Phytochemicals in Vegetables: A Valuable Source of Bioactive Compounds E-Book
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- Herausgeber: Bentham Science Publishers
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Phytochemical compounds are secondary metabolites that plants usually synthesize for their own protection from pests and diseases. Phytochemical biosynthesis is also triggered under specific environmental conditions. They cannot be classified as essential
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FOREWORD
Vegetables play a crucial role in the human diet, being relevant contributors to the intake of micronutrients (i.e., vitamins and minerals) and dietary fiber and prebiotics, as well as occasionally of digestible carbohydrates and proteins (e.g., tubers and pulses). Furthermore, beyond their nutrient composition, vegetables contain a range of non-essential bioactive compounds (i.e., phytochemicals), among which carotenoids and polyphenols, including flavonoids, phenolic acids, stilbenes, lignans or tannins, are prominent, with others such as glucosinolates (in Brassicaceae), cysteine sulfoxides (in Allium species) or betalains (in beets) having more limited distribution.
Phytochemicals have attracted much attention in recent times as they may provide additional health benefits to the consumption of vegetables and other plant foodstuffs. The dietary intake of these compounds has been related with the prevention of some chronic and degenerative diseases that constitute major causes of death and incapacity in developed countries, such as cardiovascular diseases, type II diabetes, some types of cancers or neurodegenerative disorders like Alzheimer’s and Parkinson’s diseases. Nowadays it is considered that phytochemicals contribute, at least in part, for the protective effects of fruit and vegetable-rich diets, so that the study of their role in human nutrition has become a central issue in food research.
Consumers more demand for healthy and nutritious natural foods, while they are increasingly reluctant to chemical additives. These are requirements that fresh or minimally processed plant foods like vegetables can meet. Nevertheless, time constraints in developed countries have led to a decreasing tendency in the preparation of daily meals based on fresh ingredients. In this context, phytochemicals-rich foods are of great interest for both consumers and food industry that can use them as sources of bioactive ingredients for functional foods, nutraceuticals or dietary supplements. Moreover, owing to their properties, some phytochemicals might be used as natural additives, like antioxidants, preservatives, colorants or taste enhancers. Last but not the least, their bioactivity makes them also interesting to pharmaceutical and cosmetic industries for the development of drugs or cosmeceuticals.
Acknowledged experts in their fields have collaborated in the preparation of this book under the coordination of Prof. Spyridon A. Petropoulos, Prof. Isabel C.F.R. Ferreira and Dr. Lillian Barros. Throughout 12 chapters, a comprehensive overview is provided on the main groups of cultivated edible vegetables, as well as on some particular less used or locally employed native species that might be promoted for larger use in human nutrition. The coverage is ample, while the main focus is put into the interest of vegetables as phytochemicals sources, aspects such as plant description, chemical composition, influence of breeding, post-harvest or processing on bioactive compounds, health effects, bioaccessibility or bioavailability are also dealt with. No doubt that the book will be very useful for academic and industrial scientists, but also for students and consumers concerned about their health or who wish to delve into the knowledge of vegetables, their nutrient and phytochemical composition and their undoubted relevance in the human diet.
PREFACE
The present e-book aims at presenting the phytochemicals content of the main cultivated vegetables, as well as their health and therapeutic effects based on ¬in vitro and in vivo, animal and clinical studies. The importance of vegetables on human health is mostly attributed to their nutritional value; however, not always nutrients are the sole responsible compounds for such properties and several other compounds can also contribute to health-promoting effects. These compounds have been identified as secondary metabolites and plants usually synthesize them for their own protection from pests and diseases or their biosynthesis is triggered under specific environmental conditions.
Book structure has been arranged in individual chapters, each one of them dealing with specific groups of vegetable sources of phytochemicals, either in terms of taxonomy (species of the same family) or in terms of edible parts morphology (e.g. leafy and root vegetables). For each species, a short introduction regarding the description of morphology, taxonomy and general information is included, as well as its chemical composition and its main health effects.
Chapter 1 presents the main phytochemicals that have been identified in various roots vegetables consumed throughout the world, including potato, celeriac, turnips, radish, beets, Hamburg parsley, taro, yam, parsnip and salsify. Chapter 2 presents vegetables that belong to the Allium genus. Chapter 3 presents bean, a vegetable of the Fabaceae family, which is one of the main starch and protein sources for most of the world. Chapter 4 demonstrates the chemical composition and health effects of another group of vegetables that all belong to the Cucurbitaceae family. Chapters 5-7 provides a clear insight into a diversified group of vegetables that are consumed for their edible leaves, belonging to Asteraceae and Apiaceae families. Chapter 8 discusses the phytochemicals content, their functionality and breeding tools for the enrichment of cole vegetables (Brassicaceae) in phytochemicals. Chapter 9 presents another important group of fruit vegetable that belongs to the Solanaceae family, namely, tomato, eggplant and pepper. Other important vegetables, such as globe artichoke and okra, are characterized in chapters 10 and 11. Finally chapter 12 deals with a special group of fruit and vegetables, which although they have a regional interest and are less well-known, they present important bioactive properties and health effects.
List of Contributors
Root Vegetables as a Source of Biologically Active Agents - Lesson from Soil
Dejan S. Stojkovic,Marija S. Smiljkovic,Marina Z. Kostic,Marina D. Sokovic*Abstract
Natural products and primary and secondary metabolites of plants have many biological functions, many of which are considered as health-beneficial for mankind. This chapter will focus on biologically active ingredients in widely consumed root vegetables, such as potato, celeriac, turnips, radish, beets, Hamburg parsley, taro, yam, parsnip and salsify. A recent update of studies is presented regarding underground parts of the mentioned vegetables – plant underground parts. Chemical constituents responsible for such biological activities, with focus on recent findings for each root vegetable separately are presented.
INTRODUCTION TO BIOLOGICAL ACTIVITY OF NATURAL PRODUCTS: ROOT VEGETABLES
Natural products have historically been an extremely productive source for new medicines in all cultures and continue to deliver a great variety of structural templates for drug discovery and development. Although products derived from natural sources may not necessarily represent active ingredients in their final form, the majority of all drugs in the market have their origin in nature [1, 2]. A significant number of drugs have been derived from plants that were traditionally employed in ethnomedicine or ethnobotany, while others were discovered through random screening of plant extracts for their biological potential and actual application to which our research group was focused in the past decade [3-14].
An avenue that may have influenced ethnopharmacology suggests that some traditionally used remedies may have arisen from observations of self-medication by animals [15]. Studies have shown that wild animals often consume plants and other materials for medical rather than nutritional reasons, treating parasitic infections and possible viral and bacterial diseases [16].
Cultivated plants, which have their edible part underground, are called root and tuber crops. Man domesticated various roots and tuber producing species for similar use in different parts of the world and on different elevations, such as yams in Africa and Asia, taro in Asia, cassava, sweet potato, and potato in America in low, medium and high altitudes. Additionally, different parts of the same plant species are used in different regions, such as leaves and petioles, fruit, seeds and roots and tubers which are the topic of interest in the present book chapter. The thickened taproot, the hypocotyl and the epicotyl constitute the edible parts of carrots, beets and some radishes, while early spring radish has its thickened hypocotyl belowground; potato tubers are modified underground stems (stolons), and the marketed parts of onions and garlic are modified thickened leaves (bulbs) [17].
Potato
Potato (Solanum tuberosum L.) (Fig. 1) belonging to the family Solanaceae is the fifth most important crop in the world, it is rich in calories and biologically active phytochemicals (β-carotene, polyphenols, ascorbic acid, tocopherol, α-lipoic acid, etc.) (Table 1) [18, 19]. The main nutrient in potato is starch, since tubers are the main storage organs of the species [19]. Potatoes could be prepared and used in different ways like baking, boiling, dehydrating, and frying [20].
Potato tubers are proven to have various activities and their consumption could subsequently lead to a healthier population Table 2, mostly due to numerous chemicals that could be found in the organs of this widely popular crop. Phytochemicals that play an important role in human health as antioxidants are concentrated in potato peel. Their content is higher in potato cultivars with brighter peel colors and frequent consumption of potato increases phenolic content in our nutrition [19]. Phenolic compounds prevent oxidative damage of DNA, reduce gut glucose absorption, suppress adipogenesis, reduce systolic and diastolic blood pressure and prevent proliferation of cancer cells [21-24]. It is reported that chlorogenic acid (Fig. 2A), one of the main phenolics found in potato tubers Table 1, has strong antioxidant, antidiabetic and antihypertension activity [25, 26]. The lectin StL-20 isolated from potato, showed antimicrobial activity against Listeria monocytogenes, Escherichia coli, Salmonella enteritidis, Shigella boydii, Rhizopus spp., Penicillium spp. and Aspergillus niger. Also, lectin has shown antibiofilm activity against Pseudomonas aeruginosa, while it reduced biofilm formation by 5-20% in 24h in a dose-dependent manner [27].
Lectins are reported to induce apoptosis and have potential anticancer activity [28]. Glycoalkaloids have also numerous bioactivities such as antimicrobial, anticancer, anticholesterol and anti-inflammatory [29]. Glycoalkaloids (Table 1) showed antifungal activity, with α-chaconine being the most active among them [30]. Moreover, α-chaconine (Fig. 2B) inhibited the growth of Aspergillus niger, Penicillium roqueforti, and Fusarium graminearum [31]. Other glycoalkaloids such as α-solasonine and α-solamargine demonstrated synergistic activity against Phoma medicaginis and Rhizoctonia solani [30]. Ethanolic extract of S. tuber-osum is active against Staphylococcus aureus, Streptococcus pyogenes, Klebsiella pneumonia and Pseudomonas aeruginosa with minimal inhibitory concentration (MIC) values in the range of 0.62-10 mg/ml [32]. Potato peel is rich in anthocyanins which play an important role in human health. Many researchers reported antioxidant, anticancer and anti-inflammatory activities of anthocyanins [33-36]. Patatin, a peptide present in potato tubers demonstrated antioxidant activity and could also inhibit hydroxyl radical-induced DNA damage in vitro [37].
Celeriac
Apium graveolens L., commonly known as celery Fig. (3), is an edible plant of the family Apiaceae. Literature data indicates that A. graveolens has a wide spectrum of biological properties such as antifungal, antioxidant, antihypertensive, antihyperlipidemic, diuretic, and anticancer [41], with roots being less examined than other plant parts.
Researchers identified some phenolic compounds (Fig. 4) and coumarins from celery root extract which was shown to have antioxidant and anti-inflammatory effects (Table 3) [42, 43].
Another study indicated that the root extracts of A. graveolens significantly decreased CC14-induced acute hepatic injury [44]. The root extracts have also antioxidant effect with EC50 value ranging from 2.41-3.14 mg/ml [45]. Besides antioxidant and hepatoprotective effects, no data is available about some other potential benefits suggesting that celeriac roots should be further examined (Table 4).
Turnips
Brassicaceae family (turnips, broccoli, Brussels sprouts, cauliflower, and cabbages among others) has been extensively studied due to its nutritional and health benefits. Brassica rapa, has many variants: B. rapa var. ruvo (broccoli raab), B. rapa var. chinensis (Chinese cabbage), B. rapa var. pekinensis (turnip greens), B. rapa var. parachinensis (Chinese flowering cabbage), and B. rapa var. pervidis (tender greens) among which Brassica rapa var. rapifera (turnip) is one of the oldest cultivated vegetables [46]. Turnips are usually consumed as a boiled vegetable, while its root is an ingredient in folk medicine for cold remedy.
From root essential oils 41 compounds were detected by GC and GC/MS analyses, some of these compounds are presented in (Table 5) [46]. Within terpenes (5.0 – 14.6%), menthol Fig. (5) is the most common component (4.9-6.1%) and might be one of the reasons for various biological activities of the species (Table 6). Essential oils of turnips roots showed antimicrobial effect against Listeria monocytogenes, Staphylococcus aureus, Salmonella enterica, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Fusarium culmorum, Aspergillus ochraceus, A. flavus, and Candida albicans with great antifungal activity (MIC values 0.5 to 2 mg/ml) and moderate antibacterial activity (MIC values 2 to 7 mg/ml). Antimicrobial activity can be associated with the presence of menthol, hexahydrofarnesyl aceton, allyl isothiocyanate and 2-phenylethanol [47]. Antioxidant activity of these oils was proven with different tests (DPPH, reducing power, β-carotene bleaching and chelating ability on ferrous ions) [46].
Additionally, ethanolic and aqueous extracts showed antimicrobial activity against Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, Candida albicans, and Aspergillus niger with MIC values in the range of 12.5 - 25 mg/ml [48]. The HPLC-DAD and HPLC-UV analysis showed a phenolic and organic acids profile of root aqueous extract [49] with kaempferol 3-O-sophoroside-7-O glucoside, kaempferol3-O-(feruloyl/caffeoyl)-sophoroside-7 glucoside,isorhamnetin 3,7-O-diglucoside, isorhamnetin 3-O-glucoside, and malic acid as the main components. This extract showed low antioxidant activity with IC25=1.44 mg/ml [49]. The metanolic extract of turnip root showed antioxidant activity and anticancer activity against HT-29 and MCF-7 lines [50].
Taro
Several plants from Araceae family, such as taro (Colocasia esculenta), eddoe (Colocasia antiquorum), giant taro (Alocasia macrorrhiza (L.) Schott), swamp taro (Cyrtosperma merkusii), and arrow leaf elephant's ear (Xanthosoma sagittifolium), are widely used in subtropics and tropic countries, as energy.
sources because rhizomes of these vegetables contain a large amount of starch (85% of total dry matter) [51]. Starch (Fig. 6) from these plants has a large role in the food industry, and great potential for development of products for industrial uses. Taro can be consumed roasted, baked or boiled. Giant taro is widely distributed in China and other Southeastern Asian countries. There is a record that the giant taro extract is used in folk medicine against appendicitis, chronic bronchitis and atrophic rhinitis [52].
Phytochemical investigations of taro roots have been conducted (Table 7) [52-56]. Rahman et al. [57] demonstrated that the rhizomes’ extract of A. macrorrhiza have antihyperglycemic, antioxidant and cytotoxic activity [57]. Indole alkaloids exhibited cytotoxicity against four tested human cancer cell lines (HePG2, Hep-2, HCT-116, MCF-7) with the strongest activity (IC50=10 µM) being observed against Hep-2 larynx cancer cells [54]. Isolated lignanamides and monoindoles (Table 7) showed no cytotoxicity to RAW 264.7 cells and moderate antiproliferative activity against CNE-1, MGC-803, MCF-7 cancer lines [52]. 2017). Also, piperidine alkaloids isolated from rhizomes of Alocasia macrorrhiza (Table 7) showed cytotoxicity against human cancer cell lines (CNE-1, Detroit 562, Fadu, MGC-803, and MCF-7) [53]. Alocasin showed antifungal activity against Botrytis cinerea [58]. Another species, Cyrtosperma merkusii is grown in fresh water marshes and swampy areas, its tubers are rich in carotenoids and are known for their high antioxidant activity [59]. Diverse chemical composition might be the cause of a range of activities confirmed for taro roots, from antifungal to antihyperglicemic (Table 8).
Radish
Radishes ( Fig. 7), an economically important crop belonging to the Brassicaceae family, have root which is edible, widely consumed, especially in salads, and has different compounds important for human health (Table 9) [60]. Although entire plant is edible, radishes are known for their edible tuberous roots which can vary in shape, size and diameter [61]. Roots can be eaten as raw vegetables or after processing namely pickling, canning or drying [62]. Salted roots are a traditional Japanese food and are consumed in more than 500 000 tones/year, while Daikon (Japanese white radish) served with soy sauce, boiled fish or mushroom [63, 64]. Radishes are widely cultivated due to high-yield, low-labor requirements, short growing season, and pest-resistant nature [65].
Skin of the taproot can vary in color with red radishes being the most common ones, although there are also pink, white and grey or black skinned varieties [62]. Different varieties include Amethyst (round, purple taproot), Crunchy Royale (round, red taproot), D’ Avingnon (cylindrical, red taproot), Miyashige daikon (cylindrical, white taproot), Nero Tondo (round, black taproot), Ping Pong (round, white taproot), Pink Beauty (round, pink taproot), Red Meat (round, red taproot) and these varieties can differ in antioxidant capacity, anthocyanin content, glucosinolate and isothiocyanate content and activation of the antioxidant response element (ARE) [66].
Different biological activities have been examined for different varieties of radishes (Table 10). Radish has been used in Estonian ethnopharmacology for the relief of tumor symptoms [67]; in India it has been used for health issues like urinary problems and piles [68], while in the Mexican traditional medicine black radish roots are used for the treatment of pigment and cholesterol gallstones, and also for decreasing serum lipid level [69]. It has a potential for probiotic usage due to lactic acid bacterial strains such as Lactobacillus plantarum and Lactobacillus fermentum which could be isolated from fermented radishes [70].
4-(Methylthio)-3-butenyl isothiocyanate, a compound found widely in radishes, belongs to isothiocyanates Fig. (8), a group of compounds that has been proven to exhibit antimicrobial, antimutagenic and anticarcinogenic activities [64]. N-hexane extract of Daikon has significant antimutagenic effect mainly due to 4-(Methylthio)-3-butenyl isothiocyanate and for the best results it should be eaten not later than 30 min after grating [64, 71]. 4-(Methylthio)-3-butenyl isothiocyanate extracted from Tunisian R. sativus showed good chemo-protective effect [72].
Antibacterial properties that are proven for different parts of radish plants, with root being the most active, are not linked to the total isothiocyanate content, but are positively correlated with levels of individual isothyocyanate classes [73]. Root was found to be the most efficient part of the plant also regarding the inhibition of cell proliferation and induction of apoptosis in human cancer cells, with the hexane extract of root having different classes of isothiocyanates which could be responsible for these beneficial effects [74].
Glucosinolates are plant secondary metabolites, precursors of isothiocyanates, with glucoraphasatin (4-Methylsulfanyl-3-butenylglucosinolate) accounting for more than 90% of this class in R. sativus [71]. Spanish black radish is examined as an attractive source of bioactive glucosinolates [65], and its high glucosinolates level have been found to be beneficial in cases of acute toxicity [75]. Granules from black radish root can protect cell membranes against lipid peroxidation; they also protect membrane changes caused by fat rich diet and have beneficial effect on rat colon mucosa [76].
Fig. (8)) General structure of isothiocyanates, group of compounds known for their range of biological activities, found abundantly in radish roots.Beetroot
Beet (Beta vulgaris) is part of the Chenopodiaceae family (Fig. 9). Due to different morphology, cultivated and wild maritime beets are separated in different subspecies. Sea beet (Beta vulgaris subsp. maritima) is the main member of maritime beets. Sugar beets (Beta vulgaris subsp. saccharifera), fodder beets (Beta vulgaris subsp. crassa), leaf beets (Beta vulgaris subsp. cicla) and garden beets (Beta vulgaris subsp. rubra) are the members of cultivated beets.
Beta vulgaris subsp. cicla (Swiss chard) and Beta vulgaris subsp. rubra (Red beetroot) are used as food since 1000 B.C. Even Romans ate their leaves, and used the roots in medical purpose [82].
Red beet variety is the cultivated form of Beta vulgaris subsp. vulgaris (conditiva) and it has twice less sugar than sugar beet. Its taproot has been used in food all over world; it is used as pickles, salad or juice [83].
Red beetroot owes its name to the red color produced by betalain pigment. Various biological activities are confirmed for betalains including antioxidant, anti-cancer, anti-lipidemic and antimicrobial [84].
There is an increasing interest in betalains because of recent trends in the food industry to avoid synthetic colorants, and beet is a valuable source of natural red color. Red color is the result of the mixture of yellow pigments betaxanthins and violet betacyanins (Fig. 10), both members of betalain group [85].
Beetroot is considered among the 10 best vegetables based on its antioxidant capacity thanks to high phenolic content, but probably also on the synergism between individual phenolic compounds as well as between phenolics and betalains (Table 11) [86, 87]. Phenolic content varies between different parts of root and decreases in the order of peel, crown, and flesh [88]. These combinations of compounds increase beetroot value as food and attribute to the wide range of health benefits listed in (Table 12).
Red beet juice is proven to be effective in enhancing athletes’ performance mainly due to high nitrates content, so difference found in nitrate levels between different cultivars is important in selecting the best ones for supplements development [83]. Nitrate level of beetroot is also important for its cardioprotective potential since in vivo it increases the levels of nitric oxide (NO), which is vasoprotective, it retards angiogenesis and has many other pleiotropic effects [89].
Its beneficial effect can be seen also in obese people and may be related to increased plasma NO concentration where even after a single dose of juice (140 ml) it attenuated postprandial impairment of flow mediated dilation of brachial artery [90]. In obese patients it also showed beneficial effects on daily systolic blood pressure [91].
Red beetroot juice has beneficial effects in the treatment of obesity [92] and even one shot (70 ml) could improve antioxidant status due to high polyphenol content [93].
Even wastes in food processing like beetroot pomace could be used for its biological activities, which are probably induced by betalaines and phenolic compounds that remain in this by-product (Table 11) [94]. Its beneficial effects like antioxidant and hepatoprotective have also been confirmed by in vivo studies [95]. Beetroot pomace waste was investigated as additive to ginger candies in order to obtain antioxidant rich candy [96], while red beet juice was found to be the most suitable natural colorant for fresh pork sausages [97]. Beetroot can also be used as additive in bread preparation in order to increase its cardioprotective ability [98].
Parsley
Both leafy and root parsley have been widely used in culinary practice as important spices [110]. Parsley (Petroselinum crispum (Mill) Nym) (Fig. 11) is a biennial plant from the Apiaceae family (Umbelliferae). Parsley was first grown in the Mediterranean region but nowadays is cultivated throughout the world [111]. It has three main types including two types grown for foliage: plain leaf type (ssp. neapolitanum, Danert) and the curly leaf type (ssp. crispum), and one type grown mainly for its taproots: the turnip-rooted or ‘Hamburg’ type (ssp. tuberosum) [112]. Turnip-rooted parsley has been grown primarily in northern Europe, especially Poland, but now it is becoming popular also in the Mediterranean region [113]. Different components are found in the essential oils from roots of turnip-rooted parsley, with a variety of monoterpenes being dominant (Table 13). Monoterpenes are known for its diverse biological activities including antimicrobial [114] and antioxidant [115]. Phenylpropene myristicin has hepatoprotective [116] and chemopreventive activity [117]. Apiole (Fig. (12) is thought to be a major compound contributing to the antioxidant activity of parsley [118].
Parsnip
Parsnip (Pastinaca sativa L.) is part of Apiaceae family, a root vegetable that is frequently used in food preparation and widely consumed partly due to its rich content of fibers (Fig. (13) [119]. Parsnips are more distributed in the production of baby food due to their aromatic taste [120]. Different compounds present in parsnip as well as in other apiaceous vegetables are responsible for its chemopreventive activity represented by the inhibition of some carcinogenic activation (Table 14) [121]. It is used in the traditional medicine of Bulgaria and Italy as cardio-tonic, spasmolytic, hypotensive, coronary dilator, capillarotrophic agent, dietetic, diuretic, and cholagogue [122]. In Bosnia and Herzegovina it is mainly used for stomach malignant diseases [123], which can be explained by its content of polyacetilens falcarinol (Fig. (14) and falcarindiol that are found in parsnip roots (Table 15) and are proven to have preventive effect against the development of colorectal cancer [124].
Yam
This subsection will focus on novel selected studies published in 2017 reporting an update about chemical constituents and biological properties of yam species rhizomes belonging to the genera Dioscorea.
Around 613 tuberous climbing plants are described in the genus Dioscorea (yam) [127]. According to some authors, only seven to ten species of Dioscorea are cultivated on a large scale and only two of them, D. cayennensis subsp. cayennensis and D. cayenennsis subsp. rotundata (Poir.) J. Miège, are of primary importance as staple crops for over 100 million people in Western Africa [128-130]. It was estimated that approximately around 50 species are eaten as wild-harvested staples or famine food and the genus holds great importance for global food security. Dioscorea species have been widely used as traditional medicines in different countries [131].
Four species of Dioscorea have been chemically characterized in 2017, namely D. tokoro, D. bulbifera, D. collettii, and D. septemloba [132-135]. The results of chemical analysis are presented in Table 16 Various phytochemical groups of compounds have been found in Dioscorea species as presented in Table 16.
Health promoting effects of Dioscorea spp. investigated recently are summarized in Table 17. Compounds derived from D. septemloba expressed biological activities, with clear indication that structures of individual compounds have been related to the expressed effects. It was found that one of three diarylheptanoids was active, while more potent compounds were stilbenes [135]. Methyl protodioscin derived from the rhizomes of D. collettii var. hypoglauca was explored for the molecular mechanisms by which it induced apoptosis in osteosarcoma cells (MG-63). Cell growth was significantly suppressed when treated with 8 μM of methyl protodioscin (cell viabilities: 22.5 ± 1.9%) [136]. Saponins isolated from D. collettii, namely dioscin (Fig. (15), protodioscin, gracillin, and protogracill had an obvious anti-hyperuricemic effect through down-regulation of the URAT1 mRNA and the URAT1 and GLUT9 proteins and up-regulation of the OAT1 and OAT3 proteins [137]. A Glycoprotein (DOT) obtained from D. opposita was shown as a potential immunostimulant and DOT exerted its immunomodulatory activity via mitogen-activated protein kinases and NF-κB signal pathways [138].
Salsify
Tragopogon porrifolius L. is commonly referred as white salsify, while Scorzonera hispanica L. refers to black salsify. Underground parts of both species are consumed as edible or used for their health-beneficial effects. This section will briefly summarize the recent findings of chemical constituents and biological properties of these plants.
T. porrifolius of the Asteraceae family is an edible herb and is commonly known as white salsify, oyster plant, and vegetable oyster. It is an annual or biennial herb of 30–125 cm height with lilac to reddish-purple ligules. All parts of the plant are edible, including its roots, leafy shoots, and open flowers which are consumed both cooked and raw [139]. T. porrifolius is widespread throughout the Mediterranean region where it grows wild and it is also cultivated. The nutritional value of this plant has been attributed to its monounsaturated and essential fatty acids, vitamins, polyphenols, and fructooligosaccharides components [140]. White salsify is also considered a medicinal plant as it shows antibilious, diuretic and laxative properties [141, 142].
S. hispanica L. commonly known as black salsify, Spanish salsify or serpent’s root is a perennial herbaceous plant belonging to the Asteraceae family [143]. Its natural distribution encompasses Central and Southern Europe, the Caucasus, and Southern Siberia. After removal of its robust black corky skin, fresh underground parts are boiled and eaten together with other vegetables like carrots or served separately with white sauce similar to asparagus. Nowadays underground parts of S. hispanica are widely cultivated in Western Europe as a vegetable, particular in Belgium [143]. Underground parts of black salsify were used as a coffee substitute [144], as well as to enhance digestion and perspiration, as a diuretic agent [145], and as a remedy for snakebites; this historic usage explains the vernacular name serpent’s root [143].
Since, the whole plant of white salsify is edible, rare studies are conducted focusing on chemical constituents only from roots. Tragoponol, a novel dimeric dihydroisocoumarin was isolated from the roots of T. porrifolius and this compound was reported as the first of its kind [146].
Chemical constituents described in the roots of white salsify are presented in the Table 18. Lipophilic compounds and phenolics were mainly identified.
The cytotoxic activity of the mentioned compounds isolated from black salsify roots was tested as well. It was shown that (-)-syringaresinol Fig. (16) was active against myeloma cell lines. (-)-Syringaresinol, puliglutone and 1-oxo- bisabola-(2,10E)-diene-12-carboxylic acid methyl ester were moderately active against the human colon cancer cell line SW480. Unfortunately, (-)- Syringaresinol showed cytotoxicity not only against cancer cell lines but also against peripheral blood mononuclear cells. Thus, puliglutone and 1-oxo- bisabola-(2,10E)-diene-12-carboxylic acid methyl ester could be interesting further investigations as agents or lead compounds to treat colon cancer [147].
Fig. (16)) Syringaresinol, compound showing anti-cancer properties.Conclusions
A wide range of biological activities could be attributed to selected root vegetables: potato, celeriac, turnips, radish, beets, Hamburg parsley, taro, yam, parsnip and salsify described in this chapter. These root vegetables are consumed worldwide and present important root crops. Biological activities of these vegetables could be attributed to their respected extracts and individual compounds identified in each one of them. However, the literature reporting profound studies to confirm in vivo effects is still scarce, but the results obtained so far are more than promising. As a general conclusion, it is interesting to underline the necessity for further exploration of biological effects of tuber vegetables that bring a lot of health beneficial effects to mankind, while clinical and in vivo studies have to be carried out in order to elucidate the mechanism of action, the main compounds that are responsible for the beneficial effects of these species, as well as the recommended doses in order to achieve these effects.
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CONFLICT OF INTEREST
The author (editor) declares no conflict of interest, financial or otherwise.
ACKNOWLEDGEMENTS
This work has been supported by the Serbian Ministry of Education, Science and Technological Development for financial support (Grant number 173032).
