ANSWER

Rancidity in meat products may result from the oxidation of lipid components or microbiological deterioration of the sample product. A variety of chemical compounds such as peroxides, aldehydes and free fatty acids are created as oil oxidizes.

Rancidity is measured chiefly in the following ways:-

• Thiobarbituric acid (TBA) value is widely applied in meat products. The amount of malonaldehyde is determined in a photometric way as rancidity starts at 0.4 – 0.6 mg of malonaldehyde per kilogram of the sample. Within this test, saturated aldehydes obtained during the termination phase of fat oxidation react with 2-thiobarbituric acid. TBA values generally correlate with the state of rancidity and increased values indicate an advanced state of rancidity (Feiner, 2006).

• Active Oxygen Method (AOM) is a measure of the ability of fat to resist oxidative rancidity during storage. Oil or fat is subjected to conditions known to accelerate degradation to help gauge the sample’s resistance to oxidation. Oxygen is bubbled into fat to cause oxidation of the fatty acids. The peroxide value test is used to monitor oxidation after the sample is stressed under controlled conditions for a long time or until a specific peroxide value is achieved.

• Analysis of the FFA content is based on measuring hydrolytic rancidity in fat or oil. This type of analysis is performed on fat only as hydrolytic rancidity originates from the hydrolysis of triglycerides in the presence of moisture. Enzymes such as lipase generally speed up this process and the hydrolysis results in FFA. The FFA values generally increase during storage of fat and fatty meats. FFA values in meat and meat products above 1.2 indicate rancidity (Feiner, 2006).

• Peroxide Value (PV) is the measure of the present state of rancidity of a sample. Fresh non-rancid fats have a low PV – usually less than 5. The PV of unstablised fat can change quickly. For this test, peroxides are indirectly measured under standardized conditions. The result is called the Peroxide Value, expressed as milliequivalents of peroxide per kilogram of fat (Eurofins, 2015). PVs from 0 to 6 are generally seen when fat is not rancid whilst PVs from 7 to 10 are seen when fat is slightly rancid. PVs greater than 10 clearly indicate rancidity (Feiner, 2006).

References

Eurofins. (2015). Lipid, Oil and Fat Testing: Rancidity Testing.

Feiner, G. (2006). Meat Products Handbook: Practical Science and Technology (pp. 19-32). Boca Raton: Woodhead Publishing Limited.