Applications

The Rancimat method is a widely accepted method for the determination of the oxidation stability of natural fats and oils. Its main application is quality control in oil mills and the oil processing industry. At elevated temperatures and under the exposure of air, fatty acids are oxidized. The reaction products are absorbed in ultrapure water that is continually monitored for conductivity. After an induction period with slow reaction, the formation of volatile carboxylic acids is accelerated. At that time the conductivity begins to increase rapidly. Instead of investing weeks or months, the sample can be oxidized within a few hours.The method can also be used to determine the oxidation stability of solid foodstuffs that contain natural fats or oils. Frequently, a direct determination without extraction of the fat is possible, if the fat content exceeds a minimum level. In these cases, a simple and reliable assessment of the quality of the produced foodstuff is possible.A number of fat-containing solid foodstuffs such as almonds, peanuts, peanut-flavored puffs, potato chips, muffins, butter cookies, French fries, and instant noodles were successfully tested with the Rancimat method. The experiments revealed that the comminution of the sample is one of the most important steps. The grinding procedure of the tested samples was kept as simple as possible to avoid the use of expensive milling instrumentation.

This Bulletin describes potentiometric titration methods for the determination of the acidity in milk and yoghurt according to DIN 10316, ISO/TS 11869, IDF/RM 150, ISO 6091 and IDF 86, the chloride content in milk, butter and cheese according to EN ISO 5943, IDF 88, ISO 15648, IDF 179, ISO 21422, and IDF 242. Additionally the determination of the sodium content in milk using the thermometric titration is described. The determination of the oxidation stability of butter in accordance to AOCS Cd 12b-92, ISO 6886 and GB/T 21121 as well as the determination of lactose in lactose free milk by ion chromatography is also described.For the determination of the pH value in dairy products see Application Bulletin AB-086 and for the determination of calcium and magnesium see Application Bulletin AB-235.

As the determination of the exact content of individual glycerides in fats and oils is difficult and time-consuming, several fat sum parameters or fat indices are used for the characterization and quality control of fats and oils. Fats and oils are not only essential for cooking, they are also an important ingredient in pharmaceuticals and personal care products, such as ointments and creams. Consequently, several norms and standards describe the determination of the most important quality control parameters. This Application Bulletin describes eight important analytical methods for the following fat parameters in edible oils and fats:Determination of water content in accordance with the Karl Fischer method; Oxidation stability in accordance with the Rancimat method; Iodine value; Peroxide value; Saponification value; Acid value, free fatty acids (FFA); Hydroxyl number; Traces of nickel using polarography; Special care is taken to avoid chlorinated solvents in these methods. Also, as many of the mentioned methods as possible are automated.

The Rancimat method is an accelerated ageing test. Air is conducted through the sample in the reaction vessel at a constantly increased temperature. The fatty acids are oxidized during this process. Volatile secondary reaction products are formed at the end of the test that are conducted by air flow into a measuring vessel, where they are absorbed by a measuring solution (distilled water). The continually recorded electrical conductivity increases as a result of the absorption of the ionic reaction products. The time up to which the secondary reaction products arise is called the induction time. It characterizes the oxidation stability of oils and fats.This Application Bulletin provides a detailed description of the method, in particular also of the required sample preparation.

This Application Bulletin describes the determination of the thermostability of PVC in accordance with ISO 182 Part 3 using the dehydrochlorination method with the 895 Professional PVC Thermomat. The instrument permits fully automatic determination of the stability time. The test is suitable for monitoring the manufacture and processing of PVC products manufactured in the injection molding process, for their final clearance, characterization and for the comparison of PVC products and for testing the effectiveness of heat stabilizers.

The effectiveness of antioxidants can be expressed as antioxidant activity. It can be readily determined using the Rancimat method. This is accomplished by first determining the induction time of a mixture made up of hog fat and the antioxidant to be investigated and then by determining the corresponding time for hog fat alone. The quotient expresses the efficiency of the respective antioxidant and is referred to as the antioxidant activity index (AAI).This Application describes the determination of the antioxidant activity index of five common antioxidants.

Determination of the oxidation stability of foods with a low fat content is a challenge. As an alternative, the oxidation stability can be specified indirectly. To accomplish this, a determination is made as to the extent that a sample that has been mixed with a fat as a standard solution, e.g., hog fat, will change the oxidation stability of that standard solution. This is accomplished by first determining the induction time of the mixture made up of hog fat and the sample and then by determining the corresponding time for the lard alone. The quotient is referred to as the stability index (SI).

The oxidation stability of fats and oils is an important parameter for quality controls in the food industry. Ideally, the determination is made with the Rancimat method, which is suitable for both liquid and solid samples. Its determination takes place directly in the sample or, in cases where this is not possible, in the extracted fat following cold extraction.

The thermostability of polyvinyl chloride (PVC) was determined using the dehydrochlorination procedure at 180 °C. Comparison of the thermostability of pure PVC polymer, blended PVC (blended with stabilizer, plasticizer, filler) and blended PVC after processing.

In this Application Note, the 893 Professional Biodiesel Rancimat measures the oxidation stability of biodiesel (or fatty acid methyl esters, FAME), an eco-friendly fuel.