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E6  acid value
E6  acid value
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E6 acid value

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  • 1. INTRODUCTION The acid value (AV) is a common parameter in the specification of fats and oils. It is defined as the weight of KOH in mg needed to neutralize the organic acids present in 1g of fat and it is a measure of the free fatty acids (FFA) in a sample of oil or fat indicates hydrolysis of triglycerides. Such reaction occurs by the action of lipase enzyme and it is and indicator of inadequate processing and storage conditions (i.e. high temperature, and relative humidity, tissue damage). Besides of free fatty acids, hydrolysis of triglycerides produces glycerol. RCOOH + KOH → ROO- K+ + H2O Free fatty acids are a source of flavors and aromas. On one side, short chain of free fatty acids tend to be water soluble and volatile with characteristic smell. On the other hand, we have long chain saturated and unsaturated fatty acid. The later are more prone to oxidation in their free form and their breakdown products (aldehydes, ketones, alcohols, and organic acids) provide characteristic flavors and aromas. In most cases, these flavor and aromas are considered a defect in oils, fats, and foods that contain them. However, there are instances where hydrolysis of triglycerides and oxidation of free fatty acid are key in the development of desirable flavor and aroma in foods. This is the case of aged cheeses and some processed meats. There are standard methods for determining the acid number, such as ASTM D 974 and DIN 51558 (for mineral oils, biodiesel), or specifically for Biodiesel using the European Standard EN 14104 and ASTM D664 are both widely utilised worldwide. Acid number (mg KOH/g oil) for biodiesel should to be lower than 0.50 mg KOH/g in both EN 14214 and ASTM D6751 standard fuels. This is since the FFA produced may corrode automotive parts and these limits protect vehicle engines and fuel tanks. As oil-fats rancidify, triglycerides are converted into fatty acids and glycerol, causing an increase in acid number. A similar observation is observed with Biodiesel aging through analogous oxidation processes and when subjected to prolonged high temperatures (ester thermolysis) or through exposure to acids or bases (acid/base ester hydrolysis). THEORY Different fat samples may contain varying amount of fatty acids. In addition, the fats often become rancid during storage and this rancidity is caused by chemical and enzymatic hydrolysis of fats into free acids and glycerol. The amount of free fatty acids can be determined volumetrically by titrating the sample with potassium hydroxide. The acidity of fats and oils is expressed as its acid value or number which is defined as mg KOH required to neutralize the free fatty acids present in 1g of fat or oil. The amount of free acids present or acid value of fat is a useful parameter which gives an indication about the age and extent of its deterioration.
  • 2. TITLE Determination of acid value of fats and oils APPARATUS Beakers, Conical flask, Pipette, Burette, Retort stand MATERIALS 0.1N Oxalic acid, Potassium hydroxide (KOH) solution, Phenolphthalein indicator, Fat solvent, Fat sample PROCEDURE (A)Standardize normality of potassium hydroxide solution, KOH (1) 10ml of 0.1N oxalic acid is poured into conical flask. 2-3 drops of phenolphthalein indicator is added to the solution. (2) The solution is titrated with KOH solution till a permanent pink colour appears. The volume of KOH solution used is recorded . Using the volume of KOH solution is used, the concentration of KOH is calculated by using the formula S1V1=S2V2. (B)Determination of acid value of fats and oils (1) 5g of fat sample is weighed and placed in a conical flask. Then, 25ml of fat solvent is added to the conical flask and shake it well. Few drops of phenolphthalein is added to the solution also. (2) The above solution is titrated with 0.1N KOH until a faint pink colour persists for 20- 30 seconds. The volume used is recorded. (3) Step 1 and 2 above is repeated with a blank sample which does not contain any fat sample.
  • 3. RESULTS AND CALCULATIONS (A)Standardize normality of potassium hydroxide solution, KOH Table of volume of KOH used in titration No of Observation Initial Reading (ml) Final Reading (ml) Average Reading (ml) 1 0.00 17.00 17.002 0.00 16.90 3 0.00 17.10 V1S1=V2S2 where V1= Volume of oxalic acid used S1= Normality of oxalic acid, V2= Volume of KOH used S2= Normality of KOH S2= 𝑉1 𝑆1 𝑉2 = (10.00ml)(0.1N) (17.00ml) = 0.05882N Therefore, normality of KOH is 0.05882N. (B)Determination of acid value of fats and oils Table of volume of KOH used in titration(with fat sample) No of Observation Fat sample Used (g) Volume of fat solvent(ml) Initial Reading (ml) Final Reading (ml) Average Reading (ml) 1 4.995 25.00 0.00 0.50 0.50 2 4.995 25.00 0.00 0.50 Table of volume of KOH used in titration( without fat sample) No of Observation Volume of fat solvent used (ml) Initial Reading (ml) Final Reading (ml) Average Reading (ml) 1 25.00 0.00 0.10 0.10 2 25.00 0.00 0.10 0.1N KOH solution used for blank sample (Blank) = 0.10ml 0.1N KOH solution used for sample (With fat sample) = 0.50ml Titre value for sample = 0.50ml – 0.10ml = 0.40ml Therefore, titre value of sample is 0.40ml.
  • 4. Acid value (mg KOH/g fat) = Titre value x Normality of KOH x 56.1 Weight of sample (g) 1ml of 0.1N KOH contains 56.1mg of KOH. Hence a factor of 56.1 is incorporated in the numerator in the above equation to obtain weight of KOH from the volume of 0.1N KOH solution used during this titration. Hence, 0.05882 N KOH contains 56.1mg x 0.05882N 0.1N = 32.998mg Acid value (mg KOH/ g fat) = (0.40ml) × (0.05882N) × (32.998mg) (4.995g) = 0.1554 mg KOH/ g fat Therefore, Acid value of the fat sample after calculated is 0.155 mg KOH/ g fat. DISCUSSION Acid value defined as the amount of potassium hydroxide in milligram required to neutralize the free fatty acids (FFAs) in one gram of fats and oils. . The acid number is a measure of the amount of carboxylic acid groups in a chemical compound, such as a fatty acid, or in a mixture of compounds. In a typical procedure, a known amount of sample dissolved in organic solvent (often isopropanol), istitrated with a solution of potassium hydroxide with known concentration and with phenolphthalein as a colour indicator. From the results, we can see that 0.1554mg of KOH is needed to neutralize 1 gram of fat and oils. The majority of national and international standards for AV determination in fat and oils are based on the acid-base titration techniques in non-aqueous solvents. However, these techniques have a number of drawbacks:  Currently used non-aqueous solvents are toxic, such as ethanol or isopropanol heated up to 60ºC or higher or diethyl ether-ethanol solvent.  Incomplete solubility of test oil portion in alcohol (even under heating) caused by the formation of a dispersed system.  Conditions for accurate acid-base titration in hot amphoteric solvents might deteriorate due to the increase of the solvolysis constant for anion titrable weak acids with an increase in temperature. This conclusion follows from the fact that the solvent auto-protolysis constant increases, and the acid dissociation constant decreases with increased temperature.  Need to previously neutralize the solvents. CONCLUSION The acid value of the provided sample is 0.1554mg KOH / g fat.
  • 5. REFERENCES 1. http://www.personal.psu.edu/faculty/w/x/wxm15/Online/Biochem_unit/adv_lipid_not es.htm 2. Kleiner, I.S. and Dotti, L.B.: Laboratory Instructions in Biochemistry. (The C.V. Mosby Co: Saint Louis). Pp. 37-38. ©1962. 3. Plummer, D.T.: An Introduction to Practical Biochemistry. (McGraw-Hill: London). Pp. 186-187. ©1971. 4. Pearson Biology eight edition ( Campbell Reece)

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