, the total of these volatiles tends to increase and can be measured by injecting a portion of the headspace into a gas chromatograph. Volatile flavorings may interfere and correlations of headspace values to samples of known quality are important. Free Fatty Acids (FFA) - Free acids in a fat (or fat extracted from a sample) can be determined by titration. The FFA value is then expressed as % of a fatty acid common to the product being tested. Frequently, values are expressed as % oleic acid for tallows or soybean oils. For coconut oils or other oils that contain high levels of shorter chain fatty acids, FFA may be expressed as % lauric acid. FFA is an indication of hydrolytic rancidity, but other lipid oxidation processes can also produce acids. It may also be useful to know the composition of the free fatty acids present in a sample to identify their source and understand the cause of their formation. Extracts of samples can be analyzed for free fatty acid profiles when this information is required. Kreis Test - This was one of the first tests used commercially to evaluate oxidation of fats. The procedure involves measurement of a red color that is believed to result from reaction with phloroglucinol (Kreis reagent). Deficiencies of this test include: (a) fresh samples free of oxidized flavor frequently develop some color upon reaction with the Kreis reagent, and (b) consistent results among different laboratories are difficult to obtain. Ultraviolet Spectrophotometry - Measurement of absorbance at 234 nm (conjugated dienes) and 268 nm (conjugated trienes) is sometimes used to monitor oxidation. However, the

magnitude of the absorbance does not correlate well with the degree of oxidation except in the early stages. Fluorescence - Fluorescent compounds may develop from interaction of carbonyl compounds (produced by lipid oxidation) with constituents possessing free amino groups. Fluorescence methods provide a relatively sensitive measure of oxidation products in biological tissues. Chromatographic Methods - Various chromatographic techniques, including liquid, thin-layer, high-performance liquid, size exclusion, and gas, have been used to determine oxidation in oils or lipid-containing foods. This approach is based on the separation and quantitative measurement of specific fractions, such as volatile, polar, or polymeric compounds or individual components, such as pentane or hexanal, those are known to be typically produced during autoxidation. Sensory Evaluation - The ultimate test for oxidized flavor in foods is a sensory one. The value of any objective chemical or physical method is judged primarily on how well it correlates with results from sensory evaluation. The testing of flavor is usually conducted by trained or semi trained taste panels using highly specific procedures. Several accelerated tests are also available to estimate resistance of a lipid to oxidation. Schaal Oven Test - The sample is stored at about 65 C and periodically tested until oxidative rancidity is detected. Detection can be done organoleptically or by measuring the peroxide value. Rancimat Method - Air is bubbled through the oil as in the AOM test, and the increase in electrical conductivity due to generation of oxidation products is measured, usually at 100 C, and expressed in terms of induction time. Oxygen Absorption - The sample is placed in a closed chamber and the amount of oxygen absorbed is determined and used as a measure of stability. This is done by measuring the time to produce a specific pressure decline, or by the time to absorb a pre-established quantity of oxygen under specific oxidizing conditions. This test has been particularly useful in studies of antioxidant activity.