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Table 1 Overview of the selected studies on green-leafy vegetables

From: Food intake biomarkers for green leafy vegetables, bulb vegetables, and stem vegetables: a review

Dietary
factor
InterventionDose of interventionStudy designnAnalytical methodSample typeCandidate biomarkers of food intakePrimary reference
Spinach
 Just-boiled fresh spinach1.2 kgAcute single dose8HPLC-UVPlasma (after 3 h)Chlorophyll-related compounds (CRCs) (pheophytin (Phe) and pheophorbide (Pho))[46]
 Vegetable together with fried rice200 gFirst study: acute single doses (4 distinct treatments: spinach, celery, onion, no vegetables)
Second/third studies confirmation: singles doses or combinations
10 (and 3 for secondand third)LC−MS (UPLC and Q-TOF MS) (untargeted metabolomics)Urine (up to 7 h)4-guanidino-butanoic acid with an Isoprene modification (tentative identification)[47]
 Spinach-containing diet–frozen spinach thawed and cooked453 g spinach/day2-arm cross-over intervention (2 × 3 weeks)7Atomic absorption spectrophotometry (Faecal, urinary, and dietary calcium and zinc levels)
kits for oxalate and hydroxyproline-assays
UrineHydroxyproline[48]
 Freeze-dried 13C-labeled spinach5 g (providing 160 μmol methoxyflavonols, including 70 μmol TMM4’-glucuronide)Acute single dose5UHPLC-MSnPlasma (up to 24 h)13C17TMM-glucuronide
13C17TMM-sulfate
13C16Patuletin-glucuronidesulfate-methyl
12C113C16Spinacetinglucuronide-sulfate
13C17Spinacetinglucuronide-sulfate
[49]
Lettuce
 Fresh lettuce250 gAcute single dose11HPLC-CoularrayPlasma (up to 6 h)ρ-coumaric acid
Caffeic acid
[50]
Endive
 Endive soup (300 g) with a slice of white bread150 g (precooked mass) of endive = 9 mg kaempferolAcute single dose8LC/MSplasma and urine (up to 24 h)Kaempferol-3-glucoside
Kaempferol-3-glucuronide
[51]