摘要:

ABSTRACTThe following aspects of the rheological behavior of polysaccharide and protein gels are discussed with particular emphasis on recent investigations: (1) Viscoelasticity of gels; (2) Validity of rubber elasticity theory; (3) Rupture strength of gels; and (4) Single‐point measurements of gel strength.It is concluded that in contrast to most food materials gels show linear viscoelastic behavior up to strains of the order of 0.1. Results obtained from creep and stress relaxation experiments would suggest that noncovalent crosslinks in gels move or break when the gel is stressed. Activation energies associated with crosslink breakage have been estimated from the temperature dependence of viscoelastic parameters. For gelatin and polysaccharide gels energies ranging from 5–65 Kcals/mole have been reported.The stiff and extended nature of polysaccharide chains make it unlikely that polysaccharide gels obey rubber elasticity theory, though it is possible that this theory holds for gelatin gels and also for ovalbumin gels in 6 M urea.It is emphasized that the rupture strength of a gel is not necessarily related to its elastic modulus and therefore ‘single point’ measurements of ‘gel strength’ based on rupture tests will not always rank a series of gels in the same order as tests which involve small deformations without rupture. One of the reasons for this is that the elastic modulus and rupture strength depend in different ways on the primary molecular weight of the polymer from which the ge

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1980.tb01312.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTThe viscosities of aqueous mesquite gum solutions were measured at gum concentrations extending to 16.7% (w/v). Very dilute solutions exhibited typical polyelectrolyte behavior with respect to the influence of gum concentration on the reduced viscosity in the absence and presence of electrolyte. Shear thickening was exhibited at concentrations of 1–16.67% (w/v) when the shear rate exceeded ∼100 s−1, whereas shear thinning was exhibited at lower shear rates. Shear thickening was attributed to configurational changes in the gum molecules at high shear rates. Electrolytes (0.1N NaCl and 0.1N CaCl2) reduced the viscosity of concentrated solutions at high shear rates to a larger extent than increasing the pH. Charge screening by electrolyte permits the gum molecules to assume a more compact configur

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1980.tb01313.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTOil‐in‐Water emulsions stabilised by mesquite gum have been examined by their creep compliance‐time response at a constant low shear stress and by shear stress‐shear rate studies. The Theological data were influenced by pH, electrolyte (NaCl, CaCl2) and aging time. Both pH and electrolyte altered the degree of compactness of the mesquite molecules adsorbed on the oil drops. Aging produced changes in the rheological properties, the general trend depending on the rate of drop coalescence and the ability of adsorbed mesquite layers on adjacent flocculated drops to interpenetrate and form new linkages. The drop coalescence rate was highest at pH 7.0, but this was offset by greater interpenetration so that the rheological parameters increased substantially durin

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1980.tb01314.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTAge thickening of UHT steam injected ice cream mix and melt was investigated by determining rheological model constants. By utilizing a cone and plate viscometer, rheological models (3 element solid) were developed for creep‐relaxation. Empirical relationships were derived relating the elastic and viscous constants to storage time. Soft serve ice cream mix (4.0% fat) was processed at 149°C for 3.4, 6.9, and 20.3 s. The ice cream mix was stored at 20 and 30°C and tested at four week intervals from zero through 24 weeks. Flow properties of the mixes and melts were quite stable throughout the storage period although the lowest heat treatment (3.4 s for 149°C) suggested mild age thickening by 24 weeks. The strongest element constant for all samples was the series elastic. The viscous constant was next with the Kelvin elastic constant being quite weak. Melts had lower constants than the mixes. Model constants varied little between samples stored at 20°C and those at

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1980.tb01315.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTThe back extrusion cell, Maturometer, Kramer shear press, FMC Tenderometer, and Ottawa Texture Measuring System wire extrusion cell gave useful estimates of the maturity of raw peas but, two viscosity methods gave unsatisfactory estimates. None of the instruments gave useful estimates of maturity of frozen peas that had been thawed or cooked because blanching conditions and the rate of freezing of the peas affected the readings. The most reliable estimate of raw pea maturity from thawed frozen peas was the alcohol insoluble solids content.

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1980.tb01316.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTA quick and easy method of measuring the bruise resistance of apples is described. The method is based on the strong linear correlation between energy absorbed and bruise volume from which is calculated a bruise resistance coefficient, with units mljoule−1. The bruise resistance coefficient can be accurately determined by dropping a sample of 10 apples. For each drop the energy absorbed is calculated from measured drop height, rebound height and apple mass. The bruise volume on each apple is calculated from measured apple diameter, bruise diameter and bruise depth. The bruise resistance coefficient is effective in the evaluation of packaging, handling and distribution systems for apple

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1980.tb01317.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

ABSTRACTA means of measuring the amplitude of force fluctuations during texture tests is described. A maximum‐minimum module added to the electronic force recording system gives a direct readout of amplitude. The method has potential applications in research and quality control The technique is demonstrated with the back extrusion test applied to tomato juice. The results show that the maximum amplitude of the force fluctuations during extrusion is related to the graininess of the juic

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1980.tb01318.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1980.tb01319.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

GENERAL PRINCIPLES: The Measurement of Food Texture. B. L. WedzichaGENERAL PRINCIPLES: Engineering Factors in the Production of Concentrated Fruit Juices. 1. Fluid Physical Properties of Orange Juices. M. Moresi and M. SpinosiGENERAL PRINCIPLES: Textural Properties of Cottonseed Proteins. L. C. Berardi and J. P. CherryGENERAL PRINCIPLES: Theoretical Analysis of the Relationship Between Mechanical Hardness and its Sensory Assessment. M. PelegINSTRUMENTATION AND METHODOLOGY: Evaluation of the Flowability of Melted Mozzarella Cheese by Capillary Rheometry. C. E. Smith, J. R. Rosenau, and M. PelegINSTRUMENTATION AND METHODOLOGY: Measurement of the Spreadability of Margarine and Butter Using A Single Pin Maturometer. P. W. Board, K. Aichen, and A. KuskisINSTRUMENTATION AND METHODOLOGY: A Parallel Plate Rheometer for Measuring the Viscoelaetic Properties of Wheat Flour Doughs. G. E. Hibberd and N. S. ParkerINSTRUMENTATION AND METHODOLOGY: Viscosity Measurements of Non‐Newtonian Slurry Suspensions Using Rotating Viscometers. S. K. Sikdar and F. OreOBJECTIVE MEASUREMENTS: A Physical Method for Measuring Okra Fruit Quality. J. O. Uzo and G. U. OjiakoOBJECTIVE MEASUREMENTS: Flow Properties of Milk in a Capillary at Low Shear Stress. T. Mineshita, A. Yamamoto, K. Nagano, S. Fujii, and H. Takada.OBJECTIVE MEASUREMENTSFracture Resistance of Soybeans to Compressive Loading. M. R. PaulsenOBJECTIVE MEASUREMENTSOBJECTIVE MEASUREMEN

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1980.tb01320.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY