Evaluation of glucosinolate levels throughout the production chain of Brassica vegetables towards a novel predictive modelling approach

Glucosinolates are a group of plant secondary metabolites, that can have important implications for human health. Vegetables of the Brassica genus, including cabbage, Brussels sprouts, broccoli, cauliflower and kohlrabi contribute almost exclusively to our intake of glucosinolates. Their added value towards vegetable quality can be ascribed to their health promoting properties by a role in the prevention of various cancers. The research described in this thesis was done to evaluate how levels of glucosinolates and their health-protective breakdown products are affected by various factors within the production chain of Brassica vegetables towards a better understanding of the alleged health effects of glucosinolates in Brassica vegetables. The research focused specifically on the effects of processing, namely chopping and cooking, on the content of glucosinolates.It was demonstrated that chopping of raw Brassica vegetables resulted in unexpected, increased levels of indolyl glucosinolates after chopping and storage of cabbage and broccoli under ambient conditions. In white cabbage a 15-fold increase of 4-methoxy- and 1-methoxy-3-indolylmethyl glucosinolates was noted after 48 h of storage of chopped cabbage. Chopping and storage of broccoli vegetables resulted in a strong reduction of most glucosinolates, except for 4-hydroxy- and 4-methoxy-3-indolylmethyl glucosinolates, which increased 3.5- and 2-fold respectively. In this study we showed that the well-known and accepted breakdown mechanism of glucosinolates (hydrolysis by the endogenous enzyme myrosinase) appeared to be counteracted by a yet unknown mechanism causing an increase of some indolyl glucosinolates. It is postulated that chopping, by mimicking pest damage, triggers a defence mechanism in harvested Brassica vegetables.Microwave cooking of red cabbage showed to be an interesting alternative for conventional cooking. In general, high total glucosinolate levels were observed for various microwave treatments due to the absence of leaching of glucosinolates into cooking water that takes place in conventional cooked vegetables. An increase in glucosinolate levels appeared to be associated with the time/energy input applied resulting in levels exceeding the total glucosinolate content of the untreated cabbage. This was probably caused by an increased extractability of glucosinolates from the vegetable matrix after the microwave treatment. Furthermore, at low (180 Watt) and intermediate microwave powers (540 Watt) substantial myrosinase activity was retained in cabbage. Thus, microwave prepared Brassica vegetables can offer a higher retention of glucosinolates and controllable amounts of active myrosinase, thereby increasing the health-promoting potential of the product.Overall it was demonstrated that many steps in the food production chain of Brassica vegetables or vegetable products can have a large impact on the glucosinolate content and thus affect the final intake of health-protective glucosinolates and breakdown products for humans. A novel predictive modelling approach is proposed (and elaborated in a case study on cooking) to handle the variations in the production chain and to provide a tool that can be used to assist product and process development. This model provides us with more insight in the behaviour and fate of glucosinolates and protective derivatives and may lead to options for improvement of investigations aimed at understanding the role of dietary glucosinolates and breakdown products in the protection against various cancers. Furthermore, predictive modelling can be helpful in enhancing the sensitivity of epidemiological studies and eventually provide solid evidence for assessment of the risks and benefits of glucosinolate consumption.