摘要:

ABSTRACTThe dynamic viscoelasticity and stress relaxation of ten types of starch pastes were measured. The dynamic moduli increased with increasing frequency, and were different for each starch paste, changes in tan δ for cassava and potato starch pastes being about 0.5–0.6. The stress relaxation behaviour of all the samples tested could be represented by a four‐element mechanical model. The relationship between spinnability and stress relaxation was determined, the spinning distance increasing with increased relaxation time (τ2). No satisfactory linear relationship between spinning distance and relaxation time (τ2) was apparent with the 10 starch paste s

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1995.tb00799.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe influence of granule size and size distribution in gelatinized suspensions of 2.6% cornstarch heated at fixed temperatures between 70–90C on the power law viscosity was measured by laser diffraction. In the early stages of gelatinization, where the granule size standard deviation was less than 12 μm, dilatant behavior was observed over the shear rate range 200–1100S−1. At constant starch concentration and without granule rupture, suspension consistency, K, increased exponentially with granule mean diameter while the flow behavior index, n, decreased linearly with increase in the extent of gelatinization and the standard deviation of the granule size. The variation of K with granule size and that of n with standard deviation were found to be independent of temperature over 70–90C. In the later stages of gelatinization, where the granules lose their integrity, suspension viscosity progressively decreased as granule rupture c

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1995.tb00800.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe influences of temperature, polysaccharide stabilizing agents and overrun on the rheological properties of ice cream mix and ice cream were measured using dynamic rheological techniques with a controlled stress rheometer. Storage and loss moduli and tan δ all decreased significantly with increasing temperature. Unstabilized samples demonstrated significantly greater storage and loss moduli at temperatures<–8C and tan δ at all temperatures than stabilized samples, however, polysaccharides increased mix viscosity and resulted in significant increases in viscosity as the mix was concentrated. This indicated the importance of considering both ice and unfrozen phases in determining the impact of stabilizers on ice cream rheology. Increasing overrun from 20 to 60% increased the storage modulus significantly but had less effect on the loss modulus, especially in the stabilized samples. However, as overrun increased, the maximum force required for large deformation decreased, emphasizing the need to consider the effects of small‐scale versus large‐scale deformation testing on structure. Dynamic rheological measurements can provide insights into the development of ice cream structure and are useful in complementing other tec

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1995.tb00801.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe influence of normal ripening and chilling stress on viscoelastic properties of tomato pericarp tissue were investigated by measuring creep behaviour of tissue from fruit stored at 22C (nonchilled) or 5C (chilled) for 28 days, or at 5C for 16 days prior to transfer to 22C for an additional 12 days (prechilled). Creep compliance of tissue from all treatments subjected to a constant shear stress of 150 Pa for 5 min was best represented by a 6‐element Burgers model containing two discrete Voigt‐Kelvin units characterizing fast and slow rate viscoelastic properties. The magnitude of instantaneous elastic, viscoelastic and steady‐state viscous compliances each increased steadily and contributed to the overall softening of nonchilled and prechilled tissues during ripening, but remained unchanged during chilling of tomato fruit. Increased fluidity of ripening tissues occurred at the expense of elasticity, consistent with a decrease in molecular weight‐size distribution of structural elements contributing to respective viscoelastic properties. The physico‐mechanical changes in prechilled tissue preceded those in nonchilled tissue by several days, and occurred at a faster rate. The 6‐element Burgers model defining the creep behaviour of tomato pericarp tissue was interpreted with respect to general plant cell wall structure and biochemical changes known to occur during ripening of tomato fruits. Multiple mechanisms of softening were thereby consolidated into a single physico‐mec

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1995.tb00802.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTRaw carrots were diced into 9.5 mm cubes, and subjected to gamma radiation between an array of Co60pencils. A series of doses ranging from 0 to approximately 50 kGy was given. A plot of log (extrusion force) versus dose showed two distinct regions; the first is a rectilinear plot with a steep negative slope for doses up to about 15 kGy. The second is also a rectilinear plot with a shallow negative slope beyond 15 kGy. Sixty‐seven percent of the firmness is lost with the first 15 kGy but only 4% of the firmness is lost with the highest 15 kGy increase in dose. This two‐stage softening rate curve is consistent with the model of two first‐order kinetic rate processes and is qualitatively similar to that for thermal softening of carrot. The term “radiation firmness” is proposed to describe the amount of firmness that is resistant to degradation by ir

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1995.tb00803.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe perceptibility of grittiness and the threshold value of grittiness were examined in five disperse model systems: aqueous suspensions, low and high viscous suspensions, and soft and hard gels. Fourteen types of microcrystalline cellulose were used having different particle sizes (between 6–79 μm) and physical properties (shape, degree of polymerization, and state at the material stage). In each system, the proportion of people who perceived grittiness increased with increasing particle size and decreased with increasing particle concentration demonstrating that perception of grittiness depended on both particle size and concentration. The proportion of people who perceived grittiness was found by multiple regression analysis to have a high correlation with the logarithm of (particle size × concentration). Each system gave an approximate regression equation representing this relation. The value of particle size × concentration at the grittiness threshold was defined as the point where 50% of people perceived grittiness. These values were calculated to be 6.0 (aqueous suspension). 19.7 (low viscosity), 26.7 (high viscosity suspension), 30.7 (soft), and 42.1 (hard gel). The factor contributing most to grittiness was concentration, followed by dispersion medium and particle size. The proportion of people who perceived grittiness was also expressed by a multiple regression equation which included these three factors. The obtained results suggest the possibility of predicting and controlling grittiness in f

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1995.tb00804.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTChitin and collagen powders were added as fillers to various starches (potato, sweet potato, kudzu, corn, wheat, and mung bean), heated at 100C for 10 min with stirring to make a hot paste and allowed to gel quiescently at 5C for 2 h in order to investigate the effects of the filler particle on the texture of the gels. The parameters of hardness, cohesiveness and adhesiveness were determined instrumentally and compared. The filler particles of collagen and chitin were effective in increasing hardness of corn starch gels but had no effects on hardness of the potato, sweet potato, kudzu, wheat and mung bean starch gels except at the lower starch concentrations. Cohesiveness was increased slightly in all starch gels by addition of collagen whereas chitin addition only increased the cohesiveness of sweet potato and mung bean starch gels. Collagen and chitin addition increased adhesiveness all of starch gels, but the intensity of the effect was most remarkable for collagen. The observed differences in effects was apparently due to differences in the interactions between starches and filler particles arising from differences in the surface properties of the filler particles.

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1995.tb00805.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTFlours from 21 nonwaxy rice cultivars, varying in amylose‐equivalent (AE) content and eating quality, were pasted at 12–13% concentration at 95C and then further cooked at the same temperature for another 60 min. The fall in apparent viscosity, measured in a coaxial cylinder viscometer, of the 95C–50 min as compared to that of the 95C–0 min paste (paste breakdown, bdp) was calculated. The bdpvalues were inversely correlated to the sensory and viscoelastograph hardness of cooked rice as well to the AE contents. Paste breakdown was clearly a fundamental attribute of rice quality. It appears that starch granule rigidity/fragility, as determined by its AE, is the basic element in rice quality. This principle was then used to devise an abridged Brabender viscograph procedure. The slurry concentration was adjusted, by a simple technique described, to give a predetermined viscosity value at 95C. Then the paste was heated for another 10 min at 95C. The breakdown at 95C (BD95) of the samples correlated excellently with their total and insoluble AE, sensory and instrumental measures of cooked‐rice texture, and

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1995.tb00806.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

GENERAL PRINCIPLES:Effet of Carboxymethylcellulose on the Perception of Volatile Compounds: Study of Some Odour‐Texture Interactions. S. Villaneuva‐Rodriguez, B. Colas and F. SauvageotGENERAL PRINCIPLES:Influence of Temperature on the Dynamic and Steady‐Shear Rheology of Pectin Dispersions. J. A. Lopes da Silva, M. P. Gonçalves and M. A. RaoGENERAL PRINCIPLES:Structure and Rheological Behaviour of Arabinoxylans from Canadian Bread Wheat Flours. O. Rattan, M. S. Izydorczyk and C. G. BiliaderisGENERAL PRINCIPLES:Retrogradation of Potato Starch as Studied by Fourier Transform Infrared Spectroscopy. J. J. G. van Soest, D. d e Wit, H. Tournois and J. F. G. VliegenthartGENERAL PRINCIPLES:At Last, a True Liquid‐Phase Yield Stress. R. D. Spaanz and M. C. WilliamsMETHODOLOGY&INSTRUMENTATION:Compressive Stress‐Strain Relationships of Agglomerated Instant Coffee. (Res. Note)C. Nuebel and M. PelegMETHODOLOGY&INSTRUMENTATION:A Large‐Scale Field Coaxial Cylinder Rheometer for the Study of the Rheology of Natural Coarse Suspensions. P. Coussot and J.‐M. PiauMETHODOLOGY&INSTRUMENTATION:Estimation of the Wall Slip Velocity in the Capillary Flow of Potato Granule Pastes. P. J. Halliday and A. C. SmithINSTRUMENTAL MEASUREMENTS:Thermal Softening of Potatoes and Carrots. G. S. MittalINSTRUMENTAL MEASUREMENTS:Apple Bruising Thresholds for an Instrumented Sphere. D. W. Pang, C. J. Studman and H. BanksINSTRUMENTAL MEASUREMENTS:Relationship of Sonic Resonant Frequency to Compression Tests and Magnes‐Taylor Firmness of Apples During Refrigerated Storage. J. A. Abbott and L. A. LiljedahlSENSORY MEASUREMENTS:Foods Associated with Descriptive Texture Terms. H. Rohm, Doris Jaros, U. Fischer and S. LailachSENSORY MEASUREMENTS:Texture of Sweet Orange Gels by Free‐Choice Profiling. E. Costell, C. Trujillo, M. H. Damasio and L. DuranSENSORY MEASUREMENTS:Research of Selective Tests for Discerning “Efficient Assessor” in Texture Profiling. S. Rousset‐Akrim, J.‐F. Martin, C. Pilandon and C. TourailleFACTORS AFFECTING TEXTURE:Properties of Dextran as a Cryoprotectant in Ice Cream. R. D. McCurdy, H. D. Goff and D. W. StanleyFACTORS AFFECTING TEXTURE:Firming Effects in Danish Pastry. L. G. Sternhagen and R. C. HoseneyFACTORS AFFECTING TEXTURE:Fermented Dairy Ingredients for Bread: Effects on Dough Rheology and Bread Characteristics. P. Gélinas, J. Audet, O. Lachance and M. VachonFACTORS AFFECTING TEXTURE:Studies on Frozen Doughs. IV. Effect of Shortening Systems on Baking and Rheological Properties. Y. Inoue, H. D. Sapirsein and W. BushukFACTORS AFFECTING TEXTURE:Moisture Redistribution Throughout the Bread Loaf During Staling and Its Effect on Mechanical Proper

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1995.tb00807.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1995.tb00798.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY