State Diagram of Crystallized Date-Syrup: Freezing Curve, Glass Transition, Crystals-Melting and Maximal-Freeze-Concentration Condition

Differential scanning calorimetry (DSC) was used to determine phase transitions of freeze-dried plums. Samples at low and intermediate moisture contents, were conditioned by adsorption at various water activities (0.11≤aw≤0.90) at 25°C, whereas in the high moisture content region (aw>0.90) samples were obtained by direct water addition, with the resulting sorption isotherm being well described by the Guggenheim-Anderson-deBoer (GAB) model. Freeze-dried samples of separated plum skin and pulp were also analysed. At aw≤0.75, two glass transitions were visible, with the glass transition temperature (Tg) decreasing with increasing aw due to the water plasticising effect. The first Tg was attributed to the matrix formed by sugars and water. The second one, less visible and less plasticised by water, was probably due to macromolecules of the fruit pulp. The Gordon-Taylor model represented satisfactorily the matrix glass transition curve for aw≤0.90. In the higher moisture content range Tg remained practically constant around Tg′ (−57.5°C). Analysis of the glass transition curve and the sorption isotherm indicated that stability at a temperature of 25°C, would be attained by freeze dried plum at a water activity of 0.04, corresponding to a moisture content of 12.9% (dry basis).

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State Diagrams of Two Thai Rice Varieties Differing in Amylose Contents

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.848.89 ◽

2016 ◽

Vol 848 ◽

pp. 89-94

Author(s):

Chutamas Boonrod ◽

Khongsak Srikaeo

Keyword(s):

Glass Transition ◽

Freezing Point ◽

Amylose Content ◽

State Diagram ◽

The State ◽

Published Data ◽

Rice Varieties ◽

State Diagrams ◽

Physicochemical Changes ◽

Solids Content

State diagram is a map of the different states of a food polymer as a function of water or solids content and temperature. The main advantage of drawing map is in identifying different states of a food polymer which helps in understanding the complex changes when food's water content and temperature are changed. It also assists in identifying food’s stability during storage as well as selecting suitable conditions for processing. This research successfully developed the state diagrams of two Thai rice varieties differing in amylose contents (San-pah-tawng and Phitsanulok 2) by measuring the glass line; glass transition temperature (Tg) vs. solids content, freezing curve; initial freezing point vs. solids content by using the differential scanning calorimetry (DSC) method. Rice with different amylose content exhibited similar freezing curves and glass transition patterns. The state diagrams obtained in this study are in agreement with previously published data. They can be useful in optimizing the drying and freezing processes as well as studying the physicochemical changes during storage of rice.

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Glass transition and state diagram for fresh and freeze-dried Chinese gooseberry

Journal of Food Engineering ◽

10.1016/j.jfoodeng.2007.05.024 ◽

2008 ◽

Vol 84 (2) ◽

pp. 307-312 ◽

Cited By ~ 53

Author(s):

Haiying Wang ◽

Shaozhi Zhang ◽

Guangming Chen

Keyword(s):

Glass Transition ◽

State Diagram ◽

Freeze Dried

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Empirical and theoretical models of equilibrium and non-equilibrium transition temperatures of supplemented phase diagrams in aqueous systems (IUPAC Technical Report)

Pure and Applied Chemistry ◽

10.1351/pac-rep-09-10-24 ◽

2010 ◽

Vol 82 (5) ◽

pp. 1065-1097 ◽

Cited By ~ 33

Author(s):

Horacio R. Corti ◽

C. Austen Angell ◽

Tony Auffret ◽

Harry Levine ◽

M. Pilar Buera ◽

...

Keyword(s):

Glass Transition ◽

Aqueous Solutions ◽

Standard Procedure ◽

Theoretical Models ◽

Transition Curve ◽

Concentrated Solution ◽

Equilibrium Transition ◽

Natural Foods ◽

Freezing Curve ◽

Non Equilibrium

This paper describes the main thermodynamic concepts related to the construction of supplemented phase (or state) diagrams (SPDs) for aqueous solutions containing vitrifying agents used in the cryo- and dehydro-preservation of natural (foods, seeds, etc.) and synthetic (pharmaceuticals) products. It also reviews the empirical and theoretical equations employed to predict equilibrium transitions (ice freezing, solute solubility) and non-equilibrium transitions (glass transition and the extrapolated freezing curve). The comparison with experimental results is restricted to carbohydrate aqueous solutions, because these are the most widely used cryoprotectant agents. The paper identifies the best standard procedure to determine the glass transition curve over the entire water-content scale, and how to determine the temperature and concentration of the maximally freeze-concentrated solution.

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