Volatile sulfur compounds. The volatile sulfur compounds are
found in the plants as glucosides. When treated with acid or alkali and
when acted upon by enzymes, these glucosides yield a sugar or some closely
allied carbohydrate and one or more other substances, frequently phenols,
allyl sulfide, or allyl isothiocyanate. Most of the investigations of sulfur-
splitting enzymes have been made upon myrosin. The strong flavor of old
or stored turnips, rutabagas, and cabbage is probably largely due to setting
free of sulfur compounds by enzymes. When they are cooked, plant acids
are liberated which cause hydrolysis of the volatile sulfur compounds. In
addition, hydrogen sulfide is formed by decomposition of the sulfur com-
pounds by heat.
The odor of many of these compounds is familiar, those of onions and
garlic, cooking cabbage, etc., being typical examples.
Allyl isothiocyanate is found in mustard seed. It is prepared commer-
cially by macerating the seed, the enzyme then splitting off the sulfur of
the glucoside. The oil is then obtained by distillation with steam. Allyl
SULFUR COMPOUNDS 127
sulfide IS found in the onion family, and is prepared commercially from
garlic. The strong flavor of onions, leeks, and garlic depends upon the
concentration of allyl sulfide.
These volatile compounds escape from the food more rapidly with rise
in temperature and breakdown of the plant cells. Hence, the longer onions,
leeks, and garlic are cooked the milder their flavor becomes. Also because
finely minced onion has a greater surface area for volatilization to occur
than when cut in large pieces, these substances volatilize more rapidly
from finely cut pieces. This is why it is preferable to add onion juice, very
finely minced onion, or cooked onion to some foods that are not cooked
long or that do not reach a high temperature, such as hamburger or stuff-
ing for fowl or meat. Large pieces of raw onion in a stuffing produce a
very strong onion flavor, more concentrated in some areas than others,
instead of a subtle, well-blended flavor, for the stuffing never reaches boil-
ing temperature.
The amount of onion and/or garlic added, the fineness of division of
the pieces, and the length of cooking all affect the flavor of the finished
product to which they are added. The flavor of a food like catsup or chili
sauce may be ruined by adding a large quantity of onion or garlic in large
pieces near the end of the cooking process. The same amount of onion
or garlic added in small pieces, or added in large pieces early in the cook-
ing process, could blend with, instead of dominate, the flavor of the other
ingredients.
Sulfur compounds and the cooking o£ vegetables. It is com-
monly known that long cooking of some vegetables such as cabbage, turnips,
cauliflower, and Brussels sprouts develops strong, disagreeable flavors, and
the eating of these vegetables may cause discomfort and digestive dis-
turbances. The longer cooking and stronger flavor are accompanied by
increased acidity of the vegetable. The length of time of cooking for the
strong flavor to develop varies with the vegetable, whether the cooking is
started in cold or boiling water, and the proportion of vegetable to water.
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Volatile sulfur compounds. The volatile sulfur compounds are
found in the plants as glucosides. When treated with acid or alkali and
when acted upon by enzymes, these glucosides yield a sugar or some closely
allied carbohydrate and one or more other substances, frequently phenols,
allyl sulfide, or allyl isothiocyanate. Most of the investigations of sulfur-
splitting enzymes have been made upon myrosin. The strong flavor of old
or stored turnips, rutabagas, and cabbage is probably largely due to setting
free of sulfur compounds by enzymes. When they are cooked, plant acids
are liberated which cause hydrolysis of the volatile sulfur compounds. In
addition, hydrogen sulfide is formed by decomposition of the sulfur com-
pounds by heat.
The odor of many of these compounds is familiar, those of onions and
garlic, cooking cabbage, etc., being typical examples.
Allyl isothiocyanate is found in mustard seed. It is prepared commer-
cially by macerating the seed, the enzyme then splitting off the sulfur of
the glucoside. The oil is then obtained by distillation with steam. Allyl
SULFUR COMPOUNDS 127
sulfide IS found in the onion family, and is prepared commercially from
garlic. The strong flavor of onions, leeks, and garlic depends upon the
concentration of allyl sulfide.
These volatile compounds escape from the food more rapidly with rise
in temperature and breakdown of the plant cells. Hence, the longer onions,
leeks, and garlic are cooked the milder their flavor becomes. Also because
finely minced onion has a greater surface area for volatilization to occur
than when cut in large pieces, these substances volatilize more rapidly
from finely cut pieces. This is why it is preferable to add onion juice, very
finely minced onion, or cooked onion to some foods that are not cooked
long or that do not reach a high temperature, such as hamburger or stuff-
ing for fowl or meat. Large pieces of raw onion in a stuffing produce a
very strong onion flavor, more concentrated in some areas than others,
instead of a subtle, well-blended flavor, for the stuffing never reaches boil-
ing temperature.
The amount of onion and/or garlic added, the fineness of division of
the pieces, and the length of cooking all affect the flavor of the finished
product to which they are added. The flavor of a food like catsup or chili
sauce may be ruined by adding a large quantity of onion or garlic in large
pieces near the end of the cooking process. The same amount of onion
or garlic added in small pieces, or added in large pieces early in the cook-
ing process, could blend with, instead of dominate, the flavor of the other
ingredients.
Sulfur compounds and the cooking o£ vegetables. It is com-
monly known that long cooking of some vegetables such as cabbage, turnips,
cauliflower, and Brussels sprouts develops strong, disagreeable flavors, and
the eating of these vegetables may cause discomfort and digestive dis-
turbances. The longer cooking and stronger flavor are accompanied by
increased acidity of the vegetable. The length of time of cooking for the
strong flavor to develop varies with the vegetable, whether the cooking is
started in cold or boiling water, and the proportion of vegetable to water.