Advances in extraction and purification of litchi polyphenols

Abstract: Litchi is the fruit of an evergreen tree plant, which belongs to the Sapindaceae family. Litchi is grown in China, Sri Lanka, Thailand, Vietnam, Japan, India, Bangladesh, Pakistan, Nepal, Australia,Mexico and some southern Africa countries. China is a major producer of litchi, and its cultivation history can be traced back to 2 000 BC. Found and used in traditional Chinese medicine for a long time, litchi's pulp, kernel, pericarp and root have the medicinal value. According to the ancient records of traditional Chinese medicine, litchi not only has the effect of regulating Qi-flowing, activating blood circulation, nourishing heart and calming the mind, but also can be used to treat dizziness, chest tightness,chest pain, irritable flatulence, stomachache, nerve pain, hernia, testicular swelling, gallbladder fat,cough, bleeding, eczema, diarrhea and so on. Litchi is rich in carbohydrates and fibers, as well as a small amount of lipids and proteins. In addition, there are multi-micronutrients that are beneficial to health, including vitamins(B1, B2, B3, B6, C, E, K), carotenoids, minerals(potassium, copper, iron,magnesium, phosphorus, calcium, sodium, zinc, manganese and selenium), as well as polyphenols.Polyphenols are widely distributed secondary metabolites in the plant world. Polyphenols are named because they have multiple phenolic hydroxyl groups and they belong to natural active substances. The new progress of the role of phenols in anti-oxidation, anti-mutagenesis, scavenging free radicals and preventing cancer and other diseases, aroused a new upsurge in the research and utilization of plant polyphenols. Litchi plants are rich in polyphenols, which has aroused great interest among researchers.Their main characteristics are their o-diphenols structure, which has high oxidation. For a long time, litchi polyphenols have been recognized as a good anti-oxidant, which has a variety of potential beneficial biological activities to human body, such as anti-cancer, anti-inflammation, anti-fungal, anti-viral,anti-platelet, anti-coagulant, anti-diabetes, anti-oxidant and so on. The health effects of litchi fruits are associated with phenolics and flavonoids presented in the fruit which are well-known for beneficial antioxidant activities. Numerous studies carried out in litchi have shown that there are large amounts of phenols and flavonoids in the pericarp, seeds and pulp of litchi, which are potential sources of natural antioxidants. The main phenolic constituents of litchi leaf, pericarp, seeds and fruits are flavonoids, usually composed of heterocyclic ring(C) and two benzene rings(A and B), which are important secondary metabolites in plants. The common polyphenols are rutin; proanthocyanidins A1 and A2; procyanidins B4 and B2; phlorizin; luteolin; methyl shikimate; cinnamamide B1;(-)-pinocembrin 7-O-rutinoside;(-)-pinocembrin 7-O-neohesperidoside; butylated hydroxytoluene; 3,4-dihydroxy benzoate; tamaritin 3-O-rutin; litchioside D; rhinocerol; kaempferol; kaempferol 3-O-α-rhamnoside; kaempferol 3-O-β-glucoside;kaempferol 3-O-b-glycoside; epicatechin gallate; quercetin 3-O-glucoside; kaempferol 3-O-glucoside;kaempferol-7-O-neohesperidoside; tamarixetin 3-O-rutinoside; gallic acid; protocatechuic acid; p-hydroxybenzoic acid; chlorogenic acid; caffeic acid; isolariciciresinol; taxifolin 4'-O-β-d-glucopyranoside; stigmasterol; pinocembrin-7-O-6-O-α-L-rhamnopyranosyl-β-D-glucoside; m-benzene triazine.Therefore, using natural resources to extract litchi polyphenols and strengthen its function may be a better choice to explore new possible treatment options in the future for its strong potential value. However, the research on the resource identification of litchi polyphenols and the influence of its formation conditions is still immature. At the same time, due to the inherent limitations of various conventional extraction and purification methods, the development of a single standard method for effective and rapid separation of polyphenols from plant matrix is still a challenge, and there is no systematic study on the extraction and purification system of litchi polyphenols. In view of the above contents, with the intention to promote human health and to develop litchi fruit industry, this paper expounds the classification of litchi polyphenols, provides the latest information about the working principle, research progress, advantages and disadvantages of extraction and purification technology, and makes a good prospect for the future.