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The physical and chemical properties of citric acid


Citric acid, is a tricarboxylic acid, its scientific name is 3-hydroxy-3-carboxyglutaric acid, and its molecular formula is C6H8O7 (anhydrous). It exists in lemons in nature , Citrus, plum, plum, pear, peach, fig and other fruits.

Citric acid is non-toxic, colorless, and odorless. It is generally translucent crystals or white powder. It is easily soluble in water, ethanol, acetonitrile, ether, etc., insoluble in benzene, but slightly soluble in chloroform. The relative density is 1.542g/cm3, and the melting point is 153°C (water loss).

The crystalline form of citric acid varies with different crystallization conditions. There are anhydrous citric acid and citric acid containing crystal water. Slightly weathering in dry air, deliquescent in humid air, and liberate water and carbon dioxide above 175°C. Citric acid is a strong organic acid with 3 H+ that can be ionized; the aqueous solution is acidic and can be decomposed into a variety of products when heated, and reacts with acids, alkalis, glycerol, etc.


Uses of citric acid

Citric acid has a pleasant sour taste, is refreshing in the mouth, has no aftertaste, is safe and non-toxic, and is widely used as a sour agent for food and beverages; it can form complexes with divalent or trivalent cations and is used for metal processing Chelating agents and detergents (detergency supplements that soften water); can also be derived to form many derivatives, which can be used as raw materials for the organic chemical industry.

Therefore, it is widely used in the fields of food and beverage, medicine and chemical industry, cleaning and cosmetics, organic materials, etc. It is currently the most in demand organic acid in the world. Up to now, there is no sour agent that can replace citric acid.

Beverage stabilizer consists of two parts, thickener and emulsifier. Thickeners can increase the concentration of the beverage, so that it has sufficient buoyancy to ensure uniform suspension of particles; emulsifiers can increase the hydrophilicity of the lipids in the beverage, so that the beverage juice and the lipids are mutually soluble and stably dispersed; When used together, it can synergistically improve the flavor and quality.


1. Application in fruit and vegetable beverages

Fruit and vegetable beverages are juice products obtained from fruits as raw materials through physical methods such as pressing, centrifugation, extraction, etc., generally referring to pure fruit and vegetable juice or 100% fruit and vegetable juice.
Fruit and vegetable juices are divided into two phases, clarification and turbidity according to their form. The evaluation indicators of fruit and vegetable beverages include color, taste and appearance.
Fruit and vegetable juices are prone to delamination through natural sedimentation or physical action, which seriously affects the overall quality of the beverage. Commonly used stabilizers include pectin, agar, sodium carboxymethyl cellulose (CMC), xanthan gum, sodium alginate, etc.


2. Application in vegetable protein beverages

Plant protein beverages are rich in nutrition, the market is becoming more and more extensive, and the industrial production technology is becoming more and more mature.
The product development has a variety of colors, such as cocoa soy milk, coconut soy milk, fruit juice soy milk and peanut soy milk, which greatly enriched the beverage market, and put forward higher requirements on the color, flavor and organization of the product.
In order to develop a plant protein beverage with a coordinated export feel and a stable tissue, it is particularly important to make full use of reasonable emulsion stabilizers.

Many studies have shown that the use of composite stabilizers can improve the stability of beverages.


3. Application in milk beverages

Milk beverage refers to the addition of other functional auxiliary materials on the basis of fresh milk (more than 30% milk), such as juice, coffee, cocoa, sucrose and other substances that increase the taste and rich nutrition, and are effective by mixing with a certain proportion of water. After sterilization, milk-containing beverages with various corresponding flavors are formed.
Milk beverages are often prepared into acid-flavored beverages. This is because milk proteins are easier to aggregate and precipitate under acidic conditions. Therefore, some hydrophilic acid-resistant stabilizers are often used in production to increase viscosity, such as CMC, xanthan gum, PGA, fruit glue. The acidic milk beverage can compensate for the anionic charge of the protein. Due to the electrostatic repulsion, the unstable protein nearby can be redispersed to prevent the occurrence of protein aggregation, thereby preventing precipitation and making the product more stable.

In the industry, in addition to improving the stability of yogurt beverages through relevant controls on raw milk, water quality, and process flow, the most critical way to improve the stability of yogurt beverages is to add stabilizers appropriately and use composite stabilizers to increase product Stability, in order to make full use of the synergistic interaction between various stabilizer monomers to reduce the amount of stabilizer and reduce production costs.
Pectin, CMC (Carboxymethyl Cellulose), PGA (Propylene Glycol Alginate) three stabilizers are compounded, and the optimal addition amount is 0.056%, 0.050%, 0.055%, and the total addition amount is 0.161%. The stability of yogurt beverages has been significantly improved.

Mannitol is an excellent functional sugar alcohol, which can be used in many fields such as medicine, food and chemical industry.

Mannitol is also known as D-mannitol. It has a pleasant sweetness, with a sweetness of 0.55-0.65 times that of sucrose. Among the functional sugar alcohols, mannitol is the only hexabasic sugar alcohol that is not easy to absorb moisture. It has suitable sweetness, low calories, and no toxic side effects. In the physiological metabolism of the human body, it has nothing to do with insulin and does not increase blood sugar. It does not cause dental caries, so it can be used as a sweetener for diabetic and obese patients.

Relevant studies have shown that about 50% of mannitol is finally used by the human body after being consumed, and its energy is only 8.36kJ/g, and after entering the human body, it does not need to be metabolized by insulin.

As a functional food ingredient, mannitol has a broad application prospect in the food field.

1. Develop foods for people with diabetes. The primary metabolic pathway of mannitol in the human body has nothing to do with insulin. After ingestion, it will not cause significant fluctuations in blood glucose and insulin levels, and can be consumed by people with diabetes.

2. For anti-caries sweets. Mannitol will not be used by oral microorganisms and can also inhibit the growth and reproduction of Streptococcus mutans, so it can be used to produce anti-caries sweet food. The U.S. Food and Drug Administration agreed to label "No dental caries" on sugar-free foods that use polyols such as mannitol.

3. Develop mannitol chewing gum. Mannitol has a refreshing sweetness, its sweetness is equivalent to 0.6 of sucrose, its dissolution endothermic is -29Cal/g, which is equivalent to 76% of xylitol (-38Cal/g). Using this feature, mannitol can be used as a sweetener and flavoring agent in the production of chewing gum.

4. Used as a moisture barrier. Unlike sorbitol and xylitol, mannitol is not easy to absorb moisture, and its solubility is only 18 g/100 g at 20°C, which is far lower than sorbitol, xylitol and maltitol. Therefore, it can be used as a moisture barrier to prevent adhesion during processing and use when it is used in chewing gum, gum and other foods.

In addition, mannitol does not participate in the Medela reaction. When used in food processing, the materials are not easy to coke, which helps to maintain the good color of the product and can be used for baking foods.

Mannitol can also mask the undesirable taste of other food additives, such as the rusty taste of saccharin, the bitter taste of other substances, etc., so it can be mixed with high-strength sweeteners for beverages, syrups and other foods, such as the production of confectionery, jam, Jelly etc. In addition, mannitol can also be used as a filler, quality improver, anti-caking agent, and can be added to various foods to extend its shelf life.

As a food additive, xanthan gum has become an important stabilizer, suspending agent, emulsifier, thickener, and adhesive in the fields of beverages, cakes, jelly, canned food, seafood and meat products processing, etc.

1) Food thickening stabilizer with acid and salt resistance

Xanthan gum is used in various foods such as fruit juice drinks, concentrated fruit juices, and seasonings (such as soy sauce, oyster sauce, salad dressing).
The stabilizing effect of xanthan gum is obviously better than other gums, and it has strong thermal stability. The general high temperature sterilization will not affect it. It can be used in various fruit juice drinks, pulp drinks, vegetable protein drinks, etc., the dosage is 0.08～0.3 .
Xanthan gums excellent salt resistance, acid and alkali resistance can completely replace the traditional thickener starch in soy sauce. It can overcome the shortcomings of starch precipitation, and can make the soy sauce fine and uniform, improve wall-hanging and coloring properties, and extend shelf life .
For flavored sauces such as jam and bean sauce, xanthan gum is used as a thickening stabilizer to make the sauce uniform, good mixing, non-caking, easy to fill, and improve the taste.

2) Food emulsifier

Used as an emulsifier in various protein beverages and milk beverages to prevent oily water layer and improve protein stability, prevent protein precipitation, and also use its emulsifying ability as a foaming agent and foam stabilizer, such as beer manufacturing, etc. .
After adding 0.02% xanthan gum to the emulsification system based on legume protein, the emulsification is obviously improved, and the mixed system has high shear rate and heat-induced high viscosity characteristics.

Application of Xanthan Gum in Food

3) Food filler

As a stable high-viscosity filler, it can be widely used in the processing of various types of snacks, bread, biscuits, candies and other foods. Without changing the traditional flavor of the food, the food has better shape retention and longer The shelf life and better taste are conducive to the diversification and industrial scale production of these foods.
In the production of various frozen foods, xanthan gum has the functions of preventing its loss of water, delaying aging, and extending the shelf life.

4) Food emulsion stabilizer

Used as an emulsion stabilizer in frozen foods. Xanthan gum in ice cream and ice cream can adjust the viscosity of the mixture to make it have a uniform and stable composition and a smooth and soft texture.
Because the relationship between the viscosity of xanthan gum and the temperature has plasticity and shearing properties, the viscosity decreases and the resistance decreases during the processing operation, which is beneficial to the process. In the cooling aging stage, the viscosity recovers, which is beneficial to increase the expansion rate and prevent The formation of large ice crystals in the ice cream tissue makes the ice cream smooth and delicate.
At the same time, the freeze-thaw stability of the product is improved, and the cream and water are evenly mixed during melting, and no slurry separation phenomenon occurs. The general aging time is 2～3h. The dosage is 0.2% to 0.4%.

5) Food adhesive

Xanthan gum can cross-link some water-soluble powder substances, such as sodium alginate, casein, methyl cellulose and polyethylene glycol cellulose sodium salt, to make a binder.
This adhesive is used in food processing to improve texture and increase film-forming properties.
This property of xanthan gum can be used to make granular pastes. Compared with traditional pastes, pastes made of xanthan gum have low dispersibility, high uniformity and solubility, good fluidity and filling performance, and excellent solid storage properties due to non-cohesiveness.

The aqueous solution of xanthan gum has unique rheological properties—shear thinning. As the shear rate increases, the apparent viscosity of the solution decreases significantly; it has thickening properties and has a greater viscosity at lower concentrations; it has good Water solubility, stability to heat, acid and alkali, and good compatibility with a variety of salts.
These many characteristics enable it to significantly improve the texture, taste and appearance quality of food by controlling the rheological behavior of the product, and increase its commercial value. Therefore, the application prospect in food is very broad.

As a food additive, xanthan gum has become an important stabilizer, suspending agent, emulsifier, thickener, and adhesive in the fields of beverages, cakes, jelly, canned food, seafood and meat products processing, etc.

1) Food thickening stabilizer with acid and salt resistance

Xanthan gum is used in various foods such as fruit juice drinks, concentrated fruit juices, and seasonings (such as soy sauce, oyster sauce, salad dressing).
The stabilizing effect of xanthan gum is obviously better than other gums, and it has strong thermal stability. The general high temperature sterilization will not affect it. It can be used in various fruit juice drinks, pulp drinks, vegetable protein drinks, etc., the dosage is 0.08～0.3 .
Xanthan gums excellent salt resistance, acid and alkali resistance can completely replace the traditional thickener starch in soy sauce. It can overcome the shortcomings of starch precipitation, and can make the soy sauce fine and uniform, improve wall-hanging and coloring properties, and extend shelf life .
For flavored sauces such as jam and bean sauce, xanthan gum is used as a thickening stabilizer to make the sauce uniform, good mixing, non-caking, easy to fill, and improve the taste.

2) Food emulsifier

Used as an emulsifier in various protein beverages and milk beverages to prevent oily water layer and improve protein stability, prevent protein precipitation, and also use its emulsifying ability as a foaming agent and foam stabilizer, such as beer manufacturing, etc. .
After adding 0.02% xanthan gum to the emulsification system based on legume protein, the emulsification is obviously improved, and the mixed system has high shear rate and heat-induced high viscosity characteristics.

Application of Xanthan Gum in Food

3) Food filler

As a stable high-viscosity filler, it can be widely used in the processing of various types of snacks, bread, biscuits, candies and other foods. Without changing the traditional flavor of the food, the food has better shape retention and longer The shelf life and better taste are conducive to the diversification and industrial scale production of these foods.
In the production of various frozen foods, xanthan gum has the functions of preventing its loss of water, delaying aging, and extending the shelf life.

4) Food emulsion stabilizer

Used as an emulsion stabilizer in frozen foods. Xanthan gum in ice cream and ice cream can adjust the viscosity of the mixture to make it have a uniform and stable composition and a smooth and soft texture.
Because the relationship between the viscosity of xanthan gum and the temperature has plasticity and shearing properties, the viscosity decreases and the resistance decreases during the processing operation, which is beneficial to the process. In the cooling aging stage, the viscosity recovers, which is beneficial to increase the expansion rate and prevent The formation of large ice crystals in the ice cream tissue makes the ice cream smooth and delicate.
At the same time, the freeze-thaw stability of the product is improved, and the cream and water are evenly mixed during melting, and no slurry separation phenomenon occurs. The general aging time is 2～3h. The dosage is 0.2% to 0.4%.

5) Food adhesive

Xanthan gum can cross-link some water-soluble powder substances, such as sodium alginate, casein, methyl cellulose and polyethylene glycol cellulose sodium salt, to make a binder.
This adhesive is used in food processing to improve texture and increase film-forming properties.
This property of xanthan gum can be used to make granular pastes. Compared with traditional pastes, pastes made of xanthan gum have low dispersibility, high uniformity and solubility, good fluidity and filling performance, and excellent solid storage properties due to non-cohesiveness.

The aqueous solution of xanthan gum has unique rheological properties—shear thinning. As the shear rate increases, the apparent viscosity of the solution decreases significantly; it has thickening properties and has a greater viscosity at lower concentrations; it has good Water solubility, stability to heat, acid and alkali, and good compatibility with a variety of salts.
These many characteristics enable it to significantly improve the texture, taste and appearance quality of food by controlling the rheological behavior of the product, and increase its commercial value. Therefore, the application prospect in food is very broad.