- Epidemiological studies show negative associations between consumption of Brassica vegetables and cancer
- Effects have been attributed to high levels of glucosinolates
- Food processing affects ingested level of glucosinolates by:
- Enzymatic degradation (endogenous enzyme myrosinase)
- Leaching into the cooking water
- Thermal degradation
Increasing intake of health promoting compounds, such as glucosinolates, by optimizing food processing to minimize losses.
Projects within the Food production Chain:
The available time of the thesis research (MSc: 24-39 credits) includes the initial information gathering, literature review, experimental work, report writing and presenting.
Current PhD research topics
Genetic determinants of glucosinolate degradation during Food processing in Brassica oleracea
PhD fellow: Kristin Hennig (Daily thesis supervisor)
Supervisors: Dr. Ing. R. Verkerk (PDQ), Dr. Ir. M. Dekker (PDQ) Dr. Ir. G. Bonnema (Plant Breeding) Dr.ir. M. A.J. S van Boekel (PDQ)
Introduction and aim of the PhD project
Various steps in the production chain (cultivation, processing/preparation) affect the level of potential health-protective glucosinolates, present in vegetables of the Brassica genus. At the primary production stage, most effects are ascribed to i.) the large variation in glucosinolate iii.) glucosinolate distribution in different organs of Brassica species. Processing affects glucosinolate concentrations by thermal breakdown, leaching into the cooking water and enzymatic degradation. Data from the previous research show differences in thermal stability of during processing among three Brassica oleracea types (Brussels sprouts, red cabbage, broccoli) and two Brassica rapa types (Pak choi and Chinese cabbage).
These results suggest that both glucosinolate composition and the matrix of the crop (intracellular composition, leaf structure, cell walls etc.) influence the glucosinolate degradation. Since composition and matrix of a crop are partly genetically determined, we want to investigate the relation between genetics and food processing.
Student thesis topics:
The below described topics are suitable for BSc and MSc thesis. All offered thesis topics consist of about 60% practical work, which will be bit of greenhouse work (sowing and harvesting of plants) and laboratory work (simulation of food processing, analysis of the samples). Applied analytical methods will be HPLC, GC-MS and UV measurements. The data analysis includes kinetic modeling and basic statistics.
1. Comparison of change in glucosinolate content in broccoli leaves and Chinese kale leaves during cooking
The main mechanism of glucosinolate degradation during cooking is leaching into the cooking water. In previous work it was shown that leaching differs for different vegetables, which could be explained by the structure of the vegetable. The aim of the thesis is to investigate the kinetics of glucosinolate degradation during cooking in leafy Brassica vegetables. Depending on the thesis period, additionally the effect of the growing environment or developmental stages of the plants can be included.
2. Investigation of glucosinolate breakdown product formation in different Brassica vegetables
Breakdown products of some glucosinolates are the compounds that exhibit the actual health promoting properties. Glucosinolates can be broken down during food processing and during digestion, to which extend depends on the processing method. The aim of the thesis is to compare the formation of glucosinolate breakdown products after processing in different leafy Brassica vegetables.
3. Sulfatase concentration affecting glucosinolate measurement
Accurate determination methods are required to analyze the glucosinolate content of vegetables in order to determine the effects of food processing on glucosinolates and estimate the intake of glucosinolates in the human body. The international standard organization published a glucosinolate analysis method in 1990, but lot of adjustments have been made since that time. Current research shows that glucosinolates degrade during analysis, using a method with high throughout. The aim of the thesis is to reveal the reason for this degradation during glucosinolate analysis.
The influence of the adsorption drying technology on the stability and availability of glucosinolates in broccoli (Brassica oleracea var. italica)
PhD fellow: Teresa Oliviero
Supervisors: Prof. dr. ir.M.A.J.S. van Boekel (PDQ, WU); Dr. ir. M. Dekker (PDQ, WU), Dr. Ing. R. Verkerk (PDQ, WU); Dr.ir. AJB van Boxtel (S&C, WU); Prof. Ellen Kampman (HNE, WU)
Drying technologies are an important option to remove the water from food products in order to enhance their storage capabilities and to make food products easier to cook. Both high temperatures and dehydration can have a strong impact on processed foods quality.
During drying of broccoli, glucosinolates can be broken down by means of heat or oxidation, the enzyme myrosinase can be inactivated and cellular structures can be altered. All these modifications might reduce the formation of bioactive isothiocyanates from the glucosinolates and therefore is compromising the health-protective effects of broccoli. From this standpoint a drying technology using mild process conditions would be preferred to retain the aforementioned health benefits.
Absorption drying is a novel technology which uses low or moderate temperatures to remove the water and might be regarded as a suitable option to fit the purpose of preserving the health effect of broccoli with a limited ecological impact deriving from low energy consumption and CO2 exhaust.
The aim of this study is to set up the most suitable Adsorption Drying conditions which preserves the health protective effect of broccoli and then to kinetically model the effect of the process conditions on the chemical and enzymatic degradation of the target compounds. In addition, the effect of drying of broccoli on the bioavailability of glucosinolates will be investigated in a human intervention trial.
Possibilities for thesis topics
Preliminary investigations show that moisture content affects both the rate of glucosinolates degradation and myrosinase activity during thermal treatments of broccoli, affecting the formation of the breakdown products and thus their intake. Kinetic models will be used to set up Adsorption Drying conditions.1. Influence of Adsorption Drying Technology conditions on the glucosinolates degradation rate in broccoli
By choosing this topic you will deal with Adsorption Drying technology, glucosinolates determination by using HPLC and kinetic modeling of data, in order to predict the glucosinolates fate during different drying conditions. Cell lysis and the extent of leaching of glucosinolates in the water will be also investigated in rehydrated broccoli.2. Effect of Adsorption Drying Technology conditions on myrosinase activity in broccoli
You will investigate the influence of Adsorption Drying Technology on the myrosinase activity of broccoli. Myrosinase activity will be measured by using spectrophotometric assays, and kinetic models on enzyme inactivation will be used in order to predict the formation of breakdown products during drying and rehydration.3. Breakdown products formation in broccoli during Adsorption Drying Technology
The aim of this topic will be to detect and identify the breakdown products formed during drying of broccoli. The Breakdown products will be analyzed by GC-MS. The dried samples will be rehydrated to study the fate of breakdown products also after rehydration. The data obtained will be kinetically modeled.
Development of a realistic food model describing the fate of glucosinolates during food processing
PhD fellow: Irmela Kruse
Supervisors: Prof. dr. ir. M.A.J.S. van Boekel (PDQ, WU); Dr. ir. M. Dekker (PDQ, WU); Dr. Ing. R. Verkerk (PDQ, WU)
Glucosinolates are secondary plant metabolites especially rich in vegetables of the family Brassicaceae like cabbage, Brussels sprouts, kale or turnips. A diet rich in Brassica vegetables was found to decrease the risk of getting breast, lung, colorectal and stomach cancer in epidemiological studies. This preventive characteristic is not caused by glucosinolates themselves, but by their breakdown products, in particular isothiocyanates. Isothiocyanates occur, if an enzyme that is present in the plant, but dislocated from the glucosinolates gets in contact with its substrates and hydrolyses them. Different processing mechanisms have an influence on the presence of isothiocyanates in our foods: thermal degradation of glucosinolates, enzymatic hydrolysis of glucosinolates and leaching of glucosinolates into the cooking water. These three mechanisms are studied separately and a mathematical model will be build. Thereafter the models will be linked together to a realistic food model, which can increase the knowledge of bioaccessibility of isothiocyanates as well as to be used by the industry to optimize their processes in terms of glucosinolates.
For this research topic the following MSc/BSc theses are possible:
Supervisor: Irmela Kruse, Ruud Verkerk, Matthijs Dekker
1. MSc thesis: “Are some cell components binding to glucosinolates and therewith decreasing the leaching of glucosinolates into cooking water?”
In the early stages of cooking Brassica vegetables leaching of cells occurs very quickly. After a defined time this seems to be decreased and the concentration of glucosinolates in the cooking water doesn’t increase any more. One reason could be, that parts of the cell like e.g. the cell walls bind to the glucosinolates and therewith stop a release into the cooking water.
This topic will be founded on lab work such as cooking the vegetables for different times and extract the glucosinolates from cooking water and vegetables with hot methanol. The concentration of different glucosinolates will be measured by HPLC.2. MSc/BSc thesis: “Measurement of differently cut Brassica samples and their influence on leaching and diffusion pathways”
Vegetable cut into different sample sizes will have an influence on the leaching of cell contents into cooking water. This should be determined by cooking different sizes of samples and extract glucosinolates from vegetables as well as from cooking water and measure them by HPLC. It would be also interesting to measure the heat transfer into the samples by time. This thesis will includes lab work as well as building a mathematical model.
3. BSc thesis: “Influence of salt concentration in cooking water of Brassica vegetables on the leaching characteristics”
Vegetables will be cooked at different times and with different salt concentrations to measure the influence of salt on leaching of cell components into the cooking water. The glucosinolates will be extracted from cooking water as well as from vegetables and measured by HPLC.
Effects of processing on glucosinolates, vitamin C, total phenolics and antioxidant activity of brassica vegetables commonly consumed in Indonesia
PhD fellow : Probo Y. Nugrahedi
Supervisors : Prof. dr. ir.M.A.J.S. van Boekel (PDQ, WU) Dr. ir. Matthijs Dekker (PDQ, WU) Dr. Ing. Ruud Verkerk (PDQ, WU) Prof. Dr. Budi Widianarko, MSc (FTP, SCU Indonesia)
Brassica vegetables are part of vital daily diets of Indonesian people. These vegetables, however, are rarely studied in Indonesia with respect to the contents of health promoting compounds. A study on effects of processing, commonly practiced in Indonesia, on contents of glucosinolates, vitamin C, total phenolics and antioxidant activity of brassica vegetables, will be very valuable to improve quality (healthiness) of the final products. By developing mathematical models of the effect of different parameters in processing, furthermore, variation of the dietary intake of health-promoting compounds of vegetables can be predicted and optimised. The aim of the project is to evaluate contents of glucosinolates, vitamin C, total phenolics and antioxidant activity as affected by local processing methods of selected brassica vegetables in Semarang-Indonesia. This project, therefore, is mainly conducted in Semarang, a capital of Central Java province, Indonesia
Thesis topics (for MSc and BSc students), for examples
1. Variability of glucosinolates, vitamin C, total phenolics and antioxidant activity of fresh and processed brassica vegetables commonly consumed in Semarang, Indonesia
2. Effects of local processing methods on the contents of glucosinolates, vitamin C, total phenolics and antioxidant activity of brassica vegetables
3. Quality perception and preferences of stakeholders along the supply chain of brassica vegetables from farm to table (a survey-based study).
4. Quality perception and methods of handling, preparation, and processing of brassica vegetables processors (a survey-based study)
5. A kinetic study on the effects of boiling and steaming brassica vegetables
Consumer Behaviour and Healthy Vegetables
PhD Student: ir. Radhika Bongoni
Supervisors: Dr. ir. L.P.A. Steenbekkers (PDQ) Dr. Ir. M. Dekker (PDQ) Dr. Ing. R. Verkerk (PDQ) Promotor: Prof. Dr. ir. M.A.J.S van Boekel (PDQ)
Background of the PhD project
Consumer generally is the last part of the food production, supply and consumption chain. Consumer behaviour with regard to vegetable handling practices greatly influence the level of phytochemicals – the health promoting compounds in vegetables. For instance, the level of glucosinolate – a phytochemical of Brassicaceae vegetables, can vary greatly based on the method of cooking, time-temperature profile, vegetable-water ratio. Several mechanisms like leaching of phytochemicals into cooking water, thermal degradation, enzymatic degradation play a key role for this variations in the level of phytochemicals during vegetable handling practices.
In order to increase the intake level of phytochemicals in cooked vegetables before consumption, it is necessary to understand the consumer behaviour, motives behind their behaviour, sensory preferences and at the same time study the influences of consumer behaviour on the level of phytochemicals in vegetables. Mechanistic models (describing the rate of cell lysis, leaching, enzyme activity, enzyme denaturation) can be used to estimate the variations in the amount of remaining phytochemicals in cooked vegetables as a function of variation in processing conditions (vegetable-water ratio, temperature-time profile, etc) as applied by consumers in daily life. The approach is to integrate information from social science and natural science to gain an overall understanding of effects of consumer handling during vegetable preparation on the final quality in terms of the level of phytochemical in cooked vegetables.
The aim of the study is to increase the intake level of phytochemicals (glucosinolates and β –carotene) in cooked vegetables (broccoli and carrot), given sensory preferences of consumers.
Thesis topics for BSc/MSc students
1) Exploring consumer behaviour and domestic handling practices during vegetable preparation and motives behind their consumer behaviour
Supervisors: ir. R. Bongoni (PhD student), Dr. ir. L.P.A. Steenbekkers
Consumers prepare their vegetables based on their sensory preferences, without realizing the possible detrimental effects of preparation on health promoting quality of vegetables. Currently there is no proper insight on how and why consumer prepare their vegetables as they do.
- To explore consumer behaviour during vegetable preparation and to identify the motives for their behaviour and sensory preferences
- To check the repeatability or constancy of consumer behaviour through a sequence of observations under similar conditions
- Observations (In –home/in controlled environment) and in –depth interviews
- Self administered questionnaires
Possibilities for BSc/MSc students:
The student administers one of the above method (or both) to identify consumer behaviour and motives behind their behaviour. Thesis includes literature study, report writing, and presentations.
2) Assessing the influences of consumer behaviour on the level of phytochemicals
Supervisors: ir. R. Bongoni (PhD student), Dr. ir. M. Dekker, Dr. ing. R. Verkerk
To quantify the influences of consumer behaviour on the level of phytochemicals (glucosinolates and β –carotene) in vegetables (broccoli and carrot)
- Glucosinolate extraction an d analysis by HPLC
- Mathematical modelling using software program
Possibilities for students:
The student analyses in the laboratory the level of phytochemicals in vegetables at different cooking conditions (temperature-time profile, vegetable-water ratio, etc). Model simulations through mathematical equations describing various mechanisms: leaching, cell damage, enzymatic degradation, thermal degradation of phytochemicals would also be done to estimate the final phytochemical level of cooked vegetables. Literature study, report writing and presentations are a part of the thesis.