Meat products, especially sausages, consist of many components. Aside from fat, water, protein, salts, and spices, sausages also contain stabilizers and antioxidants.
In order to measure the sausage oxidation stability of the fat contained and therefore draw conclusions about its shelf life, the fat must be extracted beforehand. This extraction must not be carried out at high temperatures, as this would falsify the oxidation stability results. Solvents must also be used that do not change the chemical properties of the fat and that can be easily removed after extraction.
By using petroleum ether, the fat from sausages can be extracted easily. Analyzing these extracted fats gives some information about the lipid oxidation.
This Application Note describes the determination of the oxidation stability of different sausages with the recommended cold extraction method from Metrohm with an 892 Professional Rancimat.
This application is demonstrated on cervelat and bratwurst sausages.
First, the sausage skin is removed, and the sausage is cut into smaller pieces. These pieces are put into a 250 mL round bottom flask.
Afterwards, about three times the amount (by weight) of low-boiling petroleum ether is added (boiling point 30–40 °C). A stir bar is carefully added, and the extraction is performed by moderate stirring for at least one hour (Figure 1).
In order to shorten the extraction time and increase the fat yield, the sausage can be more finely ground using a suitable polytron.
After extraction, the ether phase is poured through a pleated paper filter into a separate 250 mL round bottom flask. The petroleum ether is then distilled, e.g., using a rotavapor. The vacuum is gradually reduced until all solvent is removed at 15 mbar.
First, an appropriate amount of cold-extracted fat is weighed into the reaction vessel, and then the analysis is started.
The Rancimat method (Figure 3) is based on exposing the sample to an airflow at a constant temperature between 100–180 °C. Highly volatile secondary oxidation products are transferred into the measuring vessel with the airflow where they are absorbed in the measuring solution. The conductivity is continuously registered here.
The formation of secondary oxidation products leads to an increase in the conductivity of the measuring solution. The time until occurrence of this marked conductivity increase is referred to as the «induction time». The induction time is a suitable indicator for the oxidation stability of the analyzed sample (Figure 4).
Table 1. Results of the oxidation stability of cold-extracted fat of sausages with the 892 Professional Rancimat at 120 °C.
| Sample (n=4) | Mean value (h) | SD(abs) in h | SD(rel) in % |
|---|---|---|---|
| Cervelat | 5.69 | 0.04 | 0.6 |
| Bratwurst | 4.31 | 0.02 | 0.5 |
In order to make specific statements about the fat contained in sausage and other meat products, an extraction step is indispensable. For this purpose, very selective information can be collected and evaluated when measuring oxidation in sausages and similar products.
With the 892 Rancimat, reproducible and accurate determination of the oxidation stability of extracted fat can be easily and simultaneously determined in eight different samples at a time.
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