摘要:

ABSTRACTA generalized model for predicting the effects of shear rate, temperature, moisture content, time‐temperature history and strain history on viscosity has been evaluated for extruded potato flour doughs. an Instron Capillary Rheometer and a 50 mm Baker Perkins co‐rotating twin screw extruder were used to evaluate all effects incorporated in the model, except strain history. the power law model was used to describe shear rate effects in the range 10–10000 s−1. the generalized model fit observed data for temperatures of 25–95°C and moisture contents ranging from 22 to 50%, wet basis. Since potato flour by its manufacturing process is pregelatinized, it was unnecessary to evaluate the effects of time‐temperature history. Strain history was found to have an insignificant influence on t

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1990.tb00037.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTA factorial experimental design was used to study the effect of exhaust heat recovery, air flow rate and outlet temperature on the energy consumption of a spray dryer. A commercial‐scale cocurrent flow dryer with pressure atomization was used to dry 15 wt% sodium sulfate solutions. the inlet air to the dryer was preheated by using a shell‐and‐tube heat exchanger to recover energy from the exhaust air. Heat recovery reduced the energy consumption of the dryer by 12–28%, with the largest reduction occurring at the high levels of air flow rate (13,000 kg/h) and outlet temperature (104°C). the energy consumption of the dryer was lowest when heat was recovered at the low air flow rate (6500 kg/h) and low outlet temperature (82°C).No problems were encountered with fouling or cleaning of the heat exchanger. the total pressure drop across the heat exchanger varied from 0.05–0.2 kPa depending on the air flow rate. This additional flow restriction resulted in an estimated 8% decrease in air flow rate but had negligible effect on energy consumption. the warm‐up time and the space required by the heat recovery unit were insignificant factors for this dryer. the payback period of the heat recovery system was estimated as 4.1–5.4 years with a rate of r

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1990.tb00038.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTEdible coatings controlling preservative migration from surface to food bulk could control surface microbial growth which is often the main cause of spoilage for many food products. In this paper we examine the potassium sorbate permeability behavior of chitosan, methyl cellulose and hydroxypropyl methyl cellulose based films. to gain an understanding of the permeation process, permeability determinations were done at 5, 24, 32 and 40°C. Permeability rates followed the Arrhenius activation energy model. A lack of breaking points in Arrhenius plots indicated that no morphological changes occur within these films in the 5 to 40°C temperature range. Activation energy values were found to be independent of film composition and were affected only by the solvent embedded in the film. This behavior was confirmed by analysis of the same permeability data using a modified Stokes‐Einstein equation.Methyl cellulose was the most promising diffusion barrier with a permeability constant of 3.4 and 1.4×10−8(mg/s cm2) (cm)/(mg/cm3) at 24 and 5°C, respectively. Electron microscopy was used to examine the morphological characteristics of these films and showed they have no visible pores or channels at magnifications up to

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1990.tb00039.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTMuscle pigment modifications during freezing and frozen storage of beef wrapped in high (polyethylene) and low (EVA/SARAN/EVA) gaseous permeability films were analyzed. Myo (Mb), oxy (MbO2) and metmyoglobin (MetMb) concentrations were determined using reflectance spectrophotometry. Results indicated that in polyethylene wrapped samples myoglobin oxygenation took place during freezing and the only reaction observed throughout frozen storage was MetMb production from MbO2. Autoxidation was interpreted as a first order kinetic reaction. Storage temperature effect on kinetic and equilibrium constants was analyzed; reaction enthalpy and activation energy were calculated. MbO2and MetMb production during beef oxygenation was represented as a consecutive first order reaction system determining previous vacuum storage time and temperature influence on oxygenation capacity. Vacuum packaging of frozen beef increased color stability maintaining MetMb concentration levels lower than those corresponding to just frozen samples wrapped in polyethylene.

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1990.tb00040.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTTemperature and moisture content predictions of two models of simultaneous heat and moisture transfer (SHMT) in foods with and without the assumption of volume change were compared. In the first model, thermophysical and transport parameters were kept constant. In the second model, these were taken as variable functions of temperature and moisture content. Comparison of the results of both models with and without shrinkage assumption showed that there can be significant differences in predicted moisture and temperature gradients, and average moisture contents and temperatures. Biot numbers for heat and mass transfer, and the extent of overall shrinkage with moisture loss are important factors affecting these differences. the predictions of the second model were compared to experimental drying data with shrinkage. the variable‐grid finite difference method can be used successfully to solve model equations involving volume change

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1990.tb00041.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1990.tb00042.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY