Color formation of pickled vegetables
In the process of vegetable pickling, the color change and formation are mainly through the following ways.
Natural pigments in vegetables and their characteristics
There are three main types of natural pigments commonly found in vegetables. They are chlorophyll, anthocyanin and carotenoids. Chlorophyll is unstable in acidic media, easily loses its green color and becomes brown or greenish brown, and is relatively stable in slightly alkaline media. The fermented pickles produce lactic acid during the pickling process, and the water contained in the vegetables is weakly acidic (about pH 6), so that the chlorophyll cannot be preserved. When pickling weakly fermented pickles, if the acidic water is not drained and salted, the acidic vegetable water will destroy the chlorophyll and also lose the original bright green color. The color of anthocyanins is affected by acidity and alkalinity. It is red in acid, blue in alkali, and purple in neutral. Therefore, it will show different colors in different vegetables. Vegetables show red (except tomatoes), purple, blue and other colors, and most of them are anthocyanins. Decomposition and oxidation can destroy anthocyanins and lose their original color. Carotenoids, carotene, lycopene, etc. are the more stable pigments in the natural color of vegetables. They are mostly red, orange, and yellow, and they are not easy to fade during pickling.
Color change caused by browning
In the post-fermentation maturation period of vegetable pickled products, the tyrosine produced by the hydrolysis of protein undergoes a series of oxidations under the action of the tyrosinase contained in the microorganisms or raw material tissues, and finally produces a deep yellow Brown or dark brown melanin, also known as melanin. In this reaction, the source of oxygen mainly depends on the oxygen released when pentose is reduced to malondialdehyde. Therefore, although the vegetable pickled products are packed tightly and lacking oxygen, the color of the pickled products can still gradually become black due to oxidation. Of course, the change that promotes the oxidation of tyrosine to melanin is an extremely slow and complicated process.
Another important way of pigment formation is the black substance formed by non-enzymatic browning caused by amino acids and reducing sugars. The black substance formed by non-enzymatic browning is not only black in color but also has a fragrance. Generally speaking, the longer the post-cooking time and the higher the temperature, the more melanin will be formed and the faster the pickled products will be formed.
For dark pickles, soy sauce and vinegar products, the color formed by the browning reaction is the normal color of this type of product, so pickles that have been stored for a long time (such as moldy dried vegetables and winter vegetables) have their color and aroma , Are darker in color and more fragrant than freshly pickled pickles. For some pickled products, browning is often the main reason for reducing the color quality of the product. Therefore, during the processing of such products, necessary measures must be taken to prevent the browning reaction from proceeding to prevent the color of the product from turning brown and dull.
The penetration of foreign pigments changes the color of the product
Due to the high salt concentration in the pickling solution, the solubility of oxygen is greatly reduced. Vegetable cells lack a normal supply of oxygen, causing suffocation and losing vital activity. The plasma membrane of the dead cells becomes a permeable membrane, and the vegetable cells adsorb the pigment in the pickling raw materials and change the original color. For example, pickles adsorb the color of the sauce and become brown. There are also some pickled products that need to be colored. Commonly used dyes are turmeric, chili and safflower. For example, radish is dyed yellow with turmeric, and mustard is dyed red with chili.