摘要:

ABSTRACTThe conformation of hot break tomato pectins in water/glycerol solutions as a function of degree esterification was studied and compared with the conformation of apple and citrus pectin using reduced storage [G′]Rand loss [G″]Rmoduli and the theories of Marvin and McKinney for rod‐like behavior and those of Rouse as well as Zimm for random coil conformation. In all three cases the theory of Zimm implying dominant hydrodynamic interactions fit the experimenal data best. This is consistent with current knowledge on chemical structure of pectin where the charged uronides clearly readily interact with each

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1993.tb00039.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTEleven traditionally produced butter samples were evaluated for rheological properties at large deformations by lubricated and nonlubricated uniaxial compression with varying sample geometries and compression rates, by stress relaxation in shear and creep experiments in compression at 5–20C each. Compression forces required to deform cylindrical samples in nonlubricated conditions were higher than in lubricated cases. Correction of shape changes in nonlubricated stress‐strain curves resulted in good agreement with lubricated experiments at low compression rates up to stress maxima or yielding. As frictional forces were relatively smaller at high deformation rates, lower stresses were obtained in nonlubricated conditions. Samples with higher height/diameter ratios showed more pronounced stress maxima. A biaxial extensional viscosity, ηbe, was computed for nonbrittle, soft samples. Typical slopes in logarithmic plots of viscosity against strain rate were approximately ‐1. At strains of about 0.01 creep compliance depended on compression stress. The average ratios of recovered to initial instantaneous compliance were between 0.31 and 0.59, and increased with sample temperature. A calculated ηBE from creep compression showed fair agreement with ηBE from static compression experiments. At comparable strains, a conversion of creep compliance to the stress relaxation modulus by an approximate method showed a good fit of experimental

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1993.tb00040.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTThirteen continuously churned commercial butter samples were evaluated for rheological properties at small deformations. The methods performed included dynamic experiments in shear and compression, stress relaxation in shear and static compression at 5–20C each. Linear viscoelastic behaviour was observed up to a critical strain of 0.001. The structure breakdown due to shear strains between 0.001 and 0.01 was found to be fully recoverable. No qualitative differences in the rheological behaviour were observed between the samples. Temperature‐induced variations were mainly ascribed to changes in the solid fat content. Correlations between selected rheological measures in the linear viscoelastic region (i.e., complex modulus G* [Pa], relaxation modulus G(t) |t≃ 0[Pa], and modulus of deformability MD[Pa]) were found to be causal and only slightly affected by the solid fat co

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1993.tb00041.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTSlip velocities of 19 tomato concentrates and 5 apple sauces at cup and bob of a concentric cylinder (CC) system (MVI) were determined using two methods: (1) of Kiljanski using two CC systems, and (2) of Mooney using three CC systems. For many food samples, there were large differences in the magnitudes of slip velocities at the cup and bob calculated according to the two methods. However, corrected shear rates according to the two methods were in good agreement. Both the calculated slip coefficient of Mooney and the slip velocity of Kiljanski increased with applied shear stress according to power relationships; however, the former showed a weaker dependence on applied stress.

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1993.tb00042.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTRheological characteristics of stirred yoghurt, varying in dry matter content, fermentation temperature and composition of bacteria cultures, were evaluated using a Bohlin VOR Rheometer. Flow curves, covering the shear rate range 29–920 s−1, generally indicated the presence of a yield point and pseudoplastic behaviour, but also Bingham plastic behaviour was observed for some of the specimens. Systematic variations in the profile of the flow curves were observed as a result of the applied manufacturing conditions. Flow curves exhibiting pseudoplastic behaviour with a yield stress could not, over this broad shear rate interval, be described satisfactorily by the often applied Casson or Herschel‐Bulkley models, and consequently a new one, the QRS‐model was introduced. This model contains three parameters and gave a significantly better fit, with R2values generally abo

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1993.tb00043.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTThe effects of molar substitution (M.S.) and cross‐linking on the freeze‐thaw stability of hydroxypropyl potato starch pastes were studied by following the changes in the rheological behaviour during heat treatment of the thawed starch pastes, and by determination of syneresis. In addition, differential scanning calorimetry (DSC) was used to investigate the thermal transition properties of the starch pastes that exhibited syneresis. With increasing M.S., the changes in both complex modulus (G*) and phase angle (δ) indicative of destabilization, and starch paste syneresis were delayed with regard to the number of freeze‐thaw cycles. When a starch paste showed a peak in G*, related to syneresis, it also showed a thermal transition peak in the DSC measurements. The enthalpy value decreased with increasing M.S., and it appeared to be related to the extent of syneresis and the magnitude of the peak in G*. Comparison of the rheological behaviour of hydroxypropyl potato starch pastes and hydroxypropyl and cross‐linked potato starch pastes, suggested that the former were gradually transformed into coarsely aggregated structures while the latter became diluted starch dispersions, due to shrinkage of swollen starch granules and their di

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1993.tb00044.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTThe attractors of the jagged, normalized, dimensionless, stress‐strain relationships of three dry snacks, breadstick, pretzel and Zwieback, were constructed using the Packard‐Taken method. No unambiguous pattern could be revealed but the shape of the attractors differed from that of a totally random sequence. Although the existence of underlying characteristic periodicities could not be proven using the method with the available data it could not be ruled out eit

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1993.tb00045.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

FOOD PACKAGING: PRINCIPLES AND PRACTICE.G.L. RobertsonViscoelastic Properties of Foods.M.A. Rao and J.F. Steffe, eds.Rheology of Foods.R.P. Borwankar and C.E. Shoemaker, eds.

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1993.tb00046.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

GENERAL PRINCIPLES: Investigations on the Experimental Rheology of Real Shear Thinning Systems.L.J. Djakovic, I. Sefer and T. DjakovicGENERAL PRINCIPLES: Flow Behavior of Starch‐Fatty Acid Systems in Solution.S.N. RaphaelidesGENERAL PRINCIPLES: Rheological Properties of High‐Methoxyl Pectin and Locust Bean Gum Solutions in Steady Shear.J.A. Lopes da Silva, M.P. Gonçalves and M.A. RaoGENERAL PRINCIPLES: Elastic Attributes of Heated Egg Protein Gels.Y.L. Hsieh and J.M. RegensteinGENERAL PRINCIPLES: Dynamic Mechanical Analysis for Glass Transitions in Long Shelf‐Life Bread.L.M. Hallberg and P. ChinachotiGENERAL PRINCIPLES: Thermomechanical Properties of Frozen Sucrose Solutions.M. Le Meste and V. HuangGENERAL PRINCIPLES: Influence of Protein Addition on Rheological Properties of Amylose and Amylopectin Based Starches in Excess Water.L.L. Chedid and J.L.

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1993.tb00047.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY