Properties of Lipids

PPrrooppeerrttiieess ooff LLiippiiddss B.K.K.K.Jina dasa GS/MSc/FOOD /3608/08

07th Nov. 2009

2009/10

Properties of Lipids

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Properties of lipids Introduction Lipids consist of a broad group of compounds that are generally soluble in organic solvents but only sparingly soluble in water. Lipids in food exhibit unique physical and chemical properties. Their composition, crystalline structure, melting properties and ability to associate with water and other non-lipid molecules are especially important to their functional properties in many foods. During the processing, storage and handling of foods, lipids undergo complex chemical changes and react with other food constituents, producing numerous compounds both desirable and deleterious to food quality. Cooking oil includes the well-known olive, sunflower, and canola oils and the not so well-known coconut, soy, and palm oils. Palm oil is similar to coconut. Because of its highly saturated, it is used to make shortening and frying oil. The oil palm fruits produce two types of oil, palm oil which is extracted from the pericarp of the fruit and palm kernel oil from the seeds, both of which are important in the world trade. Edible palm oil shall have the following characteristics-

1. Density at 500 C, relative to the density of water at 25°C, ranging from 0.8910 to 0.9030; 2. Refractive index, at 50°C, ranging from 1.449 to 1.455 3. Saponification value ranging from 190 to 209 milligrams of potassium hydroxide per

gram of oil 4. Iodine value (Wij's) ranging from 50 to 55 5. An acid value of - not more than 10 milligrams of potassium hydroxide per gram of

virgin oil; or not more than 0.6 milligrams of potassium hydroxide per gram of non-virgin oil.

6. Peroxide value not more than 10 milli-equivalents peroxide oxygen per kilogram of oil. 7. Unsaponifiable matter of not more than 12 grams per kilogram of oil. 8. Total carotenoids of the oil of the red palm of -not less than 500 milligrams per kilogram;

and not more than 2000 milligrams per kilogram calculated as Beta-carotene. According to the Codex, Maximum level Acid Value: Refined fats and oils 0.6 mg KOH/g fat or oil Virgin fats and oils 0.4 mg KOH/g fat or oil Cold pressed fats and oils 0.4 mg KOH/g fat or oil Peroxide Value: Virgin oils and cold pressed fats and oils up to 15 milliequivalents of active oxygen/kg oil Other fats and oils up to 10 milliequivalents of active oxygen/kg oil


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4.1. Specific gravity of oils 4.1.1. Materials Oil samples Specific gravity bottles Weighing scale 4.1.2. Method Pre weighed specific gravity bottle of 50 mL capacity was filled with distilled water at 30 ºC to overflow and inserted the stopper. After inserting the stopper the bottle was immersed in a water bath at 30 ºC for 30 minutes. After 30 minutes bottle was removed from the water bath and wiped till it became completely dry. Weight of the bottle and contents was taken. Oil samples were cooled to 30 ºC and filled with oil (coconut oil) to the dried specific gravity bottle as before. Then the stopper was inserted and bottle was wiped off. Weight of the bottle and palm oil was taken. Then the specific gravity of oil was calculated using following formula.

4.1.3. Results

Where, W1= weight of SG bottle W2= weight of SG bottle + water W3=weight of SG bottle + oil Weight (g) Weight of sg bottle (I) 29.2849 Weight of sg bottle (I) + Water 79.4585 Weight of sg bottle (II) 28.4618 Weight of sg bottle (II) + Sample 73.8112

= 0.9038 4.1.4. Discussion: SG value received here 0.90, but as literature showed its between 0.898-0.907.


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4.2. Viscosity of oils 4.2.1. Materials Viscometer [canon fenska viscometer] Oil samples Water 4.2.2. Method Viscosity of oil samples were measured using Canon Fenska viscometer. 100 ml of distilled water was added to the left arm of the viscometer. Time taken for water to move from lower mark to the upper mark of the right arm was noted. Experiment was repeated for five times with water. Same procedure was followed for the oil samples and experiments were repeated for five times to get an average value. Viscosity was calculated using following formula.

4.2.3. Results Water Palm oil Time [sec] (50.95+49.96+51.18)/3=50.70 3545 Density [g/cm3] 1 0.9038 viscosity 50.70 319.94

4.2.4. Discussion: Viscosity is the thickness of oil. Viscosity is determined by measuring the amount of time taken for a given measure of oil to pass through an orifice of a given size. Density is determined by weighing a given measure of oil. Oils that are denser will contain more energy. For example petrol and diesel fuel give comparable energy by weight but diesel is denser and gives more energy per litre. The density of the oils varies with each type and temperature. The range is from 0.91 to 0.93 g/cm3 between the temperatures of 15 °C and 25 °C. Comparing to water, whose density is 1.00 g/ml, cooking oil is less dense. E.g. given in below table

Name Specific Gravity

@ 15.5 °C Name

Specific Gravity @ 15.5 °C

coconut 0.9259 peanut (arachis) 0.917-0.9209

cotton seed 0.922-0.925 safflower 0.9246-0.9280

olive 0.9150-0.9180 sesame 0.9203-0.9237

palm 0.9210-0.9240 soya beans 0.924-0.9279

palm kernel 0.9119 sunflower 0.924-0.9258


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4.3. Saponificat ion value 4.3.1. Materials Weighing scale Beakers Burettes Pipettes Conical flask Pumice stones Alcoholic KOH 0.5 M HCL 4.3.2. Method 2g of sample was weighed into conical flasks. 25 mL of alcoholic KOH and few pieces of pumice stones were added to both samples. Another conical flask was taken and 25mL of alcoholic KOH and few pieces of pumice stones were added in order to carry out the blank test. Air flux condensers were fixed to all flasks and allowed them to boil for an hour, shaking flasks frequently. After one hour samples were titrated with 0.5M HCl. Saponification values of samples were calculated using following formula.

b – mL of HCl acid used in the blank titration a – mL of HCl acid used for the sample 4.3.3. Results Sample Sample wt Volume of HCl for sample Sap value Palm oil 2.0078 g 12.20 mL 149.48 Volume of HCl for blank – 22.9 mL 4.3.4. Discussion Saponification is the hydrolysis of esters. Oils and fats are the fatty acid esters of the trihydroxy alcohol, glycerol. The safonification value of oil is defined as the number of milligrams of KOH required to neutralize the fatty acids resulting from the complete hydrolysis of 1g of the sample. Soap is formed during saponification, for example C3H5(C17H35COO)3 + 3 KOH = C3H5(OH)3 + 3C17H35COOK


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The esters of the fatty acids of lower molecular weight required more alkali for saponification, so the saponification value is inversely proportional to the mean of the molecular weights of the fatty acids in the glycerides present. As many oils have somewhat similar values, the saponification value is not, in general, so useful for identification purposes. It is useful for detecting the presence of oil and fats which contain a high proportion of lower fatty acids. According to the results it could be seen that the accurate values for Saponification value is not obtained. This may be due to practical errors or the oil is adulterated. E.g. For saponification value of some fats and oils Type of oil Saponification value Castor Oil 175-187 Coconut Oil 250-264 Olive Oil 184-196 Palm Oil 190-205 Rice Bran Oil 180-190 Soybean Oil 190 Sunflower Seed Oil 185-198


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4.4. Iodine value 4.4.1. Materials Beakers Iodine titration flask Burettes Pipettes Weighing scale Wij’s solution containing iodine monochloride KI, 100g/liter solution Sodium thiosulphate 0.1M – 500g Carbon tetra chloride solution Distilled water Starch solution 4.4.2. Method Samples were weighed into small tubes (melting point tubes). For palm oil 0.35 g were taken. Sample containing small tubes were kept in the iodine flasks separately and 20 mL of CCl4 was added to each flask. Flask was shook well until the oil gets mixed thoroughly. 20 mL of Wij’s reagent was added to all the flasks. A blank test was also carried out. All the flasks were kept in dark for 30 min. After 30 min. 20 mL of 10% KI and 150 mL of distilled water was added to each flask and titrated with 0.1M sodium thiosulphate solution. Few drops of starch were added when the colour of the solution turned into straw color while titrating. Titration was continued till the blue colour turned into colourless. Iodine values for the two oil samples were obtained using the following formula.

Where, b - Volume of sodium thio sulphate solution required for the blank test a – Volume of the sodim thio sulphate solution required for the sample. 4.4.3. Results Sample Blank reading Sample reading Sample weight Iodine value Palm oil 38.65 22.20 0.3535 59.05

4.4.4. Discussion Iodine value is determined in order to measure the unsaturated linkages in a fat/oil. This is done by reacting the fat with a solution of iodine monochloride in a mixture of acetic acid and CCl4, liberating excess iodine with KI, and titrating with Na2S2O3. The results are expressed as grams of iodine absorbed by a 100g of sample.


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The determination of iodine value involves the addition of halogen in the presence of potassium iodide and titration with standard sodium thiosulphate using starch solution as the indicator. Of the various procedures available, the most widely used is the Wijs method. Iodine value is used as a parameter in process control as well as a quality parameter in traded palm oil products. According to results iodine value of soya oil is higher than the coconut oil. That is unsaturation is higher in soya oil than in the coconut oil. To take an idea here shows a value of IV in some fats Type of oil Iodine Value Coconut oil 10 Palm kernel oil 37 Olive oil 81 Peanut oil 93 Cotton seed oil 105 Sunflower oil 125 Soybean oil 130 Linseed oil 178


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4.5. Acid value 4.5.1. Materials Conical flasks Pipette Water bath Burette Weighing scale Hot neutral alcohol Indicator (phenolphthalein) 0.5M Sodium hydroxide 4.5.2. Method 5 g from sample was weighed into conical flasks and 75-100 mL of hot neutral alcohol was added to each flask. Then 0.5 mL of indicator (phenolphthalein) was added and titrated immediately with 0.5M sodium hydroxide while shaking to the first pink colour which will persist for 30 seconds. Acid value was calculated using the following formula.

4.5.3. Results Sample Reading Sample wt Acid value Palm oil 0.05 mL 5.0335 g 0.28

4.5.4. Discussion The acid value is a measure of the extent to which the glycerides in the oil have been hydrolyzed by lipase action. The glycerides are also hydrolyzed with water in the presence of air and possibly bacteria. The decomposition is accelerated by heat and light. As rancidity is usually accompanied by free fatty acid formation, determination of acid value is often used as general indication of the condition and edibility of oils. The acid value is the number of milligrams of KOH required to neutralize the free fatty acids in 1.0 g of fat or oil. For the experiment hot neutral alcohol is used because if alcohol is not neutralized acid molecules may present in the alcohol due to oxidation of alcohol can react with hydroxyl ions and give false results. In order to check the neutrality of alcohol drop of phenolphthalein is used. If a purple colour meniscus is obtained alcohol is neutral if not alcohol is not neutral and should add sodium hydroxide drop wise till the meniscus becomes purple in colour.


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4.6. Peroxide value 4.6.1. Materials Boiling tube Conical flask Pipettes Burettes Weighing scale Powdered potassium iodide Glacial acetic acid Chloroform 5% potassium iodide solution Distilled water 0.002M sodium thiosulphate solution 4.6.2. Method 1g from sample was weighed out into clean dry boiling tubes. 1g of powdered potassium iodide and 20 mL of solvent mixture (2 volumes of glacial acetic acid + 1 volume of chloroform) were added to both sample containing boiling tubes and placed them in a water bath in order to make the solutions boiling within 30 seconds. Then the contents were poured in to a flask containing 20 mL of 5% potassium iodide solution. Tube was washed twice with 25mL of water and titrated with 0.002M sodium thiosulphate solution using starch as the indicator. Same procedure was done to for the blank. Peroxide value was calculated using the following formula.

Where, m = weight of the sample Vo = volume of sodium thio sulphate blank reading V = volume of sodium thio sulphate for sample 4.6.3. Results Sample

Sample wt Blank reading Sample reading Peroxide value

Palm oil 1.0214 g 0.4 mL 1.2 mL 783.24 4.6.4. Discussion Unsaturated oils are particularly susceptible to oxidation, developing peroxide under poor storage conditions. Peroxides are the precursors of breakdown products that cause rancid flavors in fat. The concentration of peroxides is indicative of oxidation during the early stages of lipid deterioration. This index becomes less reliable during the later stage of deterioration, because peroxide degradation increases.


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Peroxide value is defined as the milliequalivalants of peroxidises per kilo gram of sample. It is titrimetric determination (Owen R. Fennema., 1996) (The peroxide value is defined as the reactive oxygen contents expressed in terms of milliequivalant (meq) of free iodine per kilograms of fat. It is determined by titrating iodine liberated from KI with sodium thiosulphate solution) Oils with peroxide value well below 10 meq/Kg are considered fresh. A rancid taste begins to be noticeable when peroxide value is between 20-40 meq/Kg. in interpreting such figures; however it is necessary to take into account the particular oil or fat involved. The peroxide value is determined by measuring the amount of iodine which is formed by the reaction of peroxides (formed in fat or oil) with iodide ion. 2 I- + H2O + ROOH ROH + 20H- + I2 Note that the base produced in this reaction is taken up by the excess of acetic acid present. The iodine liberated is titrated with sodium thiosulphate. 2S2O3

2- + I2 S4O62- + 2 I-


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5.0. References Laboratory manual on analytical methods and procedures for fish and fish products, 2nd edition, (1992), SEAFDEC http://hypertextbook.com/facts/2000/IngaDorfman.shtml http://www.pvsoap.com/saponification_chart.htm http://www.soap-making-resource.com/saponification-table.html http://en.wikipedia.org/wiki/Saponification_value http://www.fao.org/DOCREP/004/Y2774E/y2774e03.htm http://en.wikipedia.org/wiki/Peroxide_value Udenst E.A., Iroegbu F.C.; Quality assessment of palm oil sold in major markets in Abia state, Nigeria.

Properties of Lipids

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