Brassica vegetables have been safely consumed for thousands of years, and there is little evidence of adverse effects or allergy in humans. Historically, there has been an emphasis in canola breeding on decreasing the total seed glucosinolate concentration to less than 20 mmol/g, and to less than 30 mmol/g in the oil-extracted meal, as the presence of glucosinolates in the meal reduces the feed quality for livestock. In humans, no adverse effects have been identified at doses of glucosinolates close to normal daily consumption, or even with concentrated broccoli sprout extracts (Shapiro et al., 2006).
The other phytochemical of health concern present in brassicas is erucic acid, which, in the 1970s, was thought to have a growth-retarding effect in animals and potentially adverse effects on the heart and liver. Broccoli seed has a high level of erucic acid (12.1 g/100 g). According to USA and Canada guidelines for erucic acid limits (canola oil), a relatively small amount of seed (about 35 g/wk) equaled calculated exposure limits (West et al., 2002).
Glucoraphanin itself appears to be very well tolerated. A randomized, placebo-controlled chemoprevention trial of 200 individuals in Qidong (China) also suggests glucoraphanin is generally safe and well tolerated. In the study, 200 healthy adults drank infusions containing either 400 or < 3 mmol glucoraphanin nightly for 2 weeks with no adverse effects observed (Kensler et al., 2005). Interestingly, the authors did note great inter-individual differences in bioavailability.
Further research is needed to assess both the benefits and potential adverse effects of glucosinolates on people with different genotypes and microflora, since bioavailability and response to consumption may differ considerably. Despite this, the majority of evidence suggests there is a strong health benefit in the consumption of glucoraphanin.
Due to the importance of glucosinolates as molecules for human health, there has been considerable effort devoted to the development of rapid and accurate methods for quantita-tion for glucosinolates. Many of these methods for quantitation initially focused on HPLC with UV-Vis or DAD detection. The majority of the HPLC-based methods involved a desulfa-tion step, since the removal of this polar moiety made the metabolites more tractable for analysis by reverse phase chromatography. More recently LC-MS has been employed, as it is not only more sensitive but also provides molecular weight and fragmentation information to confirm glucosinolate identity even in a complex mixture, and desulfation is not required. More rapid MS infusion methods have also been utilized as a screening tool to assess gluco-sinolate content. Both infusion and LC-MS methods are sensitive (part per trillion or low nmol/g), and have been demonstrated in a number of matrices (Rochfort et al., 2008).
Obtaining pure glucosinolates is important to provide standards for analysis and to provide material for research into biological effects. Purified glucosinolates may also be incorporated in functional foods — for example, glucoraphanin has been incorporated into health-enhancing teas. Glucoraphanin is heat stable, water soluble, has few or no negative flavor attributes, and is a direct precursor to sulforaphane, and is therefore considered an ideal candidate for inclusion in functional foods. Most purification methods start with an extraction of plant material, generally seed, in hot water, which denatures myrosinase, allowing gluco-sinolates to be extracted intact. The aqueous mixture may be semi-purified using solid phase extraction (SPE) techniques (Rochfort et al., 2006). This allows the removal of uncharged species, resulting in a much cleaner extract for final purification. Most methods rely on preparative HPLC, and this provides good quantities of pure metabolites, but alternate techniques such as counter current chromatography (CCC) have also been utilized. Both methods can quickly provide grams of purified glucosinolates.
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