Acid Value Of Edible Oil

Acid Value Of Edible Oil

In order to ensure the quality and safety of edible vegetable oils, physical and chemical indicators such as acid value and peroxide value are often used to measure their quality. Acid value (AV) is a sign of the free fatty acid (FFA) content in oils and fats. The lower the acid value, the better the quality of the oil, the fresher and more refined it is. A high AV indicates that the oil is of poor quality or has been stored for too long and has become oxidatively rancid. The main reasons for excessive acid value are, first, manufacturing process problems, and second, too long storage time. During long-term storage, oils and fats slowly hydrolyze under the action of microorganisms, enzymes and heat to produce FFA, which leads to an increase in AV. Crude oils of natural animal and plant oils contain a certain amount of FFA, such as palm oil, sunflower oil, soybean oil, rapeseed oil, etc. Therefore, oil products must reduce the its content to safety standards when used and stored.

The common production process for removing FFA from oils and fats in the market is generally called "deacidification". The main methods include alkali refining deacidification (neutralization reaction of alkali substances with free fatty acids) and physical deacidification (vacuum distillation). More specifically:

 Alkali refining refers to the reaction of alkali with acids to form fatty acid salts. The fatty acid salts generated in the process form saponin in the coexistence of oil and water. Saponin will also adsorb some impurities (such as solid particles, proteins, colloids, pigments, etc.) and separate them from the oil through sedimentation. This is also the chemical refining method we know.

 Physical deacidification: this method includes a degumming step, in which FFA are removed by a combination of steam stripping and deodorization. This process is more suitable for high daily production capacity (> 10TD).