Overall activation volumes for multistep reactions are not usually pressure independent. The pres... more Overall activation volumes for multistep reactions are not usually pressure independent. The present investigation gives a quantitative description of this effect under Theory. Simple relations are obtained which can easily be applied to experimental data and which allow more insight into the dynamics of enzyme reactions. This is demonstrated under Experimental Application for the conversion of fumarate to L-malate catalyzed by the enzyme fumarase. The volume profile of this reaction indicates a pulsation of the enzyme molecule during catalysis. The appendix discusses the question whether Eyring's transition-state theory is an appropriate basis for investigations of this kind.
Advances in High Pressure Bioscience and Biotechnology, 1999
The influence of high pressure on the autoxidation of oleic and linoleic acid methyl esters was i... more The influence of high pressure on the autoxidation of oleic and linoleic acid methyl esters was investigated as it seems to be the model system closest to the problem. The reaction was studied at 0.1, 100, 350 and 600 MPa at 40 °C. Treatment times were 1, 2, 3, 5 and 20 h. Gas chromatographic data of the decrease of oleic acid methyl ester, taken as a measure for the degree of autoxidation, showed no influence of pressure. The autoxidation of linoleic acid methy lester was accelerated by pressures from 350 MPa as shown by gas chromatographic data of the decrease of the educt as well as by the increase of primary oxidation products measured by HPLC or by the increase in UV-absorption at 234 nm. The primary oxidation products were separated by reversed phase HPLC: no effect of pressure on the distribution of isomers was found.
Ultrahigh-pressure (UHP) hydrostatic exposure in excess of 100 MPa is being used to inactivate mi... more Ultrahigh-pressure (UHP) hydrostatic exposure in excess of 100 MPa is being used to inactivate microorganisms as well as to induce texture changes to foods without thermal degradation. The UHP process is said not only to preserve flavour and food product taste but also natural properties of biological products. The influence of high pressure on functional properties of a choice of vegetables was evaluated. The treatments were at pressures around 600 MPa and also in combination with elevated temperatures and in comparison with thermal treatment. Carrots, tomatoes and broccoli were investigated (crushed or liquid extracts). The following characteristics were assessed: content of health promoting substances (e.g. vitamins, antioxidants, antimutagens), effects on water retention, glucose retardation, changes in extractability, in-vitro bioavailability. In most cases high pressure did not induce loss of beneficial substances in the vegetable matrices but induced changes in the structure of the products which resulted in altered physico-chemical properties such as higher glucose retardation index and water retention or reduced extractability.
In model experiments using the Salmonella/reversion assay (Ames test) and the carcinogen 2-amino-... more In model experiments using the Salmonella/reversion assay (Ames test) and the carcinogen 2-amino-3-methyl-imidazo[4,5-f] quinoline (IQ), antimutagenic activities against IQ had been detected in about 70% of 62 fruit and vegetable species [Edenharder, Kurz, John, Burgard and Seeger (1994) Fd Chem. Toxic. 32, 443-4591. However, thermal stability of the antimutagenic factors varied considerably. As hydrostatic pressure is an alternative to heat in food processing and preservation, homogenates of 14 fruit and vegetable species were exposed to different pressures and temperatures. According to the response of the antimutagenic potential, three groups of produce could be identified: (a) moderate antimutagenie potencies in grapefruit and strawberries were resistant to both heat and pressure; (b) moderate to strong antimutagenic potencies in carrots, cauliflower, kohlrabi, leek, and spinach were more or less sensitive to heat, but not to pressure; (c) antimutagenic activities of beet and tomatoes were affected by extreme pressure only (600 MPa, 50°C; 800 MPa, 35°C). These results should be relevant for the (industrial) processing of horticultural produce as, according to epidemiological studies, diets rich in fruit and vegetables are associated with a low incidence of human cancer.
ABSTRACT The response of suspensions of spices and spice mixtures in water to high pressure treat... more ABSTRACT The response of suspensions of spices and spice mixtures in water to high pressure treatment was investigated. Inactivation of the microbial load–mainly aerobic and unaerobic spore formers–was strongly dependent on water activity and temperature. Samples were completely decontaminated after three pressure cycles (30 min at 80 MPa followed by 30 min at 350 MPa) at 70 °C at a minimum water activity of 0.91. Pressure treated samples were examined for sensory and chemical changes. No significant changes in odour and appearance were recognized by a trained sensory panel, nor were changes in the volatile compounds of the samples detected by static headspace gaschromatography.
The inactivation of bacteria, bacterial spores, yeasts and molds by high hydrostatic pressure was... more The inactivation of bacteria, bacterial spores, yeasts and molds by high hydrostatic pressure was investigated over a pressure range up to 3000 bar. Survival curves were measured as a function of temperature and pressure applied on the microorganisms. Conditions are looked for under which heat or radiation sensitive pharmaceutical preparations can be sterilized by high pressure treatment at moderate temperatures. All organisms tested can be inactivated in the range of 2000-2500 bar and between 40-60 degrees.
Http Dx Doi Org 10 1080 08957950008202529, Aug 19, 2006
ABSTRACT The application of high hydrostatic pressure is one of the most promising novel minimal ... more ABSTRACT The application of high hydrostatic pressure is one of the most promising novel minimal processing methods for food preservation. Under optimal process conditions the natural fresh properties of foods are retained. Pressure is an important thermodynamic factor as is temperature. Both pressure and temperature may influence the position of a chemical reaction equilibrium and the reaction rate. Examples of pressure effects on food quality related reactions are presented: The effect of pressure on reactions resulting in flavour or colour defects or the formation of undesirable substances and the effect of pressure on the stability of valuable constituents like vitamin A or sulforaphane.
As part of an EU-funded research project a representative survey of consumer attitudes concerning... more As part of an EU-funded research project a representative survey of consumer attitudes concerning high pressure processing (HPP) of foods was carried out. 3000 adults aged 14 years and over, in France, Germany and the UK were interviewed in face-toface computer assisted personal interviews (CAPI) and asked to indicate their opinion by evaluating 35 positive and 25 negative statements about the new technique, to compare the new technique with the conventional techniques, and they were asked if they would buy products preserved using High Pressure Pasteurization. The concept used for the data analysis was that of a market segmentation model using sociodemographical, geographical and psychographical attributes. The average acceptability rate is discussed with respect to the MAYA threshold value (Most Advanced Yet Acceptable), a pragmatic market research threshold value.
Biochimica Et Biophysica Acta Proteins and Proteomics, Mar 31, 2006
Application of high pressure can be used for gentle pasteurizing of food, minimizing undesirable ... more Application of high pressure can be used for gentle pasteurizing of food, minimizing undesirable alterations such as vitamin losses and changes in taste and color. In addition, pressure has become a useful tool for investigating structural changes in proteins. Treatments of proteins with high pressure can reveal conformations that are not obtainable by other physical variables like temperature, since pressure favors structural transitions accompanied with smaller volumes. Here, we discuss both the potential use of high pressure to inactivate infectious TSE material and the application of this thermodynamic parameter for the investigation of prion folding. This review summarizes our findings on the effects of pressure on the structure of native infectious scrapie prions in hamster brain homogenates and on the structure of infectious prion rods isolated from diseased hamsters brains. Native prions were found to be pressure sensitive, whereas isolated prions revealed an extreme pressure-resistant structure. The discussion will be focused on the different pressure behavior of these prion isoforms, which points out differences in the protein structure that have not been taken into consideration before.
Consumer demands for high-quality foods with ''fresh-like'' characteristics that require only a m... more Consumer demands for high-quality foods with ''fresh-like'' characteristics that require only a minimum amount of effort and time for preparation has led to the introduction of convenience foods preserved by mild treatments. Non-thermal methods allow the processing of foods below temperatures used during thermal pasteurisation, so flavours, essential nutrients, and vitamins undergo minimal or no changes. Foods can be non-thermally processed by irradiation, high hydrostatic pressure, antimicrobials, ultrasound, filtration, and electrical methods such as pulsed electric fields, light pulses, and oscillating magnetic fields. Due to technological developments, high pressure processing and high electric field pulse processing have received increased attention during the last decade. This paper focuses on high pressure treatment of foods, a process which is also used to create food and food ingredients with new sensory and functional properties including also physiological functionality. Effects of high pressure on chemical and sensory changes in foods are discussed.
Overall activation volumes for multistep reactions are not usually pressure independent. The pres... more Overall activation volumes for multistep reactions are not usually pressure independent. The present investigation gives a quantitative description of this effect under Theory. Simple relations are obtained which can easily be applied to experimental data and which allow more insight into the dynamics of enzyme reactions. This is demonstrated under Experimental Application for the conversion of fumarate to L-malate catalyzed by the enzyme fumarase. The volume profile of this reaction indicates a pulsation of the enzyme molecule during catalysis. The appendix discusses the question whether Eyring's transition-state theory is an appropriate basis for investigations of this kind.
Advances in High Pressure Bioscience and Biotechnology, 1999
The influence of high pressure on the autoxidation of oleic and linoleic acid methyl esters was i... more The influence of high pressure on the autoxidation of oleic and linoleic acid methyl esters was investigated as it seems to be the model system closest to the problem. The reaction was studied at 0.1, 100, 350 and 600 MPa at 40 °C. Treatment times were 1, 2, 3, 5 and 20 h. Gas chromatographic data of the decrease of oleic acid methyl ester, taken as a measure for the degree of autoxidation, showed no influence of pressure. The autoxidation of linoleic acid methy lester was accelerated by pressures from 350 MPa as shown by gas chromatographic data of the decrease of the educt as well as by the increase of primary oxidation products measured by HPLC or by the increase in UV-absorption at 234 nm. The primary oxidation products were separated by reversed phase HPLC: no effect of pressure on the distribution of isomers was found.
Ultrahigh-pressure (UHP) hydrostatic exposure in excess of 100 MPa is being used to inactivate mi... more Ultrahigh-pressure (UHP) hydrostatic exposure in excess of 100 MPa is being used to inactivate microorganisms as well as to induce texture changes to foods without thermal degradation. The UHP process is said not only to preserve flavour and food product taste but also natural properties of biological products. The influence of high pressure on functional properties of a choice of vegetables was evaluated. The treatments were at pressures around 600 MPa and also in combination with elevated temperatures and in comparison with thermal treatment. Carrots, tomatoes and broccoli were investigated (crushed or liquid extracts). The following characteristics were assessed: content of health promoting substances (e.g. vitamins, antioxidants, antimutagens), effects on water retention, glucose retardation, changes in extractability, in-vitro bioavailability. In most cases high pressure did not induce loss of beneficial substances in the vegetable matrices but induced changes in the structure of the products which resulted in altered physico-chemical properties such as higher glucose retardation index and water retention or reduced extractability.
In model experiments using the Salmonella/reversion assay (Ames test) and the carcinogen 2-amino-... more In model experiments using the Salmonella/reversion assay (Ames test) and the carcinogen 2-amino-3-methyl-imidazo[4,5-f] quinoline (IQ), antimutagenic activities against IQ had been detected in about 70% of 62 fruit and vegetable species [Edenharder, Kurz, John, Burgard and Seeger (1994) Fd Chem. Toxic. 32, 443-4591. However, thermal stability of the antimutagenic factors varied considerably. As hydrostatic pressure is an alternative to heat in food processing and preservation, homogenates of 14 fruit and vegetable species were exposed to different pressures and temperatures. According to the response of the antimutagenic potential, three groups of produce could be identified: (a) moderate antimutagenie potencies in grapefruit and strawberries were resistant to both heat and pressure; (b) moderate to strong antimutagenic potencies in carrots, cauliflower, kohlrabi, leek, and spinach were more or less sensitive to heat, but not to pressure; (c) antimutagenic activities of beet and tomatoes were affected by extreme pressure only (600 MPa, 50°C; 800 MPa, 35°C). These results should be relevant for the (industrial) processing of horticultural produce as, according to epidemiological studies, diets rich in fruit and vegetables are associated with a low incidence of human cancer.
ABSTRACT The response of suspensions of spices and spice mixtures in water to high pressure treat... more ABSTRACT The response of suspensions of spices and spice mixtures in water to high pressure treatment was investigated. Inactivation of the microbial load–mainly aerobic and unaerobic spore formers–was strongly dependent on water activity and temperature. Samples were completely decontaminated after three pressure cycles (30 min at 80 MPa followed by 30 min at 350 MPa) at 70 °C at a minimum water activity of 0.91. Pressure treated samples were examined for sensory and chemical changes. No significant changes in odour and appearance were recognized by a trained sensory panel, nor were changes in the volatile compounds of the samples detected by static headspace gaschromatography.
The inactivation of bacteria, bacterial spores, yeasts and molds by high hydrostatic pressure was... more The inactivation of bacteria, bacterial spores, yeasts and molds by high hydrostatic pressure was investigated over a pressure range up to 3000 bar. Survival curves were measured as a function of temperature and pressure applied on the microorganisms. Conditions are looked for under which heat or radiation sensitive pharmaceutical preparations can be sterilized by high pressure treatment at moderate temperatures. All organisms tested can be inactivated in the range of 2000-2500 bar and between 40-60 degrees.
Http Dx Doi Org 10 1080 08957950008202529, Aug 19, 2006
ABSTRACT The application of high hydrostatic pressure is one of the most promising novel minimal ... more ABSTRACT The application of high hydrostatic pressure is one of the most promising novel minimal processing methods for food preservation. Under optimal process conditions the natural fresh properties of foods are retained. Pressure is an important thermodynamic factor as is temperature. Both pressure and temperature may influence the position of a chemical reaction equilibrium and the reaction rate. Examples of pressure effects on food quality related reactions are presented: The effect of pressure on reactions resulting in flavour or colour defects or the formation of undesirable substances and the effect of pressure on the stability of valuable constituents like vitamin A or sulforaphane.
As part of an EU-funded research project a representative survey of consumer attitudes concerning... more As part of an EU-funded research project a representative survey of consumer attitudes concerning high pressure processing (HPP) of foods was carried out. 3000 adults aged 14 years and over, in France, Germany and the UK were interviewed in face-toface computer assisted personal interviews (CAPI) and asked to indicate their opinion by evaluating 35 positive and 25 negative statements about the new technique, to compare the new technique with the conventional techniques, and they were asked if they would buy products preserved using High Pressure Pasteurization. The concept used for the data analysis was that of a market segmentation model using sociodemographical, geographical and psychographical attributes. The average acceptability rate is discussed with respect to the MAYA threshold value (Most Advanced Yet Acceptable), a pragmatic market research threshold value.
Biochimica Et Biophysica Acta Proteins and Proteomics, Mar 31, 2006
Application of high pressure can be used for gentle pasteurizing of food, minimizing undesirable ... more Application of high pressure can be used for gentle pasteurizing of food, minimizing undesirable alterations such as vitamin losses and changes in taste and color. In addition, pressure has become a useful tool for investigating structural changes in proteins. Treatments of proteins with high pressure can reveal conformations that are not obtainable by other physical variables like temperature, since pressure favors structural transitions accompanied with smaller volumes. Here, we discuss both the potential use of high pressure to inactivate infectious TSE material and the application of this thermodynamic parameter for the investigation of prion folding. This review summarizes our findings on the effects of pressure on the structure of native infectious scrapie prions in hamster brain homogenates and on the structure of infectious prion rods isolated from diseased hamsters brains. Native prions were found to be pressure sensitive, whereas isolated prions revealed an extreme pressure-resistant structure. The discussion will be focused on the different pressure behavior of these prion isoforms, which points out differences in the protein structure that have not been taken into consideration before.
Consumer demands for high-quality foods with ''fresh-like'' characteristics that require only a m... more Consumer demands for high-quality foods with ''fresh-like'' characteristics that require only a minimum amount of effort and time for preparation has led to the introduction of convenience foods preserved by mild treatments. Non-thermal methods allow the processing of foods below temperatures used during thermal pasteurisation, so flavours, essential nutrients, and vitamins undergo minimal or no changes. Foods can be non-thermally processed by irradiation, high hydrostatic pressure, antimicrobials, ultrasound, filtration, and electrical methods such as pulsed electric fields, light pulses, and oscillating magnetic fields. Due to technological developments, high pressure processing and high electric field pulse processing have received increased attention during the last decade. This paper focuses on high pressure treatment of foods, a process which is also used to create food and food ingredients with new sensory and functional properties including also physiological functionality. Effects of high pressure on chemical and sensory changes in foods are discussed.
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