The saponification value is an important parameter used for the characterization and assessment of the quality of edible fats and oils. Furthermore, the saponification number provides information about the average molecular weight of all fatty acids present. The higher the saponification value, the lower the molecular weight of all fatty acids.

This Application Note describes the titrimetric determination of the saponification value in rapeseed (canola) and olive oil. The analysis is performed according to the standard EN ISO 3657, and is based on a modification of the norms AOAC 920.160, ASTM D5558, USP<401>, and Ph.Eur. 2.5.6. Using potentiometric indication, very precise results can be achieved for a wide range of edible oils.

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The analysis is demonstrated for olive and canola (rapeseed) oil.

An appropriate amount of sample is weighed into a conical flask and refluxed with ethanolic potassium hydroxide solution for 60 minutes. For the blank determination, the same procedure is applied but the sample is omitted.

OMNIS system for the measurement of saponification value in edible oils consisting of an OMNIS Advanced Titrator and an OMNIS Dosing Module equipped with a dSolvotrode.
Figure 1. OMNIS system for the measurement of saponification value in edible oils consisting of an OMNIS Advanced Titrator and an OMNIS Dosing Module equipped with a dSolvotrode.

The analysis is carried out on an OMNIS system consisting of an OMNIS Advanced Titrator, an OMNIS Dosing Module, and a dSolvotrode.

The prepared sample solution is first allowed to cool down to room temperature. Next, the buret tips as well as the electrode are inserted into the conical flask. Ethanol is added, and then the solution is titrated with standardized hydrochloric acid until after the equivalence point is reached. Afterwards, the electrode is cleaned with ethanol and deionized water. The electrode is then conditioned by immersing the bulb alone in deionized water for 1 minute.

Steep and smooth curves are obtained for both oils. The results are very reproducible with relative standard deviations below 0.3 %. The results for the two oils are displayed in Table 1.

Table 1. Results of the saponification number (SN) for canola oil and olive oil (n = 5).
Sample (n = 5) SN / (mg KOH/g) SD(rel) / %
Canola oil 190.75 0.3
Olive oil 193.52 0.2
Figure 2. Titration curve of the determination of the saponification number of canola (rapeseed) oil.

The saponification number in a variety of edible oils is easily determined using automated potentiometric titration according to the standard EN ISO 3657. The dSolvotrode used in this application was designed especially for nonaqueous titrations and leads, together with the ONMIS system, to unmatched precision.

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Metrohm USA

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33578 Riverview, FL

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