摘要:

ABSTRACTThe mechanical properties of raw and cooked fish were qualitatively characterized by a generalized Maxwell model in which each of the Maxwell elements is modified by incorporation of a contact and two fracture elements. The activation and inactivation of elements have been used as a means of expressing transformation of the rheological characteristics, not only as a function of the strain and strain rate history but also as a function of temperature and time. Although no attempt has been made to quantify the number of elements and their characteristic constants, it is shown that the different modes of rheological behavior exhibited by fish flesh can consistently be described by this kind of model.

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1981.tb00258.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Stress relaxation and dynamic measurements were carried out on κ‐carrageenan and agarose gels to examine the effect of alkali metal ions. The elastic modulus of κ‐carrageenan gels increase remarkably by adding alkali metal ions Li+, Na+, K+, Cs+. This was explained as follows: the electrostatic repulsion of sulfate groups in κ‐carrageenan gels are prevented by the shielding action of the alkali metal ions stabilizing the double helical structure of κ‐carrageenan gels. The increase of the modulus was in the order: Cs+>K+≫ Na+>Li+. The difference between these two groups (Cs+, K+) and (Na+, Li+) is that the former group belongs to the structure disordering ions while the latter group belongs to the structure ordering ions. Thus, the former group prevents the repulsion of sulfate groups more directly than the latter. Agarose gel, which lacks sulfate groups, is not influenced so much by adding the alka

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1981.tb00259.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The effect of de‐esterification on the rheological properties of κ‐carrageenan gels was studied by stress relaxation and dynamic mechanical measurements. By means of de‐esterification, the elastic modulus of κ‐carrageenan gels increased. This was attributed to the increase of alternation of D‐galactose and 3,6‐anhydro‐D‐galactose, and then the stabilization of the double helical structure in the

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1981.tb00260.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The pattern of fracturability loss of 11 selected fruits and vegetables during thermal processing was studied. In general, the first‐order kinetic model is adequate in describing such changes during heating of edible plant tissue before reaching equilibrium texture. However, textural changes are less predictable by the first‐order kinetic model in tissues having thick cell walls (such as those derived from stems and roots) than in tissues having thin cell walls (such as those derived from fruits).For a given species (potato), the first‐order model can be applied regardless of sample dimension, morphological origin of the sample, heating temperature, variety, prior storage conditions, maturity and minor agronomic vari

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1981.tb00261.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Cooked rice held between glass plates was pressed by dropping a 2.5 kg load from a predetermined height. A significant variation (1.90 to 3.45 cm2) in the pressed area for raw cooked samples was found. Cooking methods exerted a significant influence on the pressed area. The pressed area of the cooked rice and the L/B ratio of uncooked samples correlated positively. This test significantly differentiated parboiled rices. The pressed area correlated negatively with the temperature of parboiling. Besides the varieties, the cooking methods and the testing time significantly influenced the pressed area of parboiled samples, thus indicating the reliability of this test even under varying testing conditions.

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1981.tb00262.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Four commercial butters (conventional batch and Westfalia, Contimab and Cherry‐Burrell continuous churned) were stored at two temperatures and evaluated periodically for rheological and textural properties. Evaluation methods included four mechanical tests (quasistatic shear, quasistatic uniaxial compression, Penetrometer, and extrusion) and sensory ratings of spreadability, firmness, and other texture parameters. The first three mechanical methods produced quasistatic shear yield stress values that had close agreement. For quality control the three tests can be considered equivalent. Shear stress‐strain rate data from extrusion testing developed using the Rabinowitch‐Mooney equation could be represented well by the Casson model. Casson yield stress values were an order of magnitude lower than the quasistatic values. The power law equation with a yield stress also represented the butter flow well, and all four butters had similar power law exponents (approx. 0.56). The Cherry‐Burrell butter had much higher quasistatic and Casson model constants than the other butters. It was also the most temperature sensitive and most stable with storage time. Temperature‐shear rate equivalent effects on shear stress were demonstrated by developing shift factors. The quasistatic yield values for the butters best predicted sensory spread‐ability and hardness. The changes in flow properties (Casson yield stress and Casson slope) correlated

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1981.tb00263.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Fruit of several pickling cucumbers (Cucumis sativusL.) grown in 1978 and 1979 in several environments under two soil nitrogen levels (high vs. normal) were stored for various time periods before fresh‐pack processing. Firmness, color and general appearance as examined after equilibration were all highly affected by cultivar, growing environment, and storage duration but somewhat less by nitrogen level. Unexpectedly, color and appearance improved during the first 24 h after harvest. Acceptable firmness was maintained for at least 72 h after harvest. Fruit of genetically firm cultivars generally showed less change in firmness than did fruit of less firm cultivar

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1981.tb00264.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The flow properties of over seventy concentrates made from four cultivars of tomatoes were determined with a concentric cylinder viscometer. The apparent viscosity (100 s−1, 25°C) of the concentrates of each variety was proportional to the 2.5 power of the concentration (% total solids). The apparent viscosity of the Nova cultivar obeyed the Arrhenius temperature relationship; the activation energy for the concentrates was 2.3 ± 0.3 kcal/mole. The simple power law and the Casson model described satisfactorily the flow data of the concentrates but the power law gave higher correlation coefficients. The Herschel‐Bulkley model with the Casson yield stress was also satisfactory but the correlation coefficients were lower than for the simple power law. The consistency index of the power law model also showed a power dependence on the concentration. The natural logarithm of the yield stress and the concentration could be correlated by a quadratic equ

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1981.tb00265.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Shear stress development data for commercial ketchup, mustard, mayonnaise, apple butter, butter, margarine and canned frosting were obtained using the cone and plate geometry of the Rheometrics Mechanical Spectrometer. At sudden imposition of four shear rates, .1, 1, 10, and 100 s−1, shear stresses displayed different degrees of overshoots with margarine exhibiting a maximum overshoot of 320% that of the steady‐state value at a shear rate of 100 s−1. The actual extent of overshoot depended on the particular food and the particular shear rate applied.An attempt was made to explain observed transient shear stresses with the Bird‐Leider equation, a four parameter empirical model which incorporates both steady viscous and elastic properties of food materials. This model assumes both the steady viscosity function, η, and the steady primary normal stress coefficient Ψ to have a prominant power‐law region with increasing shear rate. This assumption is shown to be justified for all foods studied between shear rates of .1 s−1and 100 s−1. When this assumption is justified a time constant Λ can be constructed. This time constant is found to be an approximate indicator of relative stress overshoot for the foods studied. It is found that the Bird‐Leider equation provides a moderately good prediction of peak shear stresses and peak times and only a crude prediction of shear stress decay. Nevertheless, the model is a definite improvement over time independent models such as t

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1981.tb00266.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

An attempt was made to measure the effect of lipid components on the viscosity and thixotropy of wheat starch paste in a short aging time after gelatinization. Viscometry was used to follow periodically the changes in apparent viscosity (at 76.8 s−1) of the mixed paste of wheat starch and one of a series of lipids in a cone‐plate viscometer for 210 min after gelatinization, i.e. a procedure of eight cycles of measurement with a sample. Each cycle of the measurement consisted of viscometry for 3 min and a rest period for 27 min at 30°C. The apparent viscosity of all the samples decreased greatly during the 3 min measurement due to thixotropic breakdown of the macroscopic structure in the samples. The results suggest that the presence of a small amount of free fatty acid and monoglyceride may play a role in reducing starch paste gela

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1981.tb00267.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY