Showing report on Vegetables
Cabbages belong to the Brassica genus. The main cabbages consumed are all cultivars of the species Brassica oleracea: broccoli (var. italica), cauliflower (var. botrytis), Brussel sprouts (var. gemmifera), kale (var. acephala). Chinese cabbages belong to the species Brassica rapa: pak-choy (var. chinensis) and napa cabbage (var. pekinensis).
Highest contents of total polyphenols (Folin assay) are found for red cabbage (536 mg/100 g) whereas white cabbage shows very low values (15 mg/100 g). With the exception of anthocyanins characteristic of coloured cabbages varieties (no data available in the composition table), all cabbages show similar polyphenol profiles made of complex mixtures of flavonols and hydroxycinnamic acids. Detailed contents for individual phenolic compounds are only available for broccoli, the best documented cabbage.
Flavonols in cabbages are principally kaempferol and quercetin derivatives. The highest levels of flavonols measured after acid hydrolysis are found in pak-choy (9.6 and 39 mg/100 g for respectively kaempferol and quercetin), kale (27 and 7.7 mg/100 g for respectively kaempferol and quercetin), and broccoli (5.6 and 4.2 mg/100 g for respectively kaempferol and quercetin). Isorhamnetin was detected in pak-choy but the only values available are expressed per dry weight (8.1-35.1 mg/100 g DW) and could not be included in the food composition table (150). The flavones apigenin and luteolin are also detected after acid hydrolysis in cabbages, and the highest levels are found in pak-choy (4.5 and 1.2 mg/100 g for respectively apigenin and luteolin) and Savoy cabbage (0.23 and 0.06 mg/100 g for respectively apigenin and luteolin). Flavonols in cabbages are glycosylated at the 3-, 7-, or 3,7- positions with glucose, sophorose and sophorotriose, and acylated with sinapic, ferulic, caffeic or p-coumaric acids. In broccoli, the 2 main flavonols are kaempferol 3-O-sophoroside (17 mg/100 g) and quercetin 3-O-sophoroside (6.5 mg/100g). Fourty six flavonols were identified in broccoli (151), with kaempferol 3-O-sophoroside accounting for up to 90% of the total flavonoids (152). In black cabbage, the most abundant flavonols were kaempferol 3-O-sophoroside-7-O-glucoside, kaempferol 3-O-(2-feruloylsophoroside)-7-O-glucoside, kaempferol 3-O-(2-caffeoylsophoroside)-7-O-glucoside, and quercetin 3-O-(2-caffeoylsophoroside)-7-O-glucoside (51).
Several feruloyl and sinapoyl esters of gentiobiose have been characterised in broccoli, the most abundant being the 1,2-diferuloylgentiobiose (2.6 mg/100 g). Neochlorogenic acid (3-CQA; 5.9 mg/100 g) is the main caffeoylquinic acid derivative, followed by chlorogenic acid (5-CQA; 1.8 mg/100 g). The same compounds were identified in tronchuda cabbage (153, 154). Other cabbages such as Savoy and white cabbage, cauliflower, and Brussels sprouts presented simpler phenolic acid profiles (155).
Anthocyanins in red cabbage are cyanidin 3,5-O-diglucoside, cyanidin 3-O-sophoroside-5-O-glucoside, cyanidin 3-O-diferuloyl-sophoroside-5-O-glucoside and cyanidin 3-O-p-coumaroyl-sophoroside-5-O-glucoside (156). Cyanidin 3-O-sophoroside-5-O-glucoside monosinapate and cyanidin 3-O-sophoroside-5-O-glucoside disinapate were also identified (157).
Eggplant (Solanum melongena L.), aubergine (UK), or brinjal (India) is a member of the Solanaceae family. Eggplant principally contains hydroxycinnamic acids in flesh and anthocyanins in peel. Chlorogenic acid is the predominant compound and accounts for over 75% of the total phenolic acids (158, 159). The main free phenolic acids are protocatechuic acid and caffeic acid (0.58 and 0.38 mg/100 g). Myricetin and kaempferol are also present (respectively 3.9 mg/100 g DW and 8 mg/100 g DW estimated after acid hydrolysis) (149). Eggplant peel contains a major anthocyanin: nasunin (delphinidin 3-O-[4-O-(p-coumaroyl)-L-rhamnosyl-(1->6)glucopyranoside]-5-O-glucopyranoside) (160).
Pepper (Capsicum annuum L.) is a member of the Solanaceae family. Peppers can be sweet (bell pepper) or hot (chilli pepper), according to their pungency. The color (green, yellow, or red) varies according to the maturity stage. Pepper contains flavonoids, phenolic acids, and capsaicinoids. Capsaicinoids are a group of compounds responsible for the hot flavour of Capsicum sp. Capsaicin and dihydrocapsaicin are the two major capsaicinoids (161). The other phenolic compounds identified are coumaroyl, feruloyl, and synapoyl glucosides, and luteolin, chrysoeriol (3’-methyl luteolin), and quercetin O-glycosides, and a large number of C-glycosyl flavones (6-C, 8-C, 6,8-C) (161, 162, 163). Quercetin 3-O-rhamnoside and luteolin 7-O-(2-apiosyl-6-malonyl)-glucoside are the major phenolic compounds found in sweet pepper (respectively 2.2 and 2.1 mg/100 g in green pepper and 0.10 and 0.05 mg/100 g in red pepper). The main aglycones detected after acid hydrolysis are quercetin (from not detected in red sweet pepper to 33 mg/100 g in yellow chilli pepper) and luteolin (from 0.48 mg/100 g in yellow sweet pepper to 4.8 mg/100 g in yellow chilli pepper).
Tomato (Solanum lycopersicum L.) is a member of the Solanaceae family. Polyphenols in tomato are concentrated in the skin, which contributes 52% of the total flavonoids (164), and 98% of the total flavonols (165). Cherry tomato contains more polyphenols than larger size cultivars (165, 166, 167, 168). Main polyphenols in tomato are hydroxycinnamic acids, flavonols and flavanones. The main hydroxycinnamic acids are 5-caffeoylquinic acid (1.84 and 3.7 mg/100 g in respectively tomato and cherry tomato) and 4-caffeoylquinic acid (1.17 mg/100 g in tomato). The main aglycones detected after acid hydrolysis are the flavonol quercetin (1.1 and 4.6 mg/100 g in respectively tomato and cherry tomato) and the flavanone naringenin (0.96 and 3.8 mg/100 g in respectively tomato and cherry tomato). Quercetin accounts for 96% of the total flavonols (165, 169). Quercetin 3-O-rutinoside (rutin) and naringenin 7-O-glucoside (prunin) are the two main flavonoids in tomato. Rutin accounts for 3.3 and 0.14 mg/100 g in respectively cherry tomato and tomato, and prunin for 0.14 mg/100 g in tomato.
Chalconaringenin is the main flavanone in tomato (169, 170). It accounts for 95%-98% of the total flavanones in tomato skin (171). It is also the main phenolic compound in unripe cherry tomatoes (7.4-28 mg/100 g) (170), but a large decrease occurs during postharvest storage (from 15 mg/100 g at harvest to 0.41 mg after 3 weeks at 20°C in darkness) (172, 173). Acid hydrolysis and the extraction procedures induce the cyclization of chalconaringenin into naringenin (171, 174). This could explain why most of the published composition data are for naringenin rather than chalconaringenin.
Gourds belong to the Cucurbitaceae family and contain numerous species and cultivars. The composition table shows data for some of the most largely consumed gourds, such as cucumber (Cucumis sativus), squash (US) or marrow (UK), zucchini (US) or courgette (UK) or baby squash/marrow, and pumpkin (all derivated from Cucurbita pepo and Cucurbita maxima). Muskmelon (Cucumis melo) and its cultivars cantaloupe and honeydew, and watermelon (Citrullus lanatus or Citrullus vulgaris) are principally consumed as fruits. Few studies have been published on the polyphenols found in gourds; those available are focused on specific classes of polyphenols in a given gourd: cinnamic acids in sponge gourd (Luffa cylindrica) (175) and bitter melon (176), apigenin and luteolin derivatives in chayote (177), and astilbin, catechin and naringenin in wax gourd (Benincasa hispida) (178). The main reported compounds are syringic and chlorogenic acids (resp. 2.0 and 1.9 mg/100 g in pumkin), and the luteolin aglycone quantified after acid hydrolysis (2.6, 1.8, and 1.6 mg/100 g in respectively muskmelon, watermelon and pumpkin). Quercetin 3-O-rutinoside was quantified in zucchini (1.3 mg/100 g). No data are available for gherkin (Cucumis anguria).
The main polyphenols found in lettuce (Lactuca sativa L.), endive (Cichorium endivia L.) and chicory (Cichorium intybus L.) are hydroxycinnamic acids, notably the 5-caffeoylquinic acid (chlorogenic acid), the monocaffeoyltartaric acid (caftaric acid) and the dicaffeoyltartaric acid (chicoric acid). Lettuce, endive, and chicory are also characterised by the presence of flavones and flavonols, principally quercetin in lettuce, kaempferol in endive, and quercetin and luteolin in chicory. These flavones and flavonols are present as both glycosides and glucuronides. The red cultivars additionally contain anthocyanins: cyanidin 3-O-glucoside, cyanidin 3-O-(6’’-malonyl-glucoside) and delphinidin 3-O-(6’’-malonyl-glucoside). They are also richer in polyphenols than the other cultivars.
In lettuce, 5-caffeoylquinic acid is the main compound (3.8 mg/100 g in green lettuce). The two main flavonols are quercetin 3-O-glucuronide (1.3 and 2.6 mg/100 g in respectively green and red lettuce) and quercetin 3-O-(6’’-malonyl-glucoside) (1.8 and 10 mg/100 g in green and red lettuce).
In endive, more than 75% of the total polyphenols are caffeoyl esters, and dicaffeoyltartaric esters represent more than 50% of the total polyphenols (179), but no detailed quantitative data are available for these phenolic acids. The two main flavonols in endive are kaempferol 3-O-glucuronide (18 and 15 mg/100 g in respectively curly and escarole endive) and kaempferol 3-O-(6’’-malonyl-glucoside) (3.7 and 2.3 mg/100 g in curly and escarole endive).
In chicory, the main polyphenols are 5-caffeoylquinic acid (56 and 117 mg/100 g in respectively green and red chicory) and chicoric acid (50 and 64 mg/100 g in green and red chicory). Caffeoyltartaric acid was detected in green chicory (19 mg/100 g), but not in red chicory. High levels of free gallic and protocatechuic acids were reported in green (respectively 26 and 22 mg/100 g) and red chicory (respectively 15 and 17 mg/100 g). The main flavonol in chicory is quercetin 3-O-glucuronide (8 and 50 mg/100 g in green and red chicory). Red chicory contains significant levels of luteolin 7-O-glucuronide (3 and 61 mg/100 g in green and red chicory).
Spinach (Spinacia oleracea L.) is a rich source of polyphenols. It contains high levels of flavonols unique to spinach (119 mg/100 g). They are mainly quercetagetin (6-hydroxyquercetin) derivatives (180). Quercetagetin aglycones are mono- (patuletin), di- (spinacetin), or tri- (jaceidin) methylated. These compounds are glucuronidated and acylated with ferulic and coumaric acids. The major compound is the 5,4'-dihydroxy-3,3'-dimethoxy-6:7-methylenedioxyflavone 4'-O-glucuronide (37 mg/100 g). The 5,3',4'-trihydroxy-3-methoxy-6:7-methylenedioxyflavone 4'-O-glucuronide was also reported to be the major flavonoid in baby spinach (181). Other compounds in spinach were scarcely studied, although some like p-coumaric acid contribute significantly to its antioxidant activity (182, 183). Spinach also contains 7.9 mg/100 g kaempferol and 5.9 mg/100 g quercetin estimated after acid hydrolysis.
Swiss chard (Beta vulgaris var. cicla) belongs to the same species as red beetroot (Beta vulgaris var. rubra). However, Swiss chard is consumed for the leaves or for the stems, while red beetroot is consumed for the roots. The contents of total polyphenols (Folin assay) are 1320 mg/100 g in red leaf and 830 mg/100 g in white leaf. Free syringic acid is an important compound in Swiss chard, with 45 mg/100 g obtained after hydrolysis in the red and white leaves. The main flavonoids identified in leaves of green and yellow cultivars were vitexin 2''-O-xyloside and its 6''-O-malonyl ester, which together comprise over 60% of the total flavonoids, and kaempferol 3-O-gentiobioside, isorhamnetin 3-O-gentiobioside and isorhamnetin 3-O-vicianoside (184).
For dandelion (Taraxacum officinale Web.), very little information is available. Two coumarins (esculin and cichoriin) and caftaric and chicoric acids were reported (185). No quantitative data is provided in the composition table.
Onion, shallot, and leek belong to the Alliaceae family. Onion (Allium cepa L. var. cepa) and shallot (Allium cepa L. var. aggregatum G. Don) share similar polyphenol profiles. Polyphenol content in onions differ according to their color: red onions show the highest and white onions the lowest content values. Yellow onions show intermediate content values of polyphenols.
The main polyphenols in onions are flavonols. Quercetin is the main flavonol (17, 12 and 3.2 mg/100 g in respectively red, yellow and white onions as measured after acid hydrolysis). It is largely present in glycosylated forms: quercetin 3,4'-O-diglucoside (101, 36 and 3.1 mg/100 g in respectively red, yellow and white onions) and quercetin 4'-O-glucoside (44, 23 and 2.2 mg/100 g in respectively red, yellow and white onions). These two quercetin glycosides represent over 80% of the total flavonoids in onion (186, 187). Shallot contains 75 mg/100 g quercetin 3,4'-O-diglucoside and 36 mg/100 g quercetin 4'-O-glucoside. Up to 20 additionnal minor flavonol derivatives have been detected in onion: quercetin mono-, di- and tri- glucosylated at the 3-, 7- and 4’- positions, and isorhamnetin, dihydroquercetin, and taxifolin glucosides (188, 189, 190, 191). Red onion contains 9 mg/100 g anthocyanins represented by cyanidin and delphinidin derivatives, but peonidin, petunidin and pelargonidin derivatives were also identified (192, 193, 194). Red onion contains several malonyl esters of cyanidin glucosides (195, 196). The 4 major anthocyanins were cyanidin 3-O-glucoside, cyanidin 3-O-laminaribioside, cyanidin 3-O-malonyl-glucoside and cyanidin 3-O-malonyl-laminaribioside (189, 192).
Polyphenol concentrations vary according to the part of the onion considered. Free quercetin is only detected in dry skin and the levels of quercetin glycosides decrease from the outer to the inner parts of the bulb (197, 198, 199, 200). During boiling, 25-30% of quercetin glycosides is leached into the water (201, 202, 203). Quercetin glycoside content also decreases by 20-25% upon frying for 40 min (202, 203). Microwave cooking for 1 min increased quercetin glycoside content by 1.5x but did not result in significant changes in total polyphenols (Folin assay) (202). Anthocyanins in red cultivars are largely concentrated in the skin (191). After homelike peeling, the edible portion still contained 79% of the total content of quercetin 4'-O-glucoside but only 27% of the anthocyanins (194). Storage for 6 weeks resulted in a decrease of 64-73% of the total anthocyanins (194). In shredded onion, acylated anthocyanins were more stable than non-acylated anthocyanins.
Detailed data for the quantitative and qualitative polyphenolic profile in leek (Allium porrum L.) are lacking. Five flavonoid glycosides based on kaempferol aglycone were isolated from the bulb of leek (204). Kaempferol content measured after acid hydrolysis was 2.7 mg/100 g.
Carrot cultivars are subdivided into the Eastern or anthocyanin group (Daucus carota spp. sativus var. atrorubens Alef.) and the Western or carotene group (Daucus carota spp. sativus var. sativus) (205). Phenolic acids are the main polyphenols in carrot. The main phenolic acid in carrot is the 5-caffeoylquinic acid (8.9 mg/100 g). In black carrot, 40 phenolic acids have been identified (206). Carrot also contains feruloyl and coumaroyl quinic acids and phenolic acids esterified to the cell wall (4-hydroxybenzoic acid, ferulic acid and ferulic acid dehydrodimers) (207, 208, 209). Low levels of the furanocoumarins 5-methoxypsoralen and 8-methoxypsoralen were detected in fresh carrot (210). Black carrot additionally contains anthocyanins (211). The main anthocyanin is the feruloyl ester of cyanidin xylosyl-glucosyl-galactoside which represents 43-84% of the total anthocyanins (212). Storage and processing influence the content of polyphenols in carrots. In fresh ready-to-use shredded carrots, 5-caffeoylquinic acid and 4-hydroxybenzoic acid increased in air at 4°C after 7 days of storage (213). During cold storage, the total polyphenols (Folin assay) in whole carrot also increased (214).
The colour of red beetroot (Beta vulgaris var. rubra) is due to the betacyanin pigments. The two main betacyanins in red beetroot are betanin (520 mg/100 g DW) and isobetanin (15 mg/100 g DW) (215, 216). Moisture content was not given in these sources. This is why these values could not be included in the table. Betanin content would be approx. 52 mg/ 100 g for a moisture content of 90%. Cell walls of red beetroot also contain free ferulic acid and ferulic acid dehydrodimers (217, 218).
Anthocyanins are the main studied compounds in red radish (Raphanus sativus var. sativus). However, quantitative data are lacking and these compounds were not inserted in the database. All anthocyanins in red radish are based on pelargonidin 3-O-sophoroside-5-O-glucoside (raphanusin). This compound is found mono- or di- acylated with cinnamic (coumaric, ferulic, and caffeic) or malonic acids (219, 220, 221, 222). Phenolic acids were detected in white radish, with coumaric and ferulic acids as the main hydroxycinnamic acids (223).
Burdock root is a popular vegetable in Taiwan and Japan. It belongs to the species Arctium lappa and Arctium minus. The caffeoylquinic acids are the main phenolic compounds in burdock root. They are mainly represented by 5-caffeoylquinic acid (127 mg/100 g). The other detected caffeoylquinic acids are: 1,5-di-O-caffeoylquinic acid, 1,5-di-O-caffeoyl-3-O-succinylquinic acid, 1,5-di-O-caffeoyl-4-O-succinylquinic acid, 1,5-di-O-caffeoyl-3,4-di-O-succinylquinic acid, and 1,3,5-tri-O-caffeoyl-4-O-succinylquinic acid (224, 225). These compounds were mostly present in the skin of burdock root (226).
Celeriac (Apium graveolens L. var. rapaceum) belongs to the same species as celery and is consumed for the root. Furanocoumarins (5-methoxypsoralen, 8-methoxypsoralen, isopimpinellin) were found in juices (227). The phenolic acids 5-caffeoylquinic acid, 3-p-coumaroylquinic acid, and 3-feruloylquinic acid were detected in 11 celeriac cultivars (228). No quantitative data for these compounds were inserted in the database.
Parsnip (Pastinaca sativa L.) contains linear (psoralen, 5-methoxypsoralen or bergapten, 8-methoxypsoralen or xanthotoxin, trioxsalen) and angular (angelicin) furanocoumarins (229, 230, 231, 232), but no composition data are available in the composition table. Furanocoumarin concentration in moldy parsnips stored at –18°C during 50 days was below 2.5 mg/kg, while storage of the freshly harvested parsnip 38 days at 4°C resulted in an increase up to 49 mg/kg (232). Peeling removed about 30% of the furanocoumarins, and cooking of the roots had no appreciable effect (230).
Turnip (Brassica rapa var. rapa) and swede (Brassica napus var. napobrassica) contain flavonols and flavones. Estimated after acid hydrolysis, swede contains 3.8 mg/100 g apigenin, 2.1 mg/100 g myricetin, and 0.57 mg/100 g kaempferol.
Asparagus (Asparagus officinalis L.) contains 46 mg/100 g total polyphenols (Folin assay). The main documented compound is quercetin 3-O-rutinoside (23.2 mg/100 g). Several ferulic acid dehydrodimers are detected (5,5’-, 8,4’-, 8,5’-, 8,8’), but no composition data were inserted in the database. They are ester and ether linked to the cell wall and released by alkaline hydrolysis (233). Several other cinnamic acids were reported: 4-hydroxybenzoic acid, caffeic acid, vanillic acid, syringic acid, p-coumaric acid, syringaldehyde (234).
In globe artichoke (Cynara cardunculus var. scolymus L.), the edible part is the head which comprises the artichoke heart and the internal tender bracts. Globe artichoke is a rich source of polyphenols with 1.1 g/100 g total polyphenols (Folin assay) in head. The polyphenol profile is complex with 22 major compounds identified in head, juice, and pomace (235). The predominant compounds are hydroxycinnamic acids and flavones. The main hydroxycinnamic acid in artichoke head is 5-caffeoylquinic acid (202 mg/100 g). 1,5-Dicaffeoylquinic acid is another major compound in artichoke head, while it is 1,3-dicaffeoylquinic acid in juice (235). The main flavonoids in artichoke head are the flavones apigenin 7-O-glucuronide (7.4 mg/100 g), luteolin 7-O-glucuronide (8.3 mg/100 g) and the luteolin aglycone (42 mg/100 g).
Celery (Apium graveolens var. dulce) belongs to the same species as celeriac. Celery is consumed for the stalk, while celeriac is consumed for the root. The cutting celery (var. secalineum) corresponds to the leaf consumed as an herb. Celery stalk contains low amounts of polyphenols (14 mg/100 g in stalk; Folin assay) and limited data on its composition is available. The main polyphenols in celery stalk are furanocoumarins and flavones. The furanocoumarins are subdivided in linear furanocoumarins or psoralens (psoralen, 5-methoxypsoralen or bergapten, 8-methoxypsoralen or xanthotoxin, isopimpinellin, trioxsalen), and angular furanocoumarins (angelicin). The most predominant furanocoumarins in celery stalk are bergapten (1.1 mg/100 g) and xanthotoxin (0.76 mg/100 g). They respectively represented 68% and 63% of the total furanocoumarins in 88 celery samples (231). The flavones apigenin (5.15 mg/100 g) and luteolin (1.38 mg/100 g) are the main aglycones detected in celery stalk after acid hydrolysis.
Swiss chard stem contains less polyphenols than Swiss chard leaves, with 410 mg/100 g total polyphenols (Folin assay) in red tissues and 290 mg/100 g in white tissues. Swiss chard stem contains 7.5 mg/100 g free syringic acid in red tissues and 1.5 mg/100 g in white tissues.
Potato (Solanum tuberosum L.) belongs to the Solanaceae family. Polyphenol content in potato is relatively low due to the dilution with starch. Chlorogenic acid is the main compound detected (14 mg/100 g). It accounts for almost 90% of the total polyphenols (236, 237, 238). Several other minor phenolic acids were identified (236, 239, 240, 241, 242) and some flavonoids were also detected (236). These compounds are much more concentrated in the peel (236, 243). Colored potatoes also contain acylated anthocyanins (244). The acylated anthocyanins are based on 3-O-(p-coumaroyl-rutinoside)-5-O-glucoside derivatives of peonidin, petunidin, pelargonidin, or malvidin depending on the cultivar colour (236, 245, 246). Colored potatoes contain almost twice the concentration of phenolic acids of white-skinned tubers (245).
Cooking by conventional and microwave oven reduced the content of total polyphenols in potato by about 20% (247). Oven-baked potatoes contained no more 5-caffeoylquinic acid whereas microwaved potatoes still contained 55% of the original amount of 5-caffeoylquinic acid (248). Around 70% loss of 5-caffeoylquinic acid was observed in boiled potatoes (248, 249). These losses were largely related to the high rate of diffusion of 5-caffeoylquinic acid in water (249). Steaming resulted in a higher retention of caffeic acid derivatives compared with boiling, microwaving, and frying (238). Commercially processed French-fried potatoes, mashed potato flakes and potato skins contained no 5-caffeoylquinic acid (248). Fresh cutting induces the biosynthesis of three flavonols identified as quercetin 3-O-rutinoside, quercetin 3-O-diglucoside and quercetin 3-O-glucosyl-rutinoside, the content of which increases during the following days of cold storage (238).