摘要:

ABSTRACTThe Smithet al.method has been widely used for estimating the transient state and mass average temperature of an irregularly shaped food. For the computer implementation of their method, regression formulas were obtained to estimate a characteristic root applicable to an irregular body by using their nomograph. the Smithet al.method was improved for direct determination with two heat penetration parameters, f and j, without using temperature response charts as recommended by Smithet al.

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1989.tb00032.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTThe flow properties of starch pastes prepared by different procedures were measured and modelled. an extended power law model was developed to describe the shear stress over wide ranges of shear rates, temperatures and concentrations (6‐450 s−1, 10‐90°C, 3‐10%). Each pastes preparation procedure required its own set of parameter values to be modelled since different preparation procedures produced pastes with considerably different flow properties. These effects have to be considered before the flow properties can be predicted with satisfactory precision for process applications. Such a method is presented in a subsequent paper. the exactness in the modelling was restricted by the changes of the flow properties during the measuring

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1989.tb00033.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTCompared with traditional methods, the prediction of flow properties of starch pastes is greatly improved with the new apparent concentration method proposed in this study. the new method considers the effects on the flow properties of minor variations in the preparation procedure and the composition of the product. the deviations with the new method range from ± 10% for high‐viscosity pastes down to ‐30% for low‐viscosity pastes. the deviations are mainly due to the time dependency of the shear stress, as these effects are considerable for starch pastes, but have not been considered in the modelling in this work. Successful use of the apparent concentration method requires a reference model with known parameter values, a simple rheological measurement on the actual product, and appropriate calculations. the simple measurement can be performed on‐line or in the laboratory. A special residual analysis was developed to make it possible to split up the differences between observed and predicted values and attribute the parts to the following factors: measuring instrument, changes in the sample during the measuring process, model, parameter values, and the concentration used in the prediction. This residual analysis made it possible to identify the weakest link in the pre

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1989.tb00034.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTThe time dependency of shear stress has been investigated in completely swollen modified potato starch pastes during short periods of time (30 s) over wide ranges of shear rates, temperatures and starch concentrations (6‐450 s−1, 10‐90°C, 3‐10%). A special, stepwise measuring process made it possible to correlate the kind of time dependency to the shear stress level; thixotropy or rheodestruction occurred at low shear stress (below 10 Pa); rheopexy occurred at intermediate shear stress (from 10 to 150 Pa); and thixotropy occurred at high shear stress (above 150 Pa). Bearing these results in mind, similar results can be observed in other studies on potato starch, maize starch, modified tapioca starch and tomato juice. the size and the kind of hysteresis loop in the flow curves can be related to the kind of time dependency at each shear stress level and to the duration of the effect at each level. These phenomena limit the precision when the flow properties are predicted for starch pastes and many other viscous foods, as long as the time dependency factor is disregarded in the measuring and modelling procedures. It is important to consider the time dependency when holding tubes for aseptic processing are sized; if this is not done, the sterilization effect will be too low when rheopexy prevail close to the surface of

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1989.tb00035.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Book reviewed in this article:QUALITY ASSURANCE of FOOD John E. Stauffer.

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1989.tb00036.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY