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An overview of bioactivity of onion

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  • Institute of Food Science Research (CIAL, CSIC-UAM)

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Onion (Allium cepa L.) is an important vegetable traditionally used as a food ingredient in the Mediterranean diet that has a high production, domestic, and foreign trade worldwide. It is consumed raw, cooked or processed into different onion products in the daily diet. Onion added into different foods makes these products rich in bioactive compounds with potential beneficial health effects. Among them, its effect on cardiovascular disease, including hypocholesterolemic, hypolipidemic, anti-hypertensive, antithrombotic, and hypoglycaemic activities, is one of the most extensively studied benefits. Onion consumption has also been reported to have antiproliferative effects in many cancer cell lines, to be involved in the bone metabolism and in the behaviour as a possible antidepressant agent, and to stimulate the growth of specific microorganisms in the colon (Bifidobacteria and Lactobacilli) with a general positive health effect. Moreover, traditionally, in the folk medicine, it has been described the use of onion as an antimicrobial, antioxidant, antiinflamatory and asthma-protective agent. Evidence from several investigations suggests that these biological and medical functions are mainly due to the high organo-sulphur compounds content of onion. Along with organo-sulphur compounds, flavonols (quercetin and its glucosides) and dietary fibre (fructans and fructooligosaccharides (FOS)) have been also related to the onion biological properties. Moreover, recently, it has been demonstrated that additional onion constituents such as saponins and peptides have potentially beneficial health effects, including antifungal, antitumor, antispasmodic and cholesterol-lowering activities and capacity to inhibit the development and activity of osteoclasts in vitro. As with every biologically active substance, with onion and its derivatives it is necessary to consider certain precautions to minimize the risk of adverse side effects. However, the usefulness of onion as therapeutic agent seems to be very safe, since all its possible adverse effects, such as gastrointestinal upsets and dermatological problems appear with an excessive and prolonged consumption.
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In: Onion Consumption and Health ISBN: 978-1-62100-836-1
Editors: C. B. Aguirre et al. © 2012 Nova Science Publishers, Inc.
Chapter 1
AN OVERVIEW ON BIOACTIVITY OF ONION
Marta Corzo-Martínez and Mar Villamiel
Instituto de Investigación en Ciencias de la Alimentación,
CIAL (CSIC-UAM) C/ Nicolás Cabrera.
Campus de la Universidad Autónoma de Madrid, Spain
ABSTRACT
Onion (Allium cepa L.) is an important vegetable traditionally used
as a food ingredient in the Mediterranean diet that has a high production,
domestic, and foreign trade worldwide. It is consumed raw, cooked or
processed into different onion products in the daily diet. Onion added into
different foods makes these products rich in bioactive compounds with
potential beneficial health effects. Among them, its effect on
cardiovascular disease, including hypocholesterolemic, hypolipidemic,
anti-hypertensive, antithrombotic, and hypoglycemic activities, is one of
the most extensively studied benefits. Onion consumption has also been
reported to have antiproliferative effects in many cancer cell lines, to be
involved in the bone metabolism and in the behaviour as a possible
antidepressant agent, and to stimulate the growth of specific
microorganisms in the colon (Bifidobacteria and Lactobacilli) with a
general positive health effect. Moreover, traditionally, in the folk
medicine, it has been described the use of onion as an antimicrobial,
antioxidant, anti-inflamatory and asthma-protective agent.
Author to who correspondence should be addressed: Tel +34 910017951; Fax +34 910017905.
E-mail: m.villamiel@csic.es
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Marta Corzo-Martínez and Mar Villamiel
2
Evidence from several investigations suggests that these biological
and medical functions are mainly due to the high content in organo-
sulphur compounds content of onion. Along with organo-sulphur
compounds, organo-selenium compounds, flavonols (quercetin and its
glucosides) and dietary fibre (fructans and fructooligosaccharides (FOS))
have been also related to the onion biological properties. Moreover,
recently, it has been demonstrated that additional onion constituents such
as saponins and peptides have potentially beneficial health effects,
including antifungal, antitumor, antispasmodic and cholesterol-lowering
activities and capacity to inhibit in vitro the development and activity of
osteoclasts.
As with every biologically active substance, with onion and its
derivatives it is necessary to consider certain precautions to minimize the
risk of adverse side effects. However, the usefulness of onion as
therapeutic agent seems to be very safe, since all its possible adverse
effects, such as gastrointestinal upsets and dermatological problems
appear with an excessive and prolonged consumption.
Keywords: Onion, health, beneficial effects
INTRODUCTION
Onion (Allium cepa) is original from central Asia and is one of the oldest
cultivated plants since it has been in cultivation for more than 4000 years.
Onion and other species of the genus Allium have been traditionally used
worldwide for various purposes such as food preparation and seasoning
agents. In particular, the importance of onion lies in the flavour that it imparts
to other foods due to its composition. The main constituents of onion are
shown in Table 1.
It is usually consumed as fresh, however since losses of fresh onion in
storage have been reported to be about 20-30% (Chadha and Sidhus, 1990),
processed products are the most practical solution. Thus, the international
market of onion is increasingly focused mainly on dehydrated products such as
flakes, rings, granules, kibbles, powder, etc. and frozen or canned onions, or
onion in vinegar, in brine or as essential oil, its commercial products being less
abundant than those of garlic.
Dehydrated products have great commercial value not only by their
culinary use but also their by medicinal properties as nutraceutical since they
contains higher concentrations of beneficial compounds than the fresh forms
(Lanzotti, 2006).
An Overview on Bioactivity of Onion
3
Table 1. General composition of onion
Energy
23-38 Kcal 100 g-1fresh weight
Protein
0.9-1.6 %
Fat
Trace-0.2%
Carbohydrates
5.2-9.0%
Ash
0.6%
Vitamins:
mg 100 g-1 fresh weight
Vitamin C
10.0 mg
Vitamin D
0.3 mg
Riboflavin
0.05 mg
Biotin
0.9 g
Nicotinic acid
0.2 mg
Folic acid
16.0 g
Pantothenic acid
0.14 g
Elements:
mg 100 g-1 fresh weight
Ca
190-540
P
200-430
K
80-110
Na
31-50
Mg
81-150
Al
0.5-1
Ba
0.1-1
Fe
1.8-2.6
Sr
0.8-7
B
0.6-1
Cu
0.05-0.64
Zn
1.5-2.8
Mn
0.5-1.0
S
50-51
In China, onion tea has long been recommended for several pathologies
such as fever, headache, cholera and dysentery. Evidence from several
investigations suggests that the biological and medical functions of onions are
mainly due to their high content in organo-sulphur compounds (Augusti and
Mathew, 1974; Wargovich et al., 1988). The primary sulphur-containing
constituents in this vegetable are the S-alk(en)yl-L-cysteine sulphoxides
Marta Corzo-Martínez and Mar Villamiel
4
(ACSOs), such as alliin, and -glutamylcysteines, which, besides to serve as
important storage peptides, are biosynthetic intermediates for corresponding
ACSOs from which, and by different metabolic pathways in each vegetable,
volatile, such as allicin, and lipid-soluble sulphur compounds, such as diallyl
sulphide (DAS), diallyl disulphide (DADS) and others, are originated
(Lancaster and Shaw, 1989). These compounds provide to onion its
characteristic odour and flavour, as well as most of its biological properties
(Lanzotti, 2006) (Figure 1).
Figure 1. Formation of organo-sulphur compounds during metabolic pathways in
processed onion (Taken from Corzo-Martínez et al. 2007).
An Overview on Bioactivity of Onion
5
Figure 2. Major organo-sulphur compounds present in different onion preparations
based on the extraction method (Taken from Corzo-Martínez et al. 2007).
Organo-sulphur compounds present in onion preparations depend on the
variety (Yang et al., 2004) and the extraction and/or processing conditions
(Figure 2).
Flavonoids, abundant in onion, are also responsible for a great part of the
health benefits of these vegetable. In addition, the biological effects of other
constituents of intact onion, such as lectins (the most abundant proteins),
prostaglandins, fructan, pectin, adenosine, vitamins B1, B2, B6, C and E, biotin,
nicotinic acid, fatty acids, glycolipids, phospholipids and essential amino
acids, have been studied for over several decades (Fenwick and Hanley, 1985).
The importance of biological and pharmacological activities, such as
antifungal, antibacterial, antitumor, anti-inflammatory, antithrombotic and
hypocholesterolemic properties of certain steroid saponins and sapogenins,
such as -chlorogenin, has been recently demonstrated (Matsuura, 2001;
Lanzotti, 2006).
Given the importance of this vegetable as much in food preparation as in
medicine, in this chapter the bioactivity of onions has been reviewed,
indicating the main responsible compounds.
Marta Corzo-Martínez and Mar Villamiel
6
ANTIMICROBIAL ACTIVITY
In folk medicine, onion has been used for centuries in several societies
against fungal, bacterial and viral infections. Due to the great antimicrobial
activity that onion possesses, this vegetable could be used like natural
preservative in foods to control the microbial growth (Pszczola, 2002).
Recent chemical characterization of their sulphur compounds has allowed
stating that they are the main active antimicrobial agents (Rose et al., 2005).
However, the application of onion volatile compounds seems to be limited due
to their strong flavour, pungent properties and relative biochemical instability.
Consequently, there is a growing interest in studying the antimicrobial
properties of phenolic compounds which are presumably more stable.
Moreover, some proteins and saponins can also contribute to this activity
(Griffiths et al., 2002). In the case of onion phenolic compounds, a number of
papers below reported have been also addressed not only on the antimicrobial
properties but also on the antioxidant activity.
Antibacterial Activity
The major active antibacterial components in vivo are the allicin-derived
organo-sulphur compounds, such as DAS, DADS (Tsao and Yin, 2001).
Several studies have revised the impact of organosulphur-containing
compounds on the growth of pathogen by both well diffusion assay tests and
minimal inhibitory concentration. It has been found that they present high
inhibition against gram positive bacteria of genera Bacillus, Micrococcus,
Staphylococcus, Streptococcus as well as gram negative bacteria such as
Salmonella enteritidis or some strains of Escherichia coli (Corzo-Martínez et
al., 2007) and Škerget et al., (2009). In addition to organo-sulphur compounds,
it has been reported that certain quercetin oxidation products found in onion
also present antibacterial activity against Helicobacter pylori and MRSA
(multidrog-resistant Staphylococcus aureus). Additionally, phloroglucinol-3,4-
dihydroxybenzoate, quercetin, syringaresinol, and 4-O-methylquercetin
showed a weak effect against MRSA and a mild effect against H. pylori
(Ramos et al., 2006). Santas et al. (2010) studied the antimicrobial activity of
flavonol standards and ethyl acetate subfractions of methanolic extracts of
three Spanish onion varieties against Bacillus cereus, Staphylococcus aureus,
Micrococcus luteus, Listeria monocytogenes, Escherichia coli and
An Overview on Bioactivity of Onion
7
Pseudomonas aeruginosa. These authors found that, among the onion extracts
tested, only ethyl acetate subfraction showed microbial inhibition.
Benkeblia (2004) measured the antimicrobial activity of onion and
reported that the essential oil extract had a marked antibacterial activity of
certain pathogens, including Staphylococcus aureus and Salmonella
enteritidis. Lately, the addition of dehydrated onion into fresh pork meat cuts
has been used to inhibit the growth of total bacteria and Enterobacteriaceae
(Park et al., 2008). Very recently, the antimicrobial effects of an onion peel
extract obtained by subcritical water (SWE) against Staphylococcus aureus
have been studied (Lee et al., 2011a). These authors have indicated that the
effect of the SWE extract appear to be less effective than quercetin at a similar
concentration. In spite of this, they proposed this extract as an adequate
additive for the pharmaceutical industry.
In a research on the combination of divergicin M35, a bacteriocin
produced by Carnobacterium divergens strain M35, and an aqueous extract of
onion, among other vegetables, Zouhir et al. (2008) stated that, the bactericidal
effect of onion extract against Listeria monocytogenes appears to be lost when
it was combined with divergicin M35, probably due to an antagonist effect
between both. Saxena et al. (2010) reported the synthesis of silver
nanoparticles (Figure 3) by using onion extract and demonstrated that these
nanoparticles at a concentration of 50 g/mL presented a complete
antibacterial activity against Escherichia coli and Salmonella typhimurium.
Figure 3. Transmission Electron Microscopy (TEM) micrographs of silver
nanoparticles synthesised from onion extract (Taken from Saxena et al. 2010).
Length 41.98 nm
Length 32.94 nm
Length 48.18 nm
Length 35.14 nm
Length 32.78 nm
Length 38.41 nm
Length 23.85 nm
Length 37.83 nm
Length 35.67 nm
Length 31 nm
Marta Corzo-Martínez and Mar Villamiel
8
Antiviral Activity
In comparison to the antibacterial action of onion, hardly any work has
been done to investigate its antiviral properties. In addition to sulphur
compounds, it has been reported that quercetin (3,5,7,3',4'-
tetrahydroxyflavone), the major onion flavonoid, also possesses antiviral
activity and enhances the bioavailability of some antiviral drugs (Wu et al.,
2005). Onion lectins, unlike the garlic lectins, have a pronounced anti-HIV
activity (Van Damme et al., 1993). Additionally, Goren et al., (2002) found a
novel medicinal extract derived from onion with broad antiviral activity. This
extract may be used to treat or prevent a variety of viral human and animal
infections. Examples thereof include retroviral infections such as AIDS,
herpes (genital, rectal, oral), distemper, papillomavirus, flu associated
influenza viruses, parvoviruses, rhabdoviruses, Epstein Barr virus, CMV,
hepatitis virus, RSV, rhinoviruses, and foot and mouth disease virus.
Very recently, Chen et al. (2011) have investigated the in vitro anti-
adenoviral activity of onions, among other Allium plants such as shallots,
garlic, leeks and green onions, and they have found that shallots present the
highest antiviral activity for both ADV41 and ADV3, followed by garlic and
onions. According to this and, given the high content of quercetin in onion,
even more than in garlic, is it suspected that other phytochemical present in
Allium plants different from quercetin and its derivatives, could exert a
complementary effect on the antiviral action.
Antifungal Activity
The active compounds of onion destroy fungal cells decreasing the oxygen
uptake, reducing cellular growth, inhibiting the synthesis of lipids, proteins
and nucleic acids, changing the lipid profile of the cell membrane (Ghannoum,
1988) and inhibiting the synthesis of the fungal cell wall (Gupta and Porter,
2001).
Like for the antibacterial activity, the main active antifungal agents from
onion extracts are diallyl trisulphide (DATS), DADS and DAS (Tansey and
Appleton, 1975). Recently, Borjiham et al. (2010) found that Zwiebelane A
(cis-2,3-dimethyl-5,6-dithiabicyclo 2.1.1 hexane 5-oxide), a natural product
of onion bulbs, enhances the potential fungicidal activity of the typical
bactericidal antibiotic Polymyxin B.
An Overview on Bioactivity of Onion
9
Onion extracts are effective against many yeasts species and its essential
oil inhibits the dermatophytic fungi (Zohri et al., 1995). Irkin and Korukluoglu
(2007; 2009) investigated the antifungal activities of ethyl alcohol or acetone
extracts of dehydrated onion against Aspergillus niger, Fusarium oxysporum,
Candida albicans ATCC 10231 and Metschnikowia fructicola.
De Souza et al. (2010) related the levels of total phenolic in onion with the
antifungal activity tested against Rhyzopus oryzae. The phenolic compounds of
onion were extracted in three solvent systems: aqueous, methanolic and ethyl
acetate. Among the three systems studied, onion methanolic and aceto-ethylic
extracts inhibited efficiently the development of Rhyzopus oryzae.
In addition to sulphur compounds, a great variety of antifungal proteins
and peptides have been isolated from several Allium species, such as the
peptide Ace-AMP1 obtained from onion seeds with sequence similarity to
plant lipid transfer proteins (Phillippe et al., 1995), and allicepin, a novel
isolated antifungal peptide from onion bulbs (Wang and Ng, 2004). Wu et al.
(2011) have carried out a study in which Ace-AMP1 was highly expressed in a
prokaryotic Escherichia coli system as a fusion protein. The purified protein
inhibited the growth of many plant fungal pathogens, especially Alternaria
solani, Fusarium oxysporum f. sp. Vasinfectum and Verticilium dahliae.
Antiparasitic Activity
Regarding the activity that onion and their constituents exert on parasitic
protozoa, only a few reports have been published. Due to the occurrence of
unpleasant side effects and increasing resistance to the synthetic
pharmaceuticals recommended for the treatment of giardiasis, there has been
an increasing interest to explore natural alternatives. Antiparasitic properties of
onion extracts towards different strains of Leishmania and Trichomonas
vaginalis have been reported as well (Saleheen et al., 2004; Taran et al.,
2006).
ANTIOXIDANT ACTIVITY
Oxidation of DNA, proteins and lipids by reactive oxygen species (ROS)
plays an important role in aging and in a wide range of common diseases,
including cancer and cardiovascular, inflammatory and neurodegenerative
diseases, such as Alzheimer‘s disease and other age-related degenerative
Marta Corzo-Martínez and Mar Villamiel
10
conditions (Borek, 1997; Gutteridge, 1993; Richardson, 1993). Research
studies evidence that plant-based diets, in particular those rich in vegetable and
fruits, provide a great amount of antioxidant phytochemicals, such as vitamins
C and E, glutathione, phenolic compounds (flavonoids) and vegetable
pigments, which offer protection against cellular damage (Dimitrios, 2006).
As it is known, Onion contains anthocyanins and the flavonoids quercetin
and kaempferol. However, anthocyanin pigments, concentrated in the outer
shell of red onions, are only minor constituents of the edible portion.
Kaempferol, while detectable in certain onion varieties, is present in much
smaller amount than quercetin (Bora and Sharma, 2009). Thus, quercetin is the
major flavonoid found in onion, present in conjugated form, as quercetin 4‘-O-
-glycopyranoside, quercetin 3,4‘-O--diglycopyranoside, and quercetin
3,7,4‘-O---triglycopyranoside (Sellappan and Akoh, 2002). The dry outer
layers of onion, which are wasted before food processing such as cooking,
contain large amounts of quercetin, quercetin glycoside and their oxidative
products (Gülsen et al., 2007, Bora and Sharma, 2009), which are effective
antioxidants against non-enzymatic lipid peroxidation and oxidation of low
density lipoproteins (LDL). Quercetin and its dimerized compound show the
highest antioxidative activity, which is comparable to that of -tocopherol.
Therefore, the outer layer extract of onion is expected to be a resource for food
ingredients (Ly et al., 2005; Park et al., 2007).
With regards to quercetin bioavailability, Hollman et al. (1995) showed
that quercetin was indeed absorbed in humans. Recently, it has been
demonstrated that its absorption is low in contrast to other dietary antioxidants
such as vitamins C and E, limiting its capability to act as antioxidant in plasma
in vivo (Lotito and Frei, 2006). However, very high interindividual variability
has been observed in several studies (Graefe et al., 2001; Moon et al., 2000).
Thus, some individuals could absorb quercetin better than others, possibly
because of particular polymorphism for intestinal enzymes or transporters.
The glycosides of quercetin are more efficiently absorbed than quercetin
itself (Erlund et al., 2000; Graefe et al., 2001) and the nature of the sugar
residues in the glycosides influences the extent of absorption. Quercetin is not
present in blood as an aglycone but only in conjugated forms. Quercetin-3-O-
glucuronide, 3'-O-methylquercetin-3-O-glucuronide, and quercetin-3'-O-
sulfate have been identified as the major conjugates (Day et al., 2001). Very
recently, Jan et al. (2010), in a paper on the health benefits of dietary
flavonoid quercetin, reviewed the main routes of quercetin glycosides in the
major compartments of the gastro-intestinal tract.
An Overview on Bioactivity of Onion
11
Figure 4. Simplified scheme of the route of quercetin in small intestine (Taken from
Jan et al. 2010).
According to these authors two different mechanisms could be involved to
the intestinal absorption of quercetin and its glycosides (Figure 4). First route
facilitating absorption of quercetin glycosides involves luminal
deglycosylation by lactate phlorizin hydrolase (LPH) situated in the apical
membrane of the small intestine. However, the second way appears to involve
sodium dependent glucose transporter-1 (SGLT-1).
Santas et al. (2010) confirmed the presence of flavonoids in crude onion
methanolic extracts and their activity as antioxidant compounds following the
Trolox Equivalent Antioxidant Capacity (TEAC) method. Gökçe et al. (2010)
determined the antioxidant capacities of a wide range of onion cultivars by
means of the ―ferric reducing ability of plasma‖ (FRAP) and TEAC and they
suggested that the red onions had higher antioxidant activities than yellow and
white onions although yellow onions had the richest phenolic contents. Park
and Chin (2010) studied the addition to pork patties of onion extracts (water
extract from fresh onion, methanol extract from heated onion and their
combinations) and they found that the combination of extracts (1%) had
antioxidant activities as effective as butylated hydroxytoluene (0.01%).
Another source of antioxidants can be found in onion waste and by-
products, the extraction recovery being one of the most important aspects to be
Marta Corzo-Martínez and Mar Villamiel
12
considered. Khiari et al. (2009) carried out an investigation on the recovery of
antioxidant phenolics from onion solid wastes, composed of the apical
trimmings and the outer dry layers of the bulb, employing acidified
water/ethanol-based solvent systems. The results indicated the best extraction
yields at 6 h whereas the increase of temperature from 40 to 60°C had a
negative effect. Singh et al. (2009) determined the antioxidant activity by
several methods in five extract of red onion peel and they found large amounts
of polyphenols in the ethyl acetate (EA) extract, this fraction having a great
potential as natural antioxidant in nutraceutical preparations. Benítez et al.
(2011) also indicated that brown skin and top-bottom of industrial onion
wastes could be used as functional ingredient due to their high content in total
phenolics and flavonoids with high antioxidant activity, among other bioactive
compounds.
Roldán et al. (2008) characterized by-products (juice, paste and bagasse)
derived from two Spanish onion cultivars (―Recas‖ and ―Figueres‖) that have
been stabilized by thermal treatments and they found that processing of
―Recas‖ onion wastes to obtain a paste and applying a mild pasteurisation
were the best alternatives to obtain an interesting stabilised onion by-product
with good antioxidant activities measured by DPPH method.
According to Lee et al. (2007) onion increases its physiologically active
compounds after heating, since they demonstrated that the antioxidant
activities of the ethyl acetate fraction were higher in heated (120, 130 and 140
°C) than in raw onion and the higher the temperature of the heat treatment, the
greater radical and nitrite scavenging activities. Similar results were found by
Woo et al. (2007) and they indicated that the optimal heating time and
temperature were 2 h and 130°C. Roy et al. (2007) analyzed the onion water
soluble extracts subjected to thermal treatment at 75 or 100°C for 30 and 60
min and they not only increased the total antioxidant activity but also reduced
the pro-oxidant elements. Pérez-Gregorio et al. (2011) tried to elucidate the
effect of freeze-drying process and storage on onion flavonoids content and
demonstrated that the storage of onion powder at room temperature, in dark, in
air- and water-tight glass bottles for up to 6 months was keeping rather stable
all antioxidant flavonoids.
In addition to the afore-mentioned compounds, other identified
antioxidant compound is N-fructosyl lysine, Amadori rearrangement product,
originated during the first steps of the Maillard reaction as a result of the
processing and storage, mainly to high temperatures, has been studied. Moreno
et al. (2006) determined by ORACFL assay the evolution of the antioxidant
activity (AA) of dehydrated onion stored at 0.44 aw and 30 and 50 °C, and they
An Overview on Bioactivity of Onion
13
found an increase in AA in agreement with the Maillard reaction evolution.
These authors suggested that, although the Amadori compounds could exert a
moderate effect on the AA, the advanced reaction products are the major
contributors to this property.
ANTICARCINOGENIC AND ANTIMUTAGENIC ACTIVITIES
Many epidemiologic and in vitro and in vivo laboratory studies have been
developed to evidence the chemopreventive or anticarcinogen effects of onion
and related Allium species (Bianchini and Vainio, 2001; Galeone et al. 2006;
Roldán-Marín, 2009). In general, these studies are more consistent in reporting
a protective effect of onion in gastric cancer, an inversely correlation between
onion intake and the risk of the stomach cancer being observed (Dorant et al.,
1996; You et al., 1998; Gao et al., 1999; Hsing et al., 2002; Gonzalez et al.,
2006; Kim and Kwon, 2009; Bang and Kim, 2010). The chemopreventive
effects of onion against stomach and esophagus cancers may be related to their
antibacterial properties. Inhibition of bacterial growth in the gastric cavity may
result in less conversion of nitrate to nitrite in the stomach, a decreased
probability of endogenous formation of carcinogenic N-nitroso compounds,
and reduction in H. pylori infection specifically (Dorant et al., 1996).
Onion intake has been also consistently associated with a decreased risk of
colorectal (Steinmetz et al.,1994; Millen et al., 2007; Taché et al., 2007), lung
(Sankaranarayanan et al., 1994; Dorant et al., 1996; Le Marchand et al.,
2000), brain ((Hu et al., 1999), prostate (Hsing et al. 2002), bladder
(Malaveille et al., 1996), liver (Fukushima et al., 2001), breast (Levi et al.,
1993; Challier et al., 1988), ovarian (Shen et al., 1999), endometrial (Galeone
et al., 2009a), and skin (Byun et al., 2010) cancers.
These effects appear to be mediated by various mechanisms, which are not
fully understood. On the basis of several studies, it is possible to state that
mechanisms by which onion exerts their anticarcinogenic and antimutagenic
action include (Figure 5): alteration of carcinogen metabolism by inducing
phase II enzymes such as glutathione S-transferase (GST), NAD(P)H-
dependent quinine reductase, and UDP-glucuronosyl transferase (Tsuda et al.,
2004), that increase the carcinogen polarity, facilitating its excretion from the
body (Guyonnet et al., 2001; Brisdelli et al., 2007); inhibition of bioactivating
enzymes of procarcinogens (Lautraite et al., 2002; Muto et al., 2001; Platt et
al., 2010); inhibition of oxidative damage due to its antioxidant action
(Perchellet et al., 1990; Mutoh et al., 2000; Raso et al., 2001).
Marta Corzo-Martínez and Mar Villamiel
14
Figure 5. Cholesterol biosynthesis pathway (Taken from Cardelle-Cobas et al. 2009b).
Recently, Bang and Kim (2010), in a study on the effect of onion on the
chemical induction of preneoplastic lesions in rat liver, reported that onion
inhibits early-stage hepatocellular carcinogenesis through the suppression of
oxidative stress by modulating the GST and glutathione peroxidase activity;
inhibition of cellular proliferation by induction of apoptosis and inhibition of
cell division (Perchellet et al., 1990; Brisdelli et al., 2007); gene transcription
inhibition (Miodini et al., 1999; Bora and Sharma, 2009); protection against
UV-induced immunosuppression (Steerenberg et al., 1998; Bora and Sharma,
2009); and inhibition the lipoxygenase and cyclooxygenase activities (anti-
inflammatory effect) (Perchellet et al., 1990; Mutoh et al., 2000; Raso et al.,
2001; Rose et al., 2005).
Regarding bioactive compounds, several investigations have shown that
both water- and lipid-soluble sulphur compounds from onion provide, at least
in part, its anticarcinogenic activity. Among them, DAS, diallyl disulphide
(DDS), dipropyl sulphide (DPS), dipropyl disulphide (DPDS), N-
An Overview on Bioactivity of Onion
15
acetylcysteine, S-allyl cysteine (SAC), and S-methylcysteine (SMC) have
shown to inhibit both early and late stages of colon, forestomach, esophagus,
mammary gland, lung, liver and kidney carcinogenesis (Reddy et al., 1993;
Takada et al., 1997; Fukushima et al., 1997; Guyonnet et al., 2001; Fukushima
et al., 2001; Bora and Sharma, 2009).
Another sulphur compounds, as methiin (Takada et al., 1997), inhibits the
cellular proliferation by inducing apoptosis in human cell cultures, like, for
example, in human leukaemic cells. More recently, it has been postulated that
organo-sulphur compounds such as tetrasulfides ocurring naturally in onion
are able to suppress the proliferation of sensitive and resistant human breast
carcinoma cells by targeting the cell division cycle 25 phosphatases, crucial
enzymes of the cell cycle (Viry et al., 2011)
In addition to organo-sulphur compounds, organo-selenium compounds
are largely responsible for the anticarcinogenic activity of onion (Matsuura,
1997; El-Bayoumy et al., 2006). Thus, it has been observed that Se-enriched
onion has higher anticarcinogenic activity than the common plants (Ip et al,
1992). This increased effect of cancer prevention is achieved at least partly by
S substitution with Se.
The pure Se-compounds have proved to be superior anticancer agents than
their corresponding S-analogues. For example, diallyl selenide is at least 300
times more active than DAS in the reduction of tumours of mammal cancer
(El-Bayoumi et al., 1996). The two major Se-compounds possessing
anticancer activity in onion are -glutamyl-Se-methyl selenocysteine (Finley,
2005; Hurst et al. 2010) and Se-methyl selenocysteine, this latter being the
most chemopreventive (Block et al, 2001). Other forms of selenium identified
in uncooked onions include selenomethionine, selenocysteine, and
selenite/selenate (Kotrebai et al., 2000).
Anticarcinogenic and antimutagenic properties of onion may be also
partly attributed to its abundance of phenolics, including flavonoids. Several
recent studies (Jang and Lim, 2009; Jeong et al., 2009) have reported the
different anticancer activity of extracts from flesh and peel of white, yellow
and red onion as a function of their total phenolics and flavonoids, as
quercetin, level. In general, onion peel, with the highest amounts of total
phenolics and flavonoids, inhibited the growth of several human cancer cell
lines, including cells of stomach, colon (Jang and Lim, 2009), breast, and
prostate cancer (Jeong et al., 2009), more efficiently than onion flesh. In
addition, extracts from white onion was less effective than those from yellow
and red onion, with a higher content in total phenolics and flavonoids than the
former.
Marta Corzo-Martínez and Mar Villamiel
16
Likewise, in a study on the potential antioxidant and antimutagenic
activities of several extracts with different polarity from red onion peel, Singh
et al. (2009) suggested that the large amount of polyphenols contained in the
ethyl acetate fraction, including ferulic, gallic, protocatechuic acids, quercetin
and kaempferol, might be the cause of their strong antioxidant and
antimutagenic properties.
Particularly, quercetin and derivatives exhibit anticancer properties, which
have been demonstrated in a number of malignancies, including prostate,
breast, skin, lung and liver cancers (Avila et al., 1994; Musonda and Chipman,
1998; Le Marchand et al., 2000; Le Marchand, 2002; Vijayababu et al., 2006;
Arung, Furuta, Ishikawa, Kusuma, Shimizu, and Kondo, 2011). Likewise,
several studies have reported that quercetin enhances bioavailability of some
anticancer drugs, as Tamoxifen, a non-steroidal antiestrogen for the treatment
and prevention of breast cancer, by promoting their intestinal absorption and
reducing their metabolism (Shin et al., 2006; Wu, et al, 2005).
In addition, a recent study has reported that the combined effect of
quercetin and sulforaphane [1-isothiocyanato-4-(methylsulfinyl)-butane] (a
member of an isothiocyanate family of chemopreventive agents isolated from
broccoli) on the proliferation and migration of melanoma (B16F10) cells is
more effective than either compound used alone (Pradhan et al., 2010).
Besides quercetin, luteolin (3,4,5,7-tetrahydroxyflavone), a natural
flavonoid abundant in onions, has shown antiproliferative (Huang et al., 1999),
antimetastatic (Huang et al., 1999; Lee et al., 2006), antioxidative (Manju et
al., 2005), antiangiogenic (Bagli et al., 2004), and anti-inflammatory (Ueda et
al., 2002) effects, primarily in cancer cell assay models. One study showed
that luteolin inhibits chemically induced skin tumorigenesis in a mouse model
(Ueda et al., 2003). Recently, Byun et al. (2010) reported that luteolin exerts
its protective effect against UVB-induced skin tumorigenesis in SKH-1
hairless mice by directly suppressing PKCε and c-Src kinase activity, two
protein kinases closely associated with the development of UV-induced skin
cancer.
Together with all these bioactive compounds, new chemicals are being
isolated from onion extracts and characterized. Among them, 2,3-dihydro-3,5-
dihydroxy-6-methyl-4H-pyranone and 5-hydroxy-3-methyl-4-propylsulfanyl-
5H-furan-2-one have shown to prevent or inhibit cancer cell growth in vitro by
inducing apoptotic cell death through the inhibition of NF-B (Ban et al.,
2007) and by increasing the quinone reductase activity, a phase II xenobiotic
metabolizing enzyme (Xiao and Parkin, 2007), respectively.
An Overview on Bioactivity of Onion
17
CARDIOVASCULAR PROTECTIVE EFFECTS
Cardiovascular diseases (CVD) include coronary heart disease (heart
attacks), cerebrovascular disease, raised blood pressure (hypertension),
peripheral artery disease, rheumatic heart disease, congenital heart disease and
heart failure. If current trends are allowed to continue, it has been estimated
that about 20 million people will die from CVD (mainly from heart attacks and
strokes) (WHO, Cardiovascular disease) by 2015. Therefore, CVD have a
major impact on the mortality and quality of life of human populations across
the world, despite improvements in lifestyle and innovations in the prevention
and treatment of CVD in previous decades (Wensing et al., 2009; Roldán-
Marín, 2009).
There are many factors associated with arteriosclerosis and cardiovascular
diseases, among which can be included: elevated blood cholesterol and
triglycerides levels, including LDL-cholesterol; increased platelet activity,
which can give rise to arteriosclerotic plaques formation; elevated blood
homocysteine; diabetes; hypertension; and obesity. These cardiovascular
disease risk factors are mainly determined by uncontrollable (heredity, gender
and age) and lifestyle-related causes (smoking, physical inactivity, stress and
unhealthy diet), which are possible to be modified. For this reason, a potential
approach to the prevention and treatment of CDV could be based on the diet.
In this sense, onion has been described to have hypolipidemic, hypoglycemic,
and antithrombotic effects and, therefore, could be useful in a CVD preventive
diet, according to the study carried out by Galeone et al. (2009b), the first
from Mediterranean countries.
Effects on Levels of Serum Lipids
The synthesis and utilization of cholesterol must be tightly regulated in
order to prevent over-accumulation and abnormal deposition within the body,
since the abnormal deposition of cholesterol and cholesterol-rich lipoproteins
in the coronary arteries eventually leads to atherosclerosis.
Slightly less than half of the cholesterol in the body derives from
biosynthesis de novo. Biosynthesis in the liver accounts for approximately
10%, and in the intestines approximately 15% of the amount produced each
day. Cholesterol synthesis occurs in the cytoplasm and microsomes from the
two-carbon acetate group of acetyl-CoA (King and Marchesini, 2007), as
shown in Figure 6.
Marta Corzo-Martínez and Mar Villamiel
18
Figure 6. Modes of action by which onion and its derivatives exert their
anticarcinogenic activity.
An Overview on Bioactivity of Onion
19
Onion has been reported to reduce moderately blood triglycerides levels
and to inhibit hepatic cholesterol biosynthesis in experimental animal such as
healthy rats, rabbits and pigs fed a high fat diet (Sharma et al., 1975; Vatsala et
al., 1980; Lata et al., 1991; Effendy et al., 1997; Ostrowska et al., 2004;
Gabler et al., 2006; Roldán-Marín et al., 2010), no significant differences
existing between hypolipidemic and hypocholesterolemic effects of onion and
garlic (Emmanuel and James, 2011).
Studies with humans have been also carried out. Thus, a group of
volunteers fed a high fat diet plus 100 g onion once a day and those fed fat diet
only showed a significant decrease in serum triglycerides, but not cholesterol,
as compared to those only fed with fat diet only (Sainani et al., 1978). Another
study reported that oral administration of a butanol onion extract to patients
with elementary lipemia prevented an increase in total serum cholesterol, J-
lipoprotein cholesterol, and J-lipoprotein and serum triglycerides (Jain and
Vyas, 1977). Similarly, a saponin fraction (50 mg) and the bulb (100 mg) of
onion have also shown to decrease serum cholesterol and plasma fibrinogen
levels (Dorsch and Wagner, 1991). Moreover, a recent study indicated that
intake of onion concentrated extracts exerts beneficial effects on dyslipidemia
by reducing serum total cholesterol and LDL-cholesterol levels in borderline
hypercholesterolemic subjects (Lee et al., 2010). All these studies showed that
onion intake may to inhibit the formation of atherosclerotic plaques and,
consequently, to reduce risk indices of CVD.
Among bioactive compounds involved in onion hypolipidemic and
hypocholesterolemic effects, organo-sulphur compounds are the main active,
as much in humans as in experimental animals (Yeh et al., 1997; Liu and Yeh,
2002). Volatile oil of onion and S-methyl cysteine sulphoxide (SMCS) have
shown to possess the ability of counteract the lipogenic effect of sucrose,
alcohol and cholesterol diets (Wilcox et al., 1984; Farya et al., 1986; Kumari
and Augusti, 2007; Bora and Sharma, 2009).
Mechanisms of action by which these onion bioactive compounds exert
their hypolipidemic and hypocholesterolemic activities include: inhibition
hepatic lipid/cholesterol biosynthesis by inactivating thiol enzymes (eg. HMG-
CoA), which promote it, or by reducing the level of NADPH in tissue, thus
they may not be available for cholesterol synthesis (Gebhardt et al., 1994;
Kumari and Mathew, 1995; Gupta and Porter, 2001); and enhancement of
cholesterol turnover to bile acids and its excretion through gastrointestinal
tract (Srinivasan and Sambaiah, 1991).
In addition to organo-sulphur compounds, flavonoid quercetin and
derivatives have also shown to be able to reduce serum concentrations of total
Marta Corzo-Martínez and Mar Villamiel
20
cholesterol and LDL-cholesterol, and to increase serum concentrations of
HDL-cholesterol (Glasser et al., 2002; Lee et al., 2011b). Moreover, Terao et
al. (2008) reported that quercetin metabolites are incorporated into the
atherosclerotic region and act as complementary antioxidants, when oxidative
stress is loaded in the vascular system.
Conversely to the above mentioned works, one study reported no
significant changes in cholesterol or lipid levels of the eye in rabbits, after
treatment of the animals for six months with an aqueous onion extract (20% of
diet) (WHO monographs, 1999). Similarly, Sharma and Sharma (1976; 1979)
observed that fresh onion extract (50 g) did not produce any significant effects
on serum cholesterol, fibrinogen or fibrinolytic activity in normal subjects.
Therefore, although onion appears to hold promise in reducing parameters
associated with cardiovascular disease, more in-depth investigations are
required. Moreover, it is important to note that onion is mostly consumed after
processing rather than raw which can lead to a certain decrease in its content
of bioactive compounds. In this respect, Gorinstein et al. (2010) recently
reported that blanching of onion for 90 s most fully preserves the contents of
its bioactive compounds and related antioxidant potential. Thus, diets,
supplemented with red onion and to a lesser degree with white onion,
significantly hindered the rise in plasma lipids levels and the decrease in the
plasma antioxidant activity in cholesterol-fed rats.
Hypotensive and Bradycardic Effects
Epidemiological studies have demonstrated that elevated blood pressure is
one of the major risk factors for stroke and coronary heart disease. A close
association between blood pressure and the incidence of cardiovascular
diseases is well established if systolic/diastolic blood pressure is above 140/90
mmHg. In recent years, popular blood pressure-lowering nutraceuticals and
functional foods, including onion, have attracted considerable interest as
potential alternative therapies for treatment of hypertension, especially for pre-
hypertensive patients, whose blood pressure is marginally or mildly high but
not high enough to warrant the prescription of blood pressure-lowering
medications (Chen et al., 2009).
Onion has been shown to be anti-hypertensive in many in vivo animal
studies. In L-NAME (NG-nitro-L-arginine methyl ester)-induced hypertensive
rats and stroke-prone spontaneously hypertensive rats (SHRSP), dried onion
was able to reduce blood pressure when it was added into diet at 5% (Sakai et
An Overview on Bioactivity of Onion
21
al., 2003). In addition, allylmercaptocaptopril (CPSSA), a drug assayed in
hypertensive rats and synthesised through the reaction of the pharmaceutical
drug Captopril with allicin, provides better protection against hypertension.
This is due to it has the Captopril ability to inhibit the angiotensin-converting
enzyme (ACE) and the allicin ability to reduce serum cholesterol and
triglycerides levels (Miron et al., 2004).
Although the active ingredients responsible for the blood pressure-
lowering activity of onion are not yet fully understood, some evidence
suggests that they reduce blood pressure probably by the following
mechanisms: (i) by increasing the level of nitric oxide (NO) and the activity of
nitric oxide synthetase (NOS). This has been observed in studies with SHRSP
(Sakai et al., 2003) and, recently, with cultured human umbilical vein
endothelium cells (Jiemei et al., 2011). It has also been shown that phenolics,
flavonoids and 3-mercapto-2-methylpentan-1-ol (3-MP) of onion were able to
scavenge the peroxynitrite radical in vitro, inhibiting, thus, peroxynitrite-
induced nitration of protein tyrosine residues, considered as one of the major
pathological causes of several human diseases, including cardiovascular
disorders (Rose et al., 2003; Ho et al., 2010); (ii) by inhibiting the production
of angiotensin II. A study with several rat models of hypertension has
indicated that quercetin and its methylated metabolite isorhamnetin, found in
onion, can reduce blood pressure and prevent angiotensin II-induced
endothelial dysfunction by means of the inhibition of the overexpression of
p47 (phox), a regulatory subunit of the membrane NADPH oxidase, and the
subsequent increased superoxide production, resulting in a highest NO
bioavailability (Sanchez et al., 2007); and (iii) through the inhibition of
calcium influx (Naseri et al., 2008a).
Regarding the effect of onion on blood pressure in humans, available data
are scarce. Mayer et al. (2001) conducted a randomized, placebo-controlled,
double-blind, and crossover study to investigate the effect of an onion-olive oil
maceration capsule formulation on arterial blood pressure. They found that it
produced a decrease in arterial blood pressure. Moreover, one study
investigated the efficacy of quercetin supplementation on lowering blood
pressure in hypertensive humans and demonstrated that 730 mg of quercetin
per day could reduce the systolic blood pressure by 7 mmHg, the diastolic
blood pressure by 5 mmHg, and mean arterial pressures by 5 mmHg in stage 1
hypertensive patients (Edwards et al., 2007). Similarly, Egert et al. (2009)
recently found that quercetin reduced systolic blood pressure and plasma
oxidized LDL concentrations in overweight subjects with a high-CVD risk
Marta Corzo-Martínez and Mar Villamiel
22
phenotype in a double-blinded, randomised, placebo-controlled cross-over
trial.
Anti-Hyperglycemic or Anti-Diabetic Potential
The relationship between diabetes Mellitus and atherosclerosis is likely
based on the interactions between arterial cells and atherogenic glycosylated
LDL lipoproteins originated during diabetes development. These play a key
role in the initiation of an atherosclerotic lesion, inducing cholesterol
accumulation in arterial cells (Ide and Benjamin, 2001) and other more severe
atherosclerotic manifestations at cellular level (Winocour, 1994; Sobenin et
al., 1994).
The effectiveness of onion and its derivatives as hypoglycemic agents has
been shown in several studies either with diabetic animal models or humans
(Brahmachari and Augusti, 1962; Augusti, 1973; Jain and Vyas, 1974; Sharma
et al., 1977; Bever and Zahnd, 1979; Ashwah et al., 1981; Srinivasan, 2005;
El-Demerdash et al., 2005). Results of a recent study (Bang et al., 2009) have
indicated that this beneficial ameliorating influence of dietary onion on
diabetic nephropathy may be mediated through onion's ability to decrease
blood glucose, serum lipid/cholesterol levels and lower renal oxidative stress
in streptozotocin-induced diabetic rats. Babu and Srinivasan (Babu and
Srinivasan, 1997) observed that dietary onion intake for 8 weeks produced
significant hypolipidemic effect besides hypoglycemic influence in diabetic
rats. More recently, Lee et al. (2008) showed that onion peel was effective in
controlling hyperglycemia in animal models of type 2 diabetes Mellitus, at
least in part by inhibiting alpha-glucosidase activity (Lee et al., 2008).
The organo-sulphur compounds S-methylcysteine sulphoxide (SMCS) and
S-allylcysteine sulphoxide (SACS) have been related to significant
amelioration of weight loss, hyperglycemia, low liver protein and glycogen,
and other characteristics of diabetes Mellitus in rats (Sheela and Augusti,
1995). The use of SMCS and SACS (200 mg/kg/day) gave results comparable
to treatment with insulin or glibenclamide but without the negative side effect
of cholesterol synthesis stimulation. Antidiabetic effect of SMCS was also
reported by Kumari and Mathew (1995). This compound exerts its anti-
diabetic action by 3 different ways: (i) stimulating the insulin production and
secretion by pancreas, (ii) interfering with dietary glucose absorption, and (iii)
favouring the insulin saving (Srinivasan, 2004a; Srinivasan, 2004b).
In addition to organo-sulphur compounds, anti-hyperglycemic and anti-
diabetic activities of diphenylamine (Karawya et al., 1984) and quercetin from
An Overview on Bioactivity of Onion
23
onion have been also reported. In vivo analysis of the effects of quercetin on
human diabetic lymphocytes showed a significant increase in the protection
against DNA damage from hydrogen peroxide at the tissue level (Lean et al.,
1999). Likewise, it has been reported that long-term absorption of quercetin
could be useful to prevent advanced glycation of collagens, which contributes
to development of cardiovascular complications in diabetic patients (Urios et
al., 2007). In addition, a very recent study (Jung et al., 2011) carried out with
high fat diet/streptozotocin-induced diabetic rats has shown that onion peel
extract, containing a high content in quercetin, might improve glucose
response and insulin resistance associated with type 2 diabetes, even with a
greater potency than pure quercetin equivalent, by alleviating metabolic
dysregulation of free fatty acids, suppressing oxidative stress, up-regulating
glucose uptake at peripheral tissues, and/or down-regulating inflammatory
gene expression in liver. These findings provide a basis for the use of onion
peel to improve insulin insensitivity in type 2 diabetes Mellitus.
Moreover, the use of onion has been suggested in conjunction with anti-
diabetic drugs to increase their therapeutic potential and to minimize their oral
dosage. According to experimental data, 50 g onion, daily incorporated in
diabetic diet, could serve as an effective supportive therapy in the prevention
and maintenance of long-term complications of diabetes.
Anti-Platelet or Anti-Thrombotic Effect
The major function of blood platelets is to maintain the haemostatic
integrity of blood vessels and to stop bleeding after injury (Ali et al., 2000),
through vasoconstriction, clot formation and blood coagulation. However,
when there is an imbalance in the blood coagulation system, a blood clot
called thrombus can be formed (Figure 7) and block the flow of blood through
a vein or artery, and even can detach from the vessel wall to become a life-
threatening embolus when it lodges in the lungs or other vital organs.
Likewise, blood clots in coronary arteries cause acute coronary syndrome and
blood clots that form in the heart are the major cause of stroke in people with
atrial fibrillation. Therefore, it is evident that thrombosis complications play a
major role in CVD (Becker, 1999).
Inhibition of platelet aggregation by onion has been demonstrated in vitro
and in vivo (Ali, Bordia, and Mustafa, 1999; Ali et al., 2000; Briggs et al.,
2001; Jung et al., 2002; Hubbard et al., 2006; Bora and Sharma, 2009).
Studies on the antithrombotic action of onion have reported that its aqueous
Marta Corzo-Martínez and Mar Villamiel
24
extracts inhibit adenosine diphosphate, collagen, epinephrine and arachidonic
acid-induced platelet aggregation in vitro (Srivastava, 1984).
Figure 7. Formation of a clot or thrombus into a blood vessel obstructing the flow of
blood through the circulatory system.
Likewise, the essential oil, and butanol and chloroform extracts inhibited
platelet aggregation in rabbits (Makheja et al., 1979; Ariga and Oshiba, 1981).
Moreover, both raw onion and its essential oil increased fibrinolysis in ex-vivo
and increased the coagulation time in rabbits (Breu and Dorsch, 1994).
Aggregation of human platelets by onion was also inhibited in vitro by its
essential oil and ethanol, butanol and chloroform extracts (10-60 Kg/ml)
(Vanderhoek et al., 1980) through the decrease of thromboxane A2 synthesis,
a potent inducer of platelet aggregation (Makheja and Baily, 1990; Moon et
al., 2000). In vivo effects of onion intake in rats (500 mg/kg) also showed
significant inhibition of serum thromboxane A2 (Bordia et al., 1996). Low
dose (50 mg/kg) showed little effect, but benefit was observed over long-term
consumption. Similarly, raw Welsh onion extracts showed vasodilating effects
on precontracted aortic rings of rats as well as to prolong bleeding time, reduce
An Overview on Bioactivity of Onion
25
platelet aggregation and increase cAMP level (Chen et al., 1999). Onion, in its
raw form, is recognized as an antiplatelet agent. However, as mentioned
above, onion is generally cooked before consumption, probably losing its anti-
aggregatory effect. Several studies have found that boiled onions, even at the
high dosage level, showed no anti-thrombotic effect, probably due to
degradation of bioactive compounds. Moreover, extensive heating may result
in pro-aggregatory effects (vasoconstriction and induction of thromboxane
synthesis). These results suggest that in order to obtain the maximum health
benefits, onions should be eaten raw or moderately cooked (Bordia et al.,
1996; Chen et al., 1999; Cavagnaro et al., 2007).
On the other hand, Ali et al. (1999) showed antiplatelet activity in rabbit
plasma, but not in human plasma and suggested that varietal differences may
play a role (Ali et al., 1999). In agreement with this, several studies have
reported that antiplatelet activity is substantially affected by genotype,
environment and storage duration of vegetable. It has been reported that, in
onions, the antiplatelet activity is determined, in part, by the native
concentration of organo-sulphur compounds and genotypically determined
sulphur content of the bulb (Goldman et al., 1996). According to this, a
number of epidemiologic studies have reported that antiplatelet activity of
onion is considered to be a property of organo-sulphur compounds, concretly
thiosulphinates and a class of -sulphinyl-disulphides (cepaenes) (Breu and
Dorsch, 1994; Block et al., 1997). These compounds have structural similarity
to ajoene, considered the major antiplatelet compound in garlic extracts.
In addition, other non-sulphur compounds, such as -chlorogenin and
quercetin, have also shown to inhibit platelet aggregation (Rahman et al.,
2006). Quercetin and its derivatives exert their beneficial effects on
cardiovascular health by antioxidant and anti-inflammatory activities
(Kuhlmann et al., 1998), through the inhibition of lipid peroxidation and
endothelial cell damage, which are involved in the early development of
atherosclerosis (Da Silva et al., 1998; Kaneko and Baba, 1999). An in vitro
study carried out by Janssen et al. (1998) showed that 2500 μmol/L quercetin
isolated from onions inhibited platelet aggregation by 95-97%. However, an in
vivo assay from the same authors with 18 human subjects ingesting 114 mg
quercetin/day showed no significant effects. Therefore, it was concluded that
necessary concentration levels of quercetin for beneficial effects were too high
to be obtained dietarily.
Moreover, it has been recently reported the anti-inflammatory effect of
two phenylpropenoic acid amides isolated from Allium fistulosum (green
onion), called Typheramide (N-caffeoyltyramine) and alfrutamide (N-
Marta Corzo-Martínez and Mar Villamiel
26
feruloyltyramine). These compounds have shown to significantly inhibit
cyclooxygenases COX 1 and 2, which are principally involved in catalyzing
the processing of arachidonic acid to several prostaglandins and thromboxanes
(e.g., thromboxane A2, thromboxane B2), promoting the platelet aggregation
(Park, 2011).
OTHER BENEFICIAL EFFECTS
Thiosulphinates and cepaenes derived from onion have been shown to
possess antiasthmatic activity (Dorsch, 1996), due to the inhibitory effect of
cyclooxygenase and lipoxygenase mediated reactions which initiate eicosanoid
metabolism and lead to bronchial restriction, as it has been demonstrated in
vitro (Wagner et al., 1990). In general, saturated thiosulphinates are less active
than unsaturated ones and cepaenes are more active than thiosulphinates.
Likely, these effects in vitro are responsible, at least in part, for onion extracts
anti-inflammatory and antiasthmatic properties observed in vivo (Breu and
Dorsch, 1994).
The anti-allergic effects of an herbal fraction (ALC-02) derived from the
bulb were evaluated in rats by Kaiser et al. (2009). Concretely, the efficacy
was tested against various events responsible for Type I allergic reactions and
the authors attributed the antiallergic profile of ALC-02 to its potential
antihistaminic, anti-inflammatory and antioxidant activities.
It has been reported that onion stimulates the digestive process,
accelerating digestion and reducing food transit time in the gastrointestinal
tract (Platel and Srinivasan, 2001). Naseri et al. (2008b) investigated, among
other properties, the spasmolytic activity of onion peel powder on rat ileum
contractility. Onion peel extracts obtained in 70% alcohol inhibited ileum
contractions without involving beta-adrenoceptor, opioid receptor, nitric oxide
production and potassium channels activation. According to this, the authors
suggested that quercetin in onion peel extracts seems to induce spasmolytic
effect via calcium channels.
Onion prebiotic activity has been also investigated (Sharma et al., 2006;
Benkeblia and Shiomi, 2006) due to their high soluble fibre content, specially
inulin and fructooligosaccharides (FOS) (Cardelle-Cobas et al., 2009a) which
stimulate in the colon the growth of specific microorganisms, as bifidobacteria
and lactobacilli, with a general positive health effect (Gibson, 1998; Ernst and
Feldheim, 2000). Both, inulin and FOS of onion may be used as functional
ingredients to enrich many processed foods without any negative impact on
An Overview on Bioactivity of Onion
27
their taste (Causey et al., 2000). Roldán-Marín et al. (2009) reported the
effects of onion extract and onion by-product derived from a pasteurized paste
on gut environment in healthy rats and they observed a prebiotic effect of
these products as evidecend by decreased pH, increased butyrate production
and altered gut microbiota enzyme activity.
Other positive effect of onion which has been assessed in in vivo (rats) is
the androgenic effects of different doses of onion bulb juice on sperm
parameters by using hormone measurements and histopathological studies
(Khaki et al. 2009).
In this study, freshly prepared onion juice significantly affected the sperm
number, percentage of viability, and motility. Thus, 4g/kg of freshly prepared
onion juice is effective in sperm health parameters. Moreover, onion intake
has shown to be inversely associated with benign prostatic hyperplasia (BPH),
disease that involves the formation of large, fairly discrete nodules in the
periurethral region of the prostate as a result of an accelerated proliferation of
prostate cells due to the influx of androgens (testosterone and related
hormones) at high concentrations. This was observed by Galeone et al. (2007)
in a multicenter case-control study of 1369 patients with BPH and 1451
controls.
CONCLUSION
It can be said that onion is very suitable as food ingredient, not only due to
its recognized and appreciated organoleptic properties but also because of the
wide range of important biological activities (antimicrobial, antioxidant,
anticarcinogenic and antimutagenic, hypolipidemic and hypocholesterolemic,
anti-hypertensive, anti-thrombotic, and anti-hyperglycemic activities, prebiotic
character, and immunosuppressive, neuroprotective, and anti-inflammatory
effects) that it possesses.
To date, many favourable experimental and clinical effects of onion and
onion preparations have been reported. These health properties are mainly
associated with the following types of chemical compounds: i) non-structural
and soluble carbohydrates such as FOS; ii) organo-sulphur compounds, which
are also responsible for the pungent aroma and taste; iii) organo-selenium
compounds; and iv) phenolic compounds such as flavonoids, particularly
quercetin derivatives. In most of the cases these constituents can share
different biological activities.
Marta Corzo-Martínez and Mar Villamiel
28
It is well extended the belief that the therapies based on natural remedies
have fewer side effects than pharmaceutical products. However, in spite of the
numerous studies about the beneficial effects of onion, certain aspects need to
be taken into account such as the adverse effect related to bad breath, body
odour, gastrointestinal upsets and interactions with other constituents and
drugs, although these effects depend on the dosage and susceptibility of the
individual. In this regard, the effective dosage to note the beneficial effects as
well as the most suitable preparation to avoid undesirable effect should be
defined.
Other very important topics are related to processing of onion and its
derivatives, since the sensitivity to heat of active components of onion can
question the efficacy of different commercial preparations as therapeutic
agents, moreover the hard odour and taste of onion extracts can contribute to
the reject of these products. For these reasons, more investigations are needed
to find a product without odour and taste and that preserves all the biological
properties of raw onion.
Clues of vegetable benefits are sometimes found in epidemiological
results in which studies of population diet are correlated with the incidence of
a particular type of disease. In addition, most of the research works have been
done in in vitro assays and, in some examples, in in vivo by using
experimentation animals such as rats.
In these investigations the improved benefits are viewed as positive but
whether this translates to a ―health benefit‖ in some cases is unclear. For these
reasons, although some assays have been carried out in humans, more clinical
studies are necessary to determine if the results with animals can be totally
extrapolated to humans.
In this sense, one key question is to know how and in what form the
bioactive compound is present in the digestive tract to assure a proper
bioavailability and effect. Although some recent papers have studied the
bioavailability of some component such as quercetin, more research is needed,
particularly in the case of new potential bioactive compounds.
In general, it is possible to state that onion is an adequate option in the
daily diet to prevent certain pathologies and, in some cases (mainly the
extracts), as complementary agents to existing medical treatments. Of
particular importance is the fact that, if possible, onion should be consumed as
a fresh vegetable or minimally cooked to preserve the most thermolabile
bioactive compounds.
On the other hand, during the last years, there has been a clear trend
toward the study of bioactivity of onion peel and by-products in order to
An Overview on Bioactivity of Onion
29
search new benefits or, at least, the same ones than in the bulb from waste
products and, thus, contribute to the sustainability during food processing.
ACKNOWLEGDMENTS
This work has been funded by Ministry of Science and Innovation of
Spain (project AGL2007-63462) and by Fun-C-Food CSD2007-00063
Consolider-INGENIO 2010. Marta Corzo-Martínez thanks Danone Institute
for a grant.
REFERENCES
Ali, M., Bordia, T. & Mustafa, T. (1999). Effect of raw versus boiled aqueous
extract of garlic and onion on platelet aggregation. Prostaglandins
Leukotrienes and Essential Fatty Acids, 60, 43-47.
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... Onion is a perfect blend of valuable bioactive compounds such as FOS, flavonoids, ascorbic acid, and OSCs, and these compounds have shown various health benefits to humans (Griffiths et al., 2002;Corzo-Martínez & Villamiel, 2012). Onion is a prime source of OSCs and flavonoids known for their antioxidant properties, whereas onion by-products possess a significantly higher amount of total phenols, flavonoids, and minerals compared to the edible bulb (Benítez, 2011). ...
... In their study, Bang and Kim (2010) fed rats with onion and results showed that preneo-plastic liver lesions were less and hepatocellular carcinogenesis was inhibited through suppression of ROS.Sulfur compounds were well admitted to have putative anticancer effects. Dipropyl disulfide, dipropyl sulfide, S-allyl cysteine (SAC), Smethylcysteine (SMC), and N-acetylcysteine were reported to retard the growth of early and late-stage carcinogenesis of the oesophagus, forestomach, lung, mammary gland, kidney, liver, and colon(Bora & Sharma, 2009;Fukushima et al., 2001;Guyonnet et al., 2001), whereas ajoene, methiin, SAMC, DATS, and DADS induced apoptosis and inhibited proliferation of human leukemic cells in vitro(Corzo-Martínez & Villamiel, 2012). Organoselenium compounds of onion were also reported to possess similar anticancer property and onion rich in selenium expresses higher anticancerous activity than other crops ( ...
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Bioactive compounds possess different health benefits. Onion contains various bioactive compounds, such as organosulfur compounds, flavonols, ascorbic acids, and carbohydrate prebiotics, and its by‐products have more content of flavonoids than the bulb. Diallyl monosulfide, diallyl disulfide, diallyl trisulfide, and diallyl tetrasulfide are the major organosulfur compounds, whereas quercetin, kaempferol, anthocyanin, and luteolin are considered as main flavonoids. Ascorbic acid and fructooligosaccharides are also regarded as bioactive compounds. Onion bioactive compounds have the strong antioxidant potential for neutralizing oxidative stress of the cells. These bioactive components are beneficial as anticarcinogenic, antibiotic, anti‐inflammatory, antiplatelet, antidiabetic, and cardioprotective agents along with other nutritional benefits. However, various postharvest practices have an impact on these bioactive compounds, for example, curing mostly enhances the bioactive level and processing temperature generally decreases the concentration of many of them, whereas storage studies suggest an increase of others under optimized conditions. Additionally, conventional extraction techniques showed a negative impact on bioactive compounds of onion, whereas innovative methods yielded a higher amount of bioactive components. There is a need for innovative and integrated procedures in the postharvest sector to maintain or enhance the level of bioactive compounds without compromising the quality of onions. The present review comprehensively describes different bioactive compounds of onion, their chemistry, and their pharmacotherapeutic roles. Moreover, it also explores the effects of various postharvest factors, such as temperature, storage duration, and extraction conditions on the level of the bioactive components. It also suggests industrial applications of onion waste and its bioactive compounds in the food sector.
... The high death rate caused by heart disease is reduced by limiting cholesterol through inhibiting cholesterol absorption, bile acid sequestrant, regulation of apoC-III genes, mobilization of fatty acids, and cholesteryl ester transfer protein (4). The secondary metabolites that have a major role in reducing cholesterol levels are flavonoids (such as quercetin) and organosulphur compounds (such as alliin, allyl propyl disulfide, diallyl disulfide, dimethyl disulfide, S-methyl-cysteine sulfoxide, and S-propyl-cysteine sulfoxide) (5). Those compounds reduce cholesterol by inhibiting the activity of HMG-CoA reductase, which plays a role in the synthesis of mevalonate, subsequently affecting the low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) levels (6). ...
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Introduction: Allium cepa extract has been reported to have anti-hypercholesterolemic activity in rats. This study was conducted to investigate the effects of standardized fermented A. cepa L. var aggregatum extract on cholesterol levels and HMG-CoA reductase enzyme. Methods: The fermented A. cepa extract was standardized by the presence of quercetin using a validated high performance liquid chromatography (HPLC) method. The activity of the extract on HMG-CoA reductase was determined using HMG-CoA Assay kits, then measured by Nano spectrophotometry. In vivo study was conducted in hypercholesterolemic rats. The extract was administered orally at doses of 100, 200, and 300 mg/kg body weight (bw) to rats for 21 days and the cholesterol levels were measured every week. Results: All doses of fermented A. cepa extract and its marker compound, quercetin, ameliorated the levels of high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) as compared to those of negative control (P<0.05). Of all the doses, fermented A. cepa extract at the dose of 200 mg/kg bw displayed the highest reduction in LDL-C levels. In addition, the extract at the dose of 200 mg/kg bw showed the strongest enhancement in HDL-C levels. The fermented A. cepa extract and quercetin also inhibited the HMG-CoA reductase enzyme with inhibitory activity of 61.78%. Conclusion: The ethanol extract of fermented A. cepa shows anti-hypercholesterolemic activity. The strong anti-hypercholesterolemic activity of the extract might be due to the high amounts of quercetin, although other constituents may also contribute.
... These have been proved to have properties including hypolipidemic, hypocholesterolemic, anti-hypertensive, and anti-thrombotic, in addition to antimicrobial, anti-inflammatory, and antioxidant properties in humans. Onion flavonoids have also shown a reduction in the prevalence of cardiovascular diseases (Corzo-Martínez & Villamiel, 2012;Suleria et al., 2015;Teshika et al., 2019). Onion hexane extracts have also shown potential anti-cancer properties against gastric cancer cells by inhibiting their proliferation (Toniazzo et al., 2017;Xu & Sung, 2015). ...
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Phytochemicals have gained importance in tackling viral infections and related symptoms. In this review, the role of quercetin in onions, its absorption, and metabolism have been focussed. The action mechanism of quercetin against the inflammatory responses in the human body has been discussed. Onion dehydration and its effects on phytochemicals have also been discussed. The importance of dehydration of onions and their connection with improving the health of the masses have been discussed. Onions being perishable are often wasted, causing monetary losses to farmers, traders, and the government. Making these available for public consumption in the countries deprived of onion production would help fight infections. Dehydration of onion would make onions available conveniently and economically. Studies that have used dehydrated onions for quercetin extraction have been discussed as well. This review highlights the phytochemicals essential to improving immunity and acting as immune boosters against viral infections and their fate on dehydration.
... The pharmacological activity of onion includes antibacterial activity, hypocholesterolemic, hypolipidemic, antihypertensive, antithrombotic, and hypoglycemic activities, wound healing activity, antioxidant, anti-inflammatory, asthma-protective agent, and anticancer activity. The possible reported activities are due to the presence of organic sulfur compounds along with organoselenium compounds, flavonols (quercetin and its glucosides), and dietary fiber (fructans and fructooligosaccharides) [8]. The DNA from onion is extracted by simple chemical degradation process where mechanical disruption of cell wall causes the DNA to precipitate and become visible. ...
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... Algunos au- tores 60-61 defienden que el ajo negro muestra efectos anti- inflamatorios, anticoagulantes y antialergénicos inferiores a los proporcionados con el ajo fresco. No obstante, otros investigadores han descrito efectos metabólicos positivos, como la inhibición de células cancerosas en ensayos in vitro e in vivo 62 , con reducción en la producción de NO, TNF-α, y PEG-E2 en macrófagos estimulados con LPS.Aunque en menor medida que sucede con los compuestos de ajo, las propiedades inmunoestimuladoras de compues- tos y extractos de cebolla también han sido ampliamente descritas[63][64][65]. Esta bioactividad está asociada a la presencia 191 Ars Pharm. ...
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Objectives: Review and discussion of the scientific evidence on the effects of organosulfur compounds ofAlliumgenus as immunomodulators and immunostimulators. Methods: A review of original scientific articles and reviews was conducted. Results: Numerous research and trials have shown the close relationship between food and health, pointing out the benefits that vitamins, minerals, polyunsaturated fatty acids, probiotics, prebiotics or phytochemicals exert on various diseases. Among them, the role of substances of vegetable origin, such as carotenoids, phenolic compounds, alkaloids, nitrogen and organosulfur compounds, should be remarked for their positive influence on the microbiota, intestinal health and immune system.In this work the scientific evidences about the benefits of some organosulfur compounds ofAlliumgenus, such as allicin or propyl propane thiosulfonate, are reviewed and discussed for their immunomodulatory and immune-enhancing properties. Conclusions: Numerous scientific studies have shown the positive effects of organosulfur compounds ofAlliumgenus on the immune system and inflammatory processes. In particular, of some compounds such as allicin, although its instability strongly affects its real application in nutraceutical supplements, and other compounds, such as propiin derivatives, are more promising as immunostimulators ingredients
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Vegetables are essential protective diet ingredients that supply ample amounts of minerals, vitamins, carbohydrates, proteins, dietary fiber, and various nutraceutical compounds for protection against various disease conditions. Color is the most important quality parameter for the farmers to access the harvest maturity while for the consumer's reliable indices to define acceptability or rejection. The colored vegetables contain functional compounds like chlorophylls, carotenoids, betalains, anthocyanins, etc. well recognized for their anti-oxidant, anti-microbial, hypolipidemic, neuroprotective, anti-aging, diuretic, and anti-diabetic properties. Recently, there has been a shift in food consumption patterns from processed to semi-processed or fresh fruits and vegetables to ensure a healthy disease-free life. This shifted the focus of agriculture scientists and food processors from food security to nutrition security. This has resulted in recent improvements to existing crops like blue tomato, orange cauliflower, colored/black carrots, with improved color, and thus enriched bioactive compounds. Exhaustive laboratory trials though are required to document and establish their minimum effective concentrations, bioavailability, and specific health benefits. Efforts should also be directed to breed color-rich cultivars or to improve the existing varieties through conventional and molecular breeding approaches. The present review has been devoted to a better understanding of vegetable colors with specific health benefits and to provide in-hand information about the effect of specific pigment on body organs, the effect of processing on their bioavailability, and recent improvements in colors to ensure a healthy lifestyle.
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Water management is becoming commonplace in discussions of high-yield farming and modern agricultural best practices. A field experiment undertaken in the Northern region of Egypt, Kafr El-Sheikh Governorate, with four cut-off furrow irrigation treatments (100%, full irrigation – considered as a control; 90%, 80% and 70% of strip length) was used to compare the effects of reduced water supply on onion (Allium cepa, L.) production via assessing three different cultivars (e.g., Giza red, Giza 20 and Behairy red). A strip-plot design with three replicates was employed in this regard during two successive seasons (2014–2015/2015–2016). Regardless of onion type, water supply at 80% level resulted in higher marketable and total bulb yield (t/ha) with improved quality traits and storability compared to other irrigation treatments. There have been few significant interspecies differences. The most notable significant differences were recorded in Giza red and Behairy red for all studied characteristics. The highest results were reached with Giza red under the use of 80% irrigation level. In addition to the excellence in improving the overall quality and harvestable yield, this treatment (80% watering) has produced relatively good results with respect to the consumptive water-use efficiency, water productivity and showed significant benefits in terms of saving irrigation water. Maximum water saving was obtained under the use of 70% irrigation treatment, but in the absence of a good and economically unacceptable yield. The traditional technique (100% water supply) consumed much water, surpassing the most effective treatment (80%) by 1195.77 cubic meter per hectare (i.e., 11.96 cm in depth/height). In conclusion, cut-off irrigation technique is considered an efficient and effective intervention approach for onion yield increases while maintaining post-harvesting quality and water savings. However, extending the study beyond onion is critical to increase the range of benefit with regard to other crops, as well for adequate management of water under deficit irrigation conditions.
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Background: Research on the association between fruit and vegetable intake and risk of colorectal adenoma is inconclusive. Objective: We studied whether intake of fruit, vegetables, or their subgroups is associated with a lower risk of prevalent colorectal adenoma. Design: In men and women (aged 55–74 y) who were screened for colorectal cancer in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO) (1993–2001), we compared 3057 cases with at least one prevalent histologically verified adenoma of the distal large bowel with 29 413 control subjects. Using a food-frequency questionnaire, we quantified intake of fruit and vegetables in the 12 mo before screening as energy-adjusted pyramid servings/d (ps/d). Adjusted odds ratios (ORs) and 95% CIs were estimated by logistic regression. Results: Risk of distal adenoma was significantly lower among subjects in high (≈5.7 ps/d) versus low (≈1.2 ps/d) quintiles of total fruit intake (OR: 0.75; 95% CI: 0.66, 0.86, P for trend <0.001), which was not completely explained by dietary folate or fiber intake. Inverse associations between adenoma and total fruit intake were observed regardless of adenoma histopathology and multiplicity. However, the protective effect was seen only for colon and not rectal adenoma. Total vegetable intake was not significantly associated with reduced risk of adenoma. ORs for colorectal adenoma among persons with high versus low intakes of deep-yellow vegetables, dark-green vegetables, and onions and garlic were significantly related to lower risk of adenoma, although the P for trend for dark-green vegetables was not significant. Conclusion: Diets rich in fruit and deep-yellow vegetables, dark-green vegetables, and onions and garlic are modestly associated with reduced risk of colorectal adenoma, a precursor of colorectal cancer.
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The stalk of Allium schoenoprasum L (fistular onion stalk) has been used in traditional Chinese medicine. In this study, we investigated the effects of fistular onion stalk extracts on nitric oxide (NO) production and endothelial NO synthase (eNOS) expression in cultured human umbilical vein endothelium cells (HUVECs). We found that the extracts of fistular onion stalk significantly increased the level of NO and the activity of eNOS. Our findings demonstrated that fistular onion stalk extracts could be a good candidate for new drugs to treat cardiovascular diseases by enhancing endothelial production of NO.
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We evaluated the effects of heat treatment on various properties of onion extracts (Allium cepa). Onion was heated at various temperatures (110-150°C) for various times (1-5 hr), and the total polyphenol, flavonoid, and free sugar contents, and antioxidant activity were investigated. With increased heating temperatures and exposure times, the total contents of polyphenols and flavonoids, as well as antioxidant activity increased. The highest total polyphenol content (189.80 mg/100 g) occurred after heating for 2 hr at 140°C. The highest total flavonoid content (252.51 mg/100 g) occurred after heating for 3 hr at 150°C. The antioxidant activity assessed using the DPPH method was highest, at 2.19 mg/mL (IC50 value), after heating for 2 hr at 150°C. Correlations between antioxidant activity and the total polyphenol, total flavonoid, and fructose contents were highly significant (all p<0.01). The optimal heating time and temperature were 2 hr and 130°C.
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Hypoglycemic effect of onion skin extract in vitro and in vivo was investigated. A methanol extract of onion skin inhibited yeast α-glucosidase with an IC50 of 0.159 mg/mL. A single oral administration of the onion skin extract (500 mg/kg) significantly lowered the postprandial area under the glucose response curve to starch (1 g/kg, p<0.05). Three-week-old db/db mice were fed an AIN-93G diet or a diet supplemented with a 0.5% onion skin extract for 7 weeks after a 1-week adaptation period. Consumption of onion skin extract significantly reduced the levels of plasma glucose, insulin, and blood glycated hemoglobin as compared with the control group (p<0.05). These findings suggest that onion skin is effective in controlling hyperglycemia in animal models of type 2 diabetes mellitus, at least in part by inhibiting α-glucosidase activity.
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In order to determine chemical components of onion flesh and peel, general nutrients, vitamin C, and total flavonoids were measured. Onion peel showed less moisture (14.3%) and no vitamin C compared to onion flesh. Onion peel contained more amounts of total flavonoids compared to onion flesh. In addition, the inhibitory effects of solvent extracts from onion flesh and peel on H_2O_-induced oxidative stress and growth of cancer cell lines (AGS human gastric adenocarcinoma and HT-29 human colon cancer cells) were investigated. Acetone with methylene chloride (A+M) and methanol (MeOH) extracts from onion flesh and peel appeared to significantly reduce the levels of intracellular reactive oxygen species (ROS) (p values of 85% aq. methanol fraction from onion flesh and peel on AGS were 0.04 and 0.03 mg/ml, respectively, while those on HT-29 were 0.23 and 0.04 mg/ml. From our results, 85% aq. methanol fraction had an inhibitory effect against oxidative stress and growth of cancer cells, suggesting that it may contain biological active compounds.
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In the present scenario, herbal medicines have gained global importance with both medicinal and economic implications. Widespread use of herbs throughout the world has raised serious concerns over their quality, safety and efficacy. Thus, accurate scientific assessment has become a prerequisite for acceptance of health claims. Onion (Allium cepa Linn.), a member of the genus Allium, is the second most important horticulture crop all over the world. It is used as an important source of phytoconstituents and food flavour. Onions are one of the richest sources of flavonoids and organosulphur compounds. They possess a high level of antioxidant activity attributable to flavonoids quercetin, kaempferol, myricetin; pigments such as anthocyanins, and organonosulphur compounds. The most important among the sulphur compounds are the cysteine derivatives non-volatile Samino acids, S-alk(en)yl-substituted cysteine sulphoxides and their decomposition products such as thiosulfinates and polysulfides. These sulphure compounds and flavonoids possess antioxidant, antidiabetic, anti-inflammatory, anticancer, antimicrobial, antihyperlipidaemic, anticholesterolaemic, fibrinolytic, antiatherosclerotic, anticataractogenetic, antiplatelet aggregation, immunomodulatory, neuroprotective in ischemia and reperfusion-induced cerebral injury, and various other biological activities. Wide spectrum of biological activities makes A. cepa as potential therapeutic agent.
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The effect of fructans in human nutrition became more and more important during the last years and in the same way the knowledge about the fructan metabolism in plants and the production of fructans from plants. About 15 % of higher plants and also numerous crops store fructans. The use of fructans is either indirectly as food ingredients or directly by the use of vegetables. Fructans are mostly gained from chicory, but the use of Jerusalem artichoke, transgenic potato and sugar beet lines are also discussed. Vegetable crops like onion, leek, asparagus, and sprouts from cereals contain rather high amounts of fructans and may become more important in the near future, e.g. as 'functional food'. Many foods can be enriched with fructans as dietary fibers without any negative impact on the taste of the product. With an additional uptake of 10-15 g of fructans per day, the recommended daily uptake of dietary fibers (30 g) could be reached. Fructans are stimulating the growth of specific microorganisms in the colon (e.g. Bifidobacteria) with a general positive health effect.