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 to understand the melting point and freezing point of oils and fats:
Natural oils and fats are mixtures of triglycerides, etc., and are not pure substances. Since the melting points of various triglycerides are different, the melting points and Freezing point is a range of temperatures. Generally, the highest melting point and freezing point are between 40-50℃, and there is no definite melting point and freezing point. The melting point and freezing point are related to the fatty acids that make up the oil. Oils containing more saturated fatty acids have a higher melting point range, while oils containing more unsaturated fatty acids have a lower melting point range. Only at very low temperatures can grease become completely solid. Most fats that are solid at room temperature are semi-solid plastic fats, not completely solid fats.
When the fatty acids produced by decomposing oils are gradually cooled from liquid to solid, a certain amount of crystallization heat will be released. When the liquid is cooled, the solidification produced no longer cools down, but instead heats up instantly and the maximum temperature reached becomes Freezing point of fatty acids. The freezing point of fatty acids is one of the important constants for identifying various fats and oils.
The freezing point of fatty acids is related to the length of the carbon chain of the fatty acid, the degree of unsaturation, and the degree of isomerization. The longer the carbon chain, the fewer double chains, and the less isomerization, the higher the freezing point; conversely, the lower the freezing point. For isomers, the trans form has a higher freezing point than the cis form.
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