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An Accelerated Procedure for the Determination of Lipid’s Oxidation Stability

Problem: Every matrix containing lipids undergoes oxidation of the fat portion that causes, for example in food or feed samples, the loss of its natural sensorial qualities, bad smell, and unpleasant flavor.

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Oxitest is able to perform an oxidation stability test directly on the sample as it is (solid, liquid, or doughy) with no need for a preliminary fat extraction.

One of the main causes of deterioration of lipids is lipid autoxidation. The degree of lipid oxidation can be measured by chemical or physical methods; however, those are often time-consuming, expensive, and require high-skilled operators. Chemical methods that have been widely used include peroxide value, TBA test, carbonyl compound, Kreis test, and p-anisidine. In the case of physical methods, the most common are conjugated dienes content, infrared spectroscopy, refractive index, and headspace gas chromatography.

Another possible option for food samples is to store the products at 35°C and then monitor the oxidation markers during time on the extracted fat, or aldehydes content directly on the product. This, of course, could take several months to have enough data to decide if the product is suitable or not.

Solution: The solution to reduce the time of analysis that does not require highly trained personnel is to perform accelerated oxidation stability tests with the Oxitest Official Method (AOCS Cd 12c-16).

The VELP Oxitest reactor subjects the sample to a high oxidative stress environment in order to evaluate, in a short period of time, the resistance to fat oxidation. The main innovation introduced by the Oxitest is the opportunity to work directly on the sample as it is (liquid, solid, or pasty), avoiding the critical use of chemicals for the extraction of the lipid.

This property makes it ideal for an easy quality control on both food raw materials and finished foods and guarantees representative results. In fact, other components of a product like chemical oxidants or transition metal can promote oxidation and the use of extracted matter may not be a suitable predictor of stability.

The Oxitest measures the absolute pressure change inside the two chambers, monitoring the oxygen uptake of the active components of the samples, and automatically generates a value expressed in time, called the Induction Period (IP). The longer the IP, the more resistant a sample is to lipid oxidation over time.

The instrument features two temperature regulated and hermetically sealed titanium chambers in which oxygen is purged until the pressure within both chambers is at the desired level (usually 6 bars). The temperature is then set, commonly at 90°C, in order to create the conditions to accelerate the oxidation process.

The Oxitest reactor is entirely controlled via PC through the intuitive OXISoft™ software. The information provided by the Oxitest method is crucial for shelf life study of products. The OXISoft™ manages all the analysis steps and easily provides valuable data to enable researchers to:

  • Estimate shelf-life by testing the sample at different temperatures (80-90-100°C) and elaborating an experimental curve that predicts the behavior at room temperature;
  • Study oxidation at different storage time intervals;
  • Evaluate the adequacy of storage conditions;
  • Evaluate the best packaging solution;
  • Compare the oxidative stability of different formulas for food preparations;
  • Evaluate the oxidative stability of vegetable oils of different botanical origin, different age, or different storage conditions;
  • Evaluate the effectiveness of antioxidants;
  • Control the quality of incoming raw materials and outgoing finished products.

Several preinstalled methods can help to easily identify the most suitable working conditions. Furthermore, the software allows a comprehensive reporting tool and data export.

In conclusion, the stability tests, performed with the Oxitest reactor, accelerate the oxidation process that under normal conditions may need weeks or months and provide fast, accurate, and reproducible results without using solvents or chemical reagents.

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