Advances in research on nutrient components, biological activity and comprehensive utilization of litchi fruits

Abstract: Litchi (Litchi chinensis Sonn.) is a subtropical evergreen fruit tree of the Sapotaceae family. It was planted in southern China and northern Vietnam before, but now is grown in more than 20 coun- tries in the world, mainly distributed in Southeast Asia, especially in China, Vietnam, Indonesia, Thai- land, and the Philippines. It is usually eaten in fresh or processed way. It has become one of the most popular fruits because of its delicious taste, attractive color and high nutritional value. The size of litchi is similar to a strawberry, with pendulous clusters, while the fruit size varies with species and can vary from 23 to 30 g. The skin of litchi is pink- or red-scaly at maturity, thin and hard, easily peeling off and can present a pearly white and jelly-like pulp surrounding the brown black seed. Not only is litchi loved as a fruit, but also the whole fruit of litchi is used for medicinal purposes. Traditional medicine believes that litchi is sweet and slightly acidic, flat and non-toxic, rich in sugars, fibers, vitamins, amino acids, minerals, polyphenols and other nutrients, which are beneficial to human health for long-term consump- tion, and is a good economic crop for food therapy. Litchi fruit peel, bark, and roots contain a large num- ber of tannins, which are raw materials for pharmaceuticals, with the effects of regulating vital energy, relieving pain, generating fluid and nourishing blood, and nourishing the heart and calming the mind, and are often used to treat a variety of symptoms such as cough, intestinal gas and bloating, gastric ul- cer, diabetes, obesity, and testicular swelling. In addition, litchi can also be used to kill intestinal worms. Modern research has shown that litchi also has a variety of functional effects such as antioxidant, anti- cancer, antibacterial, hypolipidemic, hypoglycemic and antiviral efficacy. In vitro and in vivo studies  have shown that litchi has protective effects on liver, anti atherosclerosis, neuroprotective and immunomodulatory activities. Litchi seeds can also be used as medicine. Traditional Chinese medicine thinks it can be used to treat diseases of urinary system, like bladder cancer. Litchi has a lot of health benefits due to its wide range of nutrients, especially polysaccharides and polyphenols in litchi, which have been proved to have various beneficial effects on human body. The nutrients contained in litchi fruit, includ- ing sugars, organic acids, amino acids and lipids, have attracted the interest of a wide range of research- ers for their anti-cancer, liver protection, immunity-boosting, lipid-lowering, antiviral and antioxidant properties. As the largest producer of litchi, the annual production in China has been steadily increasing, due to its high yield for the processing and utilization of litchi and industrial development. As a seasonal fruit, litchi is easy to deteriorate at room temperature after harvest. Further processing can extend the shelf life and meet the market demand. Therefore, in addition to being consumed fresh as a dessert fruit, litchi can also be consumed as frozen, canned, or dried fruit; or processed into juice, fruit wine, and pickles, along with ice cream and yogurt. However, pericarp browning and pulp decay lead to short shelf life of litchi, and it is highly perishable and difficult to preserve for a long time. Therefore, we can make fresh litchi into preserved fruits, drinks and fruit wine, so as to improve economic benefits. In re- cent years, more and more attention has been paid to the nutrients in natural plants, which are accepted and understood by more and more people. Therefore, in order to make rational use of these natural com- ponents, the development and utilization of natural phytochemical components are worthy of further ex- ploration and discussion. Litchi contains a lot of biological substances, such as sugars, lipids, vitamins, especially polyphenols, so litchi can also be used to produce various products, such as nutrition and health care products. Litchi extract has been developed into a food additive, litchi is rich in cellulose and pectin can be hydrolyzed and extracted to get applied to the food industry as a sugar source, gelling agent, thickener, emulsifier and other substances. Litchi can also be used as insecticides and fungicides, with the advantages of more environmentally friendly society, low toxicity, long duration, effective reduction of drug resistance, comprehensive use of invasive species and turning waste into treasure. The current research on the composition and activity identification of litchi is more scattered and has not yet emerged as a comprehensive and systematic study, and the further development and utilization of litchi- related products have been somewhat limited. Current research on the comprehensive utilization of litchi is mainly focused on consumer’s preferences for economic food, functional drugs and the development of cosmetics, data on its physiological and biochemical mechanisms are not accumulated enough, and there is no systematic research on livestock breeding applications, so further research is needed. In addition, there is an important significance about the safety evaluation of litchi extract. Therefore, in order to further develop the utilization of litchi in the fields of food, medicine and cosmetics, and effectively utilize the edible waste (Litchi shell and litchi core) to increase its economic value, this paper summarized the nutritional value, health care function and comprehensive utilization, and the research information on litchi, so as to provide reference for the follow-up development and utilization in litchi.