Acid value of cooking oil | Autotitrator - JM Science
HIRANUMA APPLICATION DATA Automatic Titrator Data No. A7 Apr. 19,2018
FOOD Acid value of cooking oil

 1. Abstract

Acid value of oils and fats is defined as “amount (mg) of potassium hydroxide required to neutralize fatty acid in 1 g of sample” (Formula (1)).
R-COOH + KOH → R-COOK + H₂O ・・・(1)


It is used for evaluation of free fatty acid content as quality index of oils and fats. This method is described in a variety of official standards such as “Japan Agricultural Standards” and Pharmacopoeias. Example of titration for acid value in cooking oil is introduced here.
Reference: 1) Japanese Pharmacopoeia Seventeenth Edition

2. Configuration of instruments and reagents

(1) Instruments    
    Main unit : Hiranuma Automatic Titrator COM series
    Electrode : Glass reference combination electrode GR-522BZ, Connect to IE-1
    Components : Buret tip (Tube Type), tubing accessories
(2) Reagents    
    Titrant : 0.1 mol/L Pottasium hydroxide ethanolic standard solution
    Titration solvent : Mixed solvent of ethanol and diethyl ether with 1 : 1 ratio [v/v]

3. Measurement procedure

(1) Take 20 g* of sample into 200 ml Erlenmeyer flask and weigh it exactly.
(2) Add 100 ml of titration solvent and dissolve the sample.
(3) Immerse the electrode and start titration.
(4) Blank measurement is also performed with procedure (2) – (3).
(5) After titration finished, wash electrode with solvent and then immersed into DI water for 5 minutes to maintain response of glass electrode.
Sample size depends on expected value, and it’s described in a standard method.

4. Measurement conditions and results

Examples of titration conditions

Measurement of blank

Measurement of blank

Measurement of sample

Measurement of sample

Measurement results
Sample Measurement
No.
Size
(g)
Titer
volume (mL)
Acid Value
(mgKOH/g)
Statistical
result
BLANK 1 0.013 Avg. 0.013 mL
2 0.013  
         
SAMPLE 1 20.2103 3.075 0.850 Avg. 0.839 mgKOH/g
2 20.0897 3.051 0.848  SD 0.017 mgKOH/g
3 20.0007 2.936 0.820 RSD  2.00 %

 

Examples of measurement curves

  • Measurement of blank

 

  • Measurement of sample

 

5. Note

(1) Maintenance of electrode
As glass electrodes continue to be used in nonaqueous solvents, sensitivity decreases. To recover the sensitivity of glass electrode, immerse the electrode into DI water for 5 minutes after each measurement. Similarly, when reference electrode is used in a nonaqueous solvent, KCl tend to crystallize on the sleeve part of reference electrode. Crystals of KCl can be easily washed off with water.
(2) Method of endpoint detection
In this report, titration curve shows clear inflection point as endpoint. When the sample is used oil, inflection points may be unclear and cannot be detected. In that case, endpoint could be defined as fixed pH value within indicator range for pH indicator reagent. Parameters “Method” could be set to “SET” to detect endpoint with fixed pH. And parameter “Endpoint pH” also could be set to defined pH value.

Keywords: Cooking oil, Acid value, Pharmacopoeia

*Some measurement would not be possible depending on optional configuration of system.

 

Food

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