Naming the Demons
I
call them the Brimstone Demons because they cause me so much pain. But
for
the other 99% of America that is not sensitive, sulfur preservatives
are
quite marvelous creatures. When sprayed on fruit and salads, they
prevent
enzymatic browning keeping the foods fresh and appetizing. When added
to
pickled peppers and red cherries, they maintain the natural, attractive
coloring
of the food. When used on shrimp and seafood, they prevent black fungus
spotting
and other forms of spoilage. Sulfur oxides perform similar tricks on
instant
potatoes, french fries, grapes, raisins, wine, lemon juice, dried
apricots, shredded coconut, dark breads, colas,
cookies, candies of every persuasion, yogurts, syrups, cereals and the
list
goes on forever. You may notice I didn’t mention guacamole avocado dip.
It’s just too painful for me. You see, I used to love guacamole before
I learned it's preserved with sulfite and one cause of my
headaches.
As preservatives, the FDA ( Food and Drug
Administration ) allows only a
few of the oxides of sulfur to be used in foods and they go by the
following
names which may appear on food labels. When you have a sulfite
intolerance,
food labels are a good friend and you should get used to reading them.
(
Note that in many European countries, sulfite is spelled sulphite and
the
preservatives are often referenced by the numbers E220 through E228. )
Sodium Sulfite (Na2SO3)
Sodium Bisulfite (NaHSO3)
Sodium Metabisulfite (Na2S2O5)
Sulfur Dioxide Gas (SO2)
The first three are true sulfite salts and potassium
may replace sodium in
some formulations. When dissolved in water, they dissociate to free the
sulfite
SO3 ion. This combination of one sulfur and three oxygen atoms is a
strong
anti-oxidant and explains why sulfites are such good preservatives.
Like
other anti-oxidants, they protect food by combining with and
neutralizing
free radicals and oxygen. If oxygen is available, sulfite ions readily
oxidize
to become sulfate SO4 ions. The sulfate form is quite stable and does
not
preserve food. ( Sulfates in food do not cause much trouble for most
people,
even those with sulfite conditions. However, an unlucky few are
sensitive
to sodium lauryl sulfate in soap and shampoo which can cause skin
rashes.
If you don't get skin rashes from soap, you shouldn't worry about
sulfates.
) Sulfites and sulfates should not be confused with nitrites or
nitrates
which are completely different chemicals commonly used to preserve
meats.
The last chemical on the list above is sulfur
dioxide. Strictly speaking,
it is not a sulfite because it lacks the third oxygen atom. However,
the
human response to sulfur dioxide mimics the response to sulfites,
probably
because it may be oxidized to become a sulfite. As a gas, sulfur
dioxide
is one of those nasty air pollutants we all like to avoid. In foods,
sulfur
can easily combine with organic molecules taking the place of carbon
and
oxygen groups. In fact, there are forms of sealife near volcanic vents
on
the ocean floor that survive on sulfur compounds as replacements for
the
carbon-based nutrients you and I need. When carbon foods or tree wood
is
burned, carbon dioxide (CO2) is produced. When sulfur is burned, sulfur
dioxide
(SO2) is produced.
Sulfur dioxide gas is used to prevent discoloration
when drying fruits such
as apricots. In the process, SO2 is trapped and bound to the fruit and
the
concentration can be quite high. Unfortunately for some of us, sulfur
dioxide
is much more than a preservative. Since ancient times, burning sulfur
has
been used to temper the fermentation of wine. Most modern wine makers
use
the sulfite salts directly, but the result is the same. Sulfur dioxide
molecules
bind to the wine and all wine bottles carry the warning "Contains
Sulfites".
Sulfur dioxide can also be dissolved in water to have a softening
effect
on fibers and other organic structures. This effect is used to
advantage
in the corn refining process that produces corn starches and syrups.
Corn
refining is no backwoods industry; over the years, corn syrup has
replaced
sugar as the number one sweetener in the United States. Since corn
refining
starts with sulfur dioxide, all corn starches and syrups wind up with a
sulfur
content. And it doesn’t stop there. Sulfur dioxide is an important
ingredient in caramel color, a colorant that is produced in much the
same
way as true caramel. Now, I never heard of caramel color before I
became
interested in foods. If it’s new to you too, read the list of
ingredients
on your next Coke or Pepsi. Diet colas are nearly all water and caramel
color.
Regular colas do add a sweetener: high fructose corn syrup, of
course.
How the oxides of sulfur cause problems in humans is
not understood. However,
from the above description of their uses in the food industry, it is
quite
clear that they interfere with normal biological functions. As a side
reaction,
sensitive body tissues swell and cause breathing problems, headaches
and
other discomforts. Sometimes it appears that the SO3 ion is the
culprit;
sometimes it appears to be SO2 bound tightly, loosely or not at all.
Whatever
the form, it would be nice to simplify things. So, I will introduce the
concept
of biologically effective sulfur oxide, which I will call SOx.
Regardless
of the form of the sulfur, if you know the effective value, you know
its
potential for causing headaches and asthma. The SOx value for a food
must
be determined experimentally. In my case, I simply eat a food sample,
note
my headache response and equate this to a similar headache caused by a
calibrated
solution of sodium sulfite. The SOx weight is then defined as the
weight
of the SO2 atoms in the calibrated solution of sulfite.
When discussing sulfur preservatives in dried
fruits, I mentioned that the
concentration may be quite high. The concentration for dried apricots
is
typically 220 PPM. The PPM means "Parts Per Million" and refers to the
weight
of the preservative as a part of the total weight of fruit. For
instance,
if you divided the fruit into one million parts, 220 of those parts
would
be biologically effective sulfur oxide. You can use PPM numbers to
calculate
weights. Since food labels use grams for weight, we will use
grams.
A gram is the weight of ten drops of water.
Grams are conveniently divided into smaller parts
called milligrams (mg)
and micrograms (ug). The abbreviation for milligrams is "mg" which
makes
common sense. However, the abbreviation for micrograms is less obvious
since
"mg" cannot be used. So, the Greek symbol "mu" that sounds like "mew"
and
looks like the letter "u" was chosen, presumably by someone that drank
too
much Greek wine. As a result, micrograms are abbreviated "ug" or
sometimes
"mcg". It takes one thousand milligrams (1,000 mg) or one million
micrograms
(1,000,000 ug) to make one gram.
You can calculate effective sulfur oxide weight by
multiplying the PPM
concentration by the weight of the food. If the food weight is in
grams,
the answer will be in micrograms.
(Food Weight) times (PPM
Concentration) = SOx
In the case of dried apricots with 220 PPM
concentration of effective sulfur
oxide, a 4 gram bite would be preserved with 4 x 220 = 880 ug of SOx.
That
would give me such a headache, I would have to bang my head against the
wall
for hours. That’s all the math you need to know to use food labels to
predict the sulfite content of your dinner. Of course,
you
have to know a little bit more about food ingredients, but that’s what
the rest of the book is about.