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Secundaire plantenstoffen, zoals essentiële oliën, hebben het vermogen om te interfereren met het selectieproces van een geschikte waardplant door een plaaginsect. In het eerste gedeelte van dit verslag worden de resultaten beschreven van laboratorium- en kasproeven waarin een aantal mogelijk afwerende plantenstoffen zijn getest tegen Californische trips (Frankliniella occidentalis). In het tweede gedeelte van dit verslag is aandacht besteed aan de extrinsieke en intrinsieke factoren die de werking van de commercieel verkrijgbare lokstof Lurem-TR op Californische trips kunnen beïnvloeden

Secundaire plantenstoffen, zoals essentiële oliën, hebben het vermogen om te interfereren met het selectieproces van een geschikte waardplant door een plaaginsect. In het eerste gedeelte van dit verslag worden de resultaten beschreven van laboratorium- en kasproeven waarin een aantal mogelijk afwerende plantenstoffen zijn getest tegen Californische trips (Frankliniella occidentalis). In het tweede gedeelte van dit verslag is aandacht besteed aan de extrinsieke en intrinsieke factoren die de werking van de commercieel verkrijgbare lokstof Lurem-TR op Californische trips kunnen beïnvloeden

De afgelopen jaren is bij PAV-proeven in dille, zomer- en winterkarwij gebleken dat oogst en destillatie van de zaadschermen, juist voor de volledige rijping van het zaad, resulteert in een 40% hogere olieopbrengst in vergelijking met destillatie van het rijpe zaad geoogst met de maaidorser

cum laude graduation (with distinction)

Zilverschurft is een knolziekte die zich in haar verschijningsvorm vooral tijdens de bewaring openbaart en ontwikkelt. Als gevolg daarvan vormt zilverschurft een ernstig cosmetisch probleem in zowel poot- als consumptieaardappelen. Zilverschurft wordt veroorzaakt door een schimmel, Helminthosporium solani. In de biologische pootgoedsector is op dit moment geen effectieve methode voorhanden om deze infectieroute te voorkomen of te beperken. Om de besmettingpotentie van de moederknollen te reduceren moet de schimmel ofwel tijdens de bewaring worden bestreden, ofwel moet de sporenvorming na het poten worden voorkomen.

Geen uitval meer door tulpengalmijt bij de bewaring en broeierij van tulpen lijkt ook in de toekomst mogelijke door nieuwe alternatieven. Een boldompeling kort na het rooien in en contactmiddel of verdampen van een etherische olie voorkwam tulpengalmijt aantasting in proeven bij PPO Bloembollen. Deze middelen en methoden kunnen in de toekomst mogelijk een volwaardig alternatief zijn voor het nu enige voor dit doel toegelaten middel Actellic

Zilverschurft is een knolziekte die zich in haar verschijningsvorm vooral tijdens de bewaring openbaart en ontwikkelt. Als gevolg daarvan vormt zilverschurft een ernstig cosmetisch probleem in zowel poot- als consumptieaardappelen. Zilverschurft wordt veroorzaakt door een schimmel, Helminthosporium solani. In de biologische pootgoedsector is op dit moment geen effectieve methode voorhanden om deze infectieroute te voorkomen of te beperken. Om de besmettingpotentie van de moederknollen te reduceren moet de schimmel ofwel tijdens de bewaring worden bestreden, ofwel moet de sporenvorming na het poten worden voorkomen.

Dit biologisch onderzoekbericht laat enkele resultaten en plannen zien van het onderzoeksprogramma Biologisch uitgangsmateriaal, dat van 2005 tot en met 2007 loopt. Een Zweedse sauna om zaad te ontsmetten of een bad met thijmolie lijken succesvol.Het programma gaat in nauwe samenwerking met de sector werken aan gezonder uitgangsmateriaal voor de biologische sector.

Dit biologisch onderzoekbericht laat enkele resultaten en plannen zien van het onderzoeksprogramma Biologisch uitgangsmateriaal, dat van 2005 tot en met 2007 loopt. Een Zweedse sauna om zaad te ontsmetten of een bad met thijmolie lijken succesvol.Het programma gaat in nauwe samenwerking met de sector werken aan gezonder uitgangsmateriaal voor de biologische sector.

Tarragon ( Artemisia dracunculus L.) is a favorite herbal and medicinal plant. Drying is necessary to achieve longer shelf life with high quality, preserving the original flavor. Essential oil content and color are the most important parameters that define the quality of herbal and medicinal plants. Hot air batch drying is the most common drying method for these plants but affects the essential oil content and color. The drying conditions affect essential oil content and color as well as the energy consumption and costs. Process engineers and farmers need to know how they have to dry to obtain the best quality. The objective of this work is to investigate the conditions for optimal drying in terms of quality, energy consumption and costs.Adsorption and desorption experiments were done to find the equilibrium moisture content and water exchange between the material and surrounding air during drying and storage at temperatures of 25ºC to 70ºC and relative humidities of 5% to 90%. Drying of tarragon leaves and chopped plants was investigated separately and the best model was selected from the drying equations in literature. The effect of drying temperature and relative humidity on the essential oil content and color change was studied. Experiments were done at temperatures of 40ºC to 90ºC and the optimal conditions were. Long‑term effects of the drying conditions were also investigated during the storage time. Material dried at 45, 60 and 90ºC was stored and the essential oil content and color of the material was measured after 15, 30, 60 and 120 days of storage. Drying at 45ºC was found as the best condition based on the changes of essential oil and color during drying and storage.Optimization of drying of tarragon was studied based on the results of the sorption isotherms, drying equations and the changes of essential oil content and color during drying and storage. Models were made for the drying process, energy consumption and cost calculation. The current conditions in The Netherlands andIranwere applied for various drying scenarios. The simulation model was run at selected ranges of temperature, humidity ratio, air speed and bed heights, with and without recirculation of the drying air. Considering the quality of dried material and costs, a temperature of 50ºC was found as the optimal temperature for drying tarragon. The costs per kg dried product was about three times higher for The Netherlands compared toIran. The recirculation is less important inIranbecause the ambient air has a higher drying potential and energy prices are lower.

Tarragon ( Artemisia dracunculus L.) is a favorite herbal and medicinal plant. Drying is necessary to achieve longer shelf life with high quality, preserving the original flavor. Essential oil content and color are the most important parameters that define the quality of herbal and medicinal plants. Hot air batch drying is the most common drying method for these plants but affects the essential oil content and color. The drying conditions affect essential oil content and color as well as the energy consumption and costs. Process engineers and farmers need to know how they have to dry to obtain the best quality. The objective of this work is to investigate the conditions for optimal drying in terms of quality, energy consumption and costs.Adsorption and desorption experiments were done to find the equilibrium moisture content and water exchange between the material and surrounding air during drying and storage at temperatures of 25ºC to 70ºC and relative humidities of 5% to 90%. Drying of tarragon leaves and chopped plants was investigated separately and the best model was selected from the drying equations in literature. The effect of drying temperature and relative humidity on the essential oil content and color change was studied. Experiments were done at temperatures of 40ºC to 90ºC and the optimal conditions were. Long‑term effects of the drying conditions were also investigated during the storage time. Material dried at 45, 60 and 90ºC was stored and the essential oil content and color of the material was measured after 15, 30, 60 and 120 days of storage. Drying at 45ºC was found as the best condition based on the changes of essential oil and color during drying and storage.Optimization of drying of tarragon was studied based on the results of the sorption isotherms, drying equations and the changes of essential oil content and color during drying and storage. Models were made for the drying process, energy consumption and cost calculation. The current conditions in The Netherlands andIranwere applied for various drying scenarios. The simulation model was run at selected ranges of temperature, humidity ratio, air speed and bed heights, with and without recirculation of the drying air. Considering the quality of dried material and costs, a temperature of 50ºC was found as the optimal temperature for drying tarragon. The costs per kg dried product was about three times higher for The Netherlands compared toIran. The recirculation is less important inIranbecause the ambient air has a higher drying potential and energy prices are lower.

Several plant essential oils were tested for their effect on behaviour and mortality of M. euphorbiae. Olfactory and contact experiments were performed to study these effects. We found that host plant and formulation of the different oils have a strong influence on repellence and mortality of the aphids. Three out of ten tested oils show potential for control of this aphid in greenhouses and field crops

Several plant essential oils were tested for their effect on behaviour and mortality of M. euphorbiae. Olfactory and contact experiments were performed to study these effects. We found that host plant and formulation of the different oils have a strong influence on repellence and mortality of the aphids. Three out of ten tested oils show potential for control of this aphid in greenhouses and field crops

In de veehouderij maakt men op dit moment veelvuldig gebruik gemaakt van antimicrobiële groeibevorderaars (AMGB's) in voeders voor landbouwhuisdieren. Het gebruik van AMGB's wordt vanaf 2005 wellicht volledig verboden, omdat het gebruik van antibiotica resistentie van bacteriepopulaties tot gevolg kan hebben. Met dit vooruitzicht is de mengvoersector bezig met het ontwikkelen van voerconcepten als alternatief voor AMGB's. In opdracht van bedrijf Crina s.a. (Gland, Zwitserland) is op het Praktijkcentrum Sterksel nagegaan wat het effect is van de etherische olie Crinae Piglets als alternatief voor AMGB's op technische resultaten en gezondheid van gespeende biggen. In dit experiment zijn drie proefbehandelingen met elkaar vergeleken: voer zonder AMGB, voer met AMGB en voer met Crinae Piglets. Op een leeftijd van gemiddeld 4 weken zijn de biggen gespeend en ingedeeld voor de proef. De biggen zijn vanaf spenen 34 dagen gevolgd. In totaal zijn 630 biggen gevolgd. De behandelingen zonder en met AMGB zijn elk 22 keer herhaald, de behandeling met Crinae Piglets 19 keer.

In de veehouderij maakt men op dit moment veelvuldig gebruik gemaakt van antimicrobiële groeibevorderaars (AMGB's) in voeders voor landbouwhuisdieren. Het gebruik van AMGB's wordt vanaf 2005 wellicht volledig verboden, omdat het gebruik van antibiotica resistentie van bacteriepopulaties tot gevolg kan hebben. Met dit vooruitzicht is de mengvoersector bezig met het ontwikkelen van voerconcepten als alternatief voor AMGB's. In opdracht van bedrijf Crina s.a. (Gland, Zwitserland) is op het Praktijkcentrum Sterksel nagegaan wat het effect is van de etherische olie Crinae Piglets als alternatief voor AMGB's op technische resultaten en gezondheid van gespeende biggen. In dit experiment zijn drie proefbehandelingen met elkaar vergeleken: voer zonder AMGB, voer met AMGB en voer met Crinae Piglets. Op een leeftijd van gemiddeld 4 weken zijn de biggen gespeend en ingedeeld voor de proef. De biggen zijn vanaf spenen 34 dagen gevolgd. In totaal zijn 630 biggen gevolgd. De behandelingen zonder en met AMGB zijn elk 22 keer herhaald, de behandeling met Crinae Piglets 19 keer.

The fumigant toxicity of selected essential oils was assessed against the Western Flower Thrips, Frankliniella occidentalis. Adult females and larvae were exposed to combinations of essential oil doses and increased carbon dioxide and decreased oxygen levels. Application of such combinations were found to significantly increase the fumigant toxicity against thrips. An increase in exposure time also led to an increase in mortalities in both essential oil alone and combined treatments. These results indicate that by combining applications of the essential oils with e.g. moderately increased carbon dioxide levels (2 to 10%), it may be possible to achieve toxicity levels similar to those of standard chemical fumigants.

A variety of non-thermal mild preservation techniques have lately been introduced in food production, or are currently being investigated thoroughly for potential use in food processing. Two of these novel preservation techniques are the use of essential oil compounds isolated from plants and of High Hydrostatic Pressure (HHP) treatment. Applications of these preservation methods, alone or combined, have shown to reduce the viable numbers of microorganisms occurring in foods, and in addition, are able to preserve the nutritional and sensory characteristics of the product. The objectives of this thesis were to asses the antimicrobial potential of these combined processing techniques against the foodborne bacterium Listeria monocytogenes , which can cause serious disease with a relatively high mortality rate. In addition, to get more insight in the primary cellular targets that are affected upon HHP treatment of L. monocytogenes , we examined the mechanism underlying increased HHP tolerance of an isolate of this organism.Chapter 1 gives a short introduction on L. monocytogenes. Furthermore, mild and novel preservation techniques in food processing are addressed, with special emphasis on the use of essential oil compounds from plants, and the use of High Hydrostatic Pressure (HHP). General characteristics and the mode of action of these preservation techniques are described, followed by resistance mechanisms that bacteria use to counteract their potentially lethal action. This chapter is concluded with the combined use of these preservation methods, and an outline of this thesis.In Chapter 2 , it is demonstrated that various plant-derived volatiles, namely, S-carvone, carvacrol, cinnamaldehyde, thymol, and decanal, have the ability to reduce the viable numbers of L. monocytogenes if used in combination with mild heat treatment, while these treatments alone were not affecting the viability of this pathogen. These findings show that essential oil compounds can play an important role in minimally processed foods, and can be used in the concept of Hurdle Technology to reduce the intensity of heat treatment or possibly other individual hurdles.In Chapter 3 , the combined antimicrobial action of carvacrol or thymol in combination with HHP was investigated at different temperatures. These treatments showed a synergistic action, with greater antimicrobial effects upon pressurisation at 1 oC than at 8°C or 20°C. Furthermore, addition of carvacrol to cells after exposure to sub-lethal HHP treatment showed reductions in viable numbers that were similar to those using simultaneous treatment with carvacrol and HHP. Synergism was also observed between carvacrol and HHP in semi-skimmed milk that was artificially contaminated with L. monocytogenes . The study demonstrates the synergistic antimicrobial effect of essential oils in combination with HHP. Together with the results described in Chapter 2, these data indicate the potential of essential oils to be employed in food processing if combined with other techniques.A major problem that successful application of HHP treatment faces is the variable piezotolerance of bacterial species, strains within a species, and even cells within pure cultures that are not homogenous. In Chapter 4 , we investigated the characteristics of a L. monocytogenes ScottA isolate, named AK01, that was derived from a wild type (wt) culture after a single pressurisation treatment. The survival of exponential and stationary phase cells of AK01 was at least 2 logs higher than that of the wt over a broad range of pressures (150-500 MPa), while both strains showed higher piezotolerance in the stationary than in the exponential phase of growth. In semi-skimmed milk, exponential phase cells of both strains showed lower reductions upon pressurisation than in buffer, but again, AK01 was more piezotolerant than the wt. The piezotolerance of AK01 was retained for at least 40 generations in rich medium, suggesting a stable phenotype. Interestingly, cells of AK01 lacked flagella and were elongated, and this strain showed slightly lower maximum specific growth rates at 8°C, 22°C and 30°C than the wt. Moreover, the piezotolerant strain AK01 showed increased resistance to heat, acid, and H 2 O 2 compared with the wt. The difference in HHP tolerance between the piezotolerant strain and the wt strain could not be attributed to differences in membrane fluidity, since strain AK01 and the wt had identical in situ lipid melting curves, as determined by Fourier Transfer Infrared spectroscopy.In Chapter 5 , the mechanisms underlying the altered phenotypic characteristics of AK01 are further examined. In this chapter, high piezotolerance, immobility, and reduced virulence were conclusively linked to a single amino acid deletion in the highly conserved glycine-rich region of the regulatory protein CtsR ( C lass t hree s tress gene r epressor). CtsR negatively regulates the expression of Class III heat shock genes ( clpP , clpE and the clpC operon). The Clp proteins prevent the accumulation of misfolded proteins that might be toxic to the cell. In the mutant strain AK01, expressing the CtsRΔGly protein, we observed upregulation ofclpP , which demonstrates the involvement of Class III heat shock genes in increased survival upon HHP treatment and other stresses. Replacement of the wt ctsR gene with the ctsRΔGly gene in a wt background resulted in a mutant strain that also lost its motile character, and importantly, also showed attenuated virulence. The deletion of three base pairs in the region of ctsR that normally encodes four glycines is seemingly not an isolated incident, since we detected the same mutation in the majority of other spontaneous piezotolerant isolates of L. monocytogenes . This suggests a functional role for this mutation in L. monocytogenes to survive unforeseen events that do not allow for adaptation of normal cells, but require genetic diversity.In conclusion, this work demonstrated some of the potentials that novel techniques, like the use of essential oils and HHP, can offer alone or combined with other novel or traditional techniques, like heat treatment. We furthermore investigated risks that could emerge from the use of those novel techniques. The occurrence of the piezotolerant strain AK01 of L. monocytogenes demonstrated the existence of bacterial heterogeneity within a supposedly pure wt population with regard to HHP resistance. The variance of piezotolerance within a microbial population, but also between different strains, is an important parameter that determines successful application of HHP treatment. This will be an important aspect for risk assessment of HHP treated foods that are, or will become, available on the market. Tailored HHP treatments, possibly in combination with additional mild preservatives, will be required for different products, and increased knowledge about the effects of these treatments will enable the food industry to produce safe foods at minimal costs.

A variety of non-thermal mild preservation techniques have lately been introduced in food production, or are currently being investigated thoroughly for potential use in food processing. Two of these novel preservation techniques are the use of essential oil compounds isolated from plants and of High Hydrostatic Pressure (HHP) treatment. Applications of these preservation methods, alone or combined, have shown to reduce the viable numbers of microorganisms occurring in foods, and in addition, are able to preserve the nutritional and sensory characteristics of the product. The objectives of this thesis were to asses the antimicrobial potential of these combined processing techniques against the foodborne bacterium Listeria monocytogenes , which can cause serious disease with a relatively high mortality rate. In addition, to get more insight in the primary cellular targets that are affected upon HHP treatment of L. monocytogenes , we examined the mechanism underlying increased HHP tolerance of an isolate of this organism.Chapter 1 gives a short introduction on L. monocytogenes. Furthermore, mild and novel preservation techniques in food processing are addressed, with special emphasis on the use of essential oil compounds from plants, and the use of High Hydrostatic Pressure (HHP). General characteristics and the mode of action of these preservation techniques are described, followed by resistance mechanisms that bacteria use to counteract their potentially lethal action. This chapter is concluded with the combined use of these preservation methods, and an outline of this thesis.In Chapter 2 , it is demonstrated that various plant-derived volatiles, namely, S-carvone, carvacrol, cinnamaldehyde, thymol, and decanal, have the ability to reduce the viable numbers of L. monocytogenes if used in combination with mild heat treatment, while these treatments alone were not affecting the viability of this pathogen. These findings show that essential oil compounds can play an important role in minimally processed foods, and can be used in the concept of Hurdle Technology to reduce the intensity of heat treatment or possibly other individual hurdles.In Chapter 3 , the combined antimicrobial action of carvacrol or thymol in combination with HHP was investigated at different temperatures. These treatments showed a synergistic action, with greater antimicrobial effects upon pressurisation at 1 oC than at 8°C or 20°C. Furthermore, addition of carvacrol to cells after exposure to sub-lethal HHP treatment showed reductions in viable numbers that were similar to those using simultaneous treatment with carvacrol and HHP. Synergism was also observed between carvacrol and HHP in semi-skimmed milk that was artificially contaminated with L. monocytogenes . The study demonstrates the synergistic antimicrobial effect of essential oils in combination with HHP. Together with the results described in Chapter 2, these data indicate the potential of essential oils to be employed in food processing if combined with other techniques.A major problem that successful application of HHP treatment faces is the variable piezotolerance of bacterial species, strains within a species, and even cells within pure cultures that are not homogenous. In Chapter 4 , we investigated the characteristics of a L. monocytogenes ScottA isolate, named AK01, that was derived from a wild type (wt) culture after a single pressurisation treatment. The survival of exponential and stationary phase cells of AK01 was at least 2 logs higher than that of the wt over a broad range of pressures (150-500 MPa), while both strains showed higher piezotolerance in the stationary than in the exponential phase of growth. In semi-skimmed milk, exponential phase cells of both strains showed lower reductions upon pressurisation than in buffer, but again, AK01 was more piezotolerant than the wt. The piezotolerance of AK01 was retained for at least 40 generations in rich medium, suggesting a stable phenotype. Interestingly, cells of AK01 lacked flagella and were elongated, and this strain showed slightly lower maximum specific growth rates at 8°C, 22°C and 30°C than the wt. Moreover, the piezotolerant strain AK01 showed increased resistance to heat, acid, and H 2 O 2 compared with the wt. The difference in HHP tolerance between the piezotolerant strain and the wt strain could not be attributed to differences in membrane fluidity, since strain AK01 and the wt had identical in situ lipid melting curves, as determined by Fourier Transfer Infrared spectroscopy.In Chapter 5 , the mechanisms underlying the altered phenotypic characteristics of AK01 are further examined. In this chapter, high piezotolerance, immobility, and reduced virulence were conclusively linked to a single amino acid deletion in the highly conserved glycine-rich region of the regulatory protein CtsR ( C lass t hree s tress gene r epressor). CtsR negatively regulates the expression of Class III heat shock genes ( clpP , clpE and the clpC operon). The Clp proteins prevent the accumulation of misfolded proteins that might be toxic to the cell. In the mutant strain AK01, expressing the CtsRΔGly protein, we observed upregulation ofclpP , which demonstrates the involvement of Class III heat shock genes in increased survival upon HHP treatment and other stresses. Replacement of the wt ctsR gene with the ctsRΔGly gene in a wt background resulted in a mutant strain that also lost its motile character, and importantly, also showed attenuated virulence. The deletion of three base pairs in the region of ctsR that normally encodes four glycines is seemingly not an isolated incident, since we detected the same mutation in the majority of other spontaneous piezotolerant isolates of L. monocytogenes . This suggests a functional role for this mutation in L. monocytogenes to survive unforeseen events that do not allow for adaptation of normal cells, but require genetic diversity.In conclusion, this work demonstrated some of the potentials that novel techniques, like the use of essential oils and HHP, can offer alone or combined with other novel or traditional techniques, like heat treatment. We furthermore investigated risks that could emerge from the use of those novel techniques. The occurrence of the piezotolerant strain AK01 of L. monocytogenes demonstrated the existence of bacterial heterogeneity within a supposedly pure wt population with regard to HHP resistance. The variance of piezotolerance within a microbial population, but also between different strains, is an important parameter that determines successful application of HHP treatment. This will be an important aspect for risk assessment of HHP treated foods that are, or will become, available on the market. Tailored HHP treatments, possibly in combination with additional mild preservatives, will be required for different products, and increased knowledge about the effects of these treatments will enable the food industry to produce safe foods at minimal costs.

Op verzoek van Ropapharm B.V. te Zaandam heeft het Praktijkonderzoek Veehouderij een onderzoek uitgevoerd naar de effectiviteit van Ropadiar e , een etherische olie van de oreganoplant, als alternatief voor AMGB. Oregano-olie heeft antibacteriële eigenschappen

Op verzoek van Ropapharm B.V. te Zaandam heeft het Praktijkonderzoek Veehouderij een onderzoek uitgevoerd naar de effectiviteit van Ropadiar e , een etherische olie van de oreganoplant, als alternatief voor AMGB. Oregano-olie heeft antibacteriële eigenschappen

A new trend in food preservation is the use of mild preservation systems, instead of more severe techniques such as heating, freezing or addition of chemical preservatives. Carvacrol, a phenolic compound present in the essential oil fraction of oreganum and thyme, is known for its antimicrobial activity since ancient times. This thesis describes a study of the antimicrobial activity of carvacrol towards the foodborne pathogen B.cereus . Carvacrol shows a dose-related inhibition of growth of B.cereus . Concentrations of 0.75 mM and higher inhibit growth completely at 8°C. Below 0.75 mM, carvacrol extends the lag-phase and reduces the specific growth rate as well as the final population density. Exposure to 0.75-3 mM carvacrol decreases the number of viable cells of B.cereus exponentially. Spores are approximately two fold more resistant towards carvacrol than vegetative cells.The incubation and exposure temperature have a significant influence on the sensitivity of B.cereus to carvacrol. An increase of the growth temperature from 8°C to 30°C decreases the fluidity of the membrane of vegetative cells and as a consequence, B.cereus becomes less sensitive to carvacrol. The change in membrane fluidity is probably the result of a higher percentage of lower melting lipids in the membranes at 8°C (chemical process) as an adaptation to lower temperature. Cells need to maintain an adequate proportion of the liquid-crystalline lipid in the membrane, as this is the ideal physical state of the membrane. On the other hand, an increase of the exposure temperature from 8 to 30°C, reduces the viability again. This can be explained by an increase of the membrane fluidity at a higher temperature as a result of melting of the lipids (physical process). At a higher membrane fluidity, relatively more carvacrol can dissolve in the membrane and the cells will be exposed to relatively higher concentrations than at a lower membrane fluidity.Not only the temperature plays a role in the activity of carvacrol, also pH is an important factor. The sensitivity of B.cereus to carvacrol is reduced at pH 7, compared to other pH-values between pH 4.5 and 8.5.Carvacrol interacts with the cytoplasmic membrane by changing its permeability for cations such as K +and H +. Consequently, the dissipation of the membrane potential (Δψ) andΔpH leads to inhibition of essential processes in the cell, such as ATP synthesis, and finally to cell death. At carvacrol concentrations as low as 0.15 mM,Δψis completely dissipated, however the viable count of B.cereus is not affected.Vegetative cells of B.cereus can adapt to carvacrol when the compound is present at concentrations below the MIC-value. Compared to non-adapted cells, lower concentrations of carvacrol are needed to obtain the same reduction in viable count of adapted cells. Adapted cells were found to have a lower membrane fluidity, caused by a change in the fatty acid composition and head group composition of the phospholipids in the cytoplasmic membrane. Adaptation to 0.4 mM carvacrol increases the phase transition temperature of the lipid bilayer (T m ) from 20.5°C to 28.3°C. Addition of carvacrol to cell suspensions of adapted B.cereus cells decreases T m again to 19.5°C, approximately the same value as was found for non-adapted cells in the absence of carvacrol.Incubation of cooked rice in the presence of different carvacrol concentrations results in a dose-related reduction of the viable count of B.cereus . Concentrations of 0.15 mg/g and above, reduce the viable count, leading to full suppression of growth at 0.38 mg/g. The influence of carvacrol on the viable count is dependent on the initial inoculum size. Although carvacrol is an effective inhibitor of growth of B.cereus in rice, it could affect the flavour and taste of the product at concentrations where full suppression of growth is observed. However, strong synergistic activity is observed when carvacrol is combined with the biosynthetic precursor cymene or the flavour enhancer soya sauce. This makes it possible to use lower carvacrol concentrations and consequently a smaller influence on the sensoric properties of the rice is expected.Besides its influence on the viability of vegetative cells, carvacrol also shows inhibition of diarrhoeal toxin production by B. cereus at concentrations below the MIC-value. Addition of 0.06 mg/ml carvacrol to the growth medium, inhibits the toxin to 21% of the control (no carvacrol added). The inhibition correlates with the reduction of the viable count of B.cereus in the presence of carvacrol. At the same time, the total amount of cells did not change. In mushroom soup, also an inhibition of the toxin production was observed, however, the viable count did not change. This effect on the toxin production is most probably caused by a lack of sufficient metabolic energy, since carvacrol affects ATP synthesis. The cell will use its low levels of ATP to maintain its viability, rather than using it for toxin production or excretion. It could also be possible that the decreased toxin synthesis in BHI was the result of the lower amount of viable cells. The inhibition of toxin production at carvacrol concentrations which do permit growth of B.cereus , reduces the risk of food intoxication by this pathogen.In conclusion, carvacrol may play an important role in future as a natural antimicrobial compound. However, its application will most probably be in combination with other natural antimicrobial systems.

In this study, some factors affecting the aroma of some plants of the families Umbelliferae and Asteraceae were evaluated. The composition of the aromas is influenced by several factors: plant family, harvesting time, anatomical part of plant, method used to isolate volatiles, cultivar, fertilisers used for the growing of plant, cultivation site. The yield of caraway fruits varies over a wide range depending on fertiliser content, cultivation area and the cultivar itself. The trends for the accumulation of essential oils differ between the families in yield and composition. Seeds and flowers of lovage ( Umbelliferae ) possess the highest yields of oil. In the leaves of lovage seasonal changes are less significant than in the stems. In leaves and flowers of costmary ( Asteraceae ) the highest oil content is obtained before full flowering, while their stems possess only negligible amount of volatiles. Various anatomical parts of lovage showed differences in flavour release measured by the dynamic headspace method. The effluents from a gas chromatography column were characterised by a sniffing panel, which attributed descriptors to the recognised constituents.Liquid essential oils can be processed by emulsification and encapsulation with milk proteins. Stability of essential oil-in-water emulsions can be improved either by adding soybean phosphatidylcholine and/or by increasing its protein concentration. Adsorption of the protein from the aqueous phase at the oil/water interface was studied by applying ellipsometry. Essential oil of caraway was encapsulated by milk derivatives either alone or combined with carbohydrates. Partial replacement of whey protein concentrate increases the retention of volatiles during spray drying and enhances the protective properties of solidified capsules against oxidation and the release of volatiles during the timed period. The structural features of spray- dried capsules indicated that good physical protection is provided to the caraway essential oil.

A new trend in food preservation is the use of mild preservation systems, instead of more severe techniques such as heating, freezing or addition of chemical preservatives. Carvacrol, a phenolic compound present in the essential oil fraction of oreganum and thyme, is known for its antimicrobial activity since ancient times. This thesis describes a study of the antimicrobial activity of carvacrol towards the foodborne pathogen B.cereus . Carvacrol shows a dose-related inhibition of growth of B.cereus . Concentrations of 0.75 mM and higher inhibit growth completely at 8°C. Below 0.75 mM, carvacrol extends the lag-phase and reduces the specific growth rate as well as the final population density. Exposure to 0.75-3 mM carvacrol decreases the number of viable cells of B.cereus exponentially. Spores are approximately two fold more resistant towards carvacrol than vegetative cells.The incubation and exposure temperature have a significant influence on the sensitivity of B.cereus to carvacrol. An increase of the growth temperature from 8°C to 30°C decreases the fluidity of the membrane of vegetative cells and as a consequence, B.cereus becomes less sensitive to carvacrol. The change in membrane fluidity is probably the result of a higher percentage of lower melting lipids in the membranes at 8°C (chemical process) as an adaptation to lower temperature. Cells need to maintain an adequate proportion of the liquid-crystalline lipid in the membrane, as this is the ideal physical state of the membrane. On the other hand, an increase of the exposure temperature from 8 to 30°C, reduces the viability again. This can be explained by an increase of the membrane fluidity at a higher temperature as a result of melting of the lipids (physical process). At a higher membrane fluidity, relatively more carvacrol can dissolve in the membrane and the cells will be exposed to relatively higher concentrations than at a lower membrane fluidity.Not only the temperature plays a role in the activity of carvacrol, also pH is an important factor. The sensitivity of B.cereus to carvacrol is reduced at pH 7, compared to other pH-values between pH 4.5 and 8.5.Carvacrol interacts with the cytoplasmic membrane by changing its permeability for cations such as K +and H +. Consequently, the dissipation of the membrane potential (Δψ) andΔpH leads to inhibition of essential processes in the cell, such as ATP synthesis, and finally to cell death. At carvacrol concentrations as low as 0.15 mM,Δψis completely dissipated, however the viable count of B.cereus is not affected.Vegetative cells of B.cereus can adapt to carvacrol when the compound is present at concentrations below the MIC-value. Compared to non-adapted cells, lower concentrations of carvacrol are needed to obtain the same reduction in viable count of adapted cells. Adapted cells were found to have a lower membrane fluidity, caused by a change in the fatty acid composition and head group composition of the phospholipids in the cytoplasmic membrane. Adaptation to 0.4 mM carvacrol increases the phase transition temperature of the lipid bilayer (T m ) from 20.5°C to 28.3°C. Addition of carvacrol to cell suspensions of adapted B.cereus cells decreases T m again to 19.5°C, approximately the same value as was found for non-adapted cells in the absence of carvacrol.Incubation of cooked rice in the presence of different carvacrol concentrations results in a dose-related reduction of the viable count of B.cereus . Concentrations of 0.15 mg/g and above, reduce the viable count, leading to full suppression of growth at 0.38 mg/g. The influence of carvacrol on the viable count is dependent on the initial inoculum size. Although carvacrol is an effective inhibitor of growth of B.cereus in rice, it could affect the flavour and taste of the product at concentrations where full suppression of growth is observed. However, strong synergistic activity is observed when carvacrol is combined with the biosynthetic precursor cymene or the flavour enhancer soya sauce. This makes it possible to use lower carvacrol concentrations and consequently a smaller influence on the sensoric properties of the rice is expected.Besides its influence on the viability of vegetative cells, carvacrol also shows inhibition of diarrhoeal toxin production by B. cereus at concentrations below the MIC-value. Addition of 0.06 mg/ml carvacrol to the growth medium, inhibits the toxin to 21% of the control (no carvacrol added). The inhibition correlates with the reduction of the viable count of B.cereus in the presence of carvacrol. At the same time, the total amount of cells did not change. In mushroom soup, also an inhibition of the toxin production was observed, however, the viable count did not change. This effect on the toxin production is most probably caused by a lack of sufficient metabolic energy, since carvacrol affects ATP synthesis. The cell will use its low levels of ATP to maintain its viability, rather than using it for toxin production or excretion. It could also be possible that the decreased toxin synthesis in BHI was the result of the lower amount of viable cells. The inhibition of toxin production at carvacrol concentrations which do permit growth of B.cereus , reduces the risk of food intoxication by this pathogen.In conclusion, carvacrol may play an important role in future as a natural antimicrobial compound. However, its application will most probably be in combination with other natural antimicrobial systems.

In this study, some factors affecting the aroma of some plants of the families Umbelliferae and Asteraceae were evaluated. The composition of the aromas is influenced by several factors: plant family, harvesting time, anatomical part of plant, method used to isolate volatiles, cultivar, fertilisers used for the growing of plant, cultivation site. The yield of caraway fruits varies over a wide range depending on fertiliser content, cultivation area and the cultivar itself. The trends for the accumulation of essential oils differ between the families in yield and composition. Seeds and flowers of lovage ( Umbelliferae ) possess the highest yields of oil. In the leaves of lovage seasonal changes are less significant than in the stems. In leaves and flowers of costmary ( Asteraceae ) the highest oil content is obtained before full flowering, while their stems possess only negligible amount of volatiles. Various anatomical parts of lovage showed differences in flavour release measured by the dynamic headspace method. The effluents from a gas chromatography column were characterised by a sniffing panel, which attributed descriptors to the recognised constituents.Liquid essential oils can be processed by emulsification and encapsulation with milk proteins. Stability of essential oil-in-water emulsions can be improved either by adding soybean phosphatidylcholine and/or by increasing its protein concentration. Adsorption of the protein from the aqueous phase at the oil/water interface was studied by applying ellipsometry. Essential oil of caraway was encapsulated by milk derivatives either alone or combined with carbohydrates. Partial replacement of whey protein concentrate increases the retention of volatiles during spray drying and enhances the protective properties of solidified capsules against oxidation and the release of volatiles during the timed period. The structural features of spray- dried capsules indicated that good physical protection is provided to the caraway essential oil.

De afgelopen jaren is bij PAV-proeven in dille, zomer- en winterkarwij gebleken dat oogst en destillatie van de zaadschermen, juist voor de volledige rijping van het zaad, resulteert in een 40% hogere olieopbrengst in vergelijking met destillatie van het rijpe zaad geoogst met de maaidorser

After harvest, potato tubers are usually stored at a temperature of 6-8°C in combination with the application of a synthetic sprout inhibitor. Frequently used sprout inhibitors are isopropyl N-phenyl-carbamate (propham or IPC), isopropyl N-(3-chlorophenyl)carbamate (chlorpropham or CIPC) or a combination of both compounds. There are several reasons for the development of alternative, natural sprout inhibitors. First, the Scandinavian market, for example, requires potato tubers free of (C)IPC residues, and the so-called "green" market, for which no or very little synthetic chemicals are allowed, does not yet have alternative sprout inhibitors. Secondly, governmental policy is directed towards a reduction of the amount of synthetic pesticides used in agricultural practice (Meerjarenplan Gewasbeschermingsmiddelen, MJPG).Natural potato sprout inhibitors were already used in the ancient Inca cultures. After harvest, the potato tubers were stored in boxes or bins together with the twigs of muña plants (Minthostachys species). Treating the tubers in this way controlled sprouting as well as insect attack during a prolonged storage. Volatiles emanating from the muña leaves during the storage were responsible for the insect repellent and sprout inhibitory effects.The monoterpene S-carvone is a related volatile compound which can be isolated from the seeds of caraway (Carum carvi L.) or dill ( Anethum graveolens L.), for example; also this compound has good potato sprout growth inhibitory effects. Application of S-carvone, derived from caraway seed, as a potato sprout inhibitor can stimulate the demand for caraway and therefore the need to grow it. This can be beneficial for Dutch growers, since cultivation of caraway is suitable on heavy clay soils in which crop rotation is limited to only a few crops. The research described in this thesis has been performed within the Dutch Caraway Research Programme in which nine research groups were amalgamated with the objective to reduce the problems with respect to the cultivation of caraway and to stimulate possible new applications of its essential oil or of S-carvone.S-carvone inhibits the sprouting of potato tubers and the sprout growth reversibly: removal of S-carvone allows sprouting and regrowth of the individual sprouts. A high dosage leads to necrosis, but the side buds remain their viability and they start to sprout again when the concentration of S-carvone in the atmosphere comes below a threshold value. The enantiomer of S-carvone, R- carvone, can be isolated from spearmint ( Mentha spicata L.) and possesses almost the same sprout growth inhibitory properties as S-carvone. Current research is focussed on the practical application of S-carvone to seed potatoes as a reversible sprout growth inhibitor.In addition to the inhibitory effects just mentioned, the growth of several storage pathogens is also reduced by S-carvone. However, the susceptibility of fungi to S-carvone, e.g. Fusarium species that cause dry-rot, differs between (sub)species. F.solani var. coeruleum is able to grow on tubers treated with S- carvone, whereas F . sulphureum cannot withstand it. This difference was not found in vitro; both fungi were susceptible to the same range of S-carvone concentrations, they were both able to convert S-carvone with the same rate, and into almost the same conversion products. Therefore, the difference in susceptibility in situ must be found in, for example, a specific interaction of the fungi with the potato tubers.Carvone is stereoselectivily converted into other compounds by potato tissue: R-carvone mainly into neodihydrocarveol, and S-carvone into neoisodihydrocarveol. The bioconversion only takes place in easily accessible tissues, such as sprouts and tuber wound tissue. More than 90% of the amount of S-carvone found in intact tubers, is located on or in the skin. In addition to the chloroform-soluble bioconversion products, water-soluble carvone derived compounds were detected in potato tissue, using 13C-labelling studies. The identity of the conjugated compounds has not been established yet, but S-carvone is found after addition of HCl to the aqueous phase containing the conjugates. The induction of glutathione S-transferase may point to the conjugation of S-carvone to glutathione. Conjugation to saccharides may be an alternative explanation.The sprout growth inhibition is correlated strongly with a decreasing 3- hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) activity, a key enzyme providing building blocks for the synthesis of various essential plant metabolites. Using specific potato HMGR antibodies, it was found that the decrease of activity correlated well with the disappearance of HMGR protein signals on Western blots derived from samples of proteins from organelle fractions and microsomal membranes.S-carvone inhibits the healing of wounded tubers temporarily; in particular, suberization is delayed for about 10 days. The formation of a cambium layer is almost completely inhibited, which indicates that S-carvone interferes with cell division processes during the healing of wounded tissue. The suberization is correlated with the activity of phenylalanine ammonia Iyase (PAL). This enzyme catalyses the first step that leads to the synthesis of suberin, and in S-carvone treated wound tissue, the induction of PAL is delayed for about 10 days. This implies that tuber wound tissue is able to adapt to the exposure to S-carvone.In conclusion, based on the research described in this thesis, it can be stated that S-carvone is a compound with a great potential because of its sprout growth inhibitory effect, possibly partly due to an inhibition of HMGR. Since S-carvone inhibits sprouting reversibly, it may also be useful as a temporary inhibitor of seed potatoes. In addition, S-carvone reduces the development and growth of several storage pathogens. These effects make the chances of an application of S-carvone as a natural potato sprout growth inhibitor even better.

After harvest, potato tubers are usually stored at a temperature of 6-8°C in combination with the application of a synthetic sprout inhibitor. Frequently used sprout inhibitors are isopropyl N-phenyl-carbamate (propham or IPC), isopropyl N-(3-chlorophenyl)carbamate (chlorpropham or CIPC) or a combination of both compounds. There are several reasons for the development of alternative, natural sprout inhibitors. First, the Scandinavian market, for example, requires potato tubers free of (C)IPC residues, and the so-called "green" market, for which no or very little synthetic chemicals are allowed, does not yet have alternative sprout inhibitors. Secondly, governmental policy is directed towards a reduction of the amount of synthetic pesticides used in agricultural practice (Meerjarenplan Gewasbeschermingsmiddelen, MJPG).Natural potato sprout inhibitors were already used in the ancient Inca cultures. After harvest, the potato tubers were stored in boxes or bins together with the twigs of muña plants (Minthostachys species). Treating the tubers in this way controlled sprouting as well as insect attack during a prolonged storage. Volatiles emanating from the muña leaves during the storage were responsible for the insect repellent and sprout inhibitory effects.The monoterpene S-carvone is a related volatile compound which can be isolated from the seeds of caraway (Carum carvi L.) or dill ( Anethum graveolens L.), for example; also this compound has good potato sprout growth inhibitory effects. Application of S-carvone, derived from caraway seed, as a potato sprout inhibitor can stimulate the demand for caraway and therefore the need to grow it. This can be beneficial for Dutch growers, since cultivation of caraway is suitable on heavy clay soils in which crop rotation is limited to only a few crops. The research described in this thesis has been performed within the Dutch Caraway Research Programme in which nine research groups were amalgamated with the objective to reduce the problems with respect to the cultivation of caraway and to stimulate possible new applications of its essential oil or of S-carvone.S-carvone inhibits the sprouting of potato tubers and the sprout growth reversibly: removal of S-carvone allows sprouting and regrowth of the individual sprouts. A high dosage leads to necrosis, but the side buds remain their viability and they start to sprout again when the concentration of S-carvone in the atmosphere comes below a threshold value. The enantiomer of S-carvone, R- carvone, can be isolated from spearmint ( Mentha spicata L.) and possesses almost the same sprout growth inhibitory properties as S-carvone. Current research is focussed on the practical application of S-carvone to seed potatoes as a reversible sprout growth inhibitor.In addition to the inhibitory effects just mentioned, the growth of several storage pathogens is also reduced by S-carvone. However, the susceptibility of fungi to S-carvone, e.g. Fusarium species that cause dry-rot, differs between (sub)species. F.solani var. coeruleum is able to grow on tubers treated with S- carvone, whereas F . sulphureum cannot withstand it. This difference was not found in vitro; both fungi were susceptible to the same range of S-carvone concentrations, they were both able to convert S-carvone with the same rate, and into almost the same conversion products. Therefore, the difference in susceptibility in situ must be found in, for example, a specific interaction of the fungi with the potato tubers.Carvone is stereoselectivily converted into other compounds by potato tissue: R-carvone mainly into neodihydrocarveol, and S-carvone into neoisodihydrocarveol. The bioconversion only takes place in easily accessible tissues, such as sprouts and tuber wound tissue. More than 90% of the amount of S-carvone found in intact tubers, is located on or in the skin. In addition to the chloroform-soluble bioconversion products, water-soluble carvone derived compounds were detected in potato tissue, using 13C-labelling studies. The identity of the conjugated compounds has not been established yet, but S-carvone is found after addition of HCl to the aqueous phase containing the conjugates. The induction of glutathione S-transferase may point to the conjugation of S-carvone to glutathione. Conjugation to saccharides may be an alternative explanation.The sprout growth inhibition is correlated strongly with a decreasing 3- hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) activity, a key enzyme providing building blocks for the synthesis of various essential plant metabolites. Using specific potato HMGR antibodies, it was found that the decrease of activity correlated well with the disappearance of HMGR protein signals on Western blots derived from samples of proteins from organelle fractions and microsomal membranes.S-carvone inhibits the healing of wounded tubers temporarily; in particular, suberization is delayed for about 10 days. The formation of a cambium layer is almost completely inhibited, which indicates that S-carvone interferes with cell division processes during the healing of wounded tissue. The suberization is correlated with the activity of phenylalanine ammonia Iyase (PAL). This enzyme catalyses the first step that leads to the synthesis of suberin, and in S-carvone treated wound tissue, the induction of PAL is delayed for about 10 days. This implies that tuber wound tissue is able to adapt to the exposure to S-carvone.In conclusion, based on the research described in this thesis, it can be stated that S-carvone is a compound with a great potential because of its sprout growth inhibitory effect, possibly partly due to an inhibition of HMGR. Since S-carvone inhibits sprouting reversibly, it may also be useful as a temporary inhibitor of seed potatoes. In addition, S-carvone reduces the development and growth of several storage pathogens. These effects make the chances of an application of S-carvone as a natural potato sprout growth inhibitor even better.

Interview with Marcel Dicke who is involved in research on the relationship between phytophagous insects and mites, their predators and the host plants. Plants produce attractants, mostly terpenes, to attrack the predators. Possible applications of this mechanism for pest control are discussed

In this thesis the applicability of S-(+)-carvone as chiral starting material in the synthesis of biologically active compounds is examined. S-(+)-carvone is the major compound of caraway essential oil. The essential oil content of caraway seed may vary from 2-7% and it contains about 50-60% of S-(+)-carvoneS-(+)-carvone exhibits a number of interesting biological activities, eg., antifungal, insecticidal and plant growth regulatory activities. Especially the inhibiting effect of S-(+)-carvone on the sprouting of potatoes attracted a lot of attention, and this was important for the start of a national caraway research program in the Netherlands. Within the framework of this "National Caraway Research Program" the potential of caraway for the production of non-food products was investigated. The outlines of this research are sketched in chapter 1. An overview of the application of S-(+)-carvone and R-(-)-carvone as chiral starting material in the synthesis of natural products is also given in chapter 1.The Lewis acid catalyzed Diels-Alder reaction of S-(+)-carvone with some silyloxy dienes is described in chapter 2. The anti -addition products 94 , with the angular methyl group and the isopropenyl group in a cis -position, are formed in high yields. The synthetic utility of these Diels-Alder adducts was demonstrated by the total synthesis of (+)-α-cyperone (95) from diketone 94b . (+)-α-Cyperone ( 95 ), that can be isolated from the tubers of Cuperus rotundus L., exhibits an interesting in vitro activity against Plasmodium flaciparum K1, a multidrug resistant malaria parasite (scheme 8.1).In chapter 3, the Robinson annulation products 33 and 96 were transformed into interesting chiral intermediates for organic synthesis and also into some biologically active compounds. The decalones 111 and 112 , were formed from 33 . Decalone 111 is a famous molecule in perfumery and 112 is an important intermediate in the synthesis of several drimanes and drimane-related natural products. Compound 33 was also converted into decalol 113 , a potent inhibitor of the cholesterol biosynthesis.(+)-Geosmin ( 97 ), an interesting olfactive compound was synthesized from decalone 96 (scheme 8.2).In chapter 4, the syntheses of the more functionalized decalones 98 , 99 , 131 and 132 from S-(+)-carvone via two different conjugate addition annulation methodologies are presented (scheme 8.3). The conjugate addition of potassium cyanide to S-(+)-carvone gave cyano ketone 135 in high yield. The base catalyzed Robinson annulation of 135 with methyl vinyl ketone followed by dehydration gave decalone 98 stereoselectively and also in high yield.The copper catalyzed conjugate addition of Grignard reagents gave alkyl substituted dihydrocarvones, which were annulated via their silyl enol ethers 127 . A Lewis acid catalyzed Michael addition of the silyl enol ether 129 to methyl vinyl ketone gave the intermediate diketones 130 in good yield. The diketones were cyclized to the substituted decalones 99 , 131 and 132 under basic conditions.Decalone 98 was used for a new chiral approach to 3-oxygenated drimanes as is described in chapter 5. Hydroxyketone 153 was formed via an ozonolysis/Criegee rearrangement procedure of the isopropenyl substituent (scheme 8.4). Hydroxyketone 153 was by total synthesis further transformed into (-)-3-β-acetoxydrimenin ( 100 ), that can be isolated from the leaves of Drimys winteri,.In chapter 6 the total synthesis of (-)-Ambrox ®( 101 ), a commercially interesting olfactive compound, from both the allyl substituted decalone 99 and the nitrile substituted decalone 98 is presented (scheme 8.5). In both synthetic sequences, alcohol 159 was formed as the key intermediate. (-)-Ambrox ®( 101 ), was synthesized by simple cyclization of alcohol 159 at room temperature under acidic conditions.&nbsp

In this thesis the base-induced reactions of perhydronaphthalene-1,4-diol monosulfonate esters are described. These compounds undergo smoothly, typical carbocationic processes upon treatment with sodium tert -amylate in refluxing benzene. The product outcome, product ratio, and (relative) rate of these reactions is satisfactorily explained when through-bond orbital interactions (TBI) over four abonds are invoked. In order to gather more detailed information about the basic stereochemical and stereoelectronic principles underlying these processes, synthetical organic, computational, and kinetic investigations were undertaken.Most experimental studies on TBI have focussed on its spectroscopic manifestations and are reviewed repeatedly. On the other hand, there are relatively few reviews on the chemical consequences of TBI over three or moreσ-bonds. A number of illustrative examples of chemical reactions in which long-range orbital interactions are believed to play an essential role are discussed in chapter 1. In the same chapter also attention is drawn to the synthetic utility of some of these reactions.In chapter 2 the syntheses of the mesylates 39 , 40 , and 58-67 are described. The compounds 39 , 40 , 58 , and 59 are prepared in order to investigate how the orientation of the sulfonate ester group in combination with the orientation of the tertiary hydroxyl group determines the outcome and rate of their reactions with sodium tert -amylate. The results of these investigations are described in chapter 3. It was found that an equatorial sulfonate ester group favors homofragmentation leading to the cyclopropane derivative 105 . In case of an axial sulfonate ester groupβ-elimination, which strongly depends on the stereochemistry of the tertiary deprotonated hydroxyl group, is the main reaction path. In the chapter 3 the synthesis of the O-silylated mesylates 106 and 107 is also described. These compounds show no reaction at all upon treatment with strong base. On the other hand, fast reactions are observed when 106 and 107 are treated with TBAF. Generation of an alcoholate is crucial for the observed reactions. Homofragmentation and an internal return reaction with inversion of configuration of the mesylate group in the axial mesylates 39 and 58 is explained by assuming a 1,3-bridged intermediate carbocation.The mesylates 60-65 are prepared (Chapter 2) to determine the influence of the geometry of the relayingσ-bonds on the reactions with sodium tert -amylate. In chapter 4 the results of these studies are described in detail. An alcoholate function intramolecularly induces heterolysis of the sulfonate ester group in an apolar solvent via orbital interactions through three intervening C-C single bonds. It is shown that the reactivity of the compounds 60-65 is only affected by the relative position of the hydroxyl function to the sulfonate ester group and not by the orientation of the hydroxyl group. The two chief pathways by which these compounds react are rearrangement ( 60 , 62 , and 63 ) and homofragmentation ( 64 and 65 ). Stereoelectronic effects play a dominant role here, except in compound 61 where steric factors primarily determine the reactivity and product outcome (ether formation). Homofragmentation is much faster than rearrangement and is only possible when a 1,3-bridged through-space interaction accompanies TBI. The extent of TBI as well as the product composition is strongly determined by theσ-relay of the fourσ-bonds between the electron donor (alcoholate) and the electron acceptor (sulfonate ester bond). These results are consistent with the " trans rule", which is in line with predictions from theoretical models regarding TBI.The product outcome, product ratio, and relative rate of the base-induced reactions of perhydronaphthalene-1,4-diol monosulfonate esters described in chapter 4 are satisfactorily explained with the concept of TBI. However, the conclusions are all based on empirical results. In chapter 5 the results of semi-empirical calculations, using the MNDO method, performed on model systems are presented. In this way a more detailed understanding of the stereoelectronic features underlying the homofragmentation and rearrangement reaction is obtained. The trends in the results of the MNDO simulations are the same as those found in the reactions of the compounds 60-65 . Whether rearrangement or homofragmentation takes place depends on the geometry of theσ-relay and the inductivity of the system. Cyclopropanoid bridged structures seem to be involved in the rearrangement process as well as in the homofragmentation process.In order to explore the effects of the order of substitution of the carbon atom that borders the carbon atom to which the mesylate group is attached the compounds 40 , 66 , and 67 were synthesized. This subject is discussed in chapter 6. The product formation is strongly dependent on the steric consequences of alkyl substituents atβcarbon atoms. Homofragmentation is highly favored when the repulsive steric interactions do not prevent a homohyperconjugatively stabilized transition state. This is only possible in an ideal "W" arrangement of theσ-relay ( 40 ). Due to the repulsive 1,3- peri -effect in 66 , and a combination of the 1,3- peri -effect and the 1,3- diaxial -effect in 67 theσ-relay diverges from the ideal "all trans " geometry as a result of which other reaction pathways (elimination, 1,3-H, and 1,2-Me shifts) are favored over homofragmentation. Introduction of inductively electron-donating substituents leads to an increase in reaction rate, despite the (slight) deviation of the "W" arrangement. It is concluded that although bridged ions are important intermediates in the observed reaction paths, they are not decisive for the reactivity of these compounds.The O-silylated mesylates 106 and 107 react fast upon treatment with TBAF in refluxing benzene (Chapter 3). At room temperature only desilylation takes place. To investigate the influence of a remote nucleofugal mesylate group on the rate of desilylation, apart from 106 and 107 , also the O-silylated compounds 127-131 are synthesized and treated with TBAF as is described in chapter 7. The rates of desilylation are determined conveniently by HPLC monitoring of the disappearance of the starting material. The desilylation rate of compounds with a mesylate group is much higher than the desilylation rate of corresponding compounds with a hydroxyl group instead ( 130 and 131 ). Furthermore, compounds having a "W" arrangement ( 107 and 129 ) of the relayingσ-bonds react considerably faster than their "sickle relay" analogs ( 106 , 127 , and 128 ). The results presented in this chapter show nicely that longrange electronic effects of distant substituents can exert a substantial influence on the reactivity of certain functional groups in general.In conclusion, the concept of TBI offers a good explanation for the reactivity of the compounds studied throughout this thesis. The stereochemical and stereoelectronic requirements for the base-induced reactions of perhydronaphthalene-1,4-diol monosulfonate esters are now well established. The general utilitly of the concept ofσ-delocalization and TBI in everyday chemistry is demonstrated