Monosodium glutamate has a distinctive taste that falls outside
the region of the four classic tastes: sweet, sour, salty, and bitter.
This taste is called “Umami,” also referred to as “Xien Wei” in Chinese
or “savory, “broth-like” or “meaty taste” in English. Due
to this special taste, many food producers use MSG to enhance the
flavor of their product [2]. Recently, Chaudhari et al. [3] identified
a specific glutamate taste receptor on the tongue. Three umami
substances (glutamate, 5-inosinate, and 5-guanylate) were found
by Japanese scientists, but umami has not been recognized in
Europe and America for a long time. In the late 1900s, umami
was internationally recognized as the fifth basic taste based on
psychophysical, electrophysiological, and biochemical studies.
Three umami receptors (T1R1+T1R3, mGluR4, and mGluR1)
were identified. There is a synergism between glutamate and
the 5-nucleotides. Among the above receptors, only T1R1+T1R3
receptor exhibits the synergism [4]. Since glutamate and 5-inosinate
are contained in various foods, umami tasted is induced by the
synergism in daily eating [4].
The safety and toxicity of MSG had become controversial in the
last few years because of reports of adverse reactions in people who
have eaten foods that contain MSG. Many studies had confirmed the
adverse reactions of MSG [1,5,6]. MSG has been reported to cause
headache, vomiting, diarrhea, irritable bowel syndrome, asthma
attacks in asthmatic patients and panic attacks [1]. Obuchi et al.
[6] studied the effect of garlic extracts on MSG induced fibroid in
wistar rats and reported that MSG alone increased total protein,
cholesterol and estradiol (estrogen), which in turn, induced fibroid
in the rats. However, treatment with garlic extracts near-completely
abrogated/mitigated any effects that have been induced by MSG
alone.
Egbuonu et al. [7] reported a study aimed at investigating the
potentials of low concentration administration of monosodium
glutamate in inducing hepatotoxicity in male albino rats. In
that study, it was observed that treating rats with monosodium
glutamate at a low concentration (5mg/kg of body weight) could
be hepatotoxic without significant cholestasis or pathologies of
the bone. Onyema et al. [8] reported that MSG at a dose of 0.6mg/g
body weight induced the oxidative stress and hepatotoxicity in
rats and vitamin E ameliorated MSG-induced oxidative stress and
hepatotoxicity. Meraiyebu et al. [9] reported that MSG increased
the number of platelets, bleeding time and clotting time in MSGtreated
rats. Onyema et al. [10] tested the hypothesis that alteration
in glucose metabolism following MSG administration might be
a contributor to the changes in the markers of oxidative stress
observed in the animals. The pattern of induction of oxidative
stress and alteration of glucose metabolic enzymes in the animals
was an indication that oxidative stress induced by MSG in the renal
tissues of rats might be contributed by increased tissue glucose
concentration resulting from enhanced renal gluconeogenesis
[10]. Nwajei et al. [11] reported that four selected food seasonings
(labeled IS, KC, SMC and BS) commonly consumed in Nigeria
adversely perturbed some sex hormones: testosterone, Estrogen
and progesterone of wistar albino rats due to the presence of MSG
in these seasonings. Kolawole [12] investigated the effect of orally
administered MSG on food consumption, body weight and some
biochemical and hematological parameters in adult wistar rats and
reported that MSG at the doses or 5-15mg/kg body weight was not
hazardous to health.
Production of MSG
The Chinese have used certain seaweeds to enhance the flavor
of food for some 2000 years. In 1908, the flavor enhancing agent
was identified as glutamic acid [1]. Shortly thereafter, methods for
extracting glutamic acid from seaweeds were developed [1]. MSG
is manufactured through a process of protein hydrolysis, where
glutamic acid is freed from protein through enzymatic fermentation
or use of chemicals. MSG is also manufactured by a fermentation
process in which bacteria are grown aerobically in a liquid nutrient
medium. The bacteria release glutamic acid as a by-product of
metabolism into the liquid nutrient medium in which they are
grown. The glutamic acid is then separated from the fermentation
broth by filtration, concentration, acidification and crystallization
and conversion to its sodium salt.
The name “monosodium glutamate” refers to a 99% pure
combination of glutamic acid and sodium [13]. About 1.9 million
tons of monosodium g1utamate are produced worldwide per year
by fermentation using Corynebacterium glutamicum or related
species [13]. These bacteria are biotin auxotrophs and biotin
(vitamin B7) is used as a cofactor. Producers prefer the use of sugars
to produce MSG. Some sugar sources used includes, sugarcane,
starch hydrolysates gotten from corn or cassava tubers, among
others. Ammonia and ammonium salts are added as Nitrogen
source. Vitamins and other nutrients are added to finish off the
process. Glutamate accumulation in the medium occurs only under
biotin-limiting condition. The requirements for biotin limitation
prevented the use of standard raw materials such as sugar molasses
because they contained biotin. Addition of penicillin, or the use of
microorganisms auxotrophic for glycerol or oleate, that allows the
bacteria to produce large amounts of glutamate without biotin
limitation (Figure 3).
Impurities Found in MSG
Monosodium glutamate contains D-glutamic acid, pyroglutamic
acid, and various other contaminants in addition to L-glutamic acid
[2].
D-Glutamate
Every amino acid (except glycine) can occur in two isomeric
forms, because of the possibility of forming two different
enantiomers around the central carbon atom. By convention, these
are called L- and D- forms, analogous to lefthanded and righthanded
configurations. Only L-amino acids are manufactured in the cells
and incorporated into proteins. Some D-amino acids are found in
the cell walls of bacteria, but not in bacteria proteins. Glutamate has
both the D- and L- enantiomers and only the L-glutamate enantiomer
has flavor enhancing properties [14]. Manufactured monosodium
glutamate contains over 99.6% of the naturally predominant
L-glutamate form, which is a higher proportion of free glutamate
ions of fermented naturally occurring foods. Fermented products
such as soy sauce steak sauce and Worcestershire sauce have
levels of glutamate like foods with added monosodium glutamate.
However, 5% or more of the glutamate may be D-enantiomer. Nonfermented
naturally occurring foods have lower relative levels of
D-glutamate than fermented products [14] (Figure 4).
Unlike other D-amino acids, D-glutamate is not oxidized by the
D-amino acid oxidases; therefore, the detoxification pathway is not
available for handling D-glutamate. Likewise, D- glutamate when
ingested, largely escapes most deamination reactions (unlike its
L-counterpart). Free D-glutamate is found in mammalian tissue at
surprisingly high levels, with D-glutamate accounting for 9% of the
total glutamate present in the Liver. D-glutamate is the most potent
natural inhibitor of glutathione synthesis identified to date and
this may account for its localization to the liver, since circulating
D-glutamate may alter redox stability [14].
Pyroglutamic acid
Pyroglutamic acid (PCA) is also known as 5-oxoproline, pidolic
acid, or pyroglutamate. It is a common but rarely studied natural
amino acid derivative in which free amino group of glutamic
acid or glutamine cyclizes to form a lactem. It is a metabolite
in the glutathione cycle that is converted to glutamate by
5-oxoprolinase. Pyroglutamate is found in many proteins including
bacteriorhodopsin. N-terminal glutamic acid and glutamine
residue can spontaneously cyclize to become pyroglutamate or
enzymatically converted by glutaminyl cyclases. Pyroglutamate is a
heterocyclic compound and is present in plasma of several species
including humans. However, local brain injections of very high
concentrations of pyroglutamate induced neurotoxic lesions that
appeared to be like those produced by kianic acid [15] (Figure 5).
Pyroglutamic acid has also been found to be produced
by glutamate in the presence of γ-GCS, glutamine synthetase
and glutamate-5-kinase enzymes [16-18]. The enzyme-bound
phosphorylated glutamate is the intermediate in all three enzymatic
reactions. Activated glutamate is transferred to an acceptor
molecule, namely cysteine, ammonia and NADPH respectively.
Phosphorylated or activated glutamate is highly unstable and
prone to spontaneous cyclization into pyroglutamic acid [19]. If
the acceptor molecule is not present or unavailable, spontaneous
cyclization of activated glutamate leads to pyroglutamic acid
generation. γ-GCS which catalyzes the first step of glutathione
biosynthesis activates glutamate that may be converted into
pyroglutamic acid in the absence of cysteine [17]. Similarly, in
methanotrophs, it has been proposed that in stress and nitrogenlimiting
conditions pyroglutamic acid is generated from glutamate
via glutamine synthetase, as found in in vitro conditions [20].
Mono and dichloro propanols
3-monochloropropane-1,2-diol (3-MCPD) is an organic
chemical compound which is the most common member of
chemical food contaminants known as chloropropanols. It is
suspected to be carcinogenic in humans. It is primarily created in
foods during protein hydrolysis when hydrochloric acid is added
at high temperature to speed up the breakdown of proteins into
amino acids. As a byproduct of this process, chloride can react
with the glycerol backbone of lipids to produce 3-MCPD. In 2000,
a survey of soy sauces and similar products available in the UK
was carried out by the Joint Ministry of Agriculture, Fisheries and
Food/Department of Health Food Safety and Standards Group
(JFSSG) and reported more than half of the samples collected
from retail outlets contained various levels of 3-MCPD [21]. In
2001, the United Kingdom Food Standards Agency (FSA) found in
tests of various oyster sauces and soy sauces that 22% of samples
contained 3-MCPD at levels considerably higher than those deemed
safe by the European Union. About two-thirds of these samples also
contained a second chloropropanol called 1,3-dichloropropane-
2-ol (1,3-DCP) which experts advise should not be present at any
levels in food. Both chemicals have the potential to cause cancer and
the Agency recommended that the affected products be withdrawn
from shelves and avoided [22] (Figure 6&7).
MSG in Seasoning Cubes
Food seasoning is a substance that adds flavor to food, for
example salt, peppers, and other spices. Spices are vegetable
substances of indigenous or exotic origin which are aromatic and
have hot piquant tastes, used to enhance the flavor of foods or
to add to them the stimulant ingredient contained in them [22].
Seasonings can also be used to replace common salt in a great
variety of other industrially prepared food items as well as in the
preparation of foods both in restaurants, catering, home kitchen
etc. Such seasonings are particularly suitable for soups, beefs, and
other foods in which salty, and/or spiced seasonings are used. The
ingredient mixture and seasonings when added to various food
items change the food composition [23].
There are several brands of food seasonings readily available
in the open markets, in-street shops and supermarkets. These
include: Star maggi, knorr, royco, doyin, jumbo (cubes), Onga, Mixpy,
Benny, Aluba shrimp seasoning (powdered), A-one, Vedan, Ajino-
moto, Salsa and Tasty (monosodium glutamate). Reports have
indicated that the major active ingredients in flavor enhancers are
salt (NaCl) and monosodium glutamate (MSG). Other ingredients
include: Hydrogenated palm oil, Caramel, Colour, Soyabeans, locust
beans, Maltodextrin, Corn starch, Chicken fat, Disodium guanylate,
Disodium inosilate, Hydrolyzed plant/Vegetable, protein, Tomatoes,
Natural spices etc. [24].
Chinese Restaurant Syndrome
The “Chinese restaurant syndrome “(CRS) was first described
over 40 years ago. The original description of the symptoms having
their onset about 20 minutes after the meal included numbness
or burning at the back of the neck, radiating into both arms and
sometimes into the anterior thorax, which was associated with a
feeling of general weakness and palpitation [25]. The symptoms of
flushing, dizziness, syncope, and facial pressure were described later
[26]. Children can react with fever, convulsion or a steady anxiety.
Monosodium glutamate was widely believed to be associated with
CRS. However, reviews of relevant studies have proposed that the
studies which associated MSG with CRS did not have the robust
experimental design, results were inconsistent and the frequency
of responses to MSG intake was not high enough to bring evidence
that MSG is the trigger of CRS [27]. CRS is said to occur in people
who are sensitive to MSG.
This issue remains controversial. Since MSG is identical to
glutamate naturally contained in many foods, it is absorbed and
metabolized by the body in the same manner. On the other hand,
damaging effects have been associated with ingesting MSG, such
as those related to Alzheimer and Parkinson diseases. This was
dismissed by a consensus conference lead by Nobel Preis laureate
Professor Dr. Konrad Beyreuther, because MSG ingested through
food cannot cross the blood-brain-barrier in healthy persons [28].
Metabolism of Dietary Glutamate
Glutamate is the main constituent of dietary protein and
is also consumed in many foods as an additive in the form of
monosodium glutamate. Evidence from human and animal studies
suggests that glutamate is a major oxidative fuel for the gut and
that dietary glutamate is extensively mobilized in the first pass
by the intestine [29]. Glutamate is also an important precursor
for bioactive molecules, including glutathione, and functions as a
key neurotransmitter. Several studies have shown that glutamate
is extensively metabolized in the intestine [29-31]. Glutamate is
the main excitatory neurotransmitter in the body and multiple
glutamate receptors and transporters have been found in the gastrointestinal tract and enteric nervous system [32]. Recent
studies have also shown that two vesicular glutamate transporters
(VGLUTs), VGLUTs1 and VGLUTs2, are present in enteric nervous
and pancreatic tissue [28,32]. It has become apparent that the
gut particularly the intestine is also a major site of catabolism of
several amino acids, mainly nonessential amino acids glutamine,
glutamate, and aspartate [29].
An important distinction to be made, however, although amino
acids are catabolized in both liver and gut tissues, the extent
to which they are completely oxidized to carbon dioxide varies
[29]. Glutamate is a key amino acid linking hepatic amino acid
catabolism and gluconeogenesis, because many amino acids are
first catabolized to glutamate by transamination [29]. The intestinal
metabolism of glutamate is presumed to occur largely in epithelial
cells lining the mucosa, enterocytes (Figure 8).
A longstanding concern with dietary glutamate consumption,
particularly monosodium glutamate (MSG), is the evidence and
potential risk of neurotoxicity [29]. Some have raised serious
concerns about the potential risk of dietary MSG, parenteral
glutamate, and its implications for human diseases, such as obesity
[28,31]. However, it is critically important to recognize that the
evidence of neurotoxicity in several experimental models only
occurred with extremely high enteral and parenteral glutamate
loads [15].
Glutamate, like other constituent amino acids ingested in
dietary protein, is normally absorbed and metabolized in the small
intestine subsequent to proteolytic digestion. However, some
amino acids, especially dietary MSG, are ingested in a free form and
thus may be metabolized differently when they are presented to the
epithelial mucosa of the stomach [29].
Effects of MSG
Glutamate receptors are synaptic receptors that are located on
the membranes of neuronal cells [33]. They play a central role in
excitotoxicity and are implicated in several neurological diseases.
Prevalence in the central nervous system, it has been linked to
many neurodegenerative diseases, and several other conditions
have been further linked to glutamate receptor gene mutations or
receptor autoantigen/antibody activity [33].
Excitotoxicity is a process of overstimulation of
glutamate receptors which can lead to neuronal damage and
neurodegeneration. This process is carried out by excitotoxins.
Excitotoxins are amino acids such as glutamate, aspartate and
cysteine which when applied to neurons will cause them to be
over stimulated and die. Unlike glutamic acid-containing proteins
in foods, glutamate is absorbed very quickly in the gastrointestinal
tract (GIT). Absorbed glutamate could spike blood plasma levels of
glutamate [34]. Its concentrations in plasma are 50-100μmol/L,
in whole brain are 10,000-12,000μmol/L but only 0.5-2 μmol/L
in extracellular fluids (ECFs). The low ECF concentrations, which
are essential for optimal brain function, are maintained by neurons,
astrocytes, and the blood-brain barrier (BBB) [34].
Central nervous system (CNS)
Glutamate is the excitatory neurotransmitter in the mammalian
central nervous system (CNS) playing an important role in both
physiological and pathological processes [34]. Glutamate receptors
include three families of ionotropic receptors (N-methyl-Daspartate,
α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid
and kainate) and three groups of metabotropic receptors (mGluR)
[35]. They are dispersed throughout the central nervous system
including amygdala, hippocampus and hypothalamus where they
regulate many vital metabolic and autonomic functions [36]. In
the brain, glutamate serves as a neurotransmitter in addition to its
general role in protein and energy metabolism.
Neurotransmitters are stored in nerve endings and are used
by nerve cells to inhibit or excite other nerve cells or target cells,
such as muscle or endocrine cells. Concerns were raised in the late
1960s that high doses of MSG may adversely affect brain function.
The possibility of MSG-induced brain lesions through injection or
force-feeding methods in rodents was also reported. The very high
concentration of glutamate in the cytosol and glutamate-containing
vesicles requires strict homeostatic mechanisms for the following
reason. Glutamate is the major excitatory neurotransmitter, yet
levels of glutamate in the extracellular fluid must be kept low (<100
μM) to avoid excitotoxicity. In fact, the concentration of glutamate
in the ambient extracellular fluid of the brain is normally 0.5-5μM
[37]. This remarkable glutamate concentration gradient between
the extracellular fluid and nerve cell cytosol is accomplished by
powerful uptake systems for glutamate in neurons, astrocytes and
synaptosomal vesicles [38].
Obesity
Data from animal studies, in which neonatal administration of
MSG provides a model of obesity with impaired glucose tolerance
and insulin resistance led to concerns about obesity in humans using
MSG in food. More hypotheses have proposed the mechanisms of
MSG influence on metabolism. The potential link between MSG and
obesity includes the MSG effect on energy balance by increasing
palatability of food and by disrupting the hypothalamic signaling
cascade of leptin action [28,39].
MSG has been reported to increase mRNA expression of
interleukin-6, tumor necrosis factor-alpha, resistin and leptin
in visceral adipose tissue, it increased insulin, resistin and leptin
levels in serum and it also impaired glucose tolerance [40]. Through
MSGs stimulation of the orosensory receptors and by improving
the palatability of meals, it influences weight gain. Monosodium
Glutamate (MSG) causes reduction in the secretion of growth
hormones, leading to stunted growth and irreversibility in obesity,
excessive weight, essentially due to accumulation of excess fats in
adipose tissue [41], arising from high cholesterol levels leading to
cardiovascular diseases and endocrinological disorder [42] (Figure
10).
Reproductive System
Testosterone is a hormone in the group of androgens which
directly stimulates spermatogenesis through androgen receptors
located in the testis [43]. The rate or level of spermatogenesis
also affects testosterone level and other reproductive hormones.
Progesterone is a female sex hormone, synthesized from
pregnenolone which in turn is derived from cholesterol. It is among
the group of steroid hormones called progestogens. It plays a
central role in ovulation, pregnancy, implantation and regulation of
uterine functions [44]. Estrogens are steroid hormones produced
primarily by the ovaries (the granulosa cells of the ovarian
follicles and corpora lutea) and placenta (during pregnancy). The
ovarian synthesis of estrogen is stimulated by Follicle-stimulating
hormone (FSH) [33]. MSG has toxic effects on the testis by causing
a significant oligozoospermia and increase abnormal sperm
morphology in a dose dependent fashion in male wistar rats [45].
It has been implicated in male infertility by causing testicular
hemorrhage, degeneration and alteration of sperm cell population
and morphology [46].
Hepatotoxicity
Liver is the largest gland in the mammalian body. The
hepatocytes have metabolic functions that deals with very essential
processes of such a detoxification, deamination, transamination,
removal of ammonia in the form of urea, biosynthesis and release of
non-essential amino acids and plasma proteins with the exception
of immuno gamma globulins, gluconeogenesis, storage of glycogen,
conversion of carbohydrates and proteins to lipids, synthesis of
lipoproteins, phospholipids and cholesterol, oxidation of fatty acids,
storage of iron in the form of ferritin as well as storage of vitamins
A, D and B12. Several function tests have been formulated to explore
hepatic status [47-50]. Several enzymes have been determined to
explore hepatic status such as alanine aminotransferase (ALT) and
aspartate aminotransferase (AST). In addition, some other tests
have include measurement of serum lactic dehydrogenase (LDH),
Gamma glutamyl transpeptidase (GGT), Alkaline phosphatases
and 5-nucleotidase activities are employed [51-53]. The use of this
substance as a flavor enhancer over time has been reported to be
hepatotoxic [7].
Nephrotoxicity
Animal studies suggest that chronic monosodium glutamate
intake induces kidney damage by oxidative stress [54]. Oxidative
stress is caused by the excessive production or a decreased
elimination of free radicals in cells, the majority of which are oxygen
radicals and other reactive oxygen species (ROS) [55]. However, the underlying mechanisms are still unclear, despite the growing
evidence and consensus that α-ketogluterate dehydrogenase,
glutamate receptors and cysteine-glutamate antiporter play
an important role in up-regulation of oxidative stress in MSGinduced
renal toxicity [55]. Nutrition metabolism and several
extracellular and intracellular factors such as hormones, cytokines,
and detoxification processes contribute to oxidative stress [56,57].
Therefore, excessive renal metabolism of glutamate in chronic MSG
intake can be a source of ROS. Decreased level of major antioxidant
enzymes and increased lipid peroxidation has been demonstrated
in the kidney of chronic MSG-exposed rats [58]. Also, high doses of
glutamate have been shown to induce significant toxicity in renal
culture cells [59].
The formation of ROS in the kidney of animals exposed to MSG
was a major contributor to their nephrotoxic effect leading to cellular
and functional damage [60]. Paul et al. [58] found reduced activities
of superoxide dismutase, catalase, glutathione-S-transferase and
glutathione (GSH) in the kidney of animals after MSG administration
[58]. They also reported that markers for lipid peroxidation such
as malondialdehyde (MDA) and conjugated dienes were increased
in MSG-treated renal tissue. It is possible that MSG leads to the
excessive production of free radicals and endogenous antioxidants
are insufficient to meet the demand. Moreover, some studies have
found the ameliorating effects of vitamin C, E and qiercetin on MSGtreated
kidneys [58]. The mechanisms whereby these antioxidants
exert such effects are yet to be fully elucidated. However, these
antioxidants do seem to play a key role against renal inflammatory
responses through a diminution of the activity of inflammatory
enzymes and cytokines secretion, or by inhibiting the activity of
NF-KB [61].
Prevention of MSG Toxic Effects
Consumption of MSG between 0.3 and 1 gram daily has been
reported to be safe. However, in studies involving mice, this has
varied according to weight. Consumer protection agencies advise
healthy persons to avoid consuming MSG frequently. The following
has been reported to minimize the toxic effect of MSG.
Frequent intake of Vitamin C
MSG has been reported to be toxic, especially the nervous
tissues. It causes cellular death through oxidative stress [61]. With
the known benefits of vitamin C, it can reduce the adverse effect of
MSG. Research has shown that vitamin C is an antioxidant, with the
ability to clean up free radicals produced in the body [62]. Vitamin C
can scavenge superoxide, hydrogen peroxide and hydroxyl radicals.
Vitamin C has been reported to reverse the impact of MSG on the
liver by causing a significant drop in the unhealthy growth cells
and reducing mutations of tumor suppressor genes [63]. It has also
been reported to have a protective effect on the liver [64].
Vitamin E
Vitamin E is an important component of the human diet. It
exerts protective effects against diseases which may be attributed to
its powerful antioxidant property [8]. As an antioxidant, it protects
against the damaging effects of free radicals, which may contribute
to the development of diseases [63]. Research has shown that MSG
induces oxidative stress and Vitamin E significantly reduces the
oxidative stress. In mammals, it has been reported to stabilize the
membrane and scavenges lipid peroxy radicals and singlet oxygen
[64].
Garlic
Garlic is a species of the onion family called Allium sativum.
It is in antioxidants, thus its numerous health benefits. Garlic also
contains enzymes, calcium, copper, iron, manganese, phosphorus,
potassium and selenium. Vitamins in garlic include vitamin A,
vitamin B
1 (thiamine), vitamin B
2 (riboflavin), vitamin B
6 and
vitamin C [63].
Curcuma longa (Tumeric)
Curcuma longa commonly referred to as turmeric is a
rhizomatous herbaceous perennial plant of the ginger family,
Zingiberaceae [65].
Curcuma longa has been used in traditional
remedy for a wide range of ailments, including wound healing,
urinary and gastrointestinal tract infections, and liver ailments
[66]. Curcumin has been defined as the most active component
in
Curcuma longa and has been shown to have considerable
gastroprotective, anti-ulcerogenic and therapeutic effect in gastric
ulcer disease [66]. Report by Airaodion et al. [67] showed that
turmeric is potent in the prevention of peptic ulcer due to the
presence of flavonoid and other antioxidants. Due to its content
stated above, turmeric has the propensity to annul the effect of MSG
on the body.
Ginger
Ginger (
Zingiber officinale) is used as spice in food and
beverages and in traditional medicine as carminative, antipyretic
and in the treatment of pain, rheumatism and bronchitis [68].
Its extracts have been extensively studied for a broad range of
biological activities including antibacterial [69], analgesic and
anti-inflammatory [70], antiangiogenesis and antitumor. It has also
been used for the treatment of gastrointestinal disorders including
gastric ulcerogenesis [71]. Ginger has also been reported to be
potent in the prevention of peptic ulcer owing to its flavonoid and
antioxidant properties [72]. With these biological activities, ginger
has the ability to minimize the effect of MSG on human health.
Locust beans
Locust bean (
Parkia biglobosa) is used as a condiment in
cooking. It is very popular in among the Yoruba people of Nigeria
where it is called ‘iru’. It can be fresh or dried. Dried locust bean is
weaker in flavor and pungency than fresh. Locust bean is high in
lipids (29%), Proteins (35%), and carbohydrates (16%). It is a good
source of calcium and fat for rural dwellers. During fermentation,
the reducing sugar content increases, and the total free amino acid
content initially decreases [73]. Locust beans can conveniently be
used instead of MSG-containing seasonings.
Conclusion
This study demonstrated that monosodium glutamate is
hazardous to the human health as it is linked to Chinese Restaurant
Syndrome (CRS). Regular intake of MSG for a long period of time
can lead to conditions such as hepatotoxicity, renal damage, Fibroid,
Obesity etc. More awareness concerning the hazardous effects of
MSG should be created to enlighten people and natural alternatives
for MSG should be promoted.
Glutamate is an important metabolic link between the
tricarboxylic acid (TCA) cycle and urea cycle involved in cellular
energy generation and nitrogen disposal [29] (Figure 9). Dietary GLU
and AKG are transported from the gut lumen into the enterocyte by
the excitatory amino acid carrier-1 (EAAC-1) and Na-dicarboxylate
cotransporter-1 (NaDC-1) transporters respectively. Within the
enterocyte, both GLU and AKG can undergo transamination and
transport into the mitochondria for oxidative metabolism to CO2
[29].
