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AOAC Official Method 939.05 Fat Acidity—Grains Titrimetric Method First Action 1939 Final Action CodexAdopted–AOAC Method. fat acidity—grains titrimetric method. Report fat acidity as mg KOH required to neutralize free fatty acids from 100 g grain (dry basis).
32.2.04 AOAC Official Method 939.05 Fat Acidity—Grains Titrimetric Method First Action 1939 Final Action Codex-Adopted–AOAC Method* A Reagents (a) Toluene–alcohol–phenolphthalein solution.—0.02% To L toluene add L alcohol and 0.4 g phenolphthalein (b) Alcohol–phenolphthalein solution.—0.04% To L alcohol add 0.4 g phenolphthalein (c) Potassium hydroxide standard solution.—0.0178M, carbonate-free mL = mg KOH B Apparatus (a) Grain mill.—Suitable for grinding small test samples (b) Fat extraction device.—Soxhlet or other suitable type (Durable paper thimbles or Alundum RA-360 thimbles are suitable for extraction.) C Method I Obtain representative test sample of ca 50 g grain (corn, 200 g) by hand quartering or by use of mechanical sampling device Preferably grind test sample so that ≥90% will pass No 40 sieve (somewhat coarser grind will not materially affect results) If test sample is too moist to grind readily, dry at temperature of ca 100°C just long enough to remove excess moisture Extract 10 ± 0.01 g test portion with petroleum ether ca 16 h in extractor Start extraction as soon as possible after grinding and never let ground test sample remain overnight Completely evaporate solvent from extract on steam bath Dissolve residue in extraction flask with 50 mL toluene–alcohol–phenolphthalein solution and titrate with standard KOH solution to distinct pink, or in case of yellow solution to orange-pink If emulsion forms during titration, dispel by adding second 50 mL portion of toluene–alcohol–phenolphthalein solution End point should match color of solution made by adding 2.5 mL 0.01% KMnO4 solution to 50 mL K2Cr2O7 solution of proper strength to match color of original solution being titrated (Add 0.5% K2Cr2O7 solution dropwise to 50 mL H2O until color matches Then add 2.5 mL 0.01% KMnO4 solution.) Make blank titration on 50 mL toluene–alcohol–phenolphthalein solution and subtract this value from titration value of test sample If additional 50 mL portion toluene–alcohol–phenolphthalein solution was added, double blank titration Report fat acidity as mg KOH required to neutralize free fatty acids from 100 g grain (dry basis) Fat acidity = 10 × (titration − blank) References: JAOAC 22, 526(1939); 23, 493(1940); 24, 587(1941); 50, 198(1967); 71, 84(1988) D Method II—Rapid Method for Corn (Result may be obtained in