Are whole extracts and purified glucosinolates from cruciferous vegetables antioxidants?

Fruits and vegetables contain several classes of compounds that can potentially contribute to antioxidant activity, including vitamins, simple and complex phenolics, sulphur-containing compounds and glucosinolates. The glucosinolates are found in high concentration in many cruciferous vegetables, and it is well established that their breakdown products induce endogenous antioxidant defences such as quinone reductase and glutathione S-transferase in cells and in vivo. Despite the anticarcinogenic effect of these compounds in animal models, the direct antioxidant properties of this class of compounds have not been systematically studied. We therefore examined the free radical-scavenging properties of representative extracts and of purified glucosinolates from cruciferous vegetables, by measuring their effect on ascorbate- or NADPH/iron-induced peroxidation of human liver microsomes, ascorbate/iron-induced peroxidation on phospholipid liposomes, iron chelation and hydroxyl radical scavenging using the deoxyribose assay, total antioxidant potential using ABTS (2,2'-azinobis(3-ethyl-benzothiazoline-6-sulphonate)) and the bleomycin assay. Most of the extracts from cruciferous vegetables exhibited some antioxidant properties, although extracts from cooked Brussels sprouts increased the rate of microsomal lipid peroxidation. The effects in these assays were dependent upon processing and species of crucifer, and the glucosinolate content appeared to play a minor role in these effects, since purified glucosinolates exhibited only weak antioxidant properties. The total antioxidant activities of extracts from cooked and autolysed Brussels sprouts were identical within experimental error. This is probably due to the content of phenolics which is unaltered by autolysis, despite the differences between these samples in other assays especially NADPH-iron-induced lipid peroxidation of human liver microsomes. The results demonstrate that glucosinolates are unlikely to account for the direct antioxidant effects of extracts from cruciferous vegetables.

Dietary glucosinolates as blocking agents against carcinogenesis: glucosinolate breakdown products assessed by induction of quinone reductase activity in murine hepa1c1c7 cells.

We have tested the ability of a representative range of dietary glucosinolates and their breakdown products, found in high concentrations in cruciferous vegetables, to act as blocking agents against carcinogenesis by inducing the activity of the anticarcinogenic phase II marker enzyme quinone reductase in murine hepa1c1c7 cells. Breakdown of glucosinolates was catalysed by the endogenous plant enzyme thioglucoside glucohydrolase at neutral and acid pH. Only two unmodified glucosinolates, p-hydroxybenzyl and 2-hydroxybut-3-enyl, significantly induced quinone reductase activity. However, after enzymic hydrolysis at near-neutral pH, some of the glucosinolates yielded breakdown products that significantly induced quinone reductase in the order: 3-methylsulphinylpropyl-->prop-2-enyl-->pent-4-enyl approximately 2-phenylethyl approximately benzyl-->all others tested. Incubation with myrosinase at acidic pH resulted in induction of quinone reductase activity by the hydrolysis products of only three of the tested glucosinolates:3-methylsulphinyl-propyl approximately 2-phenylethyl-->benzyl-->all others, activity due to the two alkenyl compounds being lost. The results show that the potential cancer-blocking action of both intact and thioglucoside glucohydrolase-treated glucosinolates, as assessed by induction of phase II enzyme activity, is dependent on the nature of the side chain of the parent glucosinolate.

Rapeseed meal-glucosinolates and their antinutritional effects. Part 6. Taint in end-products.

From the present review it is clear that glucosinolates and their breakdown products may pass in small amounts into such products as meat, milk or eggs without noticeable deterioration in their taste. When applying low glucosinolate rapeseed meal (LG-RSM) as the sole high protein component of concentrate mixture for cows, the level of rapeseed glucosinolates breakdown products should not exceed 0.1 mumol/l oxazolidinethione, 10 mumol/l unsaturated nitriles and 100 mumol/l thiocyanate. At these levels no evidence has been found to indicate the negative influence of glucosinolates breakdown products on the sensory properties of milk or threat for consumers. No published information appears to be available suggesting that glucosinolates have any deleterious effect on the carcass flavour in cattle. Even at a 20% inclusion of LG-RSM in diets no impairment on visual scores or sensory evaluation was found in pig's or broiler's carcass. Glucosinolated, chiefly progoitrin, which depress trimethylamine oxidation thus clearly affect the taint in eggs. In birds with genetically conditioned susceptibility (brown layers) fishy taint can be observed even at 0.3 microM progoitrin, i.e. approximately 0.5 microM total glucosinolates in 1 g diet. Assuming a threefold higher threshold for white layers (1 microM progoitrin in 1 g diet) fishy taint can be expected at a 10% LG-RSM level in diet, and only very low glucosinolate rapeseed meals can be fed to layers without the risk of fishy taint in eggs.

Rapeseed meal-glucosinolates and their antinutritional effects. Part 7. Processing.

This paper surveys the effect of some technological processes based on modified traditional way of obtaining oil from rapeseeds and employing polar solvents and enzymes on the content of glucosinolates and nutritional quality of the end products. Special emphasis has been put on the technologies introduced after 1980 tested mostly on a pilot scale.

Natural toxins and protective factors in brassica species, including rapeseed.

Many plant secondary metabolites exhibit a wide range of dose-related physiological properties when included in the diet of animals and man. Within the brassica family, the glucosinolates, a group of sulphur-containing glucosides have been the subject of a vast amount of study and the effects of dietary inclusion of such compounds or their metabolites on the health of animals and man are briefly reviewed. Although excessive amounts of glucosinolates in animal feed formulations may reduce growth and performance as well as affecting thyroid, liver, and kidney function, there is little evidence of such effects in man. On the contrary, compounds derived from glucosinolates as a consequence of enzymic breakdown or metabolism have been shown to activate mechanisms which moderate or reverse carcinogenic processes. Such effects may contribute to the net anti-carcinogenic benefit attributed to these vegetables in numerous epidemiological studies.

Induction of the anti-carcinogenic enzyme quinone reductase by food extracts using murine hepatoma cells.

Over 145 extracts of vegetables, fruits, herbs, spices and beverages which are consumed regularly in the European diet have been surveyed for potential anti-carcinogenic activity using an assay which measures the induction of NAD(P)H: (quinone acceptor) menadione oxidoreductase (quinone reductase, QR) activity in murine cells challenged with solutions of potential inducers. When appropriate the study has included extracts prepared from cooked and autolysed material. The results indicate that extracts of some brassicas, legumes (peas), lettuces, red pepper, grapefruit and some herbs including basil, tarragon and rosemary are inducers of QR activity. Inducing activity is strongly dependent on processing and on variety.

Rapeseed meal-glucosinolates and their antinutritional effects. Part 5. Animal reproduction.

Although there is no clear evidence to fully describe the mechanism involved in glucosinolate-related effects on animal reproduction, lowered fertility in animals fed diets with rapeseed meal (RSM) inclusion is related to glucosinolate content in the diet. Negative effects can result both from multidirectional action of glucosinolates, malnutrition of mother due to the thyroid dysfunction, transfer of goitrogenic compounds to foetus and reduced transfer of nutritive compounds (e.g. iodine) through the placenta. The degree of reproduction impairment depends both on glucosinolate content and on the type of animal. Pregnant female rats are sensitive to the presence of glucosinolates, and the first symptoms of fertility impairment and lowering of offspring survival rate may occur at low glucosinolate levels, e.g. with diets containing low glucosinolate rapeseed meal (LG-RSM). In the case of swine, the limiting value above which sows fertility may be impaired is 4 mumol of total glucosinolates per g diet and 8 mmol of daily intake of these compounds. Opinions on the permitted RSM inclusion in diet for hens are very divergent. Some authors recommend limiting of the RSM inclusion to 10%, while others did not find any lowering of egg production in hens fed with two- or three-fold greater RSM inclusion rates. Most long-term experiments with heifers, cows and ewes indicate that ruminants tolerate the level of glucosinolate in LG-RSM although feeding this fodder as the only high-protein concentrate component may lead to impaired fertility.

Rapeseed meal-glucosinolates and their antinutritional effects. Part 3. Animal growth and performance.

On the basis of literature data biological properties of rapeseed glucosinolates, and especially their influence on the growth and weight of animals were characterized. The aim was to determine a limiting value of these compounds in diets for particular animal species and age groups at which no limitation of growth or development was observed.

Rapeseed meal-glucosinolates and their antinutritional effects. Part 4. Goitrogenicity and internal organs abnormalities in animals.

This paper surveys the literature concerning biological properties of rapeseed glucosinolates, chiefly the goitrogenic activity of these compounds and their influence on the morphological and histological abnormalities of internal organs in animals. An attempt has been made to establish threshold glucosinolate levels in diet which trigger the onset or increase of internal organs impairment in animals depending on their species and breeding.

Rapeseed meal-glucosinolates and their antinutritional effects. Part 1. Rapeseed production and chemistry of glucosinolates.

This review, which will be presented in seven parts is concerned with the use of rapeseed meal as an animal feeding stuff. The presence of glucosinolates in the meal limits its use due to a number of antinutritional and physiological effects. Whilst not in itself exhaustive, this review updates earlier reviews by reference to recent papers on the above topics. In this first paper the history of the crop and the current production situation are presented and the nature of glucosinolates and methods for their analysis are reviewed in order to facilitate a better appreciation of the problems referred in later sections.

The effect of feeding brassica vegetables and intact glucosinolates on mixed-function-oxidase activity in the livers and intestines of rats.

Significant induction of mixed-function-oxidase (MFO) activity was observed in the small intestines of rats within 4-6 hr of ingestion of a single meal containing a Brassica vegetable (cabbage). Intact Brussels sprouts and a fractionated methanol-water extract of Brussels sprouts induced similar degrees of MFO activity in the livers, and small and large intestines of rats. However, the residue left after extraction of the polar compounds did not induce MFO activity. Different amounts of the various naturally-occurring thioglycosides and glucosinolates were found in the intact Brussels sprouts and in the extract, but virtually none were found in the extracted residue. When glucusinolates that were found in Brussels sprouts (sinigrin, progoitrin, glucobrassicin and glucotropaeolin) were fed separately to rats, only the indole glucosinolate, glucobrassicin, induced MFO activity (causing induction in the small intestines of the rats). This is consistent with the inducing activity of the various hydrolysis products of this glucosinolate. This is the first study in which an attempt has been made to define the inducing compounds in Brassica vegetables by feeding the individual purified glucosinolates.

Chemical and biological properties of indole glucosinolates (glucobrassicins): a review.

Glucosinolates are a group of secondary products commonly, but not exclusively, found in plants of the family Cruciferae. They give rise, upon enzymic hydrolysis, to a range of volatile, pungent and physiologically active compounds. Recently, particular attention has been focused upon those that are trytophan-derived--the indole glucosinolates (glucobrassicins). When chemically or enzymically hydrolysed these compounds give rise to a range of involatile indole compounds which have been implicated in the anti-carcinogenic and mixed-function-oxidase stimulatory activities of brassica vegetables. This review details the chemical and physiological properties of indole glucosinolates and their products and suggests possible areas for future research.

Differential induction of mixed-function oxidase (MFO) activity in rat liver and intestine by diets containing processed cabbage: correlation with cabbage levels of glucosinolates and glucosinolate hydrolysis products.

Both white and Savoy-type cabbage added to a semi-purified diet at 25% dry weight and fed to rats ad lib. for 5 days significantly induced ethoxyresorufin (ERR) deethylation in the small and large intestine. Savoy cabbage also induced hepatic activity and, in general, exhibited a greater inducing effect than white cabbage. These enzyme-inducing effects were altered when the cabbage had been processed. The content of intact glucosinolate was greater in Savoy than in white cabbage. The indole glucosinolate (glucobrassicin) content of both types of cabbage was approximately halved by cooking but was unaffected by fermentation, whilst homogenization of Savoy cabbage led to the total disappearance of intact glucosinolates. Levels of the indole glucosinolate breakdown products ascorbigen and indole-3-carbinol were highest in homogenized cabbage, and ascorbigen levels were also higher in cooked than in fresh cabbage of either type. When added to the semi-purified diet and fed ad lib. to rats for 5 days, indole-3-carbinol was a potent inducer of hepatic ERR deethylation and cytochrome P-450 activity, but had much less effect in the intestine. Other glucobrassicin metabolites, diindolylmethane and indole-3-acetonitrile, also had some inducing effect in the liver but no effect in the intestine, while ascorbigen significantly induced ERR deethylation in the small and large intestine but had no effect on hepatic MFO activity.

Determination of indole and 3-methylindole in plasma and rumen fluid from cattle with fog fever or after L-tryptophan administration.

A modified gas liquid chromatography method has been developed to analyse the concentrations of indole and 3-methylindole in samples of plasma and rumen fluid from four cows with fog fever together with four control animals and from two cattle given L-tryptophan orally. Satisfactory recoveries of the metabolites were obtained in test samples examined by the gas liquid chromatography procedure and increased levels were found in rumen fluid after tryptophan administration. Absence of abnormal concentrations of the toxic metabolite 3-methylindole in samples from field cases of fog fever was not considered to rule out the metabolite as a possible cause of the disease in view of the rapid restoration of 3-methylindole to normal levels by the second day after loading with L-tryptophan.

The isolation and characterisation of hyaluronic acid in egg shell.

Analysis showed that the organic part of the chicken's egg shell consisted of a series of proteins and polysaccharides, probably present as glycoproteins and glycosaminoglycans. A purified preparation of a glycosaminoglycan (minimum mol. wt. 25 000), homogeneous by sedimentation velocity analysis and sedimentation to equilibrium in a density gradient, contained equimolar amounts of N-acetylglucosamine (36.3% s/w) and glucuronic acid 35.6% w/w). Digestion with testicular and streptomyces hyaluronidases and identification of the degradation products showed the glycosaminoglycan to be hyaluronidases and identification of the degradation products showed the glycosaminoglycan to be hyaluronic acid.