Determine the alcoholic acidity of the given sample of flour.
After undertaking this activity, you will be able to:
• assess the acidity the given sample of flour, and
• check the given sample for conformance to the standard for its acidity.
Principle
Alcoholic acidity is defined as mg of H2SO4 required for 100 g of the sample to have the same alcohol soluble acids. Grains or their milled products on storage undergo physical, as well as, chemical changes. Acid phosphates, amino acids and free fatty acids of flours, under certain conditions increase considerably due to the enzymatic hydrolysis of phytin, protein and fat, respectively. Milled products deteriorate faster than their parent grains. The amino acids and acid phosphates are soluble in strong alcohol. The free fatty acids are insoluble in water but are soluble in fat solvents or in strong alcohol. For this reason, the acidity in flours is expressed as either fat acidity,wherein, benzene is used as a fat solvent or it is expressed as alcoholic acidity.
Materials Required
Collect the following material to carry out the activity:
• Sample of flour
• Conical flask
• Weighing balance
• Pipette
• Standard NaOH solution (approximately 0.05 N)
• Phenolphthalein
• Neutral ethyl alcohol- 90% volume by volume
Procedure
Now carry out the practical step-by-step as enumerated herewith:
1) Weigh 5 g of the flour sample. Put in conical flask.
2) Add 50 ml of neutral ethyl alcohol.
3) Stopper the flask, shake and allow to stand for 24 hours.
4) Filter the alcoholic extract (through an ordinary dry filter paper).
5) Titrate 10 ml of alcoholic extract against standard NaOH solution using phenolphthalein as indicator.
6) Calculate the percentage alcoholic acidity as sulphuric acid.
7) Calculate the alcoholic acidity of the sample using the following formula.