Acid value

it deals with acid value as per IP

1. Acid value

2. Introduction Free fatty acids are a source of flavors and aromas. short chain of free fatty acids tend to be water soluble and volatile with characteristic smell. L ong chain saturated and unsaturated fatty acids are more prone to oxidation in their free form . The breakdown products are aldehydes , ketones, alcohols, and organic acids which provide characteristic flavors and aromas

3. Different fat samples may contain varying amount of fatty acids. In addition, the fats often become rancid during storage. Rancidity is caused by chemical and enzymatic hydrolysis of fats into free acids and glycerol Introduction

4. Acid value It is the number which expresses in milligrams the amount of KOH necessary to neutralise the free acid present in 1 g of the substance.

5. Principle RCOOH + KOH → ROO- K+ + H2O  AV is also known as neutralization  number  or acid number  or acidity The acid value is determined by directly titrating the oil/fat in an alcoholic medium against standard potassium hydroxide/sodium hydroxide solution.

6. Ip procedure Dissolve about 10 g of substance [ weight mentioned in the individual monograph ] being examined accurately weighed, in a 50 ml of mixture of equal volumes of ethanol 95 % and ether, previously neutralised with 0.1 m KOH to phenolphthalein solution. If the sample does not dissolve in the cold solvent, connect the flask with a reflux condenser and warm slowly with a frequent shaking until the sample dissolves.

7. Add 1 ml of phenolphthalein solution titrate against 0.1 M KOH until the solution remains faintly pink after shaking for 30 seconds.

8. Ethanol-ether solution Prepare a mixture of ethanol and diethyl ether (1:1, v/v). Neutralize with sodium hydroxide titrant and add 1.0 mL of phenolphthalein indicator until pink colouration is observed. Freshly prepare the solution.

9. Phenolphthalein indicator Dissolve 1 g of phenolphthaein in 100 ml of rectified spirit.

10. 0.1M KOH Dissolve about 6 g of KOH in distilled water to produce 1000 ml

11. 95% ethanol 95ml of ethanol to 100 ml with water.

12. calculation Acid value = 5.61 n/w N= the number of ml of 0.1 M KOH required. W= the weight in g of the substance.

13. Note If the oil purpose of preservation has been saturated with carbon dioxide for the purpose of preservation, gently reflux the solution of the oil in ethanol 95 % and ether for 10 minutes before titration. The oil may be freed from the CO2 by exposing it in a shallow dish in a vacuum desiccator for 24 hours before weighing the sample.

14. Significance and application of Acid value It gives how much generation of free fatty acid has taken place which leads to rancidity. It gives an indication about the age and extent of its deterioration.

15. Significance and application of Acid value To Find rancid state, triglycerides are converted into fatty acids and glycerol, causing an increase in acid number. 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

16. Significance and application of Acid value it is an indicator of inadequate processing and storage conditions (i.e. high temperature, and relative humidity, tissue damage) 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

17. Drawbacks of non-aqueous solvents in determination of acid value 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.

18. 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