Index
Introduction
Glucosinolates are thioethers. They generally
consist of a sugar entity, b-D-thioglucose, with an ester bond to an organic
aglycone that is an alkyl group yielding isothiocyanate, nitrile, thiocyanate
or a similar compound upon hydrolysis. These compounds often contribute
a bitter, "hot" taste to condiments (mustard, horseradish) and
may exhibit goitrogenic or antithyroid activity. [return
to list of toxicants]
Glycosinolates are hydrolyzed by either the enzyme glucosinolase or thioglucosidase into glucose, HSO4- , and one of the following aglycone derivatives: isothiocynates, thiocyanates, nitriles, or related compounds such as oxazolidine-2-thiones. The enzymes for hydrolysis are produced by plants and by rumen organisms. They react with the glucosinolates when plant tissue is crushed, for example by mastication, or when the plant is consumed into the rumen of a ruminant animal.
Some common plants that contain glucosinolates include
Glucosinolates are found in several oil meals that have been used traditionally in the northern states, Canada, and Europe as protein supplements for livestock. Some examples include crambe, mustard, and meadowfoam meal, and most importantly, rapeseed meal. Rapeseed meal contains several glucosinolates and produces not only oxazolidine-2-thiones but also isothiocyanates, nitriles and thiocyanates.
Poultry and swine and other nonruminants can tolerate 5-10% rapeseed meal in their diets. Symptoms of poisoning in poultry may include depressed growth , goiters, perosis, poor egg production, off-flavored eggs, enlarged thyroid in chick embryos, and liver damage. Symptoms of poisoning in swine include growth depression, goiters, and enlarged livers.
Although rumen enzymes break down glucosinolate aglucones to their toxic derivatives, other rumen enzymes are able to metabolize these toxicants into less toxic compounds. Hence, ruminants can generally tolerate diets of 10% rapeseed meal. More than this canl cause antithyroid symptoms.
Glucosinolates and their derivatives can be transferred through milk and placenta to the young of female animals.
Addition of extra iodine to diets can help to counteract the antithyroid effects of thiocyanates but not of oxazolidine-2-thiones.
Canadian plant breeders have developed low-glucosinolate cultivars
of rapeweed. These cultivars are referred to as canola rather than rapeweed.
Meal from them can be used in high enough quantities to provide all the
protein supplementation demanded in livestock diets that require high levels
of protein.
Glucosinolates are responsilble for the unique taste of many of the condiments that make our foods more interesting to taste.
Research indicates that glucosinolates and their derivatives may have
potential in fighting human cancers. Inclusion of Brassica vegetables
appear to help protect against rectal and colon cancer. These vegetables
aid in the detoxification of carcinogens such as aflatoxins and polybromobiphenyl.
They enhance the activity of several hepatic enzymes used in detoxification
processes. Benzyl isothiocyanate and thiocyanate have been shown in the
lab to inhibit tumor development in animals exposed to carcinogens. Indole-3-
carbinol, a product of glucosinolates, is a compound with promise in anticancer
research.
[Index][Introduction] [How
poisoning occurs][Plants involved] [Symptons
of poisoning][Prevention of poisoning][Benefits
of glucosinolates] [References]
