,

(Key Laboratory of Basic Pharmacology of Ministry of Education and Joint International Research Laboratory of Ethnomedicine of Ministry of Education,Zunyi Medical University,Zunyi Guizhou 563099 ,China)

[Abstract] Synsepalum Dulcificum,is a magical plant that could change the taste of human beings.It also made the sour food tasted sweet in a short time after consumption.Thus,it is well known as Miracle Fruit or Miracle Berry.Synsepalum Dulcificum is native in West Africa and a rare plant of national treasure.At present,there is a small number of distributions in tropical and subtropical areas.Recent studies found that many parts of Synsepalum Dulcificum,such as pulp,peel and seeds,had high nutritional value and could be used as potential health and medicinal ingredients.To promote the development and utilization of this precious plant resource,this review expatiated on the research progress of the functional components of each part of Synsepalum Dulcificum.

[Key words] Synsepalum Dulcificum; Miracle Fruit; Functional component

SynsepalumDulcificumis a plant of the Synsepalum of Sapotaceae,which is native to the Ghana to Congo of west Africa.As a typical tropical evergreen shrub,it suitable for high temperature and humidity environment.Currently it is distributed in the tropical and subtropical regions[1].SynsepalumDulcificumhas been introduced to China since the 1960s,and is currently planted in Yunnan,Guangxi,Fujian,Hainan,Taiwan and other provinces.Because the flesh ofSynsepalumDulcificumcontains a special glycoprotein that can change the taste of food into sweetness and keep it sweet for hours after eating,it is known as the "first wonder fruit in the world",also referred to as miracle fruit or miracle berry[2-4].Researches show thatSynsepalumDulcificumand its extract have not only the function of changing human taste,but also the effects of anti-oxidation,blood sugar regulation and insulin resistance improvement[5-6].In order to better understand the development and utilization status of this precious natural plant resources,this paper will discuss the functional components,biological activities and the status of development and utilization of each part of theSynsepalumDulcificum.

1 The Functional Components of Synsepalum Dulcificum Flesh

1.1 Components of taste alteration The taste changing function of theSynsepalumDulcificumis mainly derived from a special basic protein which is contained in its pulp,miraculin.Miraculin itself does not have a sweet taste,but it can change the taste of acidic food in a short time.As early as the 1960s,studies have shown that only a small dose of purified miraculin have the function of changing taste[7-9].In recent years,it has been proved that oral administration of pulp contains 0.4 mol/L of miraculin can induce 0.02 mol/L of citric acid solution equivalent to sweetness of 0.3 mol/L of sucrose solution[10].Therefore,as a natural and safe new sweetener or food additive,theSynsepalumDulcificumcan be used in the food and drug industry to meet the desire of diabetic patients for sweet food to a certain extent,and also the needs of contemporary people to pursue a low-sugar healthy diet.

1.2 Hypoglycemic components In addition to the taste changing function,theSynsepalumDulcificumlyophilized powder has also been shown to reduce blood sugar and improve insulin resistance in diabetic rats fed with high fructose diet.Its hypoglycemic effect increases with the increase of the dose of the drug within a certain range[6].SynsepalumDulcificumjuice can reduce the blood glucose of alloxan-induced diabetic mice,and its hypoglycemic effect is close to the positive drug metformin[11].Continuous use of the fresh extract can reduce the blood glucose of streptozotocin-induced diabetic rats,improve oral glucose tolerance,and reduce levels of serum triglyceride (TG) and low-density lipoprotein cholesterol (LDL-C) in diabetic rats[12].The aqueous extract ofSynsepalumDulcificumpulp can significantly reduce serum total cholesterol (TC),TG and LDL-C levels in models induced by high fat diet,and also increase high density lipoprotein Cholesterol (HDL-C) levels in serum of diabetic mice models,confirming thatSynsepalumDulcificumhas a good effect on regulating blood lipids[13].

1.3 Antioxidant components In addition to miraculin,SynsepalumDulcificumpulp also contains rich vitamin C,vitamin E,catechin,gallic acid,ferulic acid,rutin,quercetin,kaempferol and other phenolic acids and flavonoids compounds,which features strong antioxidant activity.1,1-Diphenyl-2-picrylhydrazyl(DPPH) and 2,2'-Azino-bis-3-ethylbenzthiazoline-6-sulphonic acid(ABTS) free radical scavenging experiments were used to determine the free radical scavenging rates ofSynsepalumDulcificumextracts as 96.3% and 32.5%,and the extract also significantly inhibited the oxidation of polyunsaturated fatty acids (PUFA) in fish oil[14-16].Therefore,SynsepalumDulcificumextract can be used as a natural antioxidant in the food and drug industry.

2 Functional Components of Synsepalum Dulcificum Peel

2.1 Natural pigments The ripeSynsepalumDulcificumis bright red in color.Two natural plant pigments of anthocyanins and flavonols can be isolated from the peel.Studies have shown that 14.3mg of anthocyanin and 7.2mg of flavonol can be isolated per 100g of fresh fruit peel.With its good stability,it can be used as a natural coloring agent for food and beverages[17-18].

2.2 Antioxidant components By measuring the total phenolic content and antioxidant capacity of theSynsepalumDulcificumpeel,it can be seen that the anthocyanin extracted from theSynsepalumDulcificumpeel has high antioxidant activity,which in the proper alcohol concentration and acidity environment,increases with the increase of temperature within a certain range (not exceeding 50℃)[19].By comparing the antioxidant activities of phenolic and flavonoids inSynsepalumDulcificumpeel,pulp and seeds,the content of free phenolic compounds and free flavonoids inSynsepalumDulcificumpeels was higher than those in the pulp and seeds[16].

3 Functional Components of Synsepalum Dulcificum Seeds

3.1 Edible and medicinal valueSynsepalumDulcificumseeds are mainly composed of nutrients such as ash,crude fiber,crude fat,crude protein,reducing sugar,polyphenols,polysaccharides,fatty acids,amino acids and mineral elements.Comparing with a variety of common medicinal plant seeds,the crude protein,ash,polyphenols and polysaccharides ofSynsepalumDulcificumseeds are higher than those in other plant seeds,and they contain a variety of amino acids and mineral elements required by the human body,having high edible and medicinal value[20].

3.2 Antioxidant components By measuring the scavenging ability ofSynsepalumDulcificumseed polysaccharides on DPPH,ABTS and other four free radicals,it can be seen that theSynsepalumDulcificumseed polysaccharides have strong scavenging ability to all four free radicals,which is positively correlated with the dose.It clarifies thatSynsepalumDulcificumseeds have strong antioxidant activity[21].

3.3 Volatile oil The chemical constituents of the volatile oil ofSynsepalumDulcificumanalyzed by gas chromatography-mass spectrometry revealed that the main components were palmitic acid,oleic acid,3α-alkyl-12-oleanol acetate and methyl 14-methylpentadecanoate and the like,providing a scientific basis for comprehensive development and utilization ofSynsepalumDulcificum[22].

3.4 Antihypertensive and hypoglycemic components TheSynsepalumDulcificumseeds are rich in natural sterols and trace mineral elements such as sodium,potassium,calcium and magnesium,which have the functions of regulating blood pressure and relieving angina pectoris.Its water extract can significantly reduce TC,TG and LDL-C levels in high-fat model mice[13].In addition,intragastric administration of theSynsepalumDulcificumprotein can significantly reduce the fasting blood glucose of alloxan-induced diabetic mice and promote insulin secretion in model mice[23],suggesting thatSynsepalumDulcificumextract can provide new ideas for the treatment of cardiovascular diseases and diabetes[13].

3.5 The results of our group In our research,KK-Ay mice were used to observe the effect of seeds powder ofSynsepalumDulcificumon blood glucose.The experiments showed that the seeds powder ofSynsepalumDulcificumcould reduce the blood glucose,lipid levels of KK-Ay mice,and improved their glucose tolerance.However,no apparent influence was found for the seeds powder ofSynsepalumDulcificumon the blood sugar in normal mice.These findings suggest it might also be adopted for therapeutic purpose.Therefore,our group will extract the effective components from the seeds powder ofSynsepalumDulcificum,and explore its possible mechanism.

4 Functional Components of Synsepalum Dulcificum Leaves

4.1 Anti-inflammatory and antioxidant components Among the main nutrients ofSynsepalumDulcificumleaves,the content of crude protein and crude fiber is higher,while that of crude fat,coarse ash and vitamin C is lower; among its main functional components,the contents of polysaccharide,polyphenol and total flavonoids are higher (93.38mg/g,45.31mg/g and 36.24mg/g respectively)[24].Studies reported that polysaccharides,with their anti-inflammatory,blood sugar and lipids regulating and immunity enhancing effects[25],had been developed into a variety of functional food additives and medicinal ingredients,whileSynsepalumDulcificumleaf polyphenols had also been confirmed to have strong antioxidant capacity by free radical scavenging experiments[26].Therefore,daily intake of the right amount ofSynsepalumDulcificumleaf extract is good for health.

4.2 Hypolipidemic components In addition,seven fatty acids were detected inSynsepalumDulcificumleaves,including four saturated fatty acids:lauric acid,myristic acid,palmitic acid and stearic acid,and three unsaturated fatty acids:oleic acid,linoleic acid and α-linolenic acid.The four kinds of saturated fatty acids and three kinds of unsaturated fatty acids each accounted for 50% of the total fatty acids,and the content of α-linolenic acid was highest,reaching 0.25g/100g[24].Studies have shown that α-linolenic acid has the effects of regulating blood lipids,preventing thrombosis,promoting children's mental development and preventing Alzheimer's disease[27],suggesting thatSynsepalumDulcificumleaves can be further developed and utilized as functional health products or medicines.

4.3 Gouty therapeutic components Three kinds of quercetin compounds,such as quercetin and hyperoside,were isolated fromSynsepalumDulcificumleaves by high performance liquid chromatography.They can inhibit the activity of xanthine oxidase,a key enzyme in the production of uric acid by purine metabolism.Both ethanol and water extracts ofSynsepalumDulcificumleaf can reduce the serum uric acid level of hyperuric acid rats,and the activity of ethanol extract is higher than that of water extract.They can reduce the serum urea nitrogen content of model rats,suggeting thatSynsepalumDulcificumleaf extract can be used to prevent and treat hyperuricemia[28].In addition,continuous administration ofSynsepalumDulcificumleaf concentrated solution for seven days can reduce the blood uric acid level of mice with hyperuricemia induced by xanthine and ethambutol[29],suggesting thatSynsepalumDulcificumleaves may have certain therapeutic effects on gout.

4.4 Antimicrobial and antitumor components By gas chromatography-mass spectrometry (GC-MS),forty-four chemical constituents were isolated from the volatile oil ofSynsepalumDulcificumleaves.Among them,consitutents with higher mass fraction include spainulenol (24.19%),limonene (15.81%),diisooctyl phthalate (12.40%),dibutyl phthalate (10.33%),palmitic acid (4.88%) and linalool (2.14%).The results of in vitro antibacterial test showed that the volatile oil ofSynsepalumDulcificumleaves had good antibacterial activity against seven test strains such as Bacillus subtilis,Staphylococcus aureus and Escherichia coli.Meanwhile,the anti-tumor activity test results also showed that volatile oil of theSynsepalumDulcificumleaves can effectively inhibit the proliferation of human leukemia cell K562[30].Therefore,SynsepalumDulcificumleaves and their extracts have good development prospects as natural plant resources with high functional value.

5 Functional Components of Synsepalum Dulcificum Roots and Stems

5.1 Functional components of roots The root system ofSynsepalumDulcificumis fond of acid soil with high temperature,humidity and good drainage.In addition to the taproot,the lateral roots developed less and had stronger resistance to insect and disease.There were few existing related research achievements on the functional components of the root and stem of theSynsepalumDulcificum,which are still remains at the level of isolation and identification[31].Syringic acid,p-hydroxybenzoic acid,vanillic acid,methylparaben,isovaleric acid,N-cis-feruloyltyramine,N-trans- Feruloyltyramine,N-cis-feruloyl-3-methoxytyramine and N-trans-Feruloyl-3 -methoxytyramine could be isolated fromSynsepalumDulcificumroots[32].

5.2 Functional components of stem Among the nineteen compounds isolated from theSynsepalumDulcificumstem,dihydro-feruloyl-5-methoxytyramine is a new amino compound; (+)-epi-syringaresinol,(+)-syringaresinol have antioxidant activity and obvious inhibitory effects on melanoma activity; (+)-epi-syringaresinol,(+)-syringaresinol,N-trans-feruloyltyramine,cis-p-coumaricacid,N-cis-caffeoyltyramine have inhibitory effects on the activity of mushroom tyrosinase.The remaining compounds are:p-hydroxybenzoic acid,vanillic acid,veratric acid,syringic acid,2,5-dimethoxyphenol,4,5-trimethoxybenzoic acid,nicotinic acid,glycerol,β-sitosterol and stigmasterol[33-34].

6 Conclusions

As early as the 1960s,scholars at home and abroad successively carried out research onSynsepalumDulcificum.However,early research mainly focused on the cultivation techniques,the identification of main components and the extraction and separation of active ingredients.Moreover,since the fruit is small in size,the yield is low,it is not easy to preserve the active ingredients of the fresh fruit,and the climate requirements of the planting area are harsh[1],it cannot be planted and processed on a large scale worldwide.As a result,the resources are very limited,greatly restricting the development and utilization ofSynsepalumDulcificum.In recent years,research on the extraction and preparation of the main components ofSynsepalumDulcificumby using transgenic technology has been increasing.At present,researchers have successfully cloned the gene of miraculin,and the transgenic research has been successful in microorganisms and plants such as Escherichia coli,Saccharomyces cerevisiae,Aspergillus oryzae,tomato,strawberry,lettuce,etc.[35-40]Quantifying production or using it as a food and drug additive still requires further improvement of relevant technologies and related toxicological studies,as well as strict safety assessment[41].

Recently,in-depth research on the physical and chemical properties and pharmacological effects of various functional components ofSynsepalumDulcificumhas been carried out.At present,a certain number of studies have shown that the pulp,peel,seeds and many other parts of theSynsepalumDulcificumhave high nutritional value and can be used as potential health and medicinal ingredients[42-44].And the unique taste-changing function ofSynsepalumDulcificumcan be developed into a novel low-energy sweetener[45-46],which is undoubtedly good news for diabetic patients who cannot eat sweets.However,the taste changing mechanism ofSynsepalumDulcificumremains unclear[47-48],and further research results are needed for explanation.In addition,the mechanism of action of anti-inflammatory,anti-oxidation,anti-tumor,blood sugar regulation,blood lipids regulation and gout improvement ofSynsepalumDulcificumstill needs further experiments for verification.