VARIATIONS IN ALFALFA JUICE SOLUTE CONCENTRATIONS AS WATER IS EVAPORATED

ABSTRACT

Alfalfa juice was extracted from plants during the graving phases of the first and second crops. The alfalfa juice was dried and solute concentrations were measured periodically during the process using freezing point depression (FPD) as an indicator. Solute/solvent weight ratios were calculated from the freezing point depression of fresh unconcentrated 'uice extracted from both firsc and second crops. At the time of harvest, tie FPD was a function of this ratio. The first and second crops behaved distinctively different during the drying process, with the second having a larger soluce concentration and a greater FPD at a given moisture content. The appearance of preci itate during the drying process and the general1 large FPD makes this materiay a questionable product for drying vitg low temperature processes.     

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.     

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.     

PEAR DRYING PROCESS ANALYSIS: DRYING RATES AND EVOLUTION OF WATER AND SUGAR CONCENTRATIONS IN SPACE AND TIME

ABSTRACT

Dried pears are produced in Portugal by a traditional solar drying process and, because they represent unquestionable regional economic interest, some studies are being conducted in order to convert their production to industrial drying methods. In this work the main mass transfer phenomena occurring during drying of pears are investigated. Experiments were carried out to determine the time evolution of the radial profiles of water and sugar content. The drying rates were also studied at constant drying temperatures of 30, 40 and 50°C. The results enable to conclude that the concentration profiles of water and sugar, both in space and time, follow an expected pattern if one takes into account the rates of water removal and the diffusion mechanisms. These also allow to explain why the sugar concentration increases in the periphery of the fruit. The drying rate curves obtained are typical, with the drying process at 30°C being more gradual but also much slower than that at 50°C.     

PEAR DRYING PROCESS ANALYSIS: DRYING RATES AND EVOLUTION OF WATER AND SUGAR CONCENTRATIONS IN SPACE AND TIME

Dried pears are produced in Portugal by a traditional solar drying process and, because they represent unquestionable regional economic interest, some studies are being conducted in order to convert their production to industrial drying methods. In this work the main mass transfer phenomena occurring during drying of pears are investigated. Experiments were carried out to determine the time evolution of the radial profiles of water and sugar content. The drying rates were also studied at constant drying temperatures of 30, 40 and 50°C. The results enable to conclude that the concentration profiles of water and sugar, both in space and time, follow an expected pattern if one takes into account the rates of water removal and the diffusion mechanisms. These also allow to explain why the sugar concentration increases in the periphery of the fruit. The drying rate curves obtained are typical, with the drying process at 30°C being more gradual but also much slower than that at 50°C.