柠檬酸，亦称为枸橼酸，化学式为 C6H8O7，是一种中强度有机酸，它包括3个羧基（R-COOH）基团。柠檬酸是自然在柑橘类水果中产生的一种天然防腐剂，也是食物和饮料中的酸味添加剂。在生物化学中，它是柠檬酸循环的重要中间产物，因此在几乎所有生物的代谢中起到重要作用。此外，它也是一种对环境无害的清洁剂。
Citric acid, also known as citric acid, with chemical formula of C6H8O7, is a medium strength organic acid, which includes three carboxyl (R-COOH) groups. Citric acid is a natural preservative naturally produced in citrus fruits, and it is also an acid additive in foods and beverages. In biochemistry, it is an important intermediate product of citric acid cycle, so it plays an important role in almost all biological metabolism. In addition, it is also an environmentally friendly cleaner.
很多种水果和蔬菜，尤其是柑橘属的水果中都含有较多的柠檬酸，特别是柠檬和青柠——它们含有大量柠檬酸，在干燥之后，含量可达8%（在果汁中的含量大约为47 g/L）。在柑橘属水果中，柠檬酸的含量介于橙和葡萄柚的0.005 mol/L和柠檬和青柠的0.30 mol/L之间。这个含量随着不同的栽培品种和植物的生长情况而有所变化。
Many kinds of fruits and vegetables, especially citrus fruits, contain more citric acid, especially lemon and lime - they contain a lot of citric acid, which can reach 8% after drying (about 47 g/L in juice). In citrus fruits, the content of citric acid is between 0.005 mol/L of orange and grapefruit and 0.30 mol/L of lemon and lime. This content varies with the growth of different cultivated varieties and plants.
性质
nature
在室温下，柠檬酸是一种白色晶体粉末。它可以以无水合物或者一水合物的形式存在。柠檬酸从热水中结晶时，生成无水合物；在冷水中结晶则生成一水合物。加热到78 °C时一水合物会分解得到无水合物。在15摄氏度时，柠檬酸也可在无水乙醇中溶解。
At room temperature, citric acid is a white crystalline powder. It can exist in the form of non hydrate or monohydrate. When citric acid crystallizes from hot water, hydrate free substance is formed; Monohydrate is formed when crystallized in cold water. When heated to 78 ° C, the monohydrate will decompose to obtain hydrate free. At 15 ℃, citric acid can also be dissolved in absolute ethanol.
从结构上讲柠檬酸是一种三羧酸类化合物，并因此而与其他羧酸有相似的物理和化学性质。加热至175 °C时它会分解产生二氧化碳和水，剩余一些白色晶体。
Citric acid is a kind of tricarboxylic acid compound structurally, and therefore has similar physical and chemical properties with other carboxylic acids. When heated to 175 ° C, it will decompose to produce carbon dioxide and water, leaving some white crystals.
应用
application
1. 柠檬酸作为酸味剂广泛应用于各种饮料、果汁、罐头、糖果、果酱、果冻的 生产，使产品的酸味清爽可口，并有果味的香甜。柠檬酸本身是果汁的天然成分之一，不仅赋予饮料水果风味，而且具有增溶、缓冲、抗氧化等作用，能使饮料中的糖、香精、色素等成分交融协调，形成适宜的口味和风味。
1. As a sour agent, citric acid is widely used in the production of various drinks, fruit juice, cans, candies, jams, and jellies, making the products refreshing and tasty in sour taste and sweet in fruit taste. Citric acid itself is one of the natural ingredients of fruit juice. It not only gives the drink fruit flavor, but also has the functions of solubilization, buffering, antioxidant, etc. It can make the sugar, essence, pigment and other ingredients in the drink blend and coordinate to form a suitable taste and flavor.
2. 柠檬酸作蔗糖转化剂
2. Citric acid as sucrose invertor
在蔗糖液中添加适量柠檬酸可使其转化为糖，以提高蔗 糖的饱和度和粘度，增大渗透压，从而有效地防止糖制品的蔗糖返砂，并提高制品的保藏性和改善其质地。
Adding an appropriate amount of citric acid in the sucrose solution can convert it into sugar, so as to improve the saturation and viscosity of sucrose, increase the osmotic pressure, effectively prevent the sucrose from returning to the sand, improve the preservation and improve the texture of sugar products.
3. 柠檬酸作果蔬原料的护色剂
3. Citric acid as color fixative for raw materials of fruits and vegetables
将果蔬原料放在1%～2%的食盐和0.1%的柠檬酸 混合液中浸渍，可抑制果蔬原料酶褐变引起的变色。
The discoloration of fruit and vegetable raw materials caused by enzymatic browning can be inhibited by dipping them in a mixture of 1%~2% salt and 0.1% citric acid.
4. 柠檬酸作pH值的调整剂
4. Citric acid as pH regulator
柠檬酸在罐头、果酱、果冻等制品中使用，可使其 pH值降低，抑制腐败微生物的繁殖。一般当pH值小于5.5时，大部分腐败细菌可被抑制。同时，用柠檬酸调整食品的pH值还可达到改善品质和风味的目的。如当葡萄或其他酿酒原料成熟过度而酸度不足时，可以用柠檬酸调节，以防止所酿造的酒口味单薄，同时还有抗氧化和保护色素的作用，以保护果汁的新鲜感和防止变色。
The use of citric acid in cans, jams, jellies and other products can reduce its pH value and inhibit the propagation of putrefactive microorganisms. Generally, when the pH value is less than 5.5, most putrefactive bacteria can be inhibited. At the same time, adjusting the pH value of food with citric acid can also improve the quality and flavor. For example, when grapes or other wine making materials are too mature and the acidity is insufficient, citric acid can be used to adjust them to prevent the thin taste of the brewed wine. At the same time, it has the effect of anti-oxidation and pigment protection to protect the freshness of the juice and prevent discoloration.
5. 柠檬酸作抗氧化剂的增效剂
5. Citric acid as synergist of antioxidant
如在切去皮后的果蔬原料中加入浓度为0.1%的 抗坏血酸溶液可防止原料氧化褐变。通常以柠檬酸作为增效剂，以控制酚酶的活力，防止酶褐变。如一分子结晶水柠檬酸可用作食用油的抗氧化剂。如添加柠檬酸可以改善冰激凌的口味，增加乳化稳定性，防止氧化作用。在果酱和果冻中同样可以增进风味，并有抗氧化作用。如各种肉类和蔬菜在腌制加工时，加入或涂上柠檬酸可以改善风味，除腥去臭，抗氧化。
For example, adding 0.1% ascorbic acid solution to peeled fruits and vegetables can prevent raw materials from oxidative browning. Citric acid is usually used as a synergist to control the activity of phenolase and prevent browning of the enzyme. For example, one molecule of crystal water citric acid can be used as an antioxidant of edible oil. For example, adding citric acid can improve the taste of ice cream, increase the emulsion stability and prevent oxidation. In jam and jelly, it can also enhance the flavor and has antioxidant effect. For example, when various meats and vegetables are pickled and processed, adding or coating citric acid can improve the flavor, eliminate fishy smell, deodorize and resist oxidation.
6. 柠檬酸作疏松剂的改良剂
6. Citric acid as an improver of loosening agent
在面食制品中用小苏打作疏松剂时，制品往往碱度 大，口感差。若将柠檬酸和小苏打同时使用，可使小苏打分子在反应过程中产生的二氧化碳被吸收，不致使碳酸钠积累，从而降低面食的碱度，改善风味。
When baking soda is used as a loosening agent in pasta products, the products tend to have high alkalinity and poor taste. If citric acid and baking soda are used at the same time, the carbon dioxide generated by baking soda molecules in the reaction process can be absorbed without causing the accumulation of sodium carbonate, thus reducing the alkalinity of pasta and improving the flavor.
7. 柠檬酸作缓冲剂，蔬菜、水果在加工时由于品种、产地、收获期、存放时间不同会使它们的含酸量不同，给工业带来不便，为此根据需要在控制溶液酸度，保证产品质量，还可抑制细菌生长、减少杀菌时间及降低杀菌温度。
7. Citric acid is used as a buffer. Vegetables and fruits will have different acid content due to different varieties, places of origin, harvest periods and storage times during processing, which will bring inconvenience to industry. Therefore, the acidity of solution should be controlled according to needs to ensure product quality, inhibit bacterial growth, reduce sterilization time and reduce sterilization temperature.
8. 柠檬酸与脂肪酸单双甘油酯合用作乳化剂 在人造奶油、冰激凌生产中添加这种乳化剂有利于脂肪的破乳、凝结，从而提高产品质量，使产品口感细腻。参考用量：10g/kg,冷饮10g/kg。
8. The combination of citric acid and fatty acid monoglyceride and diglyceride is used as emulsifier. Adding this emulsifier in the production of margarine and ice cream is conducive to the demulsification and condensation of fat, thus improving the product quality and making the product taste delicate. Reference dosage: 10g/kg, cold drink 10g/kg.

9. 柠檬酸作为香料及除味剂
9. Citric acid as spice and deodorant
柠檬酸可添加到软饮料、冷饮、焙烤食品、糖果及 胶姆糖中。
Citric acid can be added to soft drinks, cold drinks, baked goods, candy and gums.
柠檬酸还可作为香料稳定剂添加到许多食品包装材料中去，起到保鲜除异味作用，如将添加1%柠檬酸等聚乙烯制成的膜用于包装鱼及其腌制品，三天后能明显降低异味。此外，柠檬酸作为海产品、水产品及羊奶等制品的除腥、除膻剂也被广泛使用，如海带饮料中常用10%的柠檬酸和0.2%的盐酸进行酸煮脱腥，沙丁鱼在加工前浸泡在pH5.5的柠檬酸中30分钟后可除去腥味。
Citric acid can also be added to many food packaging materials as a flavor stabilizer to keep fresh and remove odor. For example, the film made of polyethylene with 1% citric acid can be used to package fish and its pickles, which can significantly reduce odor after three days. In addition, citric acid is also widely used as a deodorant and deodorant for seafood, aquatic products, sheep's milk and other products. For example, 10% citric acid and 0.2% hydrochloric acid are commonly used in kelp drinks to remove fishy smell. sardine can remove fishy smell after being soaked in citric acid at pH 5.5 for 30 minutes before processing.
10. 柠檬酸对VC含量的影响
10. Effect of citric acid on VC content
所有甜橙汁样品中储藏过程中，维生素C含量都在 下降，但各自下降的特点有所不同。在对比试验中，柠檬酸对维生素C的下降有一定的减缓作用。在新制备的甜橙汁新鲜样品中，含有柠檬酸的样品菌落总数下降速度比对照样品快，且随柠檬酸浓度的增加而加快。
The content of vitamin C in all samples of sweet orange juice decreased during storage, but the characteristics of their decline were different. In the contrast test, citric acid has a certain slowing effect on the decline of vitamin C. In the newly prepared fresh sample of sweet orange juice, the total bacterial count of the sample containing citric acid decreased faster than that of the control sample, and accelerated with the increase of citric acid concentration.
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