Investigating the glassy to rubbery transition of polydextrose and corn flakes using automatic water vapor sorption instruments, DSC, and texture analysis

Li, Qingruisi

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Description

Title

Investigating the glassy to rubbery transition of polydextrose and corn flakes using automatic water vapor sorption instruments, DSC, and texture analysis

Author(s)

Li, Qingruisi

Issue Date

2010-08-20T17:55:39Z

Director of Research (if dissertation) or Advisor (if thesis)

Schmidt, Shelly J.

Department of Study

Food Science & Human Nutrition

Discipline

Food Science & Human Nutrition

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• critical relative humidity
• isotherm
• glass transition temperature
• dynamic vapor sorption (DVS)
• differential scanning calorimetry (DSC)

Abstract

The aim of this study was to investigate the usefulness of automated sorption isotherm methods for determining the glassy to rubbery transition in a model amorphous food material, polydextrose. The automated sorption isotherms were obtained from 20 to 40°C at 5°C intervals using dynamic vapor sorption (DVS). The DVS ramping isotherm was obtained at a linearly increasing relative humidity (RH), 2%RH/hr, from 10 to 85%RH. The DVS equilibrium isotherm was obtained at twelve RH values using a dm/dt criterion of 0.0005%. The traditional saturated salt slurry isotherm was obtained at 25°C using ten saturated salt slurries, with RH values ranging from 11.3 to 84.3%. The RHc was defined as the %RH that exhibited the fastest change in slope determined by the maximum of the second derivative of the isotherm curve. The RHc and temperature values were plotted in a state diagram and compared to the differential scanning calorimetry (DSC) glass transition temperature (Tg) values. As predicted from theory, RHc values decreased as temperature increased. As plotted on the state diagram, the RHc values were similar to the DSC Tg values. At the same temperature, the RHc order for the isotherms was traditional < DVS equilibrium < DVS ramping, with the RHc values depending on the time the material was exposed to the different RH conditions. Since the automated sorption isotherm methods showed promise for being a practical tool to determine the location of the glassy to rubbery transition for polydextrose, the model was applied to a complex amorphous food system, corn flakes. In addition, textural analysis was conducted in order to relate the mechanical properties of corn flakes to the glassy to rubbery transition results from the thermal method and the automated sorption isotherm methods. The results from corn flakes showed that the AquaSorp dynamic dewpoint (DDI) and DVS ramping isotherms represented the non-equilibrated isotherm whereas the DVS equilibrium and saturated salt slurry isotherms represented the equilibrated isotherm. The difference between the isotherms was most likely associated with the very dense laminated corn flake matrix and the time-dependent nature of the sorption process. The results from the textural analysis performed at ambient temperature (25°C) and the saturated salt slurry method were similar, indicating the glassy to rubbery transition for corn flakes at 25°C occurred at a relative humidity of 37.75±0.64%. The DVS equilibrium method coupled with textural analysis might be a useful tool to replace the traditional saturated salt slurry method to routinely determine the location of the glassy to rubbery transition for complex food systems.

Graduation Semester

2010-08

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Copyright 2010 Qingruisi Li

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