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The saponification number or saponification value is an important parameter used for the characterization and assessment of the quality of edible fats and oils. Furthermore, the saponification value provides information about the average molecular weight of all bound and free fatty acids present in a sample. The higher the saponification value of an oil or fat sample, the lower the molecular weight of all medium chain fatty acids.

In simple terms, the saponification value indicates how many grams of sodium hydroxide (NaOH) or potassium hydroxide (KOH) are required to neutralize the fatty acids contained in one gram of fat.

This Application Note describes the titrimetric determination of the saponification value in canola oil (rapeseed oil) 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 and animal fats as well as for waxes and other products with high saponification values.

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

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

OMNIS Advanced Titrator and OMNIS Dosing module equipped with dSolvotrode for the determination of saponification value.
Figure 1. OMNIS Advanced Titrator and OMNIS Dosing module equipped with dSolvotrode for the determination of saponification value.

This method is carried out on an OMNIS system consisting of an OMNIS Advanced Titrator, an OMNIS Dosing Module, and a dSolvotrode (Figure 1).

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 (glass membrane) alone in deionized water for one minute.

Titration curve from the determination of the saponification value of canola (rapeseed) oil.
Figure 2. Titration curve from the determination of the saponification value of canola (rapeseed) oil.

This method offers very precise results for saponification value determination. Steep and smooth titration curves are generated from the analysis (Figure 2), with SD(rel) <0.5% as displayed in Table 1.

Table 1. Results for the saponification value for canola oil (rapeseed oil) and olive oil.
Sample (n = 5) Mean saponification value in (mg KOH/g) SD(rel) / %
Canola oil 190.75 0.3
Olive oil 193.52 0.2

The saponification value 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 OMNIS system (which offers users flexibility combined with high-end software), to unmatched precision.

In addition to improving the accuracy and speed of determinations, OMNIS delivers results equal to or better than other established titration systems. OMNIS can be customized according to your needs and expanded for other titration applications required for your quality control purposes.

Furthermore, the OMNIS system is easily expandable and leaves all options open for further analysis of key fat quality parameters like iodine value or free fatty acids.

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Internal reference: AW TI CH1-1281-072019