Application of food colorants
Color is one of the important standards to evaluate the appearance quality of food. When people judge the quality of food, they often observe its color first. Natural, soft and pleasing colors can stimulate people’s appetite and increase consumers’ desire to buy; On the contrary, if the food changes color or fades during production, processing and transportation, the quality of food will be greatly reduced. Generally, we add food colorants to the food to adjust the color to meet the needs of consumers.
01. Classification
Colorants can be divided into synthetic colorants and natural colorants according to their sources; According to the structure, the synthetic colorants can be divided into azo, oxyanthracene, diphenylmethane, etc; Natural colorants can be divided into pyrrole, polyene, ketone, quinone and polyphenol; According to the solubility of colorants, they can be divided into fat soluble colorants and water soluble colorants; According to its composition, it can be divided into single colorant and composite colorant.
The color of natural colorants is easily affected by metal ions, water quality, pH value, oxidation, light and temperature, and is generally difficult to disperse. The dyeing property and compatibility between colorants are poor, and the price is high. The raw materials of synthetic colorants are mainly chemical products. Compared with natural colorants, synthetic colorants are more bright in color, less prone to fading, and cheaper.
02. Characteristics of food colorants
Food colorants have the following characteristics:
(1) Natural colorants have natural and soft colors, which can close the relationship between human and nature. However, natural colorants have poor dyeing ability and uneven dyeing; Synthetic colorants have bright colors and are welcomed by consumers, especially children and adolescents.
(2) Natural colorants generally come from animals and plants, and have no side effects on human body. Compared with synthetic colorants, they are safer. However, synthetic colorants are popular because of their strong coloring power, easy dissolution, odorless and tasteless, and low price.
(3) Most natural colorants are sensitive to light and heat, metals, acids and alkalis, and oxidants. They are unstable under these conditions, and the hue will change greatly. Synthetic colorants can just make up for this shortcoming.
(4) Some natural colorants can be used as natural antioxidants and natural preservatives. Due to the safety problems of synthetic antioxidants and preservatives, more and more consumers tend to use natural antioxidants and preservatives.
(5) Most natural colorants also have nutritional value and pharmacological effects, and food colorants also have great application prospects in the medical field. For example, red cabbage pigment has a good preventive and therapeutic effect on human heart disease and arteriosclerosis.
03. Stability factors of food colorants
The breakthrough in the study of natural colorants is to improve their quality and stability, for which chemists all over the world have done a lot of research. Generally, the research on the stability of natural colorants includes the following aspects:
(1) Illumination factor. It refers to the color change of colorants under direct sunlight. For example, chlorophyll widely exists in the leaves and stems of plants and is easy to decompose when exposed to light. In order to improve its stability, it is generally made into sodium copper salt.
(2) Temperature factor. The heat resistance of the colorant is considered. The heat resistance of safflower yellow pigment is poor. If it is used in foods with high Vc, its stability can be improved.
(3) Acid and alkali factors. It refers to changes in color and stability of colorants under acidic or alkaline conditions, such as β- Carotene widely exists in carrots and algae, which is stable under weak alkaline conditions, but easy to decompose under acidic conditions. If a small amount of Vc is added, its stability can be improved; The color of roselle pigment changes with the pH value of the solution. It is red in acidic conditions, purple in neutral conditions, and blue in alkaline conditions.
(4) Metal ion factor. Common ones are copper ions, sodium ions, magnesium ions, iron ions, etc. Gardenia pigment is not resistant to iron ions. Some metal ions can discolor or even fade colorants, while some metal ions can enhance the stability of some colorants, such as sodium copper salt made of chlorophyll.
(5) Antioxidant and reductant factors. Common antioxidants include Vc and sodium thiosulfate. For example, safflower yellow pigment is sensitive to metal ions due to its poor heat resistance. Adding a small amount of Vc can greatly improve its stability.
(6) Factors of some compounds such as sucrose, alum and tartrate. For example, the stability of rehmannia yellow pigment can be significantly increased after adding alum and tartrate.
(7) The stability of some colorants can also be improved when combined with another colorant, for example, the stability of beet red and vegetable red colorants can be significantly enhanced when combined with each other.
(8) Solubility factor. Grape skin pigment and perilla pigment are water-soluble colorants, while red rice pigment and shikonin are fat soluble colorants. In addition, the salt resistance and microbial resistance of the colorant also have a certain impact on the colorant itself.
04. Colorants used in food
1、 Amaranth red
Amaranth red, also known as acid red, bayberry red, cockscomb red and edible red pigment No. 2. The main coloring components were amaranth and betaine. Amaranth red is the concentrated liquid obtained from the edible part of amaranth by water extraction and ethanol refining, and the dried powder product is obtained after drying. Amaranth is easily hygroscopic and soluble in water and dilute ethanol solution. When the pH value of the solution is less than 7, it is purple red, clear, and insoluble in anhydrous ethanol, petroleum ether and other organic solvents. It has poor light and thermal stability, and copper, iron and other metal ions have negative effects on its stability. When the pH value is greater than 9, the solution will change from purple red to yellow.
Amaranth is often used in the production of pickled vegetables, with the maximum dosage of 0.05g/kg. Amaranth is sensitive to oxidation and reduction. It is not suitable for fermented food and food containing reduction, but also for high sugar fruit juice drinks, carbonated drinks, prepared wine, candy, etc.
2、 Lemon yellow
Lemon yellow, also known as tartar yellow, acid light yellow, hydrazine yellow, edible yellow No. 4, molecular formula C16H9N4Na3O9S2, and relative molecular weight 534.37. Lemon yellow is orange yellow to orange granules or powder, odorless. Easily soluble in water, 0.1% aqueous solution is yellow. Soluble in glycerin and propylene glycol, slightly soluble in ethanol, insoluble in oil. It has strong light resistance, heat resistance, good acid resistance, salt resistance, poor oxidation resistance, and fading during reduction. It is stable in citric acid and tartaric acid. It turns red slightly when encountering alkali, with strong coloring power and high fastness. Lemon yellow is often used in jam and pickled dishes. Lemon yellow is a relatively stable colorant, which can be used in combination with other pigments with good matching. It is the most widely used edible yellow pigment, accounting for more than 1/4 of all edible pigments.
3、 Carmine
Carmine, also known as ponceau 4R, scarlet, bright scarlet, cochineal acid, insect red, C.I. natural red No. 4. The molecular formula is C20H11N20O10S3Na3, and the relative molecular weight is 604.48. Carmine is red to dark red granules or powder, odorless. It is easily soluble in water, the aqueous solution is red, and the solubility in water at 20 ℃ is 23%. Slightly soluble in ethanol, soluble in glycerin, insoluble in oil. Carmine is highly hygroscopic. The maximum absorption wavelength is about 508nm. Good light and acid resistance, stable to citric acid and tartaric acid. Poor shading performance. In actual use, carmine is sensitive to oxidation and reduction, and is not suitable for fermented food and food containing reducing substances. If it is mixed with other colorants, it shall be converted proportionally according to the maximum use amount, and the amount shall not exceed the allowable amount of single pigment. A small amount of cold water should be used to mix well before slowly adding boiling water under stirring. The water used must be distilled water or deionized water.
05. Colorants used in condiments
1、 Caramel pigment
Caramel pigment, also known as caramel, is called Caramel in English. Caramel pigment is one of the food pigments with the longest history of human use, and it is also the most popular artificial natural pigment with the largest amount of additives currently used.
It is characterized by dark brown to black liquid or solid, with special sweet aroma and pleasant burnt bitter taste. It is easily soluble in water and insoluble in ordinary organic solvents and oils. The aqueous solution is reddish brown and transparent without turbidity or precipitation. It is stable to light and heat, has colloidal properties, has isoelectric points, and its pH value is generally about 3~4.5.
Caramel pigment is often used in the production of soy sauce and vinegar in condiments to enhance the color. According to the provisions of GB 2760-2014, caramel pigment produced by common method is applicable to soy sauce, vinegar, compound seasoning, sauce and sauce products. Caramel pigment used in soy sauce must be salt resistant, otherwise it is easy to precipitate; At the same time, in order to improve the red brightness and wall hanging property of soy sauce, the varieties with high red index and solid content should be selected. Caramel pigment used in vinegar is generally acid resistant, otherwise it will fade in a short time. The main types and dosage of caramel pigment used in soy sauce and vinegar are shown in Table 1.
Table 1 Types and dosage of caramel pigment applied to soy sauce and vinegar
2、 Curcumin
Curcumin, with molecular formula C21H20O6 and relative molecular weight of 368.37, is a chemical component extracted from the rhizomes of some plants in Zingiberaceae and Araceae. It is a rare pigment with diketones in the plant kingdom and is a diketone compound.
Curcumin is orange yellow crystalline powder with a slightly bitter taste. It is insoluble in water, soluble in ethanol and propylene glycol, and soluble in glacial acetic acid and alkaline solution. It is reddish brown when alkaline, and yellow when neutral and acidic. It has strong stability to reducing agent, but is sensitive to light, heat and iron ions, and has poor light resistance, heat resistance and iron ion resistance. Curcumin has the effects of lowering blood lipid, anti-oxidation, anti inflammation, anti atherosclerosis, anti-cancer, etc. It is often used for coloring and flavoring curry powder, mustard sauce, etc.
