摘要:

To study the influence of particle structure on quality retention of hioproducts during thermal drying, the porous particles formed of albumin and solid carriers were dried in a vibm-fluidized bed dryn at different inlet air temperatures and different initial bulk porosities. Equations to predict temperature and moishrre content of panicles as well as the kinetics of biomass degradation were developed. The particle bulk porosity was incorporated into concentration-dependent moisture diffusivity model to estimate the erect of particle structure on product quality. The analysis of both calculated and experimental results indicates that the more porous structure promotes moisture diffusion, increases drying rate and finally improves the quality retention of bio-products. An extensive literature survey on quality retention issues during thermal drylng has been done.

ISSN:0737-3937    

DOI:10.1080/07373939608917190

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Convective drying is a cost saving presewtion technique for the production of bulk products. However, heat senstive bioprodusts may be damaged by convective drying. This paper presents the conception of a convective laboratory dryer with particular features for a simple and rapid examnination of deterioration processes during the drying of biomaterials. The drayer is described and results are given concerning the preservation of microorganisms for environmental applications. The results show that deterioration of the gram-negative bacteria Pseodomonas putida during drying is mainly caused by dehydration. Membrane damage is one of the dehydration deterioration mechanisms. Drying temperatures below 40°C ensure that thermal death of P. putida is neglegible.

ISSN:0737-3937    

DOI:10.1080/07373939608917191

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Different theoretical and experimental aspects of freeze drying of dairy biomaterials are reported. The following dairy biomaterials were chosen for investigations: three kefir bacterial cultures and one bacterial concentrate of a dairy vaccine. Experiments were performed both at one-region conductive or radiative heating and at combined two-region conductive-radiative heating. Emphasis was put on quality interactions between physical and biological properties of the material to be dried and freeze drying process parameters. Qualitative estimations of the following properties of biomaterials: a) colour, b)suppleness to caking and c) suppleness to scraping born the hot surface in dependence with the process parameters were performed using four-step subjective scales. On the basis of this estimations a synthetic quality criterion SQC was defined whose numerical value reflects general product quality. The results of mathematical modelling, numerical solution of the model and comparison with experimental data indicated that the process was heat transfer controlled and that the main factors resulting in good product quality and high SQC are low temperature of the conductive heated surface and vacuum chamber pressure affecting sublimation temperature. The influence of the sample freezing parameters on the elimination of the foaming or puffing and on the product quality was observed and examined. Furthermore, preliminary measurements of the dauy biomaterials viability after freeze drying were presented.

ISSN:0737-3937    

DOI:10.1080/07373939608917192

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In the context of a research on the quality of pasta made from soft wheat, reaction kinetics had to be measured at definite temperatures and water contents. It was chosen to realize such experiments in a pilot dryer. To be able to fix temperature and water content of product for a definite period of time, it was first necessary to determine sorption curves of pasta and a drying model including the values of apparent diffusivity of water at elevated temperatures.

ISSN:0737-3937    

DOI:10.1080/07373939608917193

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

An experimental air tunnel dryer was used to investigate the kinetics of moisture transport in potato cylinders (Solanum tuberasum). Acoordingly, the experimental results, represnting only falling-rate drying behaviour and hence. dehydration completely controlled by internal mass transfer, were interpreted on the basis of Fick's diffusional model for non-stedy state radial diffusion. The effects of air velocity and temperature on the drying rate were studied. with he temperature being the principal controlling factor. Analysis of the drying curves by the method of slopes resulted in a variable effective moisture diffusivity. Shrinkage as a function of moisture content under various drying conditions was investigated. The volumetric shrinkage of the samples was affected mainly by air velocity. whilst air temperature had a negligible effect. Good agreement was obtained between the experimental apparent density data and the predicted correlation.

ISSN:0737-3937    

DOI:10.1080/07373939608917194

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Luikov approach was applied to predict drying time and temperature of a droplet containing liquid substrate of entobacterin in the falling drying rate period. Analytical expressions describing both average and local temperatures of the particle in the drying process were derived and solved. Constants necessary to solve the equations, describing certain material properties and material moisture bonding were found in simple experiments. An experimental relationship of Rebinder number and moisture content of the material enabled to calculate changes of average droplet temperature in the falling drying rate period. Analytical solutions of heat transfer equations for shrinkage core model both for a linear and exponential change of moisture content of the droplet in the drying process were delivered. Employing experimental heat transfer coefficient, drying time and droplct temperature field were determined. Comparison of experimental and predicted drying times as well as droplet temperatures shows small discrepancy. Results obtained can be used to predict quality of labile products in the course of drying.

ISSN:0737-3937    

DOI:10.1080/07373939608917195

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The UN estimates that 6.4 billion people will be living on Earth by the year 2000. As a consequence, dried biomaterials demand will rise and equipments will have to be built or redesigned to accomadate changes. The design and innovations on industrial dryers require fundamental knowledge conceived in laboratory units. The new heat pump dryer operates at a wide relative humidity and the air temperature is adjustable from –20 to 100'C. Above and belw freezing point drying modes are done in the same plant which allows the control of biomaterial properties. The technique consists of two stages, unbound weakly held water removal by freeze drying. and tightly bound moisture desorption by medium temperature drying. The fluidized and shelf heat pump dryers have the required features to dry heat sensitive biomaterials. The dryers were built and extensive research on biomaterials has been conducted at The Norwegian Institute of Technology. Many emeriments were done on effect of heat pump drying conditions on–enrime and biological active bacteria solutions, fruits, cod fish, fish feed and shrimps. At optimum heat drying conditions, the bacteria Rhodococcus reached 100% viability and dried biomolecules attained full biolosical activity. The heat pump dryer allowed adjustment of the bio–mterial properties and quality according to its phase, shape and size. Dried samples showed improvements on survival rate. rehydration, colour, hardness and mono–multimolecular sorption isotherms over poorly dried products. Beneficial results were achieved for nearly all tests. This indicates that the heat pump dryer application has high potential in processing heat sensitive biomaterials.

ISSN:0737-3937    

DOI:10.1080/07373939608917196

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Tomato concentrate and baker's yeast suspension were dried in the laboratory scale Mechanically Spouted Bed dryer with inert packing. Due to a large contact surface provided by the inert particles, very fast drying process can be achieved, ifthe thickness of the wet coating formed on the surface of the inert packing is film–like. The diffution resistance can be then considered negligible and drying can be performed at “quad–constant” rate. Derived fiom hydrodynamic characteristics the contact time between hot air and the wet coating is very short, therefore gentle drymg process can be performed. The quality of the dried yeast was controlled by counting the living cells (relative viabilny) and by measurement of the dough rise time. During continuous drying of thermoplastic tomato pure the “case hardening” periods could be shortened and tomato powder with insignificant quality loss was produced.

ISSN:0737-3937    

DOI:10.1080/07373939608917197

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Two novel approaches to modelling of thermal deterioration processes have been proposed in the paper.

ISSN:0737-3937    

DOI:10.1080/07373939608917198

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Food drying and dewatering raises a growing interest because of increasing requirements in quality, specially in the production of ingredients and additives for food formulation. Heat and mass transfers, as well as mechanical phenomena and reactions kinetics induced by these transfers must be more and more carefully controlled during drying and storage.

ISSN:0737-3937    

DOI:10.1080/07373939608917199

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor