Monoglyceride fatty acid ester, also known as monoglyceride, is formed by the esterification of one molecule of glycerin and one molecule of fatty acid.
At room temperature, monoglyceride is a white or light yellow solid, slightly bitter, insoluble in water, and soluble in organic solvents such as chloroform, ethyl acetate, ethanol, benzene, and various chlorinated hydrocarbons.
There are two hydrophilic hydroxyl groups (OH) and one lipophilic hydrocarbon group (R) in the monoglyceride molecule. So that it has excellent emulsifying properties. It belongs to non-ionic surfactant. The HLB value is between 3 and 5, with defoaming and lipophilic properties, and is a w/o type emulsifier.
Monoglycerides commercially available in recent years are mostly undistilled primary products. It is actually a mixture of monoglyceride, diglyceride and a small amount of triglyceride. Because there is only one hydroxyl group in the diglyceride molecule, the hydrophilicity is too weak, and the emulsifying ability is low, and the triglyceride, that is, fat, has no emulsifying ability at all, so it is the monoglyceride that really emulsifies the product. The monoglyceride content of this product is relatively low (below 50%), so its scope of application is greatly limited. In contrast, distilled high-purity monoglyceride (content exceeding 90%) has better performance and can meet various requirements. With the continuous progress of distillation technology, the output of this monoglyceride will increase year by year.
Application of monoglyceride
Monoglyceride is a non-ionic surfactant with excellent properties such as emulsification, lubrication, softness and wetting, and it is non-toxic. It is widely used as an emulsifier in food processing and cosmetics.
1. Used in food, monoglyceride is considered to be the safest food additive.
2. Emulsifiers for cosmetics and medical ointments such as skin creams, cold creams, emulsions, and hair creams, fiber finishing agents, antistatic agents such as polyethylene, polypropylene, and foamed polystyrene.
3. The compound of glycerol monolaurate and sorbic acid can be used as preservatives and fruit preservatives in meat products, dairy products and beer.
4. Glycerol monooleate is used for anti-rust lubricants and food additives for precision machinery. High-purity monoglyceride can be used as an internal lubricant in the probasic method
The industrial production of monoglyceride mainly uses chemical methods. The chemical synthesis of monoglyceride usually has low yield, high energy consumption, deep color and odor. In order to obtain monoglycerides of higher quality and yield, in recent years, people have begun to explore new ways to synthesize monoglycerides at lower temperatures using lipase as a catalyst. Enzymatic synthesis of monoglyceride has many advantages, such as mild reaction conditions, low energy consumption and high product purity. A large number of related studies have been carried out at home and abroad, but there are still low yields of monoglyceride and the structure of the equipment used for synthesis , The solvent system and the operation process are too complicated and other shortcomings, most research is still in the experimental stage, and commercial production has not been achieved.
Researchers at home and abroad use natural oils, fatty acids and glycerin as raw materials, using biocatalyst lipases, in the presence or absence of organic solvent systems, through a variety of reactions such as oil hydrolysis or alcoholysis, fatty acid and glycerol esterification and glycerol hydrolysis Way to synthesize monoglyceride. The main ways for lipase to synthesize monoglyceride in the organic phase are as follows.
1. The hydrolysis method refers to the process by which natural oils or triglycerides produce monoglycerides through hydrolysis. The main problem of the hydrolysis method is that the yield of monoglyceride is low, because each mol of monoglyceride produced produces 2 mol of fatty acid. The fatty acid inhibits acyl transfer and prevents the hydrolysis reaction from continuing.
2. Esterification or transesterification reaction refers to the process of glycerol and fatty acid or fatty acid ester to produce monoglyceride through esterification or transesterification reaction. The key to the esterification or transesterification reaction is to control the initial esterification product monoglyceride not to be further esterified into diesters or triesters, so the monoglyceride produced should be separated from the reaction system in time to improve the yield of monoglyceride .
3. The glycerolysis method refers to the process of synthesizing monoglyceride using natural oil or triglyceride and glycerol as substrates. The glycerolysis reaction has the highest theoretical yield because 2 mol of glycerol is consumed per 1 mol of TAG (triethylene glycol), while 3 mol of monoglyceride can be produced.
Monoglyceride as an additive widely used in food and other industries, the market has developed a series of products. Mainly include ordinary monoglyceride, high-purity (distilled) monoglyceride and monoglyceride derivative products, which are now introduced as follows:
(1) Common monoglyceride
Ordinary monoglyceride is the primary product of monoglyceride obtained by esterification or alcoholysis without distillation or purification. It is a mixture of monoglyceride and diglyceride and other components. The content of monoglyceride is generally 35-40%, diglyceride is about 35-45%, ester is about 10-15%, free glycerin is 1-7%. Because the actual content of mono-dry ester is low, it can only be used for general industry.
(2) High-purity monoglyceride
As a common monoglyceride for industrial use, the general content is 35~40%, and the highest content will not exceed 60%. In order to improve the use of monoglycerides, ordinary monoglycerides need to be purified. The purification method is to remove the catalyst and glycerin, and then polymer distillation, and finally obtain high purity monoglycerides with a monoglyceride content of more than 90%.
The method of removing the catalyst is to cool the reaction product to about 125°C and add a certain amount of phosphoric acid to neutralize the catalyst.
When deglycerinizing, it is generally carried out in a thin-film evaporator. First, the gaseous product, water and part of Ganshan (degassing) are separated from the mixture at a residual pressure of 0.13~0.25kPa (1~2mmHg) and a temperature of 140°C. Glycerin, free fatty acids and some short carbon chain monoglycerides are distilled off under high vacuum (established by a multi-stage steam vacuum pump). At this time, the operating conditions of the equipment are: residual pressure 0.013~0.039kPa (0.1~0.3mmHg), temperature about 160 ℃.
The product after preliminary separation and distillation contains about 60% of monoglyceride. To obtain more than 90% of monoglyceride, it needs to be prepared on a three-stage molecular distillation device with a thin film evaporator. The temperature range in the equipment is 205~210 ℃, residual pressure 0.0013~0.0039kPa (0.01~0.03mmHg).cessing of PVC plastics.
3) Derivatives of monoglycerides
Monoglycerides with higher purity can be esterified with organic acids such as acetic acid, lactic acid, citric acid, tartaric acid, etc. to form a variety of monoglycerides, and become a variety of special-purpose emulsifiers.
1. Diacetyl ester of monoglyceride
The diacetyl ester of monoglyceride is a yellow flake solid or brown ointment, which is mainly used as a modifier in the bread industry. Adding it to bread can promote the even distribution of fat and prevent gluten and starch paste from sticking during baking.
2. Lactate of monoglyceride
Monoglycerides and lactates are mainly used in the syrup and bread industry.
3. Polyoxyethylene ether of monoglyceride
Monoglyceride polyoxyethylene ether has good dispersibility, emulsifying power, foaming power and penetrating power. It can be used as an emulsifier and stabilizer for ointments and emulsions. It can also be used as a solubilizing agent for perfumes, pigments and pharmaceuticals. . It can be prepared by the reaction of monoglyceride and ethylene oxide.
4. Monoglyceride hydrate
This product is an emulsion of distilled monoglyceride in water. In terms of external appearance, it is a white soft substance with weak acetic acid taste. It is mainly used in the production of bread and macaroni products. Hydrates of monoglyceride and starch in flour can produce a complex compound that prevents the bread from hardening.