Edible Oil Quality Parameters PDF

Edible Oil Quality Parameters (Principles and Determination) FST 360  OILSEEDS Preparation of oilseeds for oil extraction OILMILLING Oil extraction CRUDE OIL Refining...

Edible Oil Quality Parameters (Principles and Determination) FST 360  OILSEEDS Preparation of oilseeds for oil extraction OILMILLING Oil extraction CRUDE OIL Refining REFINED EDIBLE OIL Oil Quality Parameters  Oil Quality Parameters The typical oil quality parameters may be divided into two main categories Quality parameters based on physical properties of the oil Melting point Solid fat index (SFI) or Solid fat content (SFC) Smoke point / Flash point / Fire point Quality parameters based on chemical properties of the oil Iodine value (or Iodine number) Saponification value Free fatty acids / Acid value Peroxide value / Anisidine value / Totox value 2-thiobarbituric acid value (TBA) or Thiobarbituric acid reacting substances (TBARS) Conjugated dienes/trienes Total polar compounds Phospholipids  Why are Oil Quality Parameters important? Most of the edible oils used for cooking, frying and food formulations are derived from plant sources (vegetable oils), e.g. from oilseeds such as soybean, canola, sunflower seeds, cottonseed and peanuts. Physical, chemical and nutritional properties of vegetable oils depend on their composition of: Major components i.e. triglycerides and fatty acids Minor components e.g. tocopherols, phytosterols, waxes The quality of edible vegetable oils can deteriorate by: Hydrolysis – increases the amount of free fatty acids, mono- and diglycerides and glycerols in oils Oxidation – produces hydroperoxides and low molecular weight volatile compounds such as aldehydes, ketones, carboxylic acids, and short chain alkanes and alkenes Polymerisation – dimers and polymers are formed when oil is exposed to high temperatures during cooking and frying Various parameters can therefore be measured and used to monitor and maintain edible oil quality to ensure safety for consumption. These are referred to as Oil Quality Parameters.  Melting point Definition: the temperature at which all the harder and more solid components of a fat are completely melted and dissolved in the softer and more liquid components. Methods for measuring melting point Closed capillary melting point: Fat sample is placed in a glass capillary tube and sealed at the end. Tube is placed in a refrigerator at 5-10oC until the fat sets completely. Tube is then heated slowly in a water bath. Melting point is temperature at which the fat becomes completely Wiley melting point: A round disc of fat is cast into a mold and chilled for 2 hr. Fat disc is suspended in a large test tube containing alcohol layered over an equal volume of water so that the disc floats at the interface between the alcohol and water. A thermometer is placed in the tube with its bulb alongside the disc of fat. The disc is heated slowly and the temperature at which it changes shape (becomes spherical) is taken as the melting point. Alcohol Alcohol Water Water HEAT HEAT  Melting point Methods for measuring melting point Softening point (Slip point or Open capillary melting point): Fat sample placed in a capillary tube open at both ends and chilled. Tube is then placed in a boiling water bath. The end point is the temperature at which the fat rises a definite amount in the tube. Lead shot method: Lead shot is placed on a hardened fat sample in a tube or beaker and heated. The end point is where the shot settles through the fat to the bottom.  Solid Fat Index / Solid Fat Content Solid fat index (SFI) A measure of the amount of solid fat in a fat at various temperatures as determined by the principle of dilatometry i.e. a technique that measures volume changes that occur as a result of melting or crystallisation. As a solid fat is heated, it melts into liquid oil and expands i.e. its volume increases. SFI is a measure of the change in volume of the fat as it melts and this is related to the change in the solid content. Solid fat content (SFC) A measure of the amount of solid fat in a fat at various temperatures by directly measuring the mass of solid components and liquid components in the fat usually using the technique of nuclear magnetic resonance. The SFC is determined by expressing the mass of solid components as a percentage of the total mass of the fat.  Typical SFI / SFC Curves SFI or SFC of fats and oils are represented as SFI or SFC Curves. These are plots of SFI or SFC on the y-axis and temperature on the x-axis Source: Arellano et al (2015) https://www.sciencedirect.com/science/article/pii/B9781782423768000107  Significance of SFI / SFC SFI and SFC provide an indication of the ratio of solid to liquid phase in a fat and is an important determinant of fat functionality. A high SFI value at any given temperature indicates that the fat is hard at that temperature. All purpose shortening (e.g. margarine): has a relatively flat SFI profile. Soft enough to be worked at 10oC, but still retains some solidity at 37oC. Cocoa butter: has a high profile with a steep descent. It is quite hard at 25oC, yet is liquid at 35oC. In general, at SFI greater than 35 (e.g. butter at refrigerator temperature), the fat is hard and not easily spread. At an SFI below 10, the fat is soft and almost liquid.  SFC curves of butter and margarine Source: Arellano et al (2015) https://www.sciencedirect.com/science/article/pii/B9781782423768000107  Smoke Point / Flash Point / Fire Point Smoke point – temperature at which a heated oil begins to give off or emit continuous wisps of smoke. Flash point – temperature at which a heated oil gives flashes of burning when exposed to a flame. Fire point – temperature at which a heated oil burns with a flame when ignited. Ideally, smoke point should be 20oC above maximum frying temperature (160-180oC). Smoke point is mainly related to free fatty acid (FFA) content of the fat. A 1% increase in FFA content lowers smoke point by about 60oC. Monoglycerides, proteinaceous materials and food residues also lower the smoke point of fats.  Iodine Value (IV) (or Iodine Number) Definition: Percentage of iodine (I2) absorbed by a fat (or grams of iodine [I2] absorbed by 100 g of fat). Significance: It is based on the fact that iodine can add to double bonds in unsaturated fatty acids. Therefore IV is used to measure the degree of unsaturation of a fat. Unsaturated fats contain more double bonds, will absorb more iodine and therefore have higher IV compared to saturated fats. (E.g. oleic acid – 86; linoleic acid – 173; linolenic acid – 261) Determination of IV: An amount of fat/oil is reacted with Wijs solution (iodine monochloride). The fat/oil absorbs some of the iodine in the Wijs solution. Potassium iodide is added to the mixture which releases unabsorbed iodine as I2 which is titrated against standard sodium thiosulphate solution. (I2 + 2Na2S2O3 Na2S4O6 + 2NaI). The amount of I2 in grams absorbed by 100 g of the fat/oil is then determined.  Saponification Value Definition: The number of milligrams of potassium hydroxide (KOH) needed to saponify 1 g of a fat. Significance: It is a measure of the average molecular weight (or chain length) of all the fatty acids present. Specifically, saponification value is inversely related to the average molecular weight of the fat. Long chain fatty acids (high average molecular weight) have a low saponification value because they have a relatively fewer number of carboxylic functional groups per unit mass of the fat as compared to short chain fatty acids. NB: Saponification does not give information about the exact fatty acid composition. Determination: A known weight of the fat is saponified with KOH solution. The mixture is then titrated with standard HCl to determine the amount of KOH left after the saponification reaction. The milligrams of KOH used for the saponification is then calculated.  Free Fatty Acids (FFA) / Acid Value Free Fatty Acids (FFA) Definition: A measure of the amount of fatty acids in a fat or oil sample that are not bound or esterified to a glycerol molecule (free fatty acids) Significance: FFA are not desirable in oils. Oils that are high in FFA are regarded as of low quality. These oils have lowered oxidative stability and are prone to rancidity especially if the fatty acids are unsaturated. Frying oils with FFA content exceeding 2% are usually discarded. Measurement: Fat sample is dissolved in alcohol and titrated with standard alcoholic NaOH to a phenolphthalein end point. Results are given as percent free fatty acid (%FFA) calculated as oleic acid. Acid Value (also called Acid Number) Definition: The number of milligrams of potassium hydroxide (KOH) necessary to neutralise the free fatty acids in 1 g of a fat or oil. Significance: Similar to FFA. Oils with high FFA also have high acid value. Measurement: Same as FFA. Titration is done with standard alcoholic KOH.  Peroxide Value (PV) Definition: The amount of peroxide oxygen per 1 kg of fat or oil. Expressed as milliequivalents of peroxide per kg of fat or oil. Significance: PV is an index used to quantify the amount of hydroperoxides in a fat or oil which are the primary oxidation products. PV does not always correlate with the off-flavour caused by aldehydes and other carbonyl compounds which are secondary oxidation products. The limit for PV for a fresh oil is considered as 10 milliequivalents per kg. Measurement: A known weight of a fat or oil sample is reacted with saturated potassium iodide (KI) solution. This is then titrated with standard sodium thiosulphate solution. PV measures the quantity of iodine (I 2) liberated from KI by peroxides present in the oil.  Anisidine Value (AV) / Totox Value Anisidine Value (AV) Definition: A measure of the secondary products of oxidation of oils in the form of α,β-unsaturated aldehydes such as 2,4-dienals and 2- alkenals. Significance: It provides an indication of secondary oxidation of oils and strongly related to rancid flavour or odour. Measurement: The oil is reacted with p-anisidine (4-methoxyaniline). The aldehydes form a coloured complex with p-anisidine and colour is measured spectrophotometrically at 350 nm. The absorbance is converted to AV using a calculation. Totox Value Definition: A measure of the total oxidation of a fat or oil given by Totox = AV + (2PV). Significance: During shelf-life testing of fats, PV first rises then falls (as hydroperoxides decay). Totox measures both hydroperoxides and their breakdown products. It tends to rise continuously and gives a better measure of the progressive oxidative degradation of fat.  2-Thiobarbituric Acid Value (TBA) Definition: A measure of secondary products of oil oxidation in the form of aldehyde compounds (breakdown products of hydroperoxides) that react with thiobarbituric acid and expressed in terms of malondialdehyde (MDA) equivalents. Principle of measurement: Thiobarbituric acid (TBA) reacts with a number of compounds including aldehydes (mainly malondialdehyde) to produce a coloured complex that can be measured by UV spectrophotometry. These substances are termed thiobarbituric acid reacting substances (TBARS). The measured absorbance is related to the concentration of the aldehydes. The extent of lipid oxidation is reported as TBA value, which corresponds to milligram of malonaldehyde equivalents per kilogram of sample or micromoles of malonaldehyde per gram of sample. OR 2-Thiobarbituric acid  Conjugated dienes/trienes Oxidation of polyunsaturated fatty acids results in an increase in the ultraviolet absorption of the product due to formation of conjugated dienes and trienes. Measurement of the content of conjugated dienes at 234 nm and conjugated trienes at 268 nm is a quick physical method, which may be helpful to assess the oxidative stability of vegetable oils  Total Polar Compounds Presence of polar compounds in oil is one of the best indicators of heated oil quality. Polar compounds consist of dimeric and higher polymeric triglycerides formed through thermal polymerization of triglycerides, monomeric oxidized products, mono- and diglycerides and FFA formed through hydrolytic cleavage of triglycerides. Significance: The polar compounds are not digestible and can have a negative impact on consumer health by posing a risk for heart disease. Frying oil with high levels of polar compounds is regarded as expired oil. Such oils render fried foods greasier and negatively impact flavour and colour. Monitoring fryer oil for polar content will ensure that the product is of consistent quality, and will not have a negative impact on consumer health. The analysis of the polar compounds is conducted by high- performance size exclusion chromatography, which allows the separation and quantification of polymeric compounds, dimers, oxidized triglycerides, mono- and diglycerides and FFA.  Phospholipids Phospholipid is a common name for lipids containing phosphoric acid or other phosphorus-containing acids in ester form such as glycerophospholipids (e.g. phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine) or sphingophospholipids (e.g. sphingomyelin). Lecithin from soybean is an example of a phospholipid. These phospholipids are also called “gums”. Significance: Although these phospholipids have some health benefits and surfactant/emulsifier properties, they need to be separated from crude oil during the refining process, which is referred to as degumming. Otherwise, they impart a cloudy appearance and precipitate out of the oil during storage creating an unpleasant solid residue at the bottom of the containers and adversely affect the functionality of refined oils, e.g. cause foaming during frying. Analysis: The phospholipid content of oils is commonly measured as phosphorous, which can be converted to phospholipids by using conversion factors calculated by using the phospholipid composition and the molecular weight of individual phospholipids present in the oil.