Anthocyanidin, also known as anthocyanin, is a kind of water-soluble natural pigment widely existing in plants in natureAnthocyaninColored from hydrolysisAglycone[1]。Most of the main colouring substances in fruits, vegetables and flowers are related to them.stayplant cellUnder the condition of different PH values of vacuoles, anthocyanins make petals appear colorful.It is known that there are more than 20 kinds of anthocyanins, and 6 kinds of important food, namelyPelargonium pigment, cornflower pigmentDelphinium pigment, peony pigmentMorning Glory PigmentAnd mallow pigment.Anthocyanins in natural state exist in the form of glycosides, called anthocyanins, and few free anthocyanins exist.Anthocyanins are mainly used in food coloring, as well as in dyes, medicine, cosmetics, etc.[2]
There are more than 250 known natural anthocyanins, which exist in 27 families and 73 genera of plants.20 anthocyanins have been identified, and 6 are common in plants, namely pelargonium pigment (Pg), cyanidin (Cy), delphinidin (Dp), peony pigment (Pn), morning glory pigment (Pt) and mallow pigment (Mv).
Anthocyanins have a highly molecular conjugate system, containing acidic and alkaline groups, and are easily soluble in water, methanol, ethanol, dilute alkali and dilute acid, etcPolar solventMedium.It has strong absorption in both the ultraviolet and visible light regions. The maximum absorption wavelength in the ultraviolet region is around 280 nm, and the maximum absorption wavelength in the visible light region is in the range of 500~550 nm.The color of anthocyanins changes with the change of pH value. When pH<7, they are red, when pH=7-8, they are purple, and when pH>11, they are blue.[4]
Main sources
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Anthocyanins are widely found in flowering plants (angiosperms), and their content in plants varies greatly with varieties, seasons, climates, maturity, etc.[5]According to preliminary statistics, anthocyanins are contained in 27 families and 73 genera, such as purple sweet potato, grape, blood orange, red cabbage, blueberry, eggplant, cherry, red berry, strawberry, mulberry, hawthorn, morning glory and other plant tissues.[6]
The earliest and most abundant anthocyanins are extracted from red grape residueGrape skin red pigmentIt was listed in Italy in 1879[7]The pigment can be extracted from grape residue, the waste of wine factory.Elderberries contains a large amount of anthocyanins, which are all cyanidins, with a fresh weight of 200-1000 mg per 100 grams.In addition, anthocyanins in barley, sorghum, legumes, etcgrain cropsIt also widely exists in.It was found that the anthocyanin content of grape seed and pine bark extracts was the highest.[6]
Extraction method
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Solvent extraction
Solvent extraction is the conventional extraction method of anthocyanins. Methanol, ethanol, acetone, water or mixed solvents are the most suitable solvents.In order to prevent the degradation of non acylated anthocyanins in the extraction process, a certain concentration of hydrochloric acid or formic acid is often added to the extraction solvent, but these acids will lead to partial or complete hydrolysis of acylated anthocyanins during evaporation and concentration.In addition, organic solvents such as n-hexane, petroleum ether, ether, etc. should be used to extract samples that may contain fat soluble components.The traditional solvent extraction method takes a long time to extract, has low production efficiency, and the thermal solvent is easy to cause the degradation of anthocyanins and the reduction of physiological activity.[8]
The traditional method of extracting anthocyanins abroad is to use 1% HCl methanol solution at low temperature (4~8 ℃) or normal temperature (25 ℃) and avoid light for 16~20 h, or 5% or 1% trifluoroacetic acid methanol solution for 24 h at 4 ℃.Considering the toxicity of residual methanol in food, 1% HCl is also availableEthanol solutionInstead of methanol solution.In addition, in order to avoid the hydrolysis of acylated anthocyanins, weak acids such as tartaric acid and citric acid can also be selected to replace hydrochloric acid.In China, hot solvent (50~70 ℃) is usually used to extract for 1~2h. The solvent can be alcohol solution or acidified water solution with different concentrations.[8]
Pressurized solvent extraction
Pressurized solvent extraction, also known as pressurized liquid extraction (PLE) and accelerated solvent extraction (ASE), increases the boiling point of solvent through external pressure, thus increasing the solubility of substances in solvent and extraction efficiency.
The extraction of functional ingredients in food by PSE technology mainly focuses on the research of flavonoids, phenols and other antioxidant active ingredients.This technology has also been reported in the extraction of anthocyanins.The optimal extraction process of anthocyanins from purple cabbage was optimized by this technology. The optimal parameters were: sample 215g, temperature 99 ℃, extraction time 7min, solventV(Water):V(Ethanol):V(Methanol)=94:5:1.[8]
Aqueous solution extraction method
Most anthocyanins extracted by organic solvents have toxic residues and environmental pollution during production. In view of this, aqueous solution extraction came into being.Generally, plant materials are soaked in hot water under normal pressure or high pressure, and then absorbed by non-polar macroporous resin;Or directly use deoxygenated hot water to extract, and then use ultrafiltration or reverse osmosis to concentrate to obtain crude extract.[6]
Microbial fermentation extraction method
This method willBiological fermentationThe technology is applied to the extraction of anthocyanins, which is the super penetration and effective combination between biological science and chemical production.Microbial fermentationMethods The cell wall containing anthocyanins was degraded and separated by microorganisms or enzymes, so that anthocyanins in the cell body were fully dissolved into the extract solution, thus increasing the yield and rate of extraction.[6]
Other extraction methods
Including high-voltage pulsed electric field assisted extractionAqueous two-phase extractionUltra high pressure assisted extraction.The first two can be applied to the extraction of proteins, nucleic acids and polysaccharides, while ultra-high pressure assisted extraction has been successfully used in the extraction of anthocyanins from grapes, and the comparison shows that the efficiency of high-pressure assisted extraction of anthocyanins and other polyphenols can be improved by nearly 50%.
Purification process
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The purification of anthocyanins mostly adopts liquid phase extraction, solid phase extraction, thin plate chromatography, column chromatography, enzyme method, ion exchange method, macroporous resin method, membrane separation and comprehensive technology method.Macroporous resin adsorption is one of the most commonly used methods for anthocyanin purification in recent years[9], and new purification methods such asHigh speed countercurrent chromatographyApplication and electrophoresis are still in the initial stage of development.[10]
Identification method
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The determination of total anthocyanins is commonly usedSpectrophotometryThe sample is extracted with boiling water and colored with acid ethanol to produce uniqueCongo red, measured at the wavelength of nanometerabsorbance, the law is not subject toXanthone glycosideandCatechinInterfered byProanthocyanidins、AnthocyaninInterference, the analysis results are often high, and the sensitivity is not ideal, but this method is still used to analyze the total amount of anthocyanins in tea.In addition, the single component structure of anthocyanins can also be identified by HPLC, and the structure of three anthocyanins extracted from the skin of Guizhou black glutinous rice can be identified by HPLC[11]The structure of the pure anthocyanin (cyanidin) isolated from Lonicera edulis was identified by UV-VIS, IR, H-NMR and HPLC[12]。
application
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Antioxidant and free radical scavenging function
Anthocyanins belong toBioflavonoidsThe main physiological activity function of flavonoids is free radical scavenging capacity and antioxidant capacity.Research proves that anthocyanins are the most effectiveantioxidantIs also the most effectiveFree radical scavengerAnthocyanin has 50 times more antioxidant capacity than VE and 20 times more antioxidant capacity than VC[13]。Purple sweet potato anthocyanin product p-OH, HtwoOtwo, and other reactive oxygen species have scavenging and inhibitory effects, especially the scavenging ability of - OH is stronger than that of ascorbic acid, and the scavenging effect is dose dependent[14]。
Antimutagenic function
The function of anthocyanins not only makes plants appear colorful colors, but also has active molecules with health functions such as reducing enzyme activity and anti mutation.The research shows that the extract with a certain concentration of anthocyanin can effectively prevent the occurrence of cancer at different stages, but the individual role of anthocyanin is uncertain, partly because anthocyanin is easily degraded after being separated from other stable components such as phenols by bioassay.[4]
Application in food
With the development of science and technology, peoplefood additivesThe development and utilization of natural additives has become the general trend of the development and use of additives.Anthocyanins can not only be used asNutritional fortifierAnd can also be used asFood preservativesIt can replace benzoic acid and other synthetic preservatives, and can be used asFood colorantsIt is applied to ordinary drinks and food and meets people's general requirements for natural, safe and healthy food additives[15]。
