Progress 09/15/01 to 09/30/04
Outputs
Moisture uptake into amorphous foods, in some cases followed by sugar crystallization, is a problem in many commercial food applications. However, our understanding of the exact processes of moisture diffusion and matrix relaxation are not clearly understood. This project has helped clarify the relative impacts of these two mechanisms during storage of amorphous sugar-based food products. Obj. 1: Quantify moisture uptake into sugar glasses. We have been working with Nicolet Instruments in Madison and have developed an approach that allows us to measure water content at any time and spatial dimension during sorption into a flat, two-dimensional sugar glass. We used an FT-NIR microscope technique to measure water content at incremental distances from a surface exposed to humidity to generate data for moisture content versus distance and time. Several different sugar mixtures stored at different temperature and RH were studied. Conditions of 53% RH and higher level of
corn syrup (70:30 sucrose to corn syrup), moisture penetration appears to follow approximately Fickian behavior. At other conditions, notably higher RH (75%) and higher corn syrup level (50:50 sucrose to corn syrup), there is a clear surface layer containing high moisture with a sharp demarcation front separating the interior glassy matrix with low moisture content. In these systems, the syrup front can be seen moving slowly in towards the center of the sample separating regions of high and low moisture content. Penetration of water in this case dos not appear to follow Fickian diffusion laws. In systems low in corn syrup, the syrup layer is seen to crystallize while the moisture front continues to move into the glassy matrix. The semi crystalline region behind the syrup front loses moisture (to the air) after crystallization, and essentially we measure a spike of moisture moving into the sample as function of exposure time. Obj. 2: Quantify crystallization kinetics in amorphous sugar
systems. Concentrated sugar syrups (3.5% H2O) were applied to a well in a microscope slide preparation, cooled into the glassy state and then held at temperatures above Tg (from 60 to 110C) to measure onset time for nucleation and nucleation rate. Induction time decreased and nucleation rate increased as temperature increased, in contrast with more fluid systems, which exhibit a minimum in induction time with temperature (due to competing effects of supersaturation and molecular mobility). The data were predicted reasonably well by both the heterogeneous nucleation model and the WLF equation. Obj. 3: Evaluate effects of other components (corn syrup). Completed within the scope of Objectives 1 and 2.
Impacts
The stability of sugar-based amorphous products like hard candy and milk powders is dependent on the rate of moisture sorption from the environment and the rate of crystallization of the sugars contained within the product. Stickiness and graining cause undesired changes in the appearance and texture of these products. The results of this work will provide a better understanding of the rate of moisture penetration into a relaxing matrix and quantitative measures of sugar crystallization.
Publications
- Levenson, D and R.W. Hartel, Nucleation of Amorphous Sucrose-Corn Syrup Mixtures, J. Food Eng., 69(1), 9-15 (2005).
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Progress 01/01/03 to 12/31/03
Outputs
Obj. 1: Quantify moisture uptake into sugar glasses. We have been using an FT-IT microprobe method of measuring water content in a sugar glass exposed on one side to air at different RH. This method allows us to quantify the moisture content at any time and any distance into our 1-dimensional sugar film. From this data, we can model the diffusion of water into a sugar glass. We have generated moisture data for a range of sugar glasses stored at different RH. At low RH (ca. 50%), we see a general increase in H2O at all points within the system, whereas at higher RH (ca. 80%), there is a clear demarcation between a layer of syrup and stable glass at greater depths. Our preliminary modeling work shows that the glass relaxation as moisture migrates into the glass is a limiting factor to diffusion into the matrix and a two-step model is needed. Fickian diffusion is not able to predict water migration rates in these systems, although we need to do a bit more modeling to
verify this preliminary finding. Obj. 2: Quantify crystallization kinetics in amorphous sugar systems. This part of the study has been completed, with a manuscript submitted for publication. Concentrated sugar syrups (3.5% H2O) were applied to a well in a microscope slide preparation, cooled into the glassy state and then held at temperatures above Tg (from 60 to 110C) to measure onset time for nucleation and nucleation rate. Induction time decreased and nucleation rate increased as temperature increased, in contrast with more fluid systems, which exhibit a minimum in induction time with temperature (due to competing effects of supersaturation and molecular mobility). The data were predicted reasonably well by both the heterogeneous nucleation model and the WLF equation. Obj. 3: Evaluate effects of other components (corn syrup). The effects of different types and levels of corn syrup on water migration into sugar glasses are still being studied. Experiments are underway to look at
several different systems of ingredients. However, due to the time commitment on the FT-IR microprobe (we pay to use the equipment at Nicolet), only a limited number of combinations will be possible. Further work is needed to fully understand ingredient interactions. The effects of different corn syrups on sucrose nucleation were studied (Objective 2). Within experimental error, no differences in nucleation were observed due to use of different DE corn syrups.
Impacts
The shelf life of many foods is governed by moisture migration into the matrix and subsequent quality loss. The results of this work are providing a more fundamental picture of moisture uptake in amorphous foods and will help control product quality.
Publications
- No publications reported this period
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Progress 01/01/02 to 12/31/02
Outputs
The main objectives of this project are to quantify rates of moisture penetration into sugar glasses, and to quantify the mechanisms and kinetics of nucleation in these systems. The effects of various additives on moisture penetration and crystallization will also be quantified. The specific objectives are: 1. To quantify moisture uptake into sugar glasses by monitoring moisture change with time into a one dimensional system. This simple geometry will allow easy modeling of moisture penetration into sugar glasses. 2. To quantify crystallization kinetics in amorphous sugar systems. The mechanisms and kinetics of crystallization will be quantified as function of moisture content and temperature. 3. To evaluate the effects of other components (other saccharides, proteins, salts, etc.) of importance in foods on the uptake of moisture and crystallization from amorphous sugar systems. For sucrose glasses, we will study corn syrups (practical application) and specific
oligosaccharide/maltodextrin (model systems), whereas for lactose systems, the effects of other milk components will be studied. Induction times and nucleation rates of sucrose crystals from the amorphous state in a mixture of sucrose and corn syrup have been measured. Three different types of corn syrups have been used with different degrees of hydrolysis to determine the effects of oligosaccharide chain length on nucleation. The results clearly show the strong effect of temperature on nucleation, with induction time decreasing and nucleation rate increasing significantly as temperature increases. Some differences between corn syrup types have been noted although further analysis is needed to verify their significance. The data appear to be fitted well by the WLF equation. Work on Objective 1 has begun with preliminary analysis of moisture penetration into sugar glasses using an IR microscope probe technique. Further work is underway to verify the measurement technique.
Impacts
The stability of sugar-based amorphous products like hard candy and milk powders is dependent on the rate of moisture sorption from the environment and the rate of crystallization of the sugars contained within the product. Stickiness and graining cause undesired changes in the appearance and texture of these products. The results of this work will provide a better understanding of the rate of moisture penetration into a relaxing matrix and quantitative measures of sugar crystallization.
Publications
- No publications reported this period
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Progress 01/01/01 to 12/31/01
Outputs
The main objectives of this project are to quantify rates of moisture penetration into sugar glasses, and to quantify the mechanisms and kinetics of nucleation in these systems. The effects of various additives on moisture penetration and crystallization will also be quantified. The specific objectives are: 1. To quantify moisture uptake into sugar glasses by monitoring moisture change with time into a one dimensional system. This simple geometry will allow easy modeling of moisture penetration into sugar glasses. 2. To quantify crystallization kinetics in amorphous sugar systems. The mechanisms and kinetics of crystallization will be quantified as function of moisture content and temperature. 3. To evaluate the effects of other components (other saccharides, proteins, salts, etc.) of importance in foods on the uptake of moisture and crystallization from amorphous sugar systems. For sucrose glasses, we will study corn syrups (practical application) and specific
oligosaccharide/maltodextrin (model systems), whereas for lactose systems, the effects of other milk components will be studied. We have begun this project by working on the second objective. We are manufacturing sugar glasses in the form of thin disks on microscope slides. The disks are exposed to elevated temperatures (40 to 80C) for brief periods of time to promote nucleation and then cooled rapidly back to room temperature to prevent further crystallization. The nucleation rate will be determined by counting the number of nuclei formed per unit time interval. With this data, we will be able to evaluate several models of crystallization from the glassy state and evaluate the effects of various formulation additives for controlling crystallization. Work on Objective 1 will begin in the near future in conjunction with the development personnel at Nicolet Instruments.
Impacts
The stability of sugar-based amorphous products like hard candy and milk powders is dependent on the rate of moisture sorption from the environment and the rate of crystallization of the sugars containined within the product. Stickiness and graining cause undesired changes in the appearance and texture of these products. The results of this work will provide a better understanding of the rate of moisture penetration into a relaxing matrix and quantitative measures of sugar crystallization.
Publications
- No publications reported this period
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