Zn in vegetables: A review and some insights

Abstract

Zn is an important element in both industrial and biological sense. The great industrial importance of Zn has made this element a potential hazard to vegetable consuming humans. In this review, the important biological role of Zn and the human Zn dietary requirement as well as its toxicity are discussed. The Zn in various commonly consumed vegetables have also been reviewed. Based on a range to previous studies, it is confirmed that human activities such as metal mining and smelting as well as the application of manure fertilizer could contribute to Zn enrichment in both cultivation soil and the vegetable tissues. Zn in vegetable tissues also been discovered to have a strong and positive correlation with some element such as K, Fe, Mn and Cd. Due to Zn’s industrial importance, it will always be a possibility of the occurrence of high Zn enrichment due to anthropogenic activities. Despite the biological importance, the constant monitoring of Zn in various food crops should not be neglected.

Full text

Review Article
Integrative Food, Nutrition and Metabolism
Integr Food Nutr Metab, 2019 doi: 10.15761/IFNM.1000245 Volume 6: 1-7
ISSN: 2056-8339
Zn in vegetables: A review and some insights
Koe Wei Wong1, Chee Kong Yap1*, Rosimah Nulit1, Hishamuddin Omar1, Ahmad Zaharin Aris2, Wan Hee Cheng3, Mohd Talib Latif4 and
Chee Seng Leow5
1Department of Biology, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor Malaysia
2Department of Environmental Sciences, Faculty of Environmental Studies, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor Malaysia
3Inti International University, Persiaran Perdana BBN, 71800 Nilai, Negeri Sembilan, Malaysia
4School of Environmental and Natural Resource Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
5Humanology Sdn Bhd, 73-3 Amber Business Plaza, Jalan Jelawat 1, 56000 Kuala Lumpur, Malaysia
Background
e ability of human to discover and utilize natural heavy metal
resources has been an indispensable factor in advancement of human
civilization. e term “heavy metal” can be scientically dened as the
metal (e.g. copper, zinc, iron, cadmium, lead as well as various rare
earth elements) and metalloid (e.g. arsenic) elements comprised in
Groups 3 to 16 that are in periods 4 and greater in periodic table [1].
Ecological and human health risks is imminent due to continuous and
chronic exposure of these elements [2,3]. Since metals are exists in form
of chemical element, these metal and metal containing compounds are
non-biodegradable and may accumulate and magnied in concentration
up to harmful level along food chain [4,5]. e ecological and biological
impact of these elements has been element specic and vary due to their
chemical property and their chemical forms [6].
Zinc is an essential trace element that poses great importance in
human dietary nutrition and health [7-9]. erefore, it is known to be
the second most abundant trace metal in human body aer iron [9]. It is
consisting 2-4 g within a human body mass with plasma concentration
of 12-16 µM [8]. e role of zinc on human health was originally
observed and reported by Prasad et al. [10]. Since there is no specialized
Zn storage system in human body, daily intake of Zn is necessary to
maintain a steady state [8].
e objective of this review is to summarize the role of Zn in
human physiology, the hazard of its enrichment and its appearance in
commonly consumed vegetables.
Human zinc dietary requirement
e human zinc diet can be aected by the many factors. One of
the factors is the type of food consumed. e resorption of Zn will be
poorer from vegetarian foods in comparison of meat diet [8]. is is
*Correspondence to: Chee Kong Yap, Department of Biology, Faculty of
Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor Malaysia,
E-mail: yapckong@hotmail.com
Received: January 19, 2019; Accepted: February 04, 2019; Published: February
08, 2019
Abstract
Zn is an important element in both industrial and biological sense. e great industrial importance of Zn has made this element a potential hazard to vegetable
consuming humans. In this review, the important biological role of Zn and the human Zn dietary requirement as well as its toxicity are discussed. e Zn in various
commonly consumed vegetables have also been reviewed. Based on a range to previous studies, it is conrmed that human activities such as metal mining and smelting
as well as the application of manure fertilizer could contribute to Zn enrichment in both cultivation soil and the vegetable tissues. Zn in vegetable tissues also been
discovered to have a strong and positive correlation with some element such as K, Fe, Mn and Cd. Due to Zn’s industrial importance, it will always be a possibility of
the occurrence of high Zn enrichment due to anthropogenic activities. Despite the biological importance, the constant monitoring of Zn in various food crops should
not be neglected.
due to the chelation of zinc by non-digestible plant ligands such as
dietary bers, phytates and lignin [9].e appearance of other cations
could also aect zinc availability. e resorption could also be reduced
by increased bivalent cations, such as iron, cadmium, nickel, calcium,
magnesium and copper [9,11,12].
e recommended daily intake of zinc is dependent to several
factors: age, sex, weight and the phytate content of diet [9]. e
recommended values are also diering in each country and international
regulatory organizations. e United States Food and Nutrition Board
recommended daily intake of 11 mg and 8 mg for adult male and female
respectively [13]. German Society of Nutrition’s recommendation was
set at 10 mg and 7 mg for adult male and female respectively [9]. Due to
their impact on zinc availability to human diet, the dietary phytate must
not be ignored in assessing zinc bioavailability to human. World Health
Organization categorized the potential absorption eciency of zinc, per
phytate zinc molar ratio into three groups; high (<5), moderate (5-15)
and low (>15) [14]. European Food Safety Authority (EFSA) have also
made similar categorization according to dietary phytate intake [15].
Due to the dierence of dietary zinc requirement by ages, sex,
weight and phytate ingestion [9,14,15]. ese factors must be taken
consideration when the potential health risks of dietary zinc be assessed.
e assessment of zinc related health risks must be built upon relevant
localized data. e average bodyweight and food ingestion behavior
across populations may be vastly dierent according to their religion,

Wong KW (2019) Zn in vegetables: A review and some insights
Integr Food Nutr Metab, 2019 doi: 10.15761/IFNM.1000245 Volume 6: 2-7
ethnicity and their individuals’ societal norms. ese dierences must
be taken account when health risk assessment will be done.
Biological roles and health benets
Zinc has been known to be essential to multiple crucial biological
processes. Zinc is a major component of protein ligands, it was
discovered to present in approximately 3000 human proteins based on
zinc signature motif in protein sequences [16-19]. e amount of zinc
proteins in human zinc proteome will even be larger when additional
functions of zinc in regulation [20]. Zinc is also involving in various
cellular functions.
One of the roles of zinc playing in human biology is immunity
[21,22]. Zinc deciency can result in immunodeciency [8]. Zinc ions
are crucial element in the regulation of intracellular signaling pathway
in innate and adaptive immune cells [21]. Immune systems is known
to be susceptible to alteration in zinc levels and every immunological
response by human body is related to zinc in varying extend [9]. ere
are two immunological mechanisms in human physiology; innate
and adaptive immunity. Innate immunity is the rst line of human
biological defense countering various forms of pathogens. Innate
immunity of human consists of polymorphonuclear cells (PMNs),
macrophages, and natural killer cell (NK). Zinc deciency is associated
to reduced PMN chemotaxis and phagocytosis. Deciency as well as
excess of zinc could also inhibit the activity of nicotinamide adenine
dinucleotide phosphate (NADPH) oxidase, which functions to destroy
pathogens aer it was phagocyted [23,24]. Chelation-free zinc was
also be observed to abolish the formation of neutrophil extracellular
traps (NETs) in vitro. is is a matrix of DNA, chromatin, and granule
proteins that capture extracellular pathogenic protein [25]. Zinc also
plays a role in the process of adhesion of monocytes to endothelial cells.
In the context of human umbilical endothelial cells, its zinc levels were
shown as inhibitive to monocyte adhesion to endothelial cells. It was
suggested as one of the key factors in the early stages of antherogenesis
[26]. Zinc is also heavily involved in production and signaling of
various inammatory cytokines in variety of cells [27]. Overweight
and obese adults with low dietary zinc intakes were observed to
have lower plasma zinc concentration, intracellular zinc content and
intracellular free zinc levels. Upregulated IL-1α, IL-1β and IL-6 genes
were also observed for these patients in comparison of those with
sucient zinc intake [28]. Besides these aforementioned cytokines,
zinc deciencies in humans also inuencing the production of IL-2 and
TNF-α [29]. e supplementation of zinc to patients caused decreased
expression of TNF-α, IL-1β in their phytohemagglutinin-p-stimulated
mononuclear cells, showing their antagonistic relationship. While
zinc supplementation was showed to increase the expression of IL-2
and IL-2Rα [30]. Zinc deciency is also associated with the damage of
lysosome integrity causing the activation of MLRP3 (ACHT, LRR, and
PYD domains-containing protein 3) inammasome, leading to IL-1β
activation [31]. Zinc deciency causes severe impairment of human
immune function. On the ip side, excessive zinc could also provoke
similar immune impairment as zinc deciency does. Excessive zinc
could cause the suppression of T and B cell function, overload of Treg cell
and direct activation of macrophages [21]. Worse inammatory prole
was observed in zinc decient institutionalized elders [32].
Besides regulating immunity related cytokine and suppress of
inammation, zinc also have their importance in the function of lipid
and glucose metabolism, reduction of oxidative stress, regulation and
formation of insulin [33]. e formation of reactive oxygen species
(ROS) and also the reactive nitrogen species could be inhibited by
physiological concentration of zinc [34,35]. ere are a few factors
contributing on the antioxidation eect of zinc. ese was achieved by:
(i) regulate oxidant production and metal-induced oxidative damage;
(ii) associating itself with sulfur in protein cysteine cluster, from which
metals can be released by nitric oxide, peroxides, oxidized glutathione
and other thiol species; (iii) induction of metallothionein, a zinc binding
protein that can act as oxidant scavenger; (iv) regulating glutathione
metabolism and protein thiol redox status; and (v) regulating redox
signaling directly as well as indirectly [36]. As a cofactor of antioxidant
enzyme Cu, Zn-super oxide dismutase (SOD1), zinc is an important
factor in keeping Cu, Zn-SOD functionable [37]. Glutathione peroxidase
expression could also be increased by zinc supplementation [38]. It
must be noted that zinc does not always antioxidative, prooxidative
properties could also be dominant when intracellular zinc levels are
high. Zinc oxide nanoparticle has been shown to increase oxidative
stress in 3T3-L1 adipocyte in a dose dependent manner despite
increasing the expression of antioxidant enzymes [39,40]. Higher dose
of zinc oxide nanoparticle was observed to severely increased oxidative
stress at high doses (10 mg/kg) [41].
Tight interaction between zinc and adipose dysfunction is a major
interest in lipid metabolism study [33]. It has been reported that
zinc supplementation can results in reduced total cholesterol, LDL
cholesterol and triglycerides; as well as increase in HDL cholesterol level
in patients [38,42]. Zinc nger protein ZNF202, as the name suggest,
is a zinc containing protein that are involving in HDL metabolism
[43]. is proteins was suggested as a candidate susceptibility gene for
human dyslipidemia [44]. Decrease in zinc plasma concentration has
resulted in worse lipid prole in zinc decient institutionalized elders
[32]. Zinc status was tightly associated to adipose tissue in obesity and
its pathologies. High fat intake has resulted in decrease of zinc level
in adipose tissue of Wistar rats and is tightly related with excessive
adiposity, inammation, insulin resistance and potentially atherogenic
changes [45].
Zinc is essential in normal synthesis, storage and secretion of
insulin in pancreatic β cells [33,46]. Zinc supplementation has been
benecial to the glucose homeostasis of diabetic patients [47] and vice
versa [48]. is metal have been known to playing a role in glycolysis
stimulation, gluconeogenesis inhibition and modulation of glucose in
adipocytes [49]. e contribution of zinc in insulin biosynthesis and
storage is by forming a hexamer with proinsulin molecules along with
calcium. is proinsulin hexamer assembly could form a protective
structure that protected some polypeptide chain from proteolytic
cleavage, while leaving C-peptide segment of pro insulin exposed to
processing enzymes. e alteration of solubility of proinsulin hexamer
to insulin hexamer and subsequently crystalized insulin hexamers
giving further protection of newly formed insulin chains and separating
proinsulin from insulin as the conversion to insulin occurring. Insulin
hexamers are also enjoys greater chemical and physical stability than its
monomer counterpart [50]. erefore, the formation and crystallization
of proinsulin/insulin hexamer with zinc and calcium ions stabilizes
insulin and protects it from degradation. Beside taking part in insulin
biosynthesis, storage and crystallization, zinc is also known to be
inhibitive to glucagon secretion [51]. Glucagon is a hormone that its
function is opposite of insulin’s. Zinc supplemented diabetic patients
was resulted in elevated insulin and serum zinc coupled with reduced
blood glucose, glucagon and glucose-6-phosphatase, indicating the role
of zinc in physiological glucose regulation [52].
Zinc is also a key element in the growth and development of
human. Zinc deciency during embryogenesis may inuence the
nal phenotype of all organs. Fetal growth may also inuence by zinc

Wong KW (2019) Zn in vegetables: A review and some insights
Integr Food Nutr Metab, 2019 doi: 10.15761/IFNM.1000245 Volume 6: 3-7
restriction during pregnancy. Sucient zinc supplementation reduced
the risk of pre-term birth [53].
Zinc toxicity to human
Despite the apparent biological importance of zinc, acute as well as
chronic exposure to overly high concentration of zinc could also bring
detrimental impact to human health. e manifestation of acute zinc
poisoning could include nausea, vomiting, diarrhea, fever and lethargy.
While long term chronic exposure to excessive zinc levels could resulting
in metabolic interference with other trace elements. Daily intake of
150-450 mg of zinc have been related to reduction of copper utilization,
alteration of iron function, reduction of immune function, as well as
the reduction of high-density lipoprotein (HDL) level [54,55]. Zinc
has been discovered to have an antagonistic relationship with copper.
erefore, zinc has been utilized to treat Wilson disease, an autosomal
recessive disorder of copper metabolism since 1960s. However, copper
is still an essential element crucial for the survival of human being,
imbalance in zinc intake may cause an induction of copper deciency
(hypocupremia) [14,56,57].
Chronic enriched zinc intakes could result in various chronic
eects in gastrointestinal, hematological, and respiratory system along
with alteration in cardiovascular and neurological systems of human
[57]. Human subjects supplemented with 300 mg zinc per day has
been characterized to have elevated LDL cholesterol and reduced HDL
cholesterol [58]. Cu, Zn SOD antioxidant is very sensitive toward
Zn/Cu ratio changes in plasma. Zinc supplementation may result in
excess of free radicals that are detrimental to plasma membrane. e
competition between zinc and iron will also causing a decrease if serum
ferritin and hematocrit concentration [57]
Zn in vegetables
Vegetable representing a signicant portion of recommended
human daily diet due to its richness in essential nutrients while low
in fat, sodium and calories [59]. As discussed in previous section, Zn
is considered as an essential element for human survival. However,
an excess of it will jeopardize human health, causing health risk
to human being. is review will present some of the recent studies
that investigated the concentration of Zn in a variety of commonly
consumed vegetables in several locales. ese studies have been
presented in Table 1.
Zn is essential not only to humans, but also to food crops
themselves. ere are a numerous studies that conrms the positive
correlation of Zn in plant tissues and Zn in surrounding habitat [60-
62]. An experimental exposure of 5 mM and 10 mM of Zn to common
bean, Phaseolus vulgaris, has revealed a positive Zn accumulation
in consequence of the exposure [60]. Another study that samples
common purslane Portulaca oleracea in Costa da caparica, Portugal,
also revealed similar pattern of Zn accumulation. However, due to high
Zn contamination in two of their sites, the P. oleracea from those sites
were highly contaminated and consumption were deemed unsafe [61].
Ribwort plantain, Plantago lanceolata L., is a roadside and grassland
ora that is widely used as food and herbal preparation in various
countries. Drava et al. compared the Zn levels in P. lanceolata in a series
of sites with varying anthropogenic characteristics. ey revealed that
Vegetable species Zn concentration in vegetables Findings Exposure concentrations/sample
collection site Reference
Common beans (Phaseolus vulgaris)
− Positive Zn accumulation resulted from Zn exposure.
− Reduced Zn during pods
− Reduced phytic level
5 mM, 10 mM [60]
Brassica juncea − B. juncea is more Zn tolerant in the perspective of root
damage and microelement homeostasis alteration.
− Oxidative components were predominant compared to
nitrosative components in root.
0-300 µM [67]
Brassica napus
Common Purslane (Portulaca
oleracea)
− P. oleracea collected in two stations contaminated
with high concentration of Zn. Consumption should be
avoided.
Costa da caparica, Portugal [61]
Wheat (Triticum aestivum L.)
− Oxidative stress was minimized, and root, shoot and
spike length were increased coupled with potassium.
− Enhancement of fresh and dry biomass coupled with
potassium
− Enhancement of photosynthetic pigment and osmolyte
regulator (proline, total phenolic and total carbohydrate),
coupled with potassium.
− K and Zn reduced MDA content, increased membrane
stability index.
− K and Zn improved antioxidant enzyme activities.
200 ppm [68]
Zucchini (Cucurbita pepo L.)
− Application of cow manure biochar reduced
bioavailability and translocation factor for heavy
metals, including Zn.
NA [78]
Ribwort plantain
(Plantago lanceolata L.) 97.4 – 108.7 mg/kg dw − Cd, Pb and Zn concentrations in samples near mines and
smelting plants were up to 15 times above rural areas
Genoa and province (Liguria, North-
Western Italy) [62]
garlic (Allium sativum), leek
(A. tuberosum), celery (Apium
graveolens), cabbage (Brassica
oleracea), broccoli (B. var. italica),
chicory (Cichorium endivia),
taro (Colocasia esculenta), carrot
(Daucus carota), lettuce (Lactuca
sativum), pea (Pisum sativum) and
potato (Solanum tuberosum)
3.87 - 25.50 mg/kg
− Maximum Zn level in celery stem was signicantly
lower than permissible value of WHO/FAO.
Xiguadi village, Guangdong, China
(Near Lechang Pb/Zn mine) [79]
Table 1. ReviewofZnconcentrationsandnotablendingsofpreviousstudies

Wong KW (2019) Zn in vegetables: A review and some insights
Integr Food Nutr Metab, 2019 doi: 10.15761/IFNM.1000245 Volume 6: 4-7
Bracken 1.57 μg/100g
− The Zn intakes from the 11 wild vegetables compared
with dietary reference intakes in the healthy Koreans
were1.4 % for Zn,
Market purchased [80]
Shepperd’s purse 568.31μg/100g
Wild Chive 97.85μg/100g
Codonopsis lanceolata 506.22μg/100g
Sedum 125.76μg/100g
Wild parsley 1110.33μg/100g
Butterbur 250.37μg/100g
Chinese chive 407.17μg/100g
Pimpinella brachycarpa 233.58μg/100g
Fragrant edible wild aster 686.32μg/100g
Spinach 1338.79μg/100g
Leaf vegetables (non-compositae
plants) 8.4 mg/kg − The Zn in cultivation soil originated from chicken
manure
Closed greenhouse vegetable
production system in Nanjing, China [72]
Leaf vegetables (compositae plants) 8.6 mg/kg
Other plants (non-leaf vegetables) 3.3 mg/kg
Endive 13.121 mg/kg FW
− SmeltingactivitycausedsignicantCdandZnpollution
in local soils
− Znconcentrationinsoilis oneofthefactorinuencing
Cd accumulation in cabbage
North of Huludao Zinc Plant, Liaoning
Province, China [71]
Spinach 17.632 mg/kg FW
Lettuce 7.864 mg/kg FW
Celery 15.682 mg/kg FW
Pakchoi 10.112 mg/kg FW
Cabbage 7.967 mg/kg FW
Garland chrysanthemum 7.341 mg/kg FW
Chinese cabbage 4.389 mg/kg FW
Eggplant 2.467 mg/kg FW
Green pepper 2.411 mg/kg FW
Cauliower 7.722 mg/kg FW
Cucumber 2.656 mg/kg FW
Tomato 1.544 mg/kg FW
Green bean 4.053 mg/kg FW
Carrot 9.447 mg/kg FW
Onion 21.801 mg/kg FW
Potato 10.767 mg/kg FW
Radish 8.553 mg/kg FW
30 strains of Amaranthus tricolor
Mean: 791.7 mg/kg
Min: 434.7 mg/kg
Max: 1230.0 mg/kg
− Strong positive relationship of Zn with Fe and Mn NA [70]
Apple 2.05 ppm
− Zn was strongly and positively correlated with Cd Purchased from market place in
Karachi [69]
Muskmelon 2.73 ppm
Chiku 5.11 ppm
Papaya 1.74 ppm
Mango 2.40 ppm
Lua 2.50 ppm
Bitterbourd 1.98 ppm
Onion 0.83 ppm
Garlic 5.13 ppm
Pumpkin 3.51 ppm
Indian squash 3.22 ppm
Cucumber 3.22 ppm
Brinjal 3.52 ppm
Lady’snger 4.63 ppm
Tomato 2.45 ppm
Chillies 2.69 ppm
Leafy vegetable (Contaminated area) 11.327 mg/kg FW
Zhuzhou Smelter, Zhuzhou, Hunan
Province, China. [63]
Non-leafy vegetable (Contaminated
area) 9.435 mg/kg FW
Leafy vegetable
(controlled area) 3.679 mg/kg FW
Non-leafy vegetable
(controlled area) 2.757 mg/kg FW
Bok Choy (Brassica campestris
L. ssp. chinensis Makino), Water
Spinach (Ipomoea aquatica
Forsk.), Shanghai green cabbage
(Brassica chinensis L.), leaf lettuce
(Lactuca sativa L. var. ramosa Hort.)
3.96 mg/kg FW (average of all
leafy vegetable investigated) − below the food safety limits in China Shanghai, China [73]

Wong KW (2019) Zn in vegetables: A review and some insights
Integr Food Nutr Metab, 2019 doi: 10.15761/IFNM.1000245 Volume 6: 5-7
Lettuce (Lactuca sativa var. crispa) 56.9-94.4 mg/kg
− Zn concentrations was lower than recommended
maximum limits.
wastewater-irrigated urban vegetable
farming sites of Addis Ababa, Ethiopia [74]
Ethiopian mustard (Brassica
carinata A. Br) 66.3-109 mg/kg
Beet (Beta Vulgaris var. cicla) 77.7-129 mg/kg
Coriander
400 mg/kg (leaves)
172 mg/kg (stems)
203 mg/kg (roots)
− Wastewater irrigated sample.
− The concentrations of Cd, Pb, and Zn were higher in
all studied vegetables (Mint, Fenugreek and coriander)
than the permissible limit of these metals in vegetables,
whereas Cu was far below the tolerable limits.
− The Zn concentration value of Mint and fenugreek
isn’t available. The Zn level is found to be highest in
coriander. Mint
Government College University,
Faisalabad, Pakistan [75]
Coriander (Coriandrum
Sativum)
21.4 mg/kg FW (Leaf)
10.59 mg/kg FW (Stem)
− A signicant portion of Zn in vegetable tissues were
belong to “Acetic acid extractable fraction” which is
associated to insoluble heavy metal phosphates
Jijie Town, Gejiu city, Yunnan
Province, China. [76]
Chinese cabbage (Brassica
pekinensis)
12.40 mg/kg FW (leaf)
5.13 mg/kg FW (petiole)
Cabbage (Brassica oleracea var.
capitate)
5.95 mg/kg FW (leaf)
5.65 mg/kg (petiole)
Bok Choy (Brassica chinensis)14.30 mg/kg FW (leaf)
5.60 mg/kg (petiole)
Garlic sprout (Allium
ampeloprasum)
10.18 mg/kg FW (leaf)
7.47 mg/kg FW (stem)
Leek (Allium
Schoenoprasum)
8.63 mg/kg FW (leaf)
23.98 mg/kg FW (stem)
Green onion (Allium
Schoenoprasum)
7.00 mg/kg FW (leaf)
5.97 mg/kg FW (stem)
Peppermint (Mentha haplocalyx)42.81 mg/kg FW (leaf)
11.58 mg/kg FW (stem)
Water spinach (Ipomoea aquatica)25.77 mg/kg (leaf)
8.70 mg/kg (stem)
samples collected near mines and smelting plants were up to 15 times
higher in Zn concentration compared to rural area [62]. A collective of
vegetables were also been discovered to have elevated Zn concentration
near Zhuzhou Smelter, Zhuzhou, Hunan Province, China [63].
Zn enrichment could lead to alteration in food crops’ physiology.
de Figueiredo et al. study has associated Zn exposure to P. vulgaris with
lower phytic level [60]. Lowered phytic level could lead to increase of
bioavailability of several micronutrients, including Zn since phytic acid
is an antinutritive agent capable of blocking mineral absorption [64-
66]. Reduced Zn during pods was also observed [60].
Zn tolerance diers among plants that are closely related genetically.
e physiological impact of Zn exposure of two related vegetable
species Brassica juncea and B. napus was investigated by exposing them
to varying Zn concentrations up to 300 µM. is study revealed that
in term of root damage, and microelement homeostasis alteration, B.
juncea is more Zn tolerant than B. natus. e physiology of their root
was also observed. It was discovered that the oxidative components
were predominant compared with nitrosative component in root [67].
e impact of Zn to the physiology of a food crops isn’t limited
to the elevation of its concentration in response of its exposure. In
cooperation with other physiological signicant element, varying
physiological responses may be revealed. Zn (200 ppm) was co-
exposed with varying concentration if potassium (K) to wheat
(Triticum aestivum L.). It was observed that in consequence of Zn and
K co-exposure, oxidative stress was minimized, root, shoot and root
lengths were improved. Another wheat physiological parameter, such
as wet and dry biomass, photosynthetic pigments, osmolyte regulators
and membrane stability index were also improved. Reduction of MDA
content was also observed [68]. Inter-species correlation analysis on
the heavy metal contents among wide range of vegetable and fruits
also unveiled a strong and positive correlation between Zn and Cd
[69]. Zn is also found to have a strong and positive relationship with Fe
and Mn, which are another physiological signicant nutrient [70]. Zn
concentration in soil has also been discovered to be one of the factor
inuencing Cd accumulation in cabbage [71].
e utilization of manure as fertilizers is one of the major factors
impacting Zn availability to vegetable crops. A collective of closed
greenhouse cultivated vegetables in Nanjing, China, was investigated
by Chen et al. [72]. It was concluded that the Zn in cultivation soil
was originated from chicken manure. e application of manure
in agriculture isn’t only contribute to elevation of heavy metal
accumulation. e application of cow manure biochar was revealed to
be able to reduce the bioavailability and translocation factors of several
heavy metals in Zucchini (Cucurbita pepo L.), including Zn. Mining
and smelting activity is another major Zn source for vegetable. e Zn
level along with Pb and Cd in ribwort plantain (Plantago lanceolate
L.) near mines and smelting plants were found to be enriched up to
15 times beyond rural areas in Genoa and province, Liguria, North-
Western Italy [62]. Another studies has shown that the soil Zn level
has been signicantly enriched due to smelting activity nearby Huludao
Zinc Plant, Liaoning Province, China [71].
Several recent studies have been conducted to investigate the
potential human health risks of metals in vegetables. e Zn in Bok Choy
(Brassica campestris L. ssp. chinensis Makino), Water Spinach (Ipomoea
aquatica Forsk.), Shanghai green cabbage (Brassica chinensis L.), leaf
lettuce (Lactuca sativa L. var. ramosa Hort.) from Shanghai, China. It
was determined that the Zn concentrations in these vagetables were
below the food safety limit set in China [73]. e Zn levels in Lettuce
(Lactuca sativa var. crispa), Ethiopian mustard (Brassica carinata A.
Br) and Beet (Beta Vulgaris var. cicla) from wastewater-irrigated urban
vegetable farming site in Addis Ababa, Ethiopia was also investigated
for possible human health hazard. ere was no Zn hazard discovered

Wong KW (2019) Zn in vegetables: A review and some insights
Integr Food Nutr Metab, 2019 doi: 10.15761/IFNM.1000245 Volume 6: 6-7
[74]. Wastewater irrigated coriander, mint and fenugreek in Faisalabad,
Pakistan was found to be a potential hazard to consumers due to their
higher-than- permissible-limit Cd, Pb and Zn concentration [75].
It should be noted that not all of the Zn in a biological tissue is
bioavailable. A collective of vegetables (Table 1) was sampled in Jijie
Town, Gejiu city, Yunnan Province, China. It was noticed that there
are a signicant portion of Zn in vegetable tissues were categorized
as insoluble metal phosphate [76]. is can be interpreted as the
bioavailability of Zn in these vegetables may be low [77]. is factor
should be taken account when the human health risk of heavy metals
will be assessed.
Conclusion remarks
Zn is crucial for both industries and human physiology. It involves
in various important biological processes. However, Zn would be toxic
to human health in excessive concentration. erefore, constant close
monitoring of Zn levels in commonly consuming vegetables are crucial
in public health viewpoint. e Zn concentration can be elevated due
to the application of chicken manure fertilizer, mining and smelting
activities. Zn in vegetable tissues were also been discovered to have
a correlation with other chemical elements, such as Fe, Mn and Cd,
indicating Zn enrichment could impact a vegetable by altering the level
of other biologically signicant elements. Finally, the human health
risk assessment on Zn should take Zn speciation in food biomass into
account.
References
1. Hawkes SJ (1997) What is a “heavy metal”? J Chem Educ 74: 1374.
2. Wong KW, Yap CK, Nulit R, Hamzah MS, Chen SK, et al. (2017) Eects of
anthropogenic activities on the heavy metal levels in the clams and sediments in a
tropical river. Environ Sci Pollut Res 24: 116-134. [Crossref]
3. Cheng WH, Yap CK (2015) Potential human health risks from toxic metals via
mangrove snail consumption and their ecological risk assessments in the habitat
sediment from Peninsular Malaysia. Chemosphere 135: 156-165. [Crossref]
4. Beyersmann D, Hartwig A (2008) Carcinogenic metal compounds: Recent insight into
molecular and cellular mechanisms. Arch Toxicol 82: 493-512. [Crossref]
5. Depledge MH, Weels JM, Jerregaard PB (1994) Heavy metals. In: Calow P (editor.),
HandbEcotoxicol,BlackwellScience,Sheeld,pp:543-569.
6. Badri MA, Aston SR (1983) Observations on heavy metal geochemical associations
in polluted and non-polluted estuarine sediments. Environ Pollution Ser B Chem Phys
6: 181-193.
7. HambidgeM(2000)Humanzincdeciency.J Nutr 130: 1344S-9S. [Crossref]
8. Rink L, Gabriel P (2000) Zinc and the immune system. Proc Nutr Soc 59: 541-552.
[Crossref]
9. GammohNZ,RinkL(2017)ZincinInfectionandInammation.Nutrients 9. [Crossref]
10. Prasad AS, Sandstead HH, Schulert AR, El Rooby AS (1963) Urinary excretion of
zinc in patients with the syndrome of anemia, hepatosplenomegaly, dwarsm, and
hypogonadism. J Lab Clin Med 61: 537-549. [Crossref]
11. ValbergLS,Flanagan PR,Chamberlain MJ(1984) Eectsof iron,tin,and copperon
zinc absorption in humans. Am J Clin Nutr 40: 536-541. [Crossref]
12. FavierA,FavierM(1990)Eectsofzincdeciencyinpregnancyonthemotherandthe
newborn infant. Rev Fr Gynecol Obstet 85: 13-27. [Crossref]
13. Institute of Medicine of the National Academies (2011) DRI: dietary reference intakes
of calcium and vitamin D. The National Academies Press, Washington, D.C.
14. World Health Organization (1996) Trace elements in human nutrition and health.
Geneva, Switzerland.
15. EFSAPanelonDieteticProducts NutritionandAllergies(2014)Scientic opinionon
dietary reference values for zinc. EFSA J 12: 3844.
16. Coleman JE (1992) Structure and mechanism of alkaline phosphatase. Annu Rev
Biophys Biomol Struct 21: 441-483. [Crossref]
17. Coleman JE (1992) Zinc proteins: Enzymes, storage proteins, transcription factors, and
replication proteins. Annu Rev Biochem 61: 897-946. [Crossref]
18. Andreini C, Banci L, Bertini I, Rosato A (2006) Counting the zinc-proteins encoded in
the human genome. J Proteome Res 5: 196-201. [Crossref]
19. Krężel A, Maret W (2016)The biological inorganic chemistry of zinc ions. Arch
Biochem Biophys 611: 3-19. [Crossref]
20. Maret W (2010) Metalloproteomics, metalloproteomes, and the annotation of
metalloproteins. Metallomics 2: 117-125. [Crossref]
21. Wessels I, Maywald M, Rink L (2017) Zinc as a gatekeeper of immune
function. Nutrients 9. [Crossref]
22. Maywald M, Wessels I, Rink L (2017) Zinc Signals and Immunity. Int J Mol Sci 18.
[Crossref]
23. DeCoursey TE, Morgan D, Cherny VV (2003) The voltage dependence of NADPH
oxidase reveals why phagocytes need proton channels. Nature 422: 531-534. [Crossref]
24. HasegawaH,SuzukiK,SuzukiK,NakajiS,SugawaraK(2000)Eectsofzinconthe
reactive oxygen species generating capacity of human neutrophils and on the serum
opsonic activity in vitro. Luminescence 15: 321-327. [Crossref]
25. Brinkmann V, Reichard U, Goosmann C, Fauler B, Uhlemann Y, et al. (2004) Neutrophil
extracellular traps kill bacteria. Science 303: 1532-1535. [Crossref]
26. LeeS,Eskin SG,ShahAK, SchildmeyerLA,McIntire LV(2012)Eect ofzinc and
nitric oxide on monocyte adhesion to endothelial cells under shear stress. Ann Biomed
Eng 40: 697-706. [Crossref]
27. Zhou X, Fragala MS, McElhaney JE, Kuchel GA (2010) Conceptual and methodological
issuesrelevanttocytokineandinammatorymarkermeasurementsinclinicalresearch.
Curr Opin Clin Nutr Metab Care 13: 541-547. [Crossref]
28. Costarelli L, Muti E, Malavolta M, Cipriano C, Giacconi R, et al. (2010) Distinctive
modulationofinammatory and metabolic parameters in relation to zinc nutritional
status in adult overweight/obese subjects. J Nutr Biochem 21: 432-437. [Crossref]
29. Foster M, Samman S (20120 Zinc and Regulation of inammatory cytokines:
Implications for cardiometabolic disease. Nutrients 4: 676-694. [Crossref]
30. Bao B, Prasad AS, Beck FWJ, Snell D, Suneja A, et al. (2008) Zinc supplementation
decreases oxidative stress, incidence of infection, and generation of inammatory
cytokines in sickle cell disease patients. Transl Res 152: 67-80. [Crossref]
31. Summersgill H, England H, Lopez-Castejon G, Lawrence CB, Luheshi NM, et al.
(2014) Zinc depletion regulates the processing and secretion of IL-1β. Cell Death
Dis 5: e1040. [Crossref]
32. Sales MC, de Oliveira LP, de Araújo Cabral NL, de Sousa SES, das Graças Almeida M,
et al. (2018) Plasma zinc in institutionalized elderly individuals: Relation with immune
and cardiometabolic biomarkers. J Trace Elem Med Biol 50: 615-621. [Crossref]
33. Olechnowicz J, Tinkov A, Skalny A, Suliburska J (2018) Zinc status is associated with
inammation,oxidativestress,lipid,andglucosemetabolism.J Physiol Sci 68: 19-31.
[Crossref]
34. HadwanMH,AlmashhedyLA,AlsalmanARS(2014)Studyoftheeectsoforalzinc
supplementation on peroxynitrite levels, arginase activity and NO synthase activity
in seminal plasma of Iraqi asthenospermic patients. Reprod Biol Endocrinol 12: 1.
[Crossref]
35. Ogawa D, Asanuma M, Miyazaki I, Tachibana H, Wada J, et al. (2011) High glucose
increases metallothionein expression in renal proximal tubular epithelial cells. Exp
Diabetes Res 2011: 534872. [Crossref]
36. Oteiza PI (2012) Zinc and the modulation of redox homeostasis. Free Radic Biol
Med 53: 1748-1759. [Crossref]
37. Skalny AA, Tinkov AA, Medvedeva YS, Alchinova IB, Karganov MY, et al. (2015)
Eectofshort-termzincsupplementationonzincand seleniumtissuedistributionand
serum antioxidant enzymes. Acta Sci Pol Technol Aliment 14: 269-276. [Crossref]
38. Li HT, Jiao M, Chen J, Liang Y (2010) Roles of zinc and copper in modulating the
oxidative refolding of bovine copper, zinc superoxide dismutase. Acta Biochim Biophys
Sin (Shanghai) 42: 183-194. [Crossref]
39. MuthuramanP,Ramkumar K, Kim DH (2014)Analysis of dose-dependenteectof
zinc oxide nanoparticles on the oxidative stress and antioxidant enzyme activity in
adipocytes. Appl Biochem Biotechnol 174: 2851-2863. [Crossref]
40. Pandurangan M, Veerappan M, Kim DH (2015) Cytotoxicity of zinc oxide nanoparticles
on antioxidant enzyme activities and mRNA expression in the cocultured C2C12 and
3T3-L1 cells. Appl Biochem Biotechnol 175: 1270-1280. [Crossref]

Wong KW (2019) Zn in vegetables: A review and some insights
Integr Food Nutr Metab, 2019 doi: 10.15761/IFNM.1000245 Volume 6: 7-7
41. Nazarizadeh A, Asri-Rezaie S (2016) Comparative study of antidiabetic activity and
oxidative stress induced by zinc oxide nanoparticles and zinc sulfate in diabetic rats.
AAPS PharmSciTech 17: 834-843. [Crossref]
42. El-AshmonySMA,MorsiHK,AbdelhafezAM(2011)Eectofzincsupplementation
onglycemiccontrol,lipidprole,andrenalfunctions inpatientswithtypeIIdiabetes:
A single blinded, randomized, placebo-controlled, trial. Journal of Biology, Agriculture
and Healthcare 2: 33-41.
43. SteneMC,Frikke-SchmidtR,NordestgaardBG,Tybjaerg-HansenA(2006)Zincnger
protein 202, genetic variation, and HDL cholesterol in the general population. J Lipid
Res 47: 944-952. [Crossref]
44. Wagner S, Hess MA, Ormonde-Hanson P, Malandro J, Hu H, et al. (2000) A broad
roleforthe zincngerproteinZNF202 inhumanlipid metabolism.J Biol Chem 275:
15685-15690. [Crossref]
45. Tinkov AA, Popova E V, Gatiatulina ER, Skalnaya AA, Yakovenko EN, et al. (2016)
Decreased adipose tissue zinc content is associated with metabolic parameters in high
fat fed Wistar rats. Acta Sci Pol Technol Aliment 15: 99-105. [Crossref]
46. Roth HP, Kirchgessner M (1981) Zinc and insulin metabolism. Biol Trace Elem Res 3:
13-32. [Crossref]
47. Jayawardena R, Ranasinghe P, Galappatthy P, Malkanthi R, Constantine G, et al. (2012)
Eectsof zinc supplementation on diabetes mellitus: asystematic review and meta-
analysis. Diabetol Metab Syndr 4: 13. [Crossref]
48. Yang HK, Lee SH, Han K, Kang B, Lee SY, et al. (2015) Lower serum zinc levels
are associated with unhealthy metabolic status in normal-weight adults: The 2010
Korea national health and nutrition examination survey. Diabetes Metab 41: 282-290.
[Crossref]
49. Ranasinghe P, Pigera S, Galappatthy P, Katulanda P, Constantine GR (2015) Zinc and
diabetes mellitus: understanding molecular mechanisms and clinical implications.
DARU J Pharm Sci 23: 44. [Crossref]
50. Dunn MF (2005) Zinc-ligand interactions modulate assembly and stability of the
insulin hexamer - A review. BioMetals 18: 295-303. [Crossref]
51. Egefjord L, Petersen AB, Rungby J (2010) Zinc, alpha cells and glucagon secretion. Curr
Diabetes Rev 6: 52-57. [Crossref]
52. HegaziSM,AhmedSS,MekawwyAA,MortagyMS,Abdel-KadderM(1992)Eectof
zinc supplementation on serum glucose, insulin, glucagon, glucose-6-phosphatase, and
mineral levels in diabetics. J Clin Biochem Nutr 12: 209-215.
53. Terrin G, Berni Canani R, Di Chiara M, Pietravalle A, Aleandri V, et al. (2015) Zinc in
early life: A key element in the fetus and preterm neonate. Nutrients 7: 10427-10446.
[Crossref]
54. Hooper PL, Visconti L, Garry PJ, Johnson GE (1980) Zinc lowers high-density
lipoprotein-cholesterol levels. JAMA 244: 1960-1961. [Crossref]
55. Barceloux DG (1999) Zinc. J Toxicol Clin Toxicol 37: 279-292. [Crossref]
56. Mohammad MK, Zhou Z, Cave M, Barve A, McClain CJ (2012) Zinc and liver
disease. Nutr Clin Pract 27: 8-20. [Crossref]
57. Nriagu J (2011) Zinc toxicity in humans. Encycl Environ Heal 2011: 801-807.
58. Chandra RK (1984) Excessive intake of zinc impairs immune responses. JAMA 252:
1443-1446. [Crossref]
59. DevineCM, Connors M,Bisogni CA, SobalJ (1998) Life-courseinuences on fruit
and vegetable trajectories: Qualitative analysis of food choices. J Nutr Educ 30: 361-
370.
60. de Figueiredo MA, Boldrin PF, Hart JJ, de Andrade MJB, Guilherme LRG, et al. (2017)
Zinc and selenium accumulation and their eect on iron bioavailability in common
bean seeds. Plant Physiol Biochem 111: 193-202. [Crossref]
61. Reboredo F, Simões M, Jorge C, Mancuso M, Martinez J, et al. (2019) Metal content
in edible crops and agricultural soils due to intensive use of fertilizers and pesticides
in Terras da Costa de Caparica (Portugal). Environ Sci Pollut Res Int 26: 2512-2522.
[Crossref]
62. Drava G, Cornara L, Giordani P, Minganti V (2019) Trace elements in Plantago
lanceolata L., a plant used for herbal and food preparations: new data and literature
review. Environ Sci Pollut Res 26: 2305-2313. [Crossref]
63. Li X, Li Z, Lin CJ, Bi X, Liu J, et al. (2018) Health risks of heavy metal exposure
through vegetable consumption near a large-scale Pb/Zn smelter in central China.
Ecotoxicol Environ Saf 161: 99-110. [Crossref]
64. Singh B, Kunze G, Satyanarayana T (2011) Developments in biochemical aspects and
biotechnological applications of microbial phytases. Biotechnol Mol Biol Rev 63: 69-
87.
65. Urbano G, López-Jurado M, Aranda P, Vidal-Valverde C, Tenorio E, et al. (2000) The
roleofphytic acidin legumes:antinutrient orbenecialfunction? J Physiol Biochem
56: 283-294. [Crossref]
66. Feil B (2001) Phytic acid. J New Seeds 3: 1-35.
67. Feigl G, Lehotai N, Molnár Á, Ördög A, Rodríguez-Ruiz M, et al. (2015) Zinc induces
distinct changes in the metabolism of reactive oxygen and nitrogen species (ROS and
RNS)intheroots oftwoBrassicaspecies withdierentsensitivityto zincstress.Ann
Bot 116: 613-625. [Crossref]
68. Jan AU, Hadi F, Midrarullah, Nawaz MA, Rahman K (2017) Potassium and zinc
increase tolerance to salt stress in wheat (Triticum aestivum L.). Plant Physiol Biochem
116: 139-149. [Crossref]
69. Parveen Z, Khuhro MI, Raq N (2003) Market basket survey for lead, cadmium,
copper, chromium, nickel, and zinc in fruits and vegetables. Bull Environ Contam
Toxicol 71: 1260-1264.
70. ShuklaS,BhargavaA,ChatterjeeA,SrivastavaJ,SinghN,etal.(2006)mineralprole
and variability in vegetable Amaranth (Amaranthus tricolor). Plant Foods Hum Nutr
61: 23-28.
71. Li B, Wang Y, Jiang Y, Li G, Cui J, et al. (2016) The accumulation and health risk of
heavy metals in vegetables around a zinc smelter in northeastern China. Environ Sci
Pollut Res Int 23: 25114-25126. [Crossref]
72. Chen Y, Huang B, Hu W, Weindorf DC, Yang L (2013) Environmental assessment of
closed greenhouse vegetable production system in Nanjing, China. J Soils Sediments
13: 1418-1429.
73. Bi C, Zhou Y, Chen Z, Jia J, Bao X (2018) Heavy metals and lead isotopes in soils, road
dust and leafy vegetables and health risks via vegetable consumption in the industrial
areas of Shanghai, China. Sci Total Environ 619-620: 1349-1357. [Crossref]
74. Woldetsadik D, Drechsel P, Keraita B, Itanna F, Gebrekidan H (2017) Heavy metal
accumulation and health risk assessment in wastewater-irrigated urban vegetable
farming sites of Addis Ababa, Ethiopia. Int J Food Contam 4: 9.
75. Anwar S, Nawaz MF, Gul S, Rizwan M, Ali S, et al. (2016) Uptake and distribution of
minerals and heavy metals in commonly grown leafy vegetable species irrigated with
sewage water. Environ Monit Assess 188: 541. [Crossref]
76. Li Y, Wang H, Wang H, Yin F, Yang X, et al. (2014) Heavy metal pollution in vegetables
grown in the vicinity of a multi-metal mining area in Gejiu, China: total concentrations,
speciation analysis, and health risk. Environ Sci Pollut Res 21: 12569-12582. [Crossref]
77. Qiu Q, WangY,YangZ, Yuan J (2011)Eects of phosphorus supplied in soil on
subcellular distribution and chemical forms of cadmium in two Chinese owering
cabbage(BrassicaparachinensisL.)cultivarsdieringincadmiumaccumulation.Food
Chem Toxicol 49: 2260-2267. [Crossref]
78. Eissa MA (2019) Eect of cow manure biochar on heavy metals uptake and
translocation by zucchini (Cucurbita pepo L). Arab J Geosci 12: 48.
79. Dong J, Yang Q, Sun L, Zeng Q, Liu S, et al. (2011) Assessing the concentration and
potential dietary risk of heavy metals in vegetables at a Pb/Zn mine site, China. Environ
Earth Sci 64: 1317-1321.
80. Bae YJ, Kim MH, Lee JH, Choi MK (2015) Analysis of six elements (Ca, Mg, Fe, Zn,
Cu, and Mn) in several wild vegetables and evaluation of their intakes based on Korea
national health and nutrition examination survey 2010-2011. Biol Trace Elem Res 164:
114-121. [Crossref]
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