- Email: [email protected]
1st international symposium on food rheology and structure
Conference Report
1st International quality aspects, such as phase-separation stability, homogeneity and organoleptic properties. The possibility of influencing the crystallization of milk fat and thus the structure and the rheology of the final product was presented by B. Breitschuh (Institute of Food Science, ETH, Zurich, Switzerland). By performing the crystallization under defined shear rates and temperature in a concentric cylinder rheometer, Breitschuh demonstrated that high shear accelerates the crystallization process and yields small spherulitic crystals with a narrow crystal size Bkatrice Conde-Petit distribution. However, exceeding a critical stress destroyed the crystal structure. J. Kobow (German Institute of Food Technology, Quakenbriick, Germany) demonstrated that, Structure and rheology, two important physical aspects as is the case for milk-fat crystallization, the crystallization of food and complex fluid systems, formed the subject kinetics of sugar in honey may be controlled by temperaof the 1st International Symposium on Food Rheology ture and shear forces. Honey with different structural and and Structure. More than 170 participants, from 20 dif- rheological properties can be produced by varying the conferent countries, came together for this event at the ditions for nucleation and crystal growth during processing. Swiss Federal Institute of Technology (ETH) in Zurich. During the past few years, the tailoring of food structures As expressed by the chairman of the organizing com- by using mixed biopolymer systems has received increasmittee, E.J. Windhab from the Institute of Food Science ing attention. P. WalkenstrZjm (SIK, The Swedish Institute at ETH, the aim of the symposium was to bring together for Food and Biotechnology, Gothenburg, Sweden) deexperts in rheology and food structure from academia scribed the effects of processing conditions, namely temand industry, to facilitate a synergistic exchange of ideas. perature, shearing and pressure, on the microstructure and The scientific programme included 64 oral presentations the rheological properties of mixed gels composed of gelaand 26 posters. A broad range of topics was presented, tine and whey protein. The microstructure was shown to including the rheological characterization of real and be largely dependent on the order of gel formation of the model food systems, from chocolate and cheese to glass components, which can be controlled by temperature and and carbon suspensions; the generation of structure by pressure. Furthermore, Walkenstrijm showed that by apfood processing; the relationships between structure, plying shear to affect the gel formation of whey proteins, rheology and food quality; advances in rheometry and inhomogeneities were induced, indicating increased phase methods for structure analysis; and also modelling and separation, which in turn enhanced the rigidity of the resimulation of the structure and flow behaviour of com- sulting gels. plex systems. The scientific programme was compleThe influence of processing on both the microstructure mented by an exhibition of instruments designed for the and the rheology of wheat dough was discussed by R. Kieffer (Deutsche Forschungsanstalt fiir Lebensmittelanalysis of rheology and structure. chemie, Garching, Germany). He showed that the wellknown phenomenon of strain hardening of dough in uniGeneration of structure by flow processing axial deformation, also called structural activation, is In his introductory lecture, Windhab presented an overview of the types of flow, shear and elongational, that are related to the separation of starch and gluten, which occurs on reshaping the dough after a rest period. The formation generated in different food processing operations and how of large aggregates of starch granules, as assessed by light they affect the structure of complex fluid systems. Flowinduced structural changes in food are initiated when the microscopy, may also be induced by extrusion through a mechanism-specific critical stresses are exceeded. As ex- capillary. According to Kieffer, strain hardening on uniamples, Windhab discussed the reduction of droplet size axial deformation is due to the dilatant behaviour of large starch aggregates and to the increasing thickness of the during emulsification, the aggregation of whey proteins owing to conformational changes following intensive treat- gluten strands. ment in a rotor-stator flow field, and the network characteristics of both starch and xanthan dispersions induced by Colloidal and molecular interactions influencing structure and rheology mechanical treatment. Windhab pointed out that the resulting rheological behaviour of multiphase food systems is Many food gels, especially dairy products, are proteinstabilized emulsions, containing finely dispersed particles closely related to their inner structure, the main structural (droplets) and crosslinked macromolecules. The compreelements being solid particles, droplets and gas bubbles. hensive review by E. Dickinson (Procter Department of The rheological behaviour of the final product determines Food Science, University of Leeds, UK) focused on the complex relationships between the interactions, structure *Held in Zurich, Switzerland, 16-21 March 1997 and rheology of protein-stabilized emulsion gels. He discussed factors that affect the rheology of heat-set protein Beatrice Conde-Petit is at the Institute of Food Science, Swiss Federal Institute emulsion gels, emulsion gels crosslinked by transglutaminof Technology (ETH), CH-8092 Zurich, Switzerland (fax: +41-1-632-l 123; ase, emulsion gels flocculated by bridging macromolecules e-mail: [email protected]).
Symposium on Food
Rheology and Structure*
242
Copyright @1997, Elsevie, Saence PII: 50924.2244197)01041-L?
Ltd. All rtghts reserved
0924.?244!97!$1
7.00
Trends
in Food
Science
& Technology
July
1997
[Vol.
81
and depletion-flocculated caseinate-stabilized emulsion Modelling and simulation of structure and complex gels. The speaker showed that the strength of the interfluid systems actions between the emulsion droplets, which are in turn One powerful approach for understanding the complex affected by the protein structure and concentration, by relationships between interaction, structure and rheology, processing conditions and by the interactions of ad- as well as for predicting flow behaviour during processing, sorbed and unadsorbed proteins with other components, is modelling and computer simulation. Two presentations, determines both the structural and rheological properties one given by P. Walstra and the other by T. van Vliet of oil-in-water emulsion gels. Dickinson stressed the (both from the Department of Food Science, Wageningen need for modelling and simulation of particle gelation to Agricultural University, The Netherlands), focused on better understand these complex systems. the concept of fractals for describing food structure. For Unlike emulsions, baked goods contain an entrapped instance, small particles in a liquid system tend to form air phase. It is well known that the addition of fat to fractal aggregates on being subjected to aggregation. baked goods affects the size and distribution of air Examples of particle gels are plastic fats, renneted milk bubbles, leading to a more homogeneous crumb strucand other proteinaceous gels. As the speakers demonture and an increased volume. Until recently, the role of strated, the fractal description provides a useful tool to fat was considered to be different in breads, biscuits and describe the mechanical properties of aggregates. cakes, owing to their differing composition and physical In food processing, unit operations that involve mixproperties. At the symposium, B.E. Brooker (Institute ing are very common. However, process improvements of Food Research, Reading, UK) presented his latest and performance optimization are actually hampered by results on the interactions between fat crystals and the the poor level of understanding of what is actually hapair-water interface of bubbles. He demonstrated that pening in the vessel in terms of the mixing mechanism. during mixing, the fat crystals separate from the oil P.A. Tanguy (Department of Chemical Engineering, Ecole phase and become enveloped in the oil-water interface, Polytechnique, Montreal, Canada) showed how threewhich allows them to adsorb at the air-water interface dimensional computer simulation can be used to clarify of bubbles. The crystals melt during baking and transfer the impact of rheology on the mixer performance. The interfacial material to the surface of bubbles and con- simulation allows determination of the distribution of shear tribute to their expansion without rupturing. According rates and power and the impeller pumping capabilities, to Brooker, this mechanism is common to all baked which can readily be used for design. Another important goods that contain an entrapped air phase. These recent operation in processing is the treatment of complex liquid findings suggest new ways in which the structure of fat systems in a scraped-surface heat exchanger. This process crystals can be manipulated to optimize the functionallows, for example, the continuous crystallization of chocolate. M. Stranzinger (Institute of Food Science, ETH, ality of fats in baked products. Zurich, Switzerland) presented numerical results on the An example of molecular interaction between polysaccharides, which is widely applied in the food indusshear and secondary flow effects around a scraping blade inside a channel gap of a scraped-surface heat exchanger. try, is the combination of the two non-gelling polymers, xanthan and galactomannan, to induce gelation. C. By simulation, Stranzinger was able to show the effect of the scraper angle on the streamline patterns and pressure Garnier (Institut National de la Recherche Agronomique, distribution for Cuette-type and Poiseuille-type flows. Nantes, France) presented a study on xanthan-galactoIn addition to shear flow, elongational flows are often mannan mixtures: confocal laser scanning microscopy and rheological methods were used to gain more insight present during food processing. It is well known that shear into the structure of these blends. Garnier proposed a can have a significant effect on the properties of particles in foods, but very little information is available on the new model for explaining the synergistic interaction. behaviour of particles in elongational flows. H. Nirschl According to the speaker, thermodynamic incompatibil(Technische Universitat Mtinchen, Freising, Germany) ity between xanthan and galactomannan is responsible showed that the damage caused to yeast cells varies in acfor the properties of the mixtures and not the generally considered model of specific interaction between the cordance with the type of flow to which they are exposed. With the help of a numerical technique, Nirschl described two polymers. A specific interaction between a polymer the behaviour of a single particle in a uniaxial elongational and small molecules, that is between amylose and difflow and came to the conclusion that for practical purferent flavour substances, which affects the rheological poses the forces generated by an elongational flow can be properties was reported by J. Ntissli (Institute of Food Science, ETH, Zurich, Switzerland). She showed that much higher than those generated in a shear flow situation. the combination of starch with (-)-fenchone, thymol or However, in the case of elongational flow, the particles, especially non-spherical particles with an ellipsoidal shape geraniol induces the formation of V-amylose, as determined by X-ray diffractometry, which is typical for or fibres, will orient and not change configuration. According to Nirschl, elongational flow can be used to create complexed starch. Interestingly, the formation of starchfood systems that have a defined structure and rheology. fenchone complexes induces the gelation of starch, owing to the aggregation of complexed amylose. As Ntissli pointed out, this type of interaction may affect Advances in rheometry and structure analysis The rapid developments in rheometry, together with not only the texture of starch-based food systems, but the falling costs of the instruments in relation to their also the release and retention of flavours. Trends in Food Science
& Technology
July 1997 [Vol. 81
243
capabilities, has contributed to the growing application of sophisticated rheological techniques for the characterization of real and model food systems. Many of the available rheometers were originally developed for use in materials science, especially polymer science. J. Meissner (Swiss F.I.T. Rheocenter, ETH, Zurich, Switzerland) presented a new rheometer for simple elongation, which was recently introduced onto the market and is especially designed for measuring the elongational properties of polymer melts. The suitability of this instrument for determining the elongational properties of wheat dough was shown by T. Schweizer (Swiss F.I.T. Rheocenter, ETH, Zurich, Switzerland) in a poster. Furthermore, Meissner also presented his latest development, a rheometer for equibiaxial and planar elongation of small samples. Windhab presented a new type of slit rheometer, which will be used to simulate the extrusion process and to measure the shear and elongational viscosity simultaneously. The rheometer was developed for the purpose of testing and calibrating conventional and new on-line measuring principles, such as the superposition of a pressure measuring method with the Doppler ultrasound method. The advantage of combining different measuring principles for a greater insight into the structure of biopolymer solutions and gels was presented by W-M. Kulicke (Institute of Technical and Macromolecular Chemistry, University of Hamburg, Germany). He combined the established rheo-mechanical methods with a new rheooptical measuring method, which allows the determination of flow birefringence and flow dichroism. By applying these methods to biopolymer dispersions, Kulicke showed that although the orientation of K-carrageenan polymers hardly shows any dependence on shear rate, the orientation of waxy maize starch polymers is strongly dependent on it. In mixtures of both polymers, the alignment of the polymer segments was shown to be influenced by the addition of starch. Another rheometer, which combines different measuring techniques, was described by S.T. Beckett (Nestle R&D Centre, York, UK). This high-frequency rheometer combines ‘pulse’ and ‘resonance’ techniques and exploits wave interference, and was successfully used to monitor the development of the structure (gelation) of aqueous gelatin dispersions and other gelling systems.
Other measuring principles for assessing food structure that are not based on rheology were also discussed at the symposium. Microscopy is one of the most important tools for food structure characterization, as shown by several speakers. By using light, scanning electron and transmission electron microscopy, A-M. Hermansson (SIK, The Swedish Institute of Food Biotechnology, Gothenburg, Sweden) successfully characterized the microstructure of protein and polysaccharide gels. W. Buchheim (Federal Dairy Research Centre, Kiel, Germany) presented an overview of various types of interfacial layers in emulsions and foams, as assessed by different microscopy techniques. Finally, a comprehensive review on light and neutron scattering and their application to complex fluids was presented by P. Schurtenberger (Institute of Polymer Science, ETH, Zurich, Switzerland). He demonstrated a few nonstandard applications for systems that are of interest in food science. One interesting application is the characterization of extremely turbid suspensions, such as undiluted baby milk, using dynamic light-scattering experiments combined with novel cross-correlation schemes. This short summary of the symposium, which covers only some of the contributions, clearly reflects the multidisciplinary character of the event; it successfully brought together different disciplines and approaches related to food rheology and structure. The strong interest of the participants was manifested by the lively discussions that followed the presentations.
Proceeding of the symposium have been published as Proceedings of the 1st International Symposium on Food Rheology and Structure, Zurich, Switzerland, March 1997 (Windhab, E.J. and Wolf, B., eds), by Vincentz Verlag, Hanover, Germany. Copies are available for DM150.00 (+ postage and packaging) from the publisher: Curt R. Vincentz, Ute Weber-Steltner, Schiffgraben 43, D-30175 Hanover, Germany (tel. +49-511-99-10-360; fax: +49-511-99-10-399; e-mail: [email protected]). It is envisaged that a second symposium will be held in Zurich, Switzerland, in 1999.
Coming up in the August issue of TIFS The Trends Guide to the Internet (1997) Feeling left behind? Worried about time-wasting? This free guide will lead you through those all-important first steps towards using the Internet efficiently and effectively. Written by an international panel of experts, the guide will tell you what to expect and where to find it. Articles include: l Creating your own home page l The origins of the Internet l FTP: retrieving files from around the world . Key terms: the jargon explained l What’s new in online journals l Basic facilities and how to connect l Where to go next for help l The World Wide Web l Poster listing useful sitesto visit l Setting up and joining newsgroups For information concerning bulk sales, please contact Thelma Reid (tel. +44-l 223-311114; fax: +44-l 223-321410; e-mail: [email protected]).
244
Trends in Food Science & Technology July 1997 [Vol. 81
1st International quality aspects, such as phase-separation stability, homogeneity and organoleptic properties. The possibility of influencing the crystallization of milk fat and thus the structure and the rheology of the final product was presented by B. Breitschuh (Institute of Food Science, ETH, Zurich, Switzerland). By performing the crystallization under defined shear rates and temperature in a concentric cylinder rheometer, Breitschuh demonstrated that high shear accelerates the crystallization process and yields small spherulitic crystals with a narrow crystal size Bkatrice Conde-Petit distribution. However, exceeding a critical stress destroyed the crystal structure. J. Kobow (German Institute of Food Technology, Quakenbriick, Germany) demonstrated that, Structure and rheology, two important physical aspects as is the case for milk-fat crystallization, the crystallization of food and complex fluid systems, formed the subject kinetics of sugar in honey may be controlled by temperaof the 1st International Symposium on Food Rheology ture and shear forces. Honey with different structural and and Structure. More than 170 participants, from 20 dif- rheological properties can be produced by varying the conferent countries, came together for this event at the ditions for nucleation and crystal growth during processing. Swiss Federal Institute of Technology (ETH) in Zurich. During the past few years, the tailoring of food structures As expressed by the chairman of the organizing com- by using mixed biopolymer systems has received increasmittee, E.J. Windhab from the Institute of Food Science ing attention. P. WalkenstrZjm (SIK, The Swedish Institute at ETH, the aim of the symposium was to bring together for Food and Biotechnology, Gothenburg, Sweden) deexperts in rheology and food structure from academia scribed the effects of processing conditions, namely temand industry, to facilitate a synergistic exchange of ideas. perature, shearing and pressure, on the microstructure and The scientific programme included 64 oral presentations the rheological properties of mixed gels composed of gelaand 26 posters. A broad range of topics was presented, tine and whey protein. The microstructure was shown to including the rheological characterization of real and be largely dependent on the order of gel formation of the model food systems, from chocolate and cheese to glass components, which can be controlled by temperature and and carbon suspensions; the generation of structure by pressure. Furthermore, Walkenstrijm showed that by apfood processing; the relationships between structure, plying shear to affect the gel formation of whey proteins, rheology and food quality; advances in rheometry and inhomogeneities were induced, indicating increased phase methods for structure analysis; and also modelling and separation, which in turn enhanced the rigidity of the resimulation of the structure and flow behaviour of com- sulting gels. plex systems. The scientific programme was compleThe influence of processing on both the microstructure mented by an exhibition of instruments designed for the and the rheology of wheat dough was discussed by R. Kieffer (Deutsche Forschungsanstalt fiir Lebensmittelanalysis of rheology and structure. chemie, Garching, Germany). He showed that the wellknown phenomenon of strain hardening of dough in uniGeneration of structure by flow processing axial deformation, also called structural activation, is In his introductory lecture, Windhab presented an overview of the types of flow, shear and elongational, that are related to the separation of starch and gluten, which occurs on reshaping the dough after a rest period. The formation generated in different food processing operations and how of large aggregates of starch granules, as assessed by light they affect the structure of complex fluid systems. Flowinduced structural changes in food are initiated when the microscopy, may also be induced by extrusion through a mechanism-specific critical stresses are exceeded. As ex- capillary. According to Kieffer, strain hardening on uniamples, Windhab discussed the reduction of droplet size axial deformation is due to the dilatant behaviour of large starch aggregates and to the increasing thickness of the during emulsification, the aggregation of whey proteins owing to conformational changes following intensive treat- gluten strands. ment in a rotor-stator flow field, and the network characteristics of both starch and xanthan dispersions induced by Colloidal and molecular interactions influencing structure and rheology mechanical treatment. Windhab pointed out that the resulting rheological behaviour of multiphase food systems is Many food gels, especially dairy products, are proteinstabilized emulsions, containing finely dispersed particles closely related to their inner structure, the main structural (droplets) and crosslinked macromolecules. The compreelements being solid particles, droplets and gas bubbles. hensive review by E. Dickinson (Procter Department of The rheological behaviour of the final product determines Food Science, University of Leeds, UK) focused on the complex relationships between the interactions, structure *Held in Zurich, Switzerland, 16-21 March 1997 and rheology of protein-stabilized emulsion gels. He discussed factors that affect the rheology of heat-set protein Beatrice Conde-Petit is at the Institute of Food Science, Swiss Federal Institute emulsion gels, emulsion gels crosslinked by transglutaminof Technology (ETH), CH-8092 Zurich, Switzerland (fax: +41-1-632-l 123; ase, emulsion gels flocculated by bridging macromolecules e-mail: [email protected]).
Symposium on Food
Rheology and Structure*
242
Copyright @1997, Elsevie, Saence PII: 50924.2244197)01041-L?
Ltd. All rtghts reserved
0924.?244!97!$1
7.00
Trends
in Food
Science
& Technology
July
1997
[Vol.
81
and depletion-flocculated caseinate-stabilized emulsion Modelling and simulation of structure and complex gels. The speaker showed that the strength of the interfluid systems actions between the emulsion droplets, which are in turn One powerful approach for understanding the complex affected by the protein structure and concentration, by relationships between interaction, structure and rheology, processing conditions and by the interactions of ad- as well as for predicting flow behaviour during processing, sorbed and unadsorbed proteins with other components, is modelling and computer simulation. Two presentations, determines both the structural and rheological properties one given by P. Walstra and the other by T. van Vliet of oil-in-water emulsion gels. Dickinson stressed the (both from the Department of Food Science, Wageningen need for modelling and simulation of particle gelation to Agricultural University, The Netherlands), focused on better understand these complex systems. the concept of fractals for describing food structure. For Unlike emulsions, baked goods contain an entrapped instance, small particles in a liquid system tend to form air phase. It is well known that the addition of fat to fractal aggregates on being subjected to aggregation. baked goods affects the size and distribution of air Examples of particle gels are plastic fats, renneted milk bubbles, leading to a more homogeneous crumb strucand other proteinaceous gels. As the speakers demonture and an increased volume. Until recently, the role of strated, the fractal description provides a useful tool to fat was considered to be different in breads, biscuits and describe the mechanical properties of aggregates. cakes, owing to their differing composition and physical In food processing, unit operations that involve mixproperties. At the symposium, B.E. Brooker (Institute ing are very common. However, process improvements of Food Research, Reading, UK) presented his latest and performance optimization are actually hampered by results on the interactions between fat crystals and the the poor level of understanding of what is actually hapair-water interface of bubbles. He demonstrated that pening in the vessel in terms of the mixing mechanism. during mixing, the fat crystals separate from the oil P.A. Tanguy (Department of Chemical Engineering, Ecole phase and become enveloped in the oil-water interface, Polytechnique, Montreal, Canada) showed how threewhich allows them to adsorb at the air-water interface dimensional computer simulation can be used to clarify of bubbles. The crystals melt during baking and transfer the impact of rheology on the mixer performance. The interfacial material to the surface of bubbles and con- simulation allows determination of the distribution of shear tribute to their expansion without rupturing. According rates and power and the impeller pumping capabilities, to Brooker, this mechanism is common to all baked which can readily be used for design. Another important goods that contain an entrapped air phase. These recent operation in processing is the treatment of complex liquid findings suggest new ways in which the structure of fat systems in a scraped-surface heat exchanger. This process crystals can be manipulated to optimize the functionallows, for example, the continuous crystallization of chocolate. M. Stranzinger (Institute of Food Science, ETH, ality of fats in baked products. Zurich, Switzerland) presented numerical results on the An example of molecular interaction between polysaccharides, which is widely applied in the food indusshear and secondary flow effects around a scraping blade inside a channel gap of a scraped-surface heat exchanger. try, is the combination of the two non-gelling polymers, xanthan and galactomannan, to induce gelation. C. By simulation, Stranzinger was able to show the effect of the scraper angle on the streamline patterns and pressure Garnier (Institut National de la Recherche Agronomique, distribution for Cuette-type and Poiseuille-type flows. Nantes, France) presented a study on xanthan-galactoIn addition to shear flow, elongational flows are often mannan mixtures: confocal laser scanning microscopy and rheological methods were used to gain more insight present during food processing. It is well known that shear into the structure of these blends. Garnier proposed a can have a significant effect on the properties of particles in foods, but very little information is available on the new model for explaining the synergistic interaction. behaviour of particles in elongational flows. H. Nirschl According to the speaker, thermodynamic incompatibil(Technische Universitat Mtinchen, Freising, Germany) ity between xanthan and galactomannan is responsible showed that the damage caused to yeast cells varies in acfor the properties of the mixtures and not the generally considered model of specific interaction between the cordance with the type of flow to which they are exposed. With the help of a numerical technique, Nirschl described two polymers. A specific interaction between a polymer the behaviour of a single particle in a uniaxial elongational and small molecules, that is between amylose and difflow and came to the conclusion that for practical purferent flavour substances, which affects the rheological poses the forces generated by an elongational flow can be properties was reported by J. Ntissli (Institute of Food Science, ETH, Zurich, Switzerland). She showed that much higher than those generated in a shear flow situation. the combination of starch with (-)-fenchone, thymol or However, in the case of elongational flow, the particles, especially non-spherical particles with an ellipsoidal shape geraniol induces the formation of V-amylose, as determined by X-ray diffractometry, which is typical for or fibres, will orient and not change configuration. According to Nirschl, elongational flow can be used to create complexed starch. Interestingly, the formation of starchfood systems that have a defined structure and rheology. fenchone complexes induces the gelation of starch, owing to the aggregation of complexed amylose. As Ntissli pointed out, this type of interaction may affect Advances in rheometry and structure analysis The rapid developments in rheometry, together with not only the texture of starch-based food systems, but the falling costs of the instruments in relation to their also the release and retention of flavours. Trends in Food Science
& Technology
July 1997 [Vol. 81
243
capabilities, has contributed to the growing application of sophisticated rheological techniques for the characterization of real and model food systems. Many of the available rheometers were originally developed for use in materials science, especially polymer science. J. Meissner (Swiss F.I.T. Rheocenter, ETH, Zurich, Switzerland) presented a new rheometer for simple elongation, which was recently introduced onto the market and is especially designed for measuring the elongational properties of polymer melts. The suitability of this instrument for determining the elongational properties of wheat dough was shown by T. Schweizer (Swiss F.I.T. Rheocenter, ETH, Zurich, Switzerland) in a poster. Furthermore, Meissner also presented his latest development, a rheometer for equibiaxial and planar elongation of small samples. Windhab presented a new type of slit rheometer, which will be used to simulate the extrusion process and to measure the shear and elongational viscosity simultaneously. The rheometer was developed for the purpose of testing and calibrating conventional and new on-line measuring principles, such as the superposition of a pressure measuring method with the Doppler ultrasound method. The advantage of combining different measuring principles for a greater insight into the structure of biopolymer solutions and gels was presented by W-M. Kulicke (Institute of Technical and Macromolecular Chemistry, University of Hamburg, Germany). He combined the established rheo-mechanical methods with a new rheooptical measuring method, which allows the determination of flow birefringence and flow dichroism. By applying these methods to biopolymer dispersions, Kulicke showed that although the orientation of K-carrageenan polymers hardly shows any dependence on shear rate, the orientation of waxy maize starch polymers is strongly dependent on it. In mixtures of both polymers, the alignment of the polymer segments was shown to be influenced by the addition of starch. Another rheometer, which combines different measuring techniques, was described by S.T. Beckett (Nestle R&D Centre, York, UK). This high-frequency rheometer combines ‘pulse’ and ‘resonance’ techniques and exploits wave interference, and was successfully used to monitor the development of the structure (gelation) of aqueous gelatin dispersions and other gelling systems.
Other measuring principles for assessing food structure that are not based on rheology were also discussed at the symposium. Microscopy is one of the most important tools for food structure characterization, as shown by several speakers. By using light, scanning electron and transmission electron microscopy, A-M. Hermansson (SIK, The Swedish Institute of Food Biotechnology, Gothenburg, Sweden) successfully characterized the microstructure of protein and polysaccharide gels. W. Buchheim (Federal Dairy Research Centre, Kiel, Germany) presented an overview of various types of interfacial layers in emulsions and foams, as assessed by different microscopy techniques. Finally, a comprehensive review on light and neutron scattering and their application to complex fluids was presented by P. Schurtenberger (Institute of Polymer Science, ETH, Zurich, Switzerland). He demonstrated a few nonstandard applications for systems that are of interest in food science. One interesting application is the characterization of extremely turbid suspensions, such as undiluted baby milk, using dynamic light-scattering experiments combined with novel cross-correlation schemes. This short summary of the symposium, which covers only some of the contributions, clearly reflects the multidisciplinary character of the event; it successfully brought together different disciplines and approaches related to food rheology and structure. The strong interest of the participants was manifested by the lively discussions that followed the presentations.
Proceeding of the symposium have been published as Proceedings of the 1st International Symposium on Food Rheology and Structure, Zurich, Switzerland, March 1997 (Windhab, E.J. and Wolf, B., eds), by Vincentz Verlag, Hanover, Germany. Copies are available for DM150.00 (+ postage and packaging) from the publisher: Curt R. Vincentz, Ute Weber-Steltner, Schiffgraben 43, D-30175 Hanover, Germany (tel. +49-511-99-10-360; fax: +49-511-99-10-399; e-mail: [email protected]). It is envisaged that a second symposium will be held in Zurich, Switzerland, in 1999.
Coming up in the August issue of TIFS The Trends Guide to the Internet (1997) Feeling left behind? Worried about time-wasting? This free guide will lead you through those all-important first steps towards using the Internet efficiently and effectively. Written by an international panel of experts, the guide will tell you what to expect and where to find it. Articles include: l Creating your own home page l The origins of the Internet l FTP: retrieving files from around the world . Key terms: the jargon explained l What’s new in online journals l Basic facilities and how to connect l Where to go next for help l The World Wide Web l Poster listing useful sitesto visit l Setting up and joining newsgroups For information concerning bulk sales, please contact Thelma Reid (tel. +44-l 223-311114; fax: +44-l 223-321410; e-mail: [email protected]).
244
Trends in Food Science & Technology July 1997 [Vol. 81