Pure oil is a colorless and odorless liquid in the molten state. It becomes a white waxy solid when solidified. Most natural oils are light yellow to brown and have a certain smell. Various odors are generally caused by non-fermented ingredients. For example, the aroma of coconut oil comes from nonyl ketone, rapeseed oil and mustard oil can produce pungent and odor due to their glucosinolates, and oxidative rancidity can also Produces odor. The color of natural oils is due to the carotenoid substances they contain.
The characteristics of oils, such as color, odor, melting point and freezing point, acid value, saponification value, iodine value, vinegar value, etc., are closely related to the composition and properties of fatty acids. Let’s take you through the four values of acid value, saponification value, ester value, and iodine value of oil:
Acid value: potassium hydroxide required to neutralize 1g of free fatty acids in oil The mass (mg) is called the acid value. The acid value indicates the content of free fatty acids in oil. It is an important indicator to identify the quality of oil. The more rancid the oil is, the higher its acid value.
Saponification value: The mass (mg) of potassium hydroxide used to completely saponify 1g of grease is called the saponification value of calcium grease. The saponification value of ordinary oils and fats is 180-200. The saponification value indicates the length of the fatty acid carbon chains in the fat. The shorter the fatty acid carbon chain, the higher the saponification value. The higher the content of unsaponifiable matter in oil, the lower the saponification value.
Ester value: The ester value refers to the mass of potassium hydroxide (mg) required to saponify the ester substances contained in 1g of oil. The saponification value of neutral oil is equal to the ester value. When the free fatty acid is contained in the oil, the acid value is equal to the saponification value minus the acid value.
Iodine value: The mass (g) of iodine absorbed per 100g of oil is called the iodine value. The iodine value of the oil reflects the degree of unsaturation of the oil. The higher the iodine value of the oil, the greater the degree of unsaturation. By measuring the iodine value, the average number of double bonds of the mixed fatty acids in the oil can be calculated. When the oil is hydrogenated, the theoretical hydrogen consumption can be calculated. Traditionally, oils with an iodine value below 100 are called drying oils, oils with an iodine value between 100-130 are called semi-drying oils, and oils with an iodine value greater than 130 are called non-drying oils. Dry oils and semi-dry oils are prone to rancidity and deterioration due to their high degree of unsaturation. For this reason, dry oils and semi-dry oils are usually hydrogenated or partially hydrogenated before use in soap making.
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