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Sweetpotato (Ipomoea batatas L.) Leaf: ItsPotential Effect on Human Health and NutritionSSSSSHAHIDULHAHIDULHAHIDULHAHIDULHAHIDUL I I I I ISLAMSLAMSLAMSLAMSLAM

ABSTRAABSTRAABSTRAABSTRAABSTRACTCTCTCTCT: P: P: P: P: Prrrrrevious experevious experevious experevious experevious experiments riments riments riments riments revevevevevealed that swealed that swealed that swealed that swealed that sweetpotato leaveetpotato leaveetpotato leaveetpotato leaveetpotato leaves contain a high content of polyphenolicses contain a high content of polyphenolicses contain a high content of polyphenolicses contain a high content of polyphenolicses contain a high content of polyphenolics,,,,,namely anthocyanins and phenolic acids, compared with the major commercial vegetables. Sweetpotato leavesnamely anthocyanins and phenolic acids, compared with the major commercial vegetables. Sweetpotato leavesnamely anthocyanins and phenolic acids, compared with the major commercial vegetables. Sweetpotato leavesnamely anthocyanins and phenolic acids, compared with the major commercial vegetables. Sweetpotato leavesnamely anthocyanins and phenolic acids, compared with the major commercial vegetables. Sweetpotato leavescontain at least 15 biologically active anthocyanins that have significant medicinal value for certain humancontain at least 15 biologically active anthocyanins that have significant medicinal value for certain humancontain at least 15 biologically active anthocyanins that have significant medicinal value for certain humancontain at least 15 biologically active anthocyanins that have significant medicinal value for certain humancontain at least 15 biologically active anthocyanins that have significant medicinal value for certain humandiseases and may also be used as natural food colorants. The anthocyanins were acylated cyanidin and peonidindiseases and may also be used as natural food colorants. The anthocyanins were acylated cyanidin and peonidindiseases and may also be used as natural food colorants. The anthocyanins were acylated cyanidin and peonidindiseases and may also be used as natural food colorants. The anthocyanins were acylated cyanidin and peonidindiseases and may also be used as natural food colorants. The anthocyanins were acylated cyanidin and peonidintype. The phenolic acids were composed of caffeic acid (CA) and 5 kinds of caffeoylquinic acid derivatives, 3-type. The phenolic acids were composed of caffeic acid (CA) and 5 kinds of caffeoylquinic acid derivatives, 3-type. The phenolic acids were composed of caffeic acid (CA) and 5 kinds of caffeoylquinic acid derivatives, 3-type. The phenolic acids were composed of caffeic acid (CA) and 5 kinds of caffeoylquinic acid derivatives, 3-type. The phenolic acids were composed of caffeic acid (CA) and 5 kinds of caffeoylquinic acid derivatives, 3-mono-mono-mono-mono-mono-OOOOO-caffeoylquinic acid (chlorogenic acid, ChA), 3,4-di--caffeoylquinic acid (chlorogenic acid, ChA), 3,4-di--caffeoylquinic acid (chlorogenic acid, ChA), 3,4-di--caffeoylquinic acid (chlorogenic acid, ChA), 3,4-di--caffeoylquinic acid (chlorogenic acid, ChA), 3,4-di-OOOOO-caffeoylquinic acid (3,4-diCQA), 3,5-di--caffeoylquinic acid (3,4-diCQA), 3,5-di--caffeoylquinic acid (3,4-diCQA), 3,5-di--caffeoylquinic acid (3,4-diCQA), 3,5-di--caffeoylquinic acid (3,4-diCQA), 3,5-di-OOOOO-----caffeoylquinic acid (3,5-diCQA), 4,5-di-caffeoylquinic acid (3,5-diCQA), 4,5-di-caffeoylquinic acid (3,5-diCQA), 4,5-di-caffeoylquinic acid (3,5-diCQA), 4,5-di-caffeoylquinic acid (3,5-diCQA), 4,5-di-OOOOO-caffeoylquinic acid (4,5-diCQA), and 3,4,5-tri--caffeoylquinic acid (4,5-diCQA), and 3,4,5-tri--caffeoylquinic acid (4,5-diCQA), and 3,4,5-tri--caffeoylquinic acid (4,5-diCQA), and 3,4,5-tri--caffeoylquinic acid (4,5-diCQA), and 3,4,5-tri-OOOOO-caffeoylquinic acid-caffeoylquinic acid-caffeoylquinic acid-caffeoylquinic acid-caffeoylquinic acid(3,4,5-triCQA). These polyphenolics showed various kinds of physiological functions, radical scavenging activ-(3,4,5-triCQA). These polyphenolics showed various kinds of physiological functions, radical scavenging activ-(3,4,5-triCQA). These polyphenolics showed various kinds of physiological functions, radical scavenging activ-(3,4,5-triCQA). These polyphenolics showed various kinds of physiological functions, radical scavenging activ-(3,4,5-triCQA). These polyphenolics showed various kinds of physiological functions, radical scavenging activ-ityityityityity, antimutagenic activity, antimutagenic activity, antimutagenic activity, antimutagenic activity, antimutagenic activity, anticancer, anticancer, anticancer, anticancer, anticancer, antidiabetes, antidiabetes, antidiabetes, antidiabetes, antidiabetes, and antibacter, and antibacter, and antibacter, and antibacter, and antibacterial activity in vitrial activity in vitrial activity in vitrial activity in vitrial activity in vitro or in vivo or in vivo or in vivo or in vivo or in vivooooo, which may be, which may be, which may be, which may be, which may behelpful for maintaining and promoting human health. The physiological function of caffeoylquinic acid (CQA)helpful for maintaining and promoting human health. The physiological function of caffeoylquinic acid (CQA)helpful for maintaining and promoting human health. The physiological function of caffeoylquinic acid (CQA)helpful for maintaining and promoting human health. The physiological function of caffeoylquinic acid (CQA)helpful for maintaining and promoting human health. The physiological function of caffeoylquinic acid (CQA)derivatives with the plural caffeoyl group is more effective than with a monocaffeoyl one. This review describesderivatives with the plural caffeoyl group is more effective than with a monocaffeoyl one. This review describesderivatives with the plural caffeoyl group is more effective than with a monocaffeoyl one. This review describesderivatives with the plural caffeoyl group is more effective than with a monocaffeoyl one. This review describesderivatives with the plural caffeoyl group is more effective than with a monocaffeoyl one. This review describesthe nutritional composition and physiological functions of sweetpotato leaves when used as a vegetable, and asthe nutritional composition and physiological functions of sweetpotato leaves when used as a vegetable, and asthe nutritional composition and physiological functions of sweetpotato leaves when used as a vegetable, and asthe nutritional composition and physiological functions of sweetpotato leaves when used as a vegetable, and asthe nutritional composition and physiological functions of sweetpotato leaves when used as a vegetable, and asa resource for products with these functions.a resource for products with these functions.a resource for products with these functions.a resource for products with these functions.a resource for products with these functions.

KKKKKeyworeyworeyworeyworeywords: swds: swds: swds: swds: sweetpotato leaveetpotato leaveetpotato leaveetpotato leaveetpotato leaveseseseses, polyphenol, antio, polyphenol, antio, polyphenol, antio, polyphenol, antio, polyphenol, antioxidant, antimutagenicityxidant, antimutagenicityxidant, antimutagenicityxidant, antimutagenicityxidant, antimutagenicity, caffeo, caffeo, caffeo, caffeo, caffeoylquinic acid derylquinic acid derylquinic acid derylquinic acid derylquinic acid derivivivivivativativativativativeeeee, an-, an-, an-, an-, an-ticancerticancerticancerticancerticancer, antidiabetes, antidiabetes, antidiabetes, antidiabetes, antidiabetes, anti-HIV, anti-HIV, anti-HIV, anti-HIV, anti-HIV

Introduction

The sweetpotato [(Ipomoea batatas (L.) Lam.] is the 7th mostimportant food crop in the world (FAO 1997) and is among the

crops selected by the U. S. Natl. Aeronautics and Space Administra-tion to be grown in a controlled ecological life-support system as aprimary food source (Hoff and others 1982). Sweetpotato cultivarswhose roots are used for a beverage, a paste, a powder, an alcoholdrink, and a natural colorant have been developed in this decade(Yoshimoto 2001; Islam and Jalaluddin 2004).

However, sweetpotato leaves have largely been neglected ex-cept for partial use as livestock feed. Utilization of sweetpotatoleaves as a vegetable could significantly increase food availabilityin countries with recurring food shortages. Sweetpotato greens areconsumed to a limited extent as a fresh vegetable in some parts ofthe world (Villareal and others 1982; Nwinyi 1992). Faced with in-creasing food shortages, agriculturists and food scientists are becom-ing increasingly interested in previously neglected tropical greenleafy vegetables such as sweetpotato greens. Low yield is a commondeficit for tropical greens. However, the sweetpotato can be har-vested several times during the year, thus yielding substantiallymore than other greens. In addition, it is 1 of the few vegetablesthat can be grown during the monsoon season of the tropics, oftenmaking sweetpotato leaves the only greens available in some coun-tries after a flood or a typhoon. Sweetpotato leaves are rich in vita-min B, �-carotene, iron, calcium, zinc, and protein; and as a crop,sweetpotato is more tolerant of diseases, pests, and high moisturethan many other leafy vegetables grown in the tropics (AVRDC1985; Pace and others 1985; Woolfe 1992; Ishiguro and others 2002,2004; Yoshimoto and others 2003).

Functional food products are aimed at introducing human di-etary ingredients that aid specific bodily functions in addition tobeing nutritious. Several authors report that sweetpotato leaves arean excellent source of antioxidative polyphenolics, among themanthocyanins and phenolic acids such as caffeic, monocafeoylquinic (chlorogenic), dicaffeoylquinic, and tricaffeoylquinic acids(Islam and others 2002a, 2002b, 2003c), and are superior in thisregard to other commercial vegetables (Ishiguro and others 2002,2004; Islam and others 2002a, 2002b, 2002c, 2003b, 2003c; Yoshim-oto and others 2002a, 2003). The nutritional attributes of sweetpo-tato leaves are increasingly recognized, as a better understandingemerges in the relationship between diet and human health.

The anthocyanins are the predominant group of visiblepolyphenols and comprise the red, purple, and blue pigmentationof many plants. They represent a diverse group of secondary me-tabolites (Rhodes and others 1986; Harborne 1994; Meyer and oth-ers 1998) including important natural antioxidants and food colo-rants. Anthocyanins have been shown to have some positivetherapeutic effects such as in the treatment of diabetic retinopa-thy (Scharrer and Ober 1981), fibrocystic disease of the breast (Le-onardi 1993), and vision disorders (Politzer 1977; Timberlake andHenry 1988). Anthocyanins may also have other potential physio-logic effects as antineoplastic agents (Kamei and others 1995), ra-diation-protective agents (Minkova and others 1990; Akhmadievaand others 1993), vasotonic agents (Colantuoni and others 1991),vasoprotective and anti-inflammatory agents (Lietti and others1976), chemoprotective agents against platinum toxicity in anti-cancer therapy (Karaivanova and others 1990), hepatoprotectiveagents against carbon tetrachloride damage (Mitcheva and others1993), and possible other beneficial effects due to their interactionwith various enzymes and metabolic processes (Ferrel and others1979; Gibb and others 1987; Saija and others 1990; Costantino andothers 1995). No adverse effects were observed in animals fed agrape color extract containing principally anthocyanins (Becci and

MS 20050682 Submitted 11/14/05, Revised 1/2/06, Accepted 1/15/06. Theauthor is with Dept. of Agriculture,, Univ. of Arkansas at Pine Bluff, Mail Slot4913, 1200 North Univ. Drive, Pine Bluff, AR 71601. Direct inquiries to au-thor Islam (E-mail: islam_s@uapb.edu).

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others 1983), nor were there any adverse effects on humans con-suming a grape skin extract that has been approved by the Foodand Drug Administration as a food colorant (Timberlake and Henry1988).

There is a growing demand in the food industry for use of natu-ral food colorants, and purple-fleshed sweetpotatoes are consid-ered a good source of stable anthocyanins that can be used as a redfood colorant (Odake and others 1994, 1998). As a food additive,anthocyanins are high in this color compared with cochineal pig-ments (Odake and others 1994, 1998). Sweetpotato anthocyaninsare equal in stability to light and heat as those derived from redcabbage and have a superior shelf life (Odake and others 1998). Ahigh anthocyanin-producing cell line (APL) has been establishedfrom the storage roots of sweetpotato cultivar ‘Ayamurasaki’ (K-Is-lam and others 2000). The anthocyanins from the APL are superi-or as a natural food additive to those from red cabbage, elderber-ry, and purple corn (Odake and others 1994, 1998) due to their freeradical scavenging and antimutagenic activity (Furuta and others1998; Yoshimoto and others 1999a, 1999b; K-Islam and others 2003).Anthocyanin composition in sweetpotato affects the quality of foodcolorants (Odake and others 1994) and paste color (Yoshinaga andothers 1999). The major coloring constituents in sweetpotato havebeen identified as acylated anthocyanins (Miyazaki and others1991; Zulin and others 1992), and the chemical structures of majorstorage root anthocyanins have been determined (Odake and oth-ers 1992; Goda and others 1997; Terahara and others 1999; Teraharaand others 2000). Their base structure is either cyanidin or peoni-din, which are acylated with caffeic, ferulic, and P-hydroxybenzoicacid.

Phenolic compounds are a diverse group of secondary metabo-lites present in higher plants that play important roles in the struc-ture of plants and are involved in a number of metabolic pathways(Harborne 1980). Plant phenolics, because of their diversity andextensive distribution, can be argued to be an important group ofnatural antioxidants, and contribute to organoleptic and nutritionalqualities of fruit and vegetables. Phenolic compounds exist univer-sally in most of the vegetables, which are also rich sources of naturalantioxidants (Huang and Ferraro 1991; Tsushida and others 1994;Murata and others 1995; Peluso and others 1995; Chuda and others1996; Shahrzed and Bitsch, 1996; Shimozono and others 1996; Kauland Khanduja, 1998; Yoshimoto and others 1999a,1999b, 2001, 2002a,2003; Murayama and others 2002; Islam and others 2002c, 2003b,2003c), and in fruits (Coseteng and Lee 1987; Robards and others1999). Dietary antioxidants have attracted special attention because

they can protect the human body from oxidative stress, which maycause many diseases including cancer, aging, and cardiovascular dis-eases (Huang and Ferraro 1991; Ho 1992; Hertog and others 1993,1995; Kinsella and others 1993; Peluso and others 1995; Stevens andothers 1995; Shahrzad and Bitsch 1996; Shimozono and others 1996;Hagerman and others 1998; Kaul and Khanduja 1998; Prior and oth-ers 1998; Robards and others 1999; Yoshimoto and others 1999a, 2001,2002a, 2002b, 2003; Islam and others 2003a, 2003b, 2003c). Therefore,sweetpotato leaves with high nutritive value (Yoshimoto and others2002a; Ishiguro and others 2002, 2004) and antioxidants, namelyphenolics (Islam and others 2002b, 2003a, 2003b, 2003c, 2004, 2005;Islam and Jalaluddin 2003, 2005) may become an excellent sourcematerial for biologically active compounds. This review describes thenutritional composition and physiological functions of sweetpotatoleaves and its related components as a resource for products withthese functions.

Nutritional Value

Sweetpotato leaves posses a variety of chemical compounds thatare relevant to human health. Depending on genotypes and

growing conditions, sweetpotato leaves are comparable with spin-ach in nutrient contents (Woolfe 1992; Yoshimoto and others 2002a;Ishiguro and others 2002, 2004). The average contents of mineralsand vitamins in recently developed cultivars ‘Suioh’ were 117 mgcalcium, 1.8 mg iron, 3.5 mg carotene, 7.2 mg vitamin C, 1.6 mg vi-tamin E, and 0.56 mg vitamin K/100 g fresh weight of leaves. Levelsof iron, calcium and carotene rank among the top, as comparedwith other major vegetables (Ishiguro and others 2004). Sweetpo-tato leaf is also rich in vitamin B, �-carotene, iron, calcium, zinc andprotein, and as a crop is more tolerant of diseases, pests, and highmoisture than many other leafy vegetables grown in the tropics(AVRDC 1985; Woolfe 1992; Yoshimoto and others 2003). We previ-ously reported that sweetpotato leaves were an excellent source ofantioxidative polyphenolics, among them anthocyanins (Islam andothers 2002b, 2003c, 2005) and phenolic acids such as caffeic,monocafeoyl quinic (chlorogenic), dicaffeoylquinic, and tricaf-feoylquinic acids (Islam and others 2002b, 2003a, 2003b, 2003c),superior in this regard to other commercial vegetables (Yoshimotoand others 2001a, 2002b, 2003; Ishiguro and others 2002, 2004).Sweetpotato leaves and others tropical leafy vegetables have beenshown to contain higher levels of oxalic acid than common temper-ate climate vegetables, with the exception of spinach (Evenson andStandal 1984). Oxalate concentrations in food crops have long beena concern in human diet. Because of the negative health effects

Table 1—Chemical names of the 15 anthocyanin identified in sweetpotato leaves (Islam and others 2002a)

Common name Chemical name

YGMZ–0a cyanidin 3 – sophoroside – 5 – glucosideYGM–0b peonidin 3 – sophoroside – 5 – glucosideYGM–0c P–hydroxybenzoylated (cyanidin 3 – sophoroside – 5 – glucoside)YGM–0d caffeoylated (cyanidin 3 – sophoroside – 5 – glucoside)YGM–0e P-hydroxybenzoylated (peonidin 3 – sophoroside – 5 – glucoside)YGM–0f caffeoylated (peonidin 3 – sophoroside – 5 – glucoside)YGM–0g feruloylated (cyanidin 3 – sophoroside – 5 – glucoside)YGM-1a cyanidin 3 – (6,6� – caffeoyl–P–hydroxybenzoylsophoroside) – 5 – glucosideYGM-1b cyanidin 3 – (6,6� – dicaffeoylsophoroside) – 5 – glucosideYGM–2 cyanidin 3 – (6 – caffeoylsophoroside) – 5 – glucosideYGM–3 cyanidin 3 – (6,6� – caffeoylferuloylsophoroside) – 5 – glucosideYGM- 4b peonidin 3 – (6,6� – dicaffeoylsophoroside) – 5 – glucoside]YGM-5a peonidin 3 – (6,6� – caffeoyl–P–hydroxybenzoylsophoroside) – 5 – glucosideYGM-5b cyanidin 3 – (6 – caffeoylsophoroside) – 5 – glucosideYGM-6 peonidin 3 – (6,6� – caffeoylferuloylsophoroside) – 5 – glucosideZYGM = Yamagawamurasaki.

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associated with high intake of oxalate levels cancause acute poisoning, resulting in hypocalcae-mia, or chronic poisoning in which calcium oxalateis deposited as crystals in the kidneys, causing re-nal damage. Furthermore, oxalic acid and solubleoxalates can bind calcium, reducing its bioavail-ability and calcium oxalate itself is poorly utilizedby humans. The average content of oxalic acid ofsweetpotato variety ‘Suioh’ leaves was 280 mg/100 g fresh weight. This content was not high com-pared with the 930 mg/100 g fresh weight in spin-ach (Ishiguro and others 2004). Oxalic acid con-tents of other sweetpotato varieties tested werealso several times less than that of spinach(Yoshimoto and others 2002b).

Anthocyanin Compositions

We reported that sweetpotato leaves repre-sent 1 of the richest and most commonly

available sources of anthocyanin among fruitsand vegetables (Islam and others 2002a; 2005).Fifteen anthocyanin compounds were identifiedand characterized in sweetpotato leaves (Table 1).The chemical characteristics of the sweetpotatoleaves anthocyanin are presented in Figure 1. Theanthocyanins were acylated cyanidin and peoni-din type. But the content of cyanidin in leaves aremuch higher than that of peonidin, suggestingthat the anthocyanin composition of sweetpotatoleaf is cyanidin type (Islam and others 2002a;2005). The cyanidin type anthocyanins are supe-rior to the peonidin type in antimutagenicity(Yoshimoto and others 1999a, 1999b) and antiox-idative activity (Rice-Evans and others 1995). Thesweetpotato anthocyanins are ubiquitous bioac-tive compounds because of its potential antioxi-dant activities that may exert cardioprotective ef-fects (Knekt and others 1996; Furuta and others1998; Suda and others 1998; Yoshimoto and others1999a), antidiabetic effects (Matsui and others2001a, 2001b, 2002), and anticancer effects (K-Is-lam and others 2003). These activities might de-pend on the number of hydroxyl group in thestructure (Yoshimoto and others 2001; Hou 2003).Cyanidin containing 2 hydroxyl groups showedstronger activity on antimutagenicity than that ofpeonidin, which has only 1 (Yoshimoto and others1999b; 2001). Based on additional studies with enzyme activity, theauthors concluded that anthocyanins protected against the mu-tagenesis partly by direct reactions with enzymatically activatedcarcinogens (heterocyclic amines) rather than by the interactionwith metabolic enzyme (Yoshimoto and others 1999a).

Recently, growing demand in the food industry for use of naturalfood colorants has led to the evaluation of various vegetables as foodcolorant sources. Sweetpotatoes are considered a good source of sta-ble anthocyanins that can be used as a red food colorant (Odake andothers 1994; 1998; K-Islam and others 2003). Sweetpotato anthocy-anins are equal in stability to light and heat as those derived from redcabbage and have a superior shelf life (Odake and others 1998). Thesweetpotato anthocyanins are also superior as a natural food addi-tive to those from red cabbage, elderberry, and purple corn (Odakeand others 1994, 1998; K-Islam and others 2003) due to their positivetherapeutic and physiological functions (Becci and others 1983; Gibb

and others 1987; Karaivanova and others 1990; Akhmadieva andothers 1993; Mitcheva and others 1993; Costantino and others 1995;Kamei and others 1995; Furata and others 1998; Yoshimoto and oth-ers 2001; Hou 2003). Furthermore, anthocyanin composition insweetpotato affects the quality of food colorants (Odake and others1994) and paste color (Yoshinaga and others 1999).

As indicated previously, sweetpotato anthocyanins possessmultifaceted action, including antioxidation, antimutagenicity,anti-inflammation, and anticarinogenesis. Extensive structure-ac-tivity studies show that the number of sugar units and hydroxylgroups on aglycons is associated with biological activities of antho-cyanins. The activities appear to increase with a decreasing num-ber of sugar units, and with an increasing number of hydroxylgroups on aglycons (Yoshimoto and others 2001; Hou 2003). Futureresearches are necessary on the bioavailability of anthocyaninsusing molecular marker analysis-based animal experiments.

Figure 1—Chemical structures and characteristics of the anthocyanincompositions in sweetpotato leaves (Islam and others 2002a)

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Polyphenolics Content

Sweetpotato leaves contain a much higher content of totalpolyphenols than any other commercial vegetables, including

sweetpotato roots and potato tubers (Walter and others 1979; Lu-gasi 1999; Islam and others 2002b; Yoshimoto and others 2002a,2003). We analyzed and characterized the total leaf polyphenolcontents of 1389 genotypes, collected from all over the world, weregrown in 2000 and 2001 (Islam and others 2002a, 2003c). A highlysignificant (P > 0.001) liner correlation was found between thepolyphenol contents of the genotypes from 2000 and the geno-types from 2001 (r = 0.812; n = 700) (Figure 2). This result indicatesthat the yearly variations of total phenolics in leaves of sweetpotatogenotypes are less. Furthermore, our previous data (n = 10) re-vealed that the highest polyphenol concentration was in leaves(6.19 ± 0.14 g/100 g dry weight), followed by petioles (2.97 ± 0.26 g/100 g dry weight), stems (1.88 ± 0.19 g/100 g dry weight), and finallyroots (<1.00 g/100 g dry weight), indicating that polyphenolic con-centrations are organ-dependent (Islam and others 2002b). Thefrequency distribution of total leaf polyphenolic content of 1389genotypes collected from world wide is shown in Figure 3. The high-est content found was 17.1 g/100 g dry weight and the lowest was1.42 g/100 g dry weight. Most of the genotypes (75%) contained>6.00 g/100 g dry leaf powder of total polyphenolics, which was avery high concentration compared with other commercial vegeta-bles (Yoshimoto and others 2003; Ishiguro and others 2002, 2004).

Polyphenolics Composition

Caffeic acid (CA) and 5 caffeoylquinic acid (CQA) derivatives: 3-mono-O-CQA (chlorogenic acid; ChA), 3,4-di-O-caffeoylquinic

acid (3,4-diCQA), 3,5-di-O-caffeoylquinic acid (3,5-diCQA), 4,5-di-O-caffeoylquinic acid (4,5-diCQA), and 3,4,5-tri-O-caffeoylquinicacid (3,4,5-triCQA) are found in sweetpotato leaves (Islam and oth-ers 2002b). Recently we isolated, identified and characterized the

above compounds in sweetpotato leaves for the 1st time (Figure 4).All caffeoylquinic acid derivatives (except C0A and CA; P < 0.05) arepositively correlated (P > 0.001) with total polyphenol contents ofsweetpotato leaves (Figure 5). The correlation of total phenolicswith ChA (r = 0.84), 3, 4-diCQA (r = 0.78), 3, 5-diCQA (r = 0.81), 4, 5-diCQA (r = 0.85) and 3, 4, 5-triCQA (0.59) were positive and signif-icant. The results indicate that the correlation between total phe-nolics with different CQA derivatives is an important aspect, whichshould be kept in mind for better planning for improvement of thedesired parameters. ChA, di- and triCQA are esters of quinic acid(QA) and bear 1-, 2-, and 3-caffeoyl groups (Figure 4).

Chlorogenic acid and diCQA derivatives have been isolated fromvarious plants including sweetpotato (Walter and others 1979; Shi-mozono and others 1996), as mentioned previously, but there arevery few reports on 3, 4, 5-triCQA. Isolation of 3, 4, 5-triCQA was re-

Table 2—3, 4, 5-tri-0-caffeoylquinic acid contents in Ipomoea batatas L. and others plant materials

Plant materials Amount (mg/100 g dry weight) Reference

Ipomoea batatas L Highest- 220.95a Islam and others (2002b)Lowest-6.37a

Average-49.00a

Securidaka longipedunculata 23.81 Mahmood and others (1993)Tessaria integrifolia 7.33 Peluso and others (1995)Mikania cordifolia 6.19 Peluso and others (1995)aHighest, lowest, and average of 60 sweetpotato genotypes.

Figure 2—Correlations between the total polyphenol con-tent (g/100 g dry weight) of sweetpotato leaves growingduring the y 2000 and 2001 (n = 700) (Islam and others2003a)

Figure 3—Frequency distribution of total polyphenol con-tent (g/100 g dry powder) of 1389 sweetpotato genotypes(Islam and others 2002b)

Figure 4—Chemical structures of caffeic acid derivativesin sweetpotato leaves (Islam and others 2002b)

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Table 3—Physiological functions of Ipomoea batatas L. and their related components

Physiological function Related components References

Antioxidative activity/radical scavenging activity Polyphenol, anthocyanin Islam and others (2002c, 2003a, 2003b);Tsushida and others 1994

Antimutagenicity Polyphenol, anthocyanin Yoshimoto and others (2001, 2003); Islamand others (2003a)

Anticarcinogenesis Polyphenol, anthocyanin Hou (2003); K-Islam and others (2003);Shimozono and others (1996)

Antihypertension Polyphenolics, anthocyanin Yoshimoto others (2001); Suda and others(1998)

Antimicrobial activity Fiber, pectin-like polysaccharide Islam and others (2004b, 2005a); Yoshimotoothers (2001)

Anti-inflammation Polyphenol Peluso (1995)Antidiabetic effect Anthocyanin, polyphenol Toeller (1994); Matsui and others (2001a,

2001b, 2002, 2004)Anti HIV Polyphenolics Mahmood and others (1993)Promotion of Bibidobacterium growth Dietary fiber Islam and others (2005a); Yoshimoto others

(2001)Reduction of liver injury Polyphenol Suda and others (1998)Relief from constipation Dietary fiber, jalapin Yoshimoto others (2001)Ultraviolet protection effect Polyphenolics Yoshimoto others (2001)

Figure 5—Correlations between different caffeic acid derivatives (g/100 gdry weight) and total polyphenol contents (g/100 g dry weight) ofsweetpotato leaves (n = 60). 4,5-diCQA = 4,5-di-O-caffeoyl quinic acid; 3,5-diCQA = 3,5-di-O-caffeoyl quinic acid; 3,4-diCQA = 3,4-di-O-caffeoyl quinicacid; 3,4,5-triCQA = 3,4,5-tri-O-caffeoyl quinic acid. (Islam and others 2003a)

vegetables described above (Islam and others 2003b, 2003c). Therewere significant positive correlations between radical scavengingactivity and polyphenol contents of sweetpotato leaves (Figure 6).The radical scavenging activity of CQA derivatives in order of effec-tiveness was ChA > 3, 4, 5-triCQA > 3, 4-diCQA = 3, 5-diCQA = 4, 5-diCQA > CA = CoA (Figure 7). These data indicate that sweetpota-to leaves are a good supplementary resource of antioxidants.

ported in Securidaka longipedunculata (Polygalaceae) (Mahmoodand others 1993) and Tessaria integrifolia (Asteraceae) (Peluso andothers 1995). Several varieties of sweetpotato contain a high content(>0.2%) of 3, 4, 5-triCQA (Islam and others 2002b; 2003c), suggestingthat the sweetpotato leaf is a source of not only mono- and diCQA de-rivatives but also 3, 4, 5-triCQA (Table 2).

Physiological Function of Sweetpotato Leavesand its Components

In the recent past, active research has beenconducted to determine health-promoting

functions of sweetpotato leaves. The followingaspects (Table 3) of these functions are impor-tant to look into when considering new uses ofsweetpotato leaves:

Antioxidative and RadicalScavenging Activity

Although lipids are essential for humanhealth, certain polyunsaturated fatty acids

have many double bonds and cause radicalchain reactions with oxygen, and thereby pro-duce various lipid peroxide and oxidized resol-vents. Lipid peroxides cause deterioration incell functions, arterial sclerosis, liver disorders,and retinopathy, and are also involved in car-cinogenesis and aging. From this viewpoint, an-tioxidative substances contained in plantshave attracted much attention recently. Severalauthors have reported the antioxidative andradical scavenging activities of sweetpotatoleaves (2002b, 2003b, 2003c, Islam and Jalalud-din). Polyphenolic content and antioxidative ac-tivity in vegetables show a good correlation,with the antioxidative activity of edible chry-santhemum (Chrysanthemum morifolium),which has the highest polyphenolic content be-ing the most effective among 43 commercialvegetables (Tsushida and others 1994). Sweet-potato leaves also revealed relatively muchhigher activity in 1-diphenyl-2-picrylhydrazyl(DPPH) radical scavenging activity than the

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Antimutagenicity and Anticarcinogenicity

Cancers occur through such processes as initiation, promotion,and progression in body cells. Initiation is a kind of mutation

that occurs in cancer and anticancer genes. Thus, controlling thegene mutation, brought about by the carcinogens, leads to cancerprevention. The mutagens contained in food may include ingredi-ents of vegetables, mold toxins, and others pollutants in food.These mutagens are considered as factors involved in occurrenceof human cancers. The recent development of screening methodsfor environmental carcinogens by determining their mutagenicityhas enabled various types of mutagens and carcinogens to be de-tected and identified in daily foods (Ames and others 1975). It isnow known that various types of inhibitors that act against mu-tagens and carcinogens are present in our daily food and that theyplay an important role in reducing the risks of mutagenesis and car-cinogenesis (Shinohara and others 1988; Yoshimoto and others1999b). CQA derivatives effectively inhibited the reverse muta-tions induced by Trp-P-1 on Salmonella typhimurium TA and theantimutagenicity of these derivatives in order of effectiveness was3, 4, 5-triCQA > 3, 4-diCQA = 3, 5-diCQA = 4, 5-diCQA > ChA > CA >C0A (Islam and others 2003c) (Figure 8).

Antidiabetes

At the later stage of non-insulin-dependent diabetes mellitus(NIDDM), which is the predominant type of human diabetes,

symptoms result mainly from decreased secretion of insulin bypancreatic Langerhans cells. Prevention of the NIDDM and inhibi-tion of the serious adverse effects of diabetes such as retinopathy,neuropathy, and cataracts, are important subjects for researchers.At present, the diabetic mellitus population in the United States isincreasing markedly and is estimated at more than 18 million per-sons. Diabetes contributes to the death of more than 213000 Amer-icans each year and is a leading cause of heart disease, blindness,and kidney failure (ADA 2005). Therefore, food materials with an-tidiabetic effect are desired for diet therapy. �-Glucosidase (EC3.2.1.20), a membrane-bound enzyme located at the epithelium ofthe small intestine, catalyzes the cleavage of glucose from disaccha-rides (Hauri and others 1982). Thus, retardation of the action of thisenzyme by any inhibitor may be one of the most effective ap-proaches to control non-insulin-dependent diabetes (Toeller 1994).Matsui and others (2004) reported that the maltase inhibitory ef-fect (IC50) of 3, 4-diCQA, 3, 5-diCQA, and 4, 5-diCQA were at levelsof 1910, 1890, and 413 �M, respectively. Maltase inhibitory effect of3, 4, 5-triCQA is much higher than the other 3 diCQAs and YGM-6,

1 of anthocyanin pigments from sweetpotato (Islam and others2002a, 2005), and was about 1/56 of acarbose. Acarbose is a thera-peutic �–glucosidase inhibitor used to delay glucose absorptionfrom small intestine (Goto and others 1989; Odaka and others1992). Furthermore, Matsui and others (2004) indicated that oraladministration of 3, 4, 5-triCQA to diabetic model rats reduced sig-nificantly their blood glucose content.

Anti-bacterial Activity

Removal of pathogenic fungi in the food, extension of storagetime by the control of putrefying bacteria, and eradication of

parasites are important for the maintenance of human health. Inthe meantime, an orientation toward healthy and natural foods isstrengthening among consumers, and a condition might exit in

Figure 6—Linear correlations between the total polyphe-nol contents (g/100 g dry powder) and radical scavengingactivities (�mole trolox/mg) of sweetpotato leaves. DM =dry matter (Islam and others 2003c).

Figure 7—Radical scavenging activity (%) of caffeoylquinicacid derivatives isolated from sweetpotato leaves. Valuesare mean ± SE of 3 separate experiments done in tripli-cate. C0A = P-coumaric acid, CA = caffeic acid; ChA =chlorogenic acid; 3,4-diCQA = 3,4-di-0-caffeoyl quinic acid;3,5-diCQA = 3,5-di-0-caffeoyl quinic acid; 4,5-diCQA = 4,5-di-0-caffeoyl quinic acid; 3,4,5-triCQA = 3,4,5-tri-0-caffeoylquinic acid (Islam and others 2003a)

Figure 8—Effect of caffeoylquinic acid derivatives isolatedfrom sweetpotato leaves on the antimutagenicity (% inhi-bition) of Trp-P-1 against Salmonella typhimurium TA 98.Trp-P-1 was added at a dose of 0.075 �g plate-1. Themutagenicity was tested with S-9 mix. Values are mean ±SE of 3 separate experiments done in triplicate. The val-ues shown have had the spontaneous mutation frequencysubtracted. The His+ revertant values of the controls forthe caffeoylquinic acid derivatives were 518 ± 49 plate-1.C0A = P-coumaric acid, CA = caffeic acid; ChA = Chloro-genic acid; 3,4-diCQA = 3,4-di-o-caffeoyl quinic acid; 3,5-diCQA = 3,5-di-0-caffeoyl quinic acid; 4,5-diCQA = 4,5-di-0-caffeoyl quinic acid; 3,4,5-triCQA = 3,4,5-tri-0-caffeoylquinic acid. (cited from Islam and others 2003a).

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which it will be difficult to use food preservatives and disinfectants.There is an indication of a worldwide prevalence of infection byEscherichia coli O-157, and surveillance and preventive measuresare required for this emerging infectious disease (Itoh and Kai1997). Lyophilized leaf powder from the ‘Simon-1’ sweetpotatocultivar strongly suppressed the growth of O-157, and its effect wasdetectable even after autoclave treatment. The antibacterial ex-tract revealed that the main components were polysaccharides (Is-lam and others 2004). In the polysaccharide fraction, the relativequantities of neutral sugars were in the order of xylose > galactose> arabinose > glucose > rhamnose > mannose > fucose. Galacturonicacid accounted for 28.7%, which is the highest among the sugarcomponents detected. These results suggest that the antibacterialcomponent of sweetpotato leaves may be pectin-like material (Is-lam and Jalaluddin 2005). Furthermore, the water extract from theleaves suppressed effectively the growth of other food-poisoningbacteria such as Staphylococcus aureus and Bacillus cereus as wellas pathogenic E. coli (Islam and Jalaluddin 2005).

Other Physiological Function(including anti-HIV) of Sweetpotato Leaves

Caffeoylquinic Acid Derivatives

Among other polyphenolic compounds, CA has been shown tobe most effective inhibitor of tumor promotion in the skin of

mice; and ChA, 3-4-diCQA, 3,5-diCQA, and 4,5-diCQA, which wereextracted from steamed sweetpotato, suppressed melanogenesisequally effectively (Shimozono and others 1996; Tsuchiya and oth-ers 1996; Kaul and Khanduja 1998). Kapil and others (1995) describedthe antihepatotoxic effect of ChA from Anthocephalus cadamba. The3, 5-diCQA and 4, 5-diCQA from Tessaria integrifolia and Mikaniacordifolia exhibited an appreciable anti-inflammatory activity in vitro(Peluso and others 1995). The inhibitory effect of CA, ChA, and 3, 5-diCQA showed over 50% inhibition of the histamine induced by con-canavalin plus phosphatidylserine from mast cells (Kimura and oth-ers 1985). Yagasaki and others (2000) indicated that ChA, CA, andquinic acid suppressed hepatoma cell invasion without altering thecell proliferation. Although ChA and dicaffeoylquinic acid deriva-tives isolated from various plant parts as just described, there havebeen few reports on the 3, 4, 5-triCQA. The present review demon-strate that sweetpotato leaf contains much higher contents of 3, 4, 5-triCQA than other plant materials reported in the literature (Table 2)(Parker and others 1989; Mahmood and others 1993). The 3, 4, 5-triC-QA exhibited a greater selective inhibition of HIV replication than 4,5-diCQA and CA had only slight anti-HIV activity (Mahmood andothers 1993). Thus, the caffeoylquinic acid derivatives can be expect-ed to protect humans from various kinds of diseases. This review alsosuggest that 3, 4, 5-triCQA have better physical function than thoseof mono-or dicaffeoylquinic acid.

Relationship of PhysiologicalFunction and Structure

As reviewed previously, sweetpotato anthocyanins have beenreported to possess multifaceted action, including antioxida-

tion, antimutagenicity, anti-inflammatory and anticarinogenesis.Extensive structure-activity studies have shown that the numberof sugar units and hydroxyl groups on aglycons is associated withbiological activities of anthocyanins. The activities appear to in-crease with a decreasing number of sugar units, and with an in-creasing number of hydroxyl groups on aglycons (Yoshimoto andothers 2001; Hou 2003). Future investigations are necessary on thebioavailability of anthocyanins with molecular marker analysis-based animal experiments.

The structural feature responsible for the antioxidative and free

radical scavenging activity of Calif. is the ortho-dihydroxyl func-tionality in the catechol (Mahmood and others 1993). Therefore,the physiological function of the CQA derivatives with plural caf-feoyl groups is more effective than with a monocaffeoyl one. Theradical scavenging activity and the anti-mutagenicity of these de-rivatives in order of efficacy is triCQA > diCQAs > monoCQA, sug-gesting that the number of caffeoyl groups bound to QA plays arole in the radical scavenging activity of the CQA derivatives. Inother words, additional caffeoyl groups bound to QA are necessaryfor higher function.

Conclusions

Naturally occurring polyphenolic compounds in plant partshave the properties to protect human health against certain

dangerous diseases. Sweetpotato leaf contains high concentrationsof polyphenolics, when compared with the major commercial veg-etables such as spinach, broccoli, cabbage, lettuce, and so forth.Sweetpotato leaf is a physiologically functional food that offers pro-tection from diseases linked to oxidation, such as cancer, hepato-toxicity, allergies, aging, human immunodeficiency virus, and car-diovascular problems. Therefore, sweetpotato leaves used as avegetable, a tea, in noodles, breads, confectioneries, and as a nu-tritional supplement can become a beneficial food source for ben-eficial polyphenolic compounds. To the best of our knowledge, nopublished information is available on the specific dose of sweetpo-tato leaves for human consumption. But cooperation with food com-panies has started in the development of appropriate rate of drypowder for juice, paste, ice cream, and others food ingredients. Ourinitial sensory evaluation (unpublished data) showed that the fol-lowing ratio (other food ingredients:sweetpotato leaf powder) aremore acceptable by taste panel of people: Ice cream 10:4, juice (3 g/10 fl oz), tea (2.0 g/8 fl oz), and bread (10:3).

Direction of Future Research

Future investigation on the functional properties and applica-tion potential of isolated bioactive compounds from sweetpo-

tato leaves is necessary. Future research should include the use ofin vivo techniques such as molecular marker analysis. Additional re-search on polyphenolic should include a standardization of meth-ods for quantification, evaluation of physiological activities, andbioavailability. The interactions of the various polyphenolics withpharmaceutical should also be emphasized in future studies. Thus,any clinical trials involving polyphenolic compounds contained inthe sweetpotato leaf should be based on the precise understandingof the physiologically relevant action mechanisms.

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