SIMULTANEOUS WATER AND SOLUTE TRANSPORT IN SHRINKING MEDIA - PART 2

A simple compartmental model of simultaneous water and solute transport was developed on agar gel cubes, for particular situations in which high water loss is accompanied by shrinkage and flux interaction. The model provided a good fit for the different situations tested, and proved to behave adequately in a wider application field. Furthermore, it made it possible to obtain a simulation of the evolution of the solute contents in both compartments which was consistent with the previous studies.     

Food Drying and Dewatering

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.

This chapter relates recent advances in

- drying of solids

- spray-drying

- drum-dryine

- superheateded steam drying

- osmotice dehydration

- hot oil immersion drying     

SIMULTANEOUS WATER AND SOLUTE TRANSPORT IN SHRINKING MEDIA - PART 1

Agar model gel cubes, with initial low solute content, were soaked in higher concentration solutions. The influence of the concentration and molecular weight of the solute in the soaking solution, the temperature. the agar and solute content of the model food on water loss and solute gain rates were observed. The achievement of a prevailing dewatering effect with only marginal solute pick-up proved to be related to a inverse relationship between the cross-flows of water and solute, reinforced by shrinkage. As a preliminary to further modelling, reasonable assumptions were drawn from experimental result analysis.     

SIMULTANEOUS WATER AND SOLUTE TRANSPORT IN SHRINKING MEDIA - PART 3

Agar agar model gel cubes, with initial low sucrose content, were soaked in 40% and 60% sucrose solutions. In both situations, sucrose profiles were obtained by slicing and HPLC analysis. Results provided an experimental validation for the concentrated surface layer assumption and the compartmental model of mass transfer, described in Parts 1 and 2. respectively.     

Food Drying and Dewatering

ABSTRACT

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.

This chapter relates recent advances in

- drying of solids

- spray-drying

- drum-dryine

- superheateded steam drying

- osmotice dehydration

- hot oil immersion drying     

MULTICRITERIA OPTIMIZATION OF FOOD PROCESSING COMBINING SOAKING PRIOR TO AIR DRYING

Abstract

A method for multicriteria optimization is illustrated by the example of apples processed by Dewatering and Impregnation Soaking (DIS) in concentrated aqueous sucrose solutions, and then air dried. The influence of the product history (modifications linked to DIS treatment) on its behaviour during drying process is assessed according to an experimental design. Five operating variables are taken into account: temperature, solution concentration and soaking time for DIS pre-step, and temperature and relative humidity for air drying. Results show a limiting effect of internal water transport by the sucrose impregnated superficial layer. This effect can be reduced by drying at high temperature (80°C). On the other hand, the relative humidity of air has little influence on the behaviour of soaked materials. Multicriteria optimization takes into account six criterias and shows that stable and optimal quality products can be obtained at interesting energetic costs and for a short processing time duration (50 to 300 min).     

Etude des parametres de controle et de commande du procede de deshydratation–impregnation par immersion, sur systeme probatoire automatise: application au traitement des pommes “Golden”

The work presented here is a study aiming at the control and checking of dewatering and impregnation soaking process (DISP). The studies are carried out using an automatic experimental system. Apples of the “Golden” variety are used exclusively. Two kinds of agitation system are studied; mechanical agitation using a vertical screw without an end, and hydraulic agitation. There is hardly any difference between the two kinds of agitation; parameter variations are almost the same. These results are compared with those obtained in agitated thermostated water-bath system and they show that mass transfers are better on the experimental system than with the water-bath system. Temperature influences were studied for the agitated thermostated water-bath system only. They show that the increase of temperature favours water loss and sugar intake. We have shown that during experiments with old syrup, only the conductivity of syrup is higher but kinetics of water loss, solute intake and weight reduction are not significantly affected.     

Transport phenomena in immersion-cooled apples

The effect of immersion chilling and freezing (ICF) process parameters (solution temperature, concentration and composition, initial food temperature) on heat and mass transfer was studied on apple cylinders dipped into a sodium chloride aqueous solution, with particular emphasis on the unsteady-state period (first hour of treatment). Food behaviour was characterized for various thermal processes; the levels of salt impregnation in chilling and supercooling conditions, at 2 °C and −10 °C, respectively, were similar (3% i.m. after 1 h of processing) and much higher than in freezing at −17.8 °C (0.6% initial mass for the same processing time). Further control of solute entrance in freezing conditions could be achieved through food surface treatments, including precoating with cold water before ICF; use of a complex immersion solution containing a high molecular weight of solute; quick freezing of the outer food layer. Above all, the frozen water fraction inside the food was found to be an important factor governing solute entrance in freezing conditions.     

INDIRECT MEASUREMENT AND CONTROL OF MOISTURE CONTENT DURING DEHYDRATION PERFORMED BY FRYING

ABSTRACT

Frying is one of the way for performing drying of food material that permits to obtain very short duration. However the control of such operation is difficult because of the immersion of product into hot oil bath that imply difficult or impossible sensors implementation. Such problems are encoutered for Dehydration Soaking Process (DISP). In the case of Batch drying using frying of food stuffs, an original approach is presented. An indirect measurement of moisture content is performed as a combination of easy to do oil bath temperature mesasurement and an estimator. Validation is provided and performance is well established. Because of the ability of moisture content real time measurements, a control strategy is studied and put into practice. An optimal predictive controller is proprosed, able to put into practice several kind of control objectives. Results are discussed and extension of the strategy is introduced.     

SIMULTANEOUS WATER AND SOLUTE TRANSPORT IN SHRINKING MEDIA - PART 3

Agar agar model gel cubes, with initial low sucrose content, were soaked in 40% and 60% sucrose solutions. In both situations, sucrose profiles were obtained by slicing and HPLC analysis. Results provided an experimental validation for the concentrated surface layer assumption and the compartmental model of mass transfer, described in Parts 1 and 2. respectively.