摘要:

AbstractSince most solid food materials are biologically active or physically unstable, they do not reach mechanical equilibrium in the true sense of the term. Consequently, their stress relaxation data alone cannot provide information sufficient to decide whether these materials are true solids or not. The implications of this problem in the selection of rheological models for foods are emphasized and a method by which the problem can be bypassed is presented and its capabilities and limitations evaluated.

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1982.tb00873.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractA modified viscometric method was developed for evaluating sweet corn maturity. The optimal deformation (shear) rate of the test was found to be 48.6 s‐1. A simple power‐law flow model was applied. Apparent viscosity correlated highly with maturity parameters. Freezing increased the viscosity of the corn slurries. Apparent viscosity and Back Extrusion maximum force were satisfactory indexes of quality for frozen c

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1982.tb00874.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

The stickiness and consistency (an inverse estimate of tenderness) of cooked rice were measured by the sieve test and with the Haake consistometer. The values varied with the rice quality type. Stickiness was not appreciably affected by the water‐to‐rice ratio used during cooking, but was markedly reduced by storage especially in the cold, i.e. by starch retrogradation. Consistency was affected by both: it decreased with increasing water ratio and increased with storage. Stickiness was inversely proportional to consistency. Consistency of cooked rice varied with the force used in the consistometer test, from which it is postulated that cooked rice is a pseudoplastic system. Different rice samples should be compared only under identical rice‐to‐water ratio used for cooking and under identical force used for the consisten

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1982.tb00875.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractComplete characterization of flow of apricot puree is obtained by evaluation and quantification of thixotropy, measurement and calculation of yield stress, and application of selected mathematical models. Additionally, a structural model is tested. Apricot puree is slightly thixotropic, exhibiting a definite yield stress and obeying the Herschel‐Bulkley equation, Information related to structural characteristics is obtained by applying the Michaels and Bolger model to experimental rheological dat

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1982.tb00876.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThe dependence of mechanical and water‐holding properties of soy protein gels upon their structures was examined. Gels varying in extent of network formation were prepared by heating 20% paste of the isolated soy protein (ISP) containing L‐cysteine hydrochloride (CySH) which has an ability to cleave intermolecular disulfide bonds. A rapid decrease in gel hardness and cohesiveness was observed with the increase in added amount of CySH up to 2.5 times 10‐5mole/g ISP, and then a gradual decrease to 5.0 times 10‐5mole/g ISP. The changes in these mechanical parameters appeared to depend on the degree of the network formation interpreted from the solubility changes of gels in the phosphate buffer containing 6 M urea. The relaxation time, estimated by compression stress relaxation, was also dependent on the degree of the network formation, while the modulus of elasticity was hardly affected. On the other hand, there was an inverse correlation between the NMR line width of the water proton and expressible water by the pressure method as an index of water‐holding properties of the gel; the broader the former, the lesser the latter. The change in the water‐holding capacity estimated from expressible water was also associated with that in the degree of the network formation. This confirms that both mechanical and water‐holding properties of the gel are qualitatively governed by the extent of the structure formation controlled by the intermolecular di

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1982.tb00877.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractA simple machine is described for measuring yield point in strips of raw muscle, by registering maximum tension generated at a low rate of extension. Values are not highly dependent on the rate or degree of extension. The method has been used to measure rate of ageing at 15°C and 2°C, with parallel measurements of shear force in the cooked muscle. The machine provides a sensitive tool, complementary to the tenderometer, and particularly suited to studies on agein

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1982.tb00878.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractAn understanding of mechanical failure in fruits and vegetables is essential to the reduction of damage in processing, handling and transport operations and to the evaluation of textural characteristics of foods. This paper proposes a theory of failure for solid horticultural materials based on the classification of failure as cleavage, slip or bruising. For each of these three modes of failure, the role of intensity of loading or stress in initiating failure is described. It is shown that cleavage is a normal stress phenomenon and that slip and bruising are shear stress phenomena. The mechanical properties of horticultural produce are described in terms of cleavage strength, slip strength and bruising strength; properties which may vary with ripening and loading conditions.A failure diagram is constructed by superimposing strength boundaries on the normal and shear stress axes of the Mohr's circles representation of the applied stress state. This novel diagram is shown to apply to selected fruits and vegetables. The model can be extended to include buckling. It is shown that horticultural materials do not fail according to one failure criterion alone, but fail, on a rising load, according to the current strength boundary first encountered by an expanding stress state. Potatoes, for example, may fail by cleavage, slip or bruising, depending on the loading conditions.

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1982.tb00879.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractFourteen ammonia‐demethylated low‐methoxyl pectins were chemically defined. Each was used to prepare a 30% sucrose gel. The texture of each gel was evaluated by an eight member, semi‐trained sensory panel. Each gel was also subjected to dynamic uniaxial loading at seven frequencies ranging from 100 Hz to 280 Hz. Rheological response was found to be highly dependent on test frequency, and a resonance dispersion effect was revealed at several frequencies. The frequency that exhibited the greatest resonance dispersion was also the most sensitive in distinguishing between the 14 gels, based on absolute modulus. Ninety‐two percent of the total variation in absolute modulus could be significantly explained by the chemical composition of the pectin. Significant correlations were found between the sensory descriptors and the rheological parameters calculated from the dynami

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1982.tb00880.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractA range of concentrations (c) of wheat starch granules dispersed in water were heated at 60, 65, 70 and 75°C for 15, 30, 45, 60 and 75 min. Viscosity (η)‐shear rate plots for these cooked dispersions, determined with a Haake Rotovisco rotational viscometer at 60°C and 23°C, varied markedly, often showing dilatant behavior, particularly at the shorter cooking times but always becoming typically non‐Newtonian shear thinning fluids at the longer cooking times. A t the lowest temperature, 60°C, the viscosity increases very rapidly with concentration above 16%. As the cooking temperature is raised to 65, 70, and 75°C these rapid viscosity increases occur at progressively lower concentrations. These concentration curves for the longest cooking times could be superimposed on a master curve by plotting, instead of 77 versus c, η/cQ versus cQ, where Q is determined in a separate experiment and is the weight of the swollen starch granules after the specified time at cooking temperature divided by the dry weight of the starch prior to cooking. This method of reducing viscosity/concentration data has been reported by Taylor and Bagley (1977) for highly swollen gel systems and by Urbanski (1981) for soy beverages, and thus appears to be a general method for treating viscosity data for suspensions of deformable particles that sorb solvent. Where excess solvent is present, CQ is less than unity and is equivalent to volume fraction; for deformable particles, however, CQ can be greater than unity, and for our systems concentrations in this range repres

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1982.tb00881.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Food Law Handbook. H. W. Schultz.Protein Food Supplements. M. A. Maltz.

ISSN:0022-4901    

DOI:10.1111/j.1745-4603.1982.tb00882.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY