Methods for the detection of spoilage of oils
View Patent ↗Methods for the detection of spoilage of oils containing unsaturated fatty acids is disclosed. Specific methods include the determination of p-anisidine in oils containing unsaturated fatty acids using high performance liquid chromatography after p-anisidine is added to the oil containing unsaturated fatty acids, and allowed to react with oxidation products.
1. A method of determining oxidation of an oil comprising an unsaturated fatty acid, comprising the steps of: preparing a standard p-anisidine solution comprising an amount of p-anisidine; preparing a sample solution comprising an amount of p-anisidine and an amount of a sample of oil, wherein the sample of oil comprises an unsaturated fatty acid and wherein the amount of p-anisidine in the sample solution before any p-anisidine reacts with the sample of oil is the same as the amount of p-anisidine in the standard p-anisidine solution; measuring the amount of p-anisidine in the standard p-anisidine solution; measuring the amount of p-anisidine in the sample solution, wherein measuring the p-anisidine is done by one of chromatography, nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR), and ultraviolet-visible spectroscopy (UV-VIS); and calculating a percent of p-anisidine remaining in the sample solution after the p-anisidine reacts with the sample of oil as compared with the standard p-anisidine solution, wherein the percent of p-anisidine remaining in the sample solution is an indication of oxidation of the sample of oil in the sample solution.
2. The method of claim 1 , wherein the chromatography is HPLC.
3. The method of claim 1 , wherein the percent p-anisidine remaining in the sample solution of less than 50%, 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, or 95% is an indication of oxidation of the sample of oil in the sample solution.
4. The method of claim 1 , wherein the amount of p-anisidine in the standard p-anisidine solution is from about 0.1 mg/mL to 1 mg/mL, from about 0.1 mg/mL to 0.5 mg/mL, or from about 0.2 mg/mL to 0.3 mg/mL.
5. The method of claim 1 , wherein the amount of p-anisidine in the standard p-anisidine solution is about 0.2 mg/mL, about 0.25 mg/mL, about 0.3 mg/mL, about 0.4 mg/mL, or about 0.5 mg/mL.
6. The method of claim 1 , wherein the amount of the sample of oil in the sample solution is from about 0.01 mL/mL to 0.2 mL/mL, from about 0.02 mL/mL to 0.1 mL/mL, or from about 0.05 mL/mL to 0.1 mL/mL.
7. The method of claim 1 , wherein the amount of the sample of oil in the sample solution is about 0.2 mL/mL, about 0.1 mL/mL, about 0.05 mL/mL, or about 0.02 mL/mL.
8. The method of claim 1 , wherein the measuring of the amount of p-anisidine in the sample solution is done more than 1 minute, 5 minutes, 10 minutes, 20 minutes, 30 minutes, 60 minutes, 120 minutes, 180 minutes or more than 180 minutes after preparing the sample solution.
9. The method of claim 1 , wherein the measuring of the amount of p-anisidine produces a peak arca, a mass, a weight, a concentration, a molar concentration, a mass concentration or weight concentration.
10. The method of claim 1 , wherein the standard p-anisidine solution and sample solution further comprise acetic acid.
11. The method of claim 1 , wherein the sample of oil comprises one or more oils selected from the group of vegetable oil, animal oil and marine oil.
12. The method of claim 11 , where in the sample of oil comprises marine oil.
13. The method of claim 12 , wherein the marine oil comprises a fish oil containing omega-3 fatty acids.
14. The method of claim 5 , wherein the amount of p-anisidine in the standard p-anisidine solution is about 0.25 mg/mL.
15. The method of claim 7 , wherein the amount of the sample of oil in the sample solution is about 0.1 mL/mL.
16. The method of claim 1 , wherein the sample of oil comprises an additive.
17. The method of claim 16 , wherein the additive has a molar absorptivity at 350 nm of at least 100 M −1 cm −1 .
18. The method of claim 16 , wherein the additive is a coloring agent, a flavoring agent, a preserving agent, an antioxidant, or a vitamin.
19. The method of claim 16 , wherein a reaction product of the additive with p-anisidine has a molar absorptivity at 350 nm of at least 1000 M −1 cm −1 .
20. The method of claim 1 , wherein a ratio of the amount of p-anisidine in the sample solution to the amount of the sample of oil in the sample solution is from about 4:1 to 1:4, about 2:1 to 1:2, about 4:1 to 1:1, wherein the ratio is volume to volume, mass to volume, volume to mass, or mass to mass.
21. The method of claim 1 , wherein a ratio of the amount of p-anisidine in the sample solution to the amount of the sample of oil in the sample solution is about 3:1 to 2:1, about 4:1, about 3:1, about 2.5:1, about 2:1, about 1.5:1 or about 1:1, wherein the ratio is volume to volume, mass to volume, volume to mass, or mass to mass.
22. The method of claim 21 , where the ratio is 2.5:1, mass to volume.