Chemicals
Chemical contaminants of food include
heavy metals, pesticides, and food additives. The last mentioned will be
discussed in this section, while the other two entities are discussed
elsewhere.
Food additives may be antioxidants, flavouring agents,colouring
agents, sweetening agents, thickening agents, or preservatives (Table 33.11).
Accent, Ajinomoto, Chinese
Seasoning, Glutacyl, Vetsin, Zest.
■■ Flavouring agent in
foods, especially Chinese food, sausages, canned soup, etc.* MSG is generally
sold as a fine, white crystalline substance, similar in appearance to salt or
sugar. It has a sweetish saline taste.
■■ MSG has been used to treat patients with hyperammon-aemia
in conditions such as hepatic encephalopathy.
·
Glutamate, a major building block of
proteins, is released during breakdown of a protein molecule, and occurs
naturally in many foods (meat, milk, mushrooms, cheese, tomatoes, etc.).
Monosodium glutamate (MSG) is the monosodium salt of L-glutamic acid. It is
produced by the following processes:
o
Fermentation of carbohydrate sources
such as sugar beet molasses.
o
Hydrolysis of vegetable proteins.
o
Waste from beet-sugar molasses by
acid hydrolysis.
o
By action of Micrococcus glutamicus upon a carbohy-drate, and subsequent partial
neutralisation.
·
Ingestion of large quantities of MSG
is said to cause the Chinese restaurant
syndrome ( CRS), though doubts
havebeen expressed of late on the role of MSG in the aetiology of the syndrome.
·
Features include burning or tingling
sensation and numb-ness of face, trunk, and upper limbs, weakness, dizziness,
syncope, flushing, lacrimation, sweating, chest pain, head-ache, nausea,
gastric distress, and rarely bronchospasm and angioedema. In young children, a
convulsive attack may occur (shudder
attack). Symptoms resolve on their own, and rarely last for more than half
to one hour.
·
Treatment is symptomatic and
supportive. Gastrointestinal decontamination is generally not indicated after
an acute inges-tion. Toxicity is very unlikely.
·
The syndrome can generally be prevented by prior ingestion
of “safe foods” such as a glass of milk or a slice of cottage cheese. The
following preventive measures have been suggested for MSG-sensitive
individuals:
·
When shopping for food items, read labels and avoid foods
which contain MSG—canned foods (except vegetables and fruits), soya sauce,
dried foods, and processed meats. Avoid catered food (including airline meals).
·
If it is planned to dine out at a hotel
o Phone ahead and request food without
MSG.
o Eat a snack before you go: cottage
cheese or a glass of milk.
o Avoid alcohol.
o Do not eat hors d’oeuvres or soup.
o Avoid casserole dishes, Chinese
foods, and marinated meats.
o Avoid salad dressings.
o Eat only freshly prepared, broiled,
or sauteed meats or fish (without
sauces or seasoning).
o Drink a cup of coffee along with the
meal, or soon thereafter.
Of late, there are doubts being
raised about the actual role of MSG in human illness. The USFDA has studied
adverse reac- tion reports and other data concerning MSG’s safety for several
years, and believes that while some sensitive people can have mild and
transitory reactions when they consume significant amounts of MSG, it is still
a safe food ingredient for the general population. In 1995, a report from the
Federation of American Societies for Experimental Biology (FASEB) affirmed the
FDA’s belief that MSG and related substances are safe food ingredients for most
people when eaten at moderate levels. This report identified short-term
reactions known as ‘MSG Symptom Complex’ in two groups of people. Individuals
in the first group suffer a reaction after eating large doses (3 gm or more per
meal) of MSG, particularly on an empty stomach. In the second group,
individuals with severe and poorly controlled asthma may, in addition,
experience difficulty in breathing.
Although some studies have reported
MSG-induced asthma attacks in asthmatic patients, several other studies could
not confirm their results.
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