Progress 10/01/98 to 09/30/05
Outputs
The overall objective of this research project is to study the water and biopolymer mobility (as monitored by NMR relaxation rates and self-diffusion constant) and the glass transition temperature (Tg as monitored by differential scanning calorimetry) of model food systems. The focus of the work done during this past year was to: 1) finish the research and publication associated with the recently developed technique (Dynamic Vapor Sorption-Fast Gas Chromatography-Flame Ionization Detection [DVS-Fast GC-FID]) designed to rapidly and continuously measure the extent of volatile release that occurs from encapsulated glassy matrices as a function of relative humidity and temperature, and 2) to collect preliminary Tg data on commercially-available glassy food systems for the establishment of a Tg database. Three publications are in print regarding the operation and reliability of the DVS-GC-FID system, which are listed in the publications section of this report. Regarding
the development of a Tg database, a variety of commercially available amorphous carbohydrate glasses, such as Brachs Butterscotch, cherry Jolly Ranchers, Brachs Starlight Mints, grape Jolly Ranchers, and Halls Honey-Lemon cough drops, were studied. Samples were prepared by crushing and sifting to a uniform particle size using standard mesh screens (between 0.2972 and 0.5944 mm). Initial sample moisture contents were determined by vacuum oven. Aw values were measured using an AquaLab Series 3 TE Aw Meter. Initial Tg values were determined using approximately 8 mg of product in sealed differential scanning calorimetry (DSC) pans using a TA Instruments DSC model 2920. Humidified samples were prepared by placing 8 mg of product in unsealed DSC pans and exposing them to 55% and 65% RH at 25C for 1,440 minutes (one day) using Dynamic Vapor Sorption. The pans were then sealed and Tg values were determined using the DSC model 2920. The Tg values (midpoint) of the unhumidified samples ranged
from 31.48 to 55.93 C. Increases in moisture content after 1,440 min at 55% RH and 65% RH were, on average, 7.29% and 11.11% (wb), respectively. Tg values (midpoint) after 55% RH ranged from -4.46 to 15.78 C, and after 65% RH ranged from 30.44 to -4.59C. Thus, moisture sorption caused Tg values to drop below ambient temperature, resulting in products that were no longer glassy and hard, but sticky at room temperature.
Impacts
Publication of the DVS-Fast GC-FID method will allow others to test and implement this new flavor release method. The development of a Tg database for commercially-available amorphous carbohydrate glasses will make these values available for others to use and result in improved products that rely on a high Tg value for their stability.
Publications
- Bohn, D.M., Cadwallader, K.R. and Schmidt, S.J. 2005. Using DSC, DVS-DSC, and DVS-fast GC-FID to evaluate the physiochemical changes that occur in artificial cheery Durarome upon humidification. Journal of Food Science, 70(2):E109-116.
- Bohn, D.M., Cadwallader, K.R. and Schmidt, S.J. 2005. Development and validation of a Dynamic Vapor Sorption-Fast Gas Chromatography-Flame Ionization Detection method for rapid analysis of volatile release from glassy matrices. Journal of Agricultural and Food Chemistry, 53(8):3149-3155.
- Bohn, D.M., Schmidt A.R. and Schmidt, S.J. 2005. Uncertainty analysis of a Dynamic Vapor Sorption-Fast Gas Chromatography-Flame Ionization Detection method for rapid analysis of volatile release from glassy matrices. Journal of Agricultural and Food Chemistry, 53(11):4493-4502.
|
Progress 01/01/04 to 12/31/04
Outputs
The overall objective of this research project is to study the water and biopolymer mobility (as monitored by NMR relaxation rates and self-diffusion constant) and the glass transition temperature (Tg as monitored by differential scanning calorimetery) of model food systems. The focus of the research done during this past year was to investigate the robustness of a recently developed technique (Dynamic Vapor Sorption-fast Gas Chromatography-Flame Ionization Detection [DVS-GC-FID]) designed to rapidly and continuously measure the extent of volatile release that occurs from encapsulated glassy matrices as a function of relative humidity and temperature. A vital, but often overlooked aspect of method development is determination of measurement uncertainty. Thus, the objective of this study was to assess the variability of the DVS-fast GC-FID method by performing uncertainty analysis. Artificial cherry Durarome, containing approximately 5-10% (w/w) benzaldehyde, was used
as the model system. Triplicate samples progressed through a two-step method in the DVS. In step one, samples were allowed to equilibrate to the target temperature (15, 25, or 35 degrees C) at 30% relative humidity. In step two, samples were exposed to a target relative humidity (40, 50, 60, 70, 80, or 90%) for 600 minutes during which the amount of volatile released was measured. Uncertainty analysis showed that DVS-fast GC-FID method uncertainty was significantly smaller than sample uncertainty, indicating that the variability in the physical properties of the sample had a dominant impact on the overall uncertainty of the volatile retention results obtained. Uncertainty analysis also indicated that, in the early part of volatile release, when the cumulative mass of benzaldehyde measured is small, the variance associated with the mass of benzaldehyde measured by the DVS-fast GC-FID is the largest source of variance in the calculated benzaldehyde retention. However, as the experiment
progressed and as the mass of volatile released (and measured) increased, the initial mass of benzaldehyde in the sample became the largest source of variance in the calculated benzaldehyde retention.
Impacts
The uncertainty associated with the DVS-fast GC-FID method itself was found to be small, which is an important finding that further supports the reliability and usefulness of this new method.
Publications
- Bohn, D.M., Cadwallader, K.R. and Schmidt, S.J. 2004. Using DSC, DVS-DSC, and DVS-fast GC-FID to evaluate the physiochemical changes that occur in artificial cheery Durarome upon humidification. Journal of Food Science (Accepted).
- Bohn, D.M., Cadwallader, K.R. and Schmidt, S.J. 2004. Development and validation of a Dynamic Vapor Sorption-fast Gas Chromatography-Flame Ionization Detection method for rapid analysis of volatile release from glassy matrices. Journal of Agricultural and Food Chemistry (Submitted).
- Bohn, D.M., Schmidt A.R. and Schmidt, S.J. 2004. Uncertainty analysis of a Dynamic Vapor Sorption-fast Gas Chromatography-Flame Ionization Detection method for rapid analysis of volatile release from glassy matrices. Journal of Agricultural and Food Chemistry (Submitted).
|
Progress 01/01/03 to 12/31/03
Outputs
The overall objective of this research project is to study the water and biopolymer mobility (as monitored by NMR relaxation rates and self-diffusion constant) and the glass transition temperature (Tg as monitored by differential scanning calorimetery) of model food systems. The focus of the research done during this past year was to investigate the relationship between the glass transition temperature and flavor release in amorphous carbohydrate systems. Incorporating volatile compounds into amorphous matrices is a common practice within the food industry due to the ability of the amorphous matrix to retain a high percentage of the volatile. However, the amorphous structure can be disrupted when exposed to an increase in relative humidity and/or temperature that results in the ambient temperature to be above the glass transition temperature (Tg). This structural disruption, in turn, results in volatile release. Dynamic Vapor Sorption (DVS) is a fully automated system
that can expose a food matrix to select relative humidity (ranging from 0 to 98%) and temperature (ranging from 5 C to 85 C) conditions as specified by the researcher. Using DVS technology for humidification and temperature regulation, the impact of the depression of Tg on volatile retention by a model amorphous encapsulating matrix (Durarome, Firmenich) was studied. Initial moisture content of the sample was determined by Karl Fischer. Water activities were measured using an AquaLab Series 3 TE Aw Meter. Approximately 10mg of sample were placed in the DVS 2000 and exposed to relative humidities between 40% and 90% for varying lengths of time at 25 C. The purge air containing the volatile component was expelled from the DVS, and the extent of volatile release was measured using purge and trap gas chromatography-flame ionization detection technology connected to the DVS. The Tg values of the humidified samples were determined using a TA Instruments Differential Scanning Calorimeter
model 2920. Results showed that as moisture was sorbed and Tg depressed below ambient temperatures, volatile release occurred rapidly and in large quantities. The initial moisture content (db) was 4.67% and the initial Tg was approximately 28.37 C. At all relative humidities, sorption of merely 0.70% caused the Tg to drop below ambient temperature (25 C) to 10.26 C; simultaneously, a burst of volatiles was released from the amorphous matrix.
Impacts
The glass transition temperature (Tg) is a pivotal temperature at which radical physical and chemical changes can occur in a food system. This study explores the relationship between the glass transition temperature and volatile release in amorphous carbohydrate matrices.
Publications
- Bohn, D.M., Cadwallader, K.R. and Schmidt, S.J. 2003. Measurement of volatile release from an amorphous carbohydrate matrix as a function of relative humidity using dynamic vapor sorption technology. June 2003. 64rd Annual Institute of Food Technologists, Chicago, IL.
|
Progress 01/01/02 to 12/31/02
Outputs
The overall objective of this research project is to study the water and biopolymer mobility (as monitored by NMR relaxation rates and self-diffusion constant) and the glass transition temperature (Tg as monitored by differential scanning calorimetery) of model food systems. The focus of the research done during this past year was to explore the effect of relative humidity on the Tg of commercially available amorphous carbohydrate glasses. Maintaining the glass transition temperature (Tg) of amorphous carbohydrate food products above ambient temperature is an important quality control factor. These products gain moisture when exposed to relative humidities greater than their innate water activity (Aw). Water acts as a plasticizer when adsorbed by low-moisture, hygroscopic, amorphous foods. Hard candies are traditional examples of amorphous carbohydrate glasses. The average hard candy Aw is less than 0.5, whereas the average annual relative humidity in the United
States is 61%, implicating the potential for hard candies to sorb moisture from the air. A variety of commercially available amorphous carbohydrate glasses, such as Brach's Butterscotch, Brach's Starlight Mints, cherry and grape Jolly Ranchers, and Halls Honey-Lemon cough drops, were studied. Sample were prepared by crushing and sifting to a uniform particle size (between 0.2972 and 0.5944 mm). Initial sample moisture contents were determined by vacuum oven and Karl Fischer. Aw values were measured using an AquaLab Series 3 TE Aw Meter. Initial Tg values were determined using approximately 8mg of product in sealed differential scanning calorimetery (DSC) pans using a TA Instruments DSC model 2920. Humidified samples were prepared by placing 8mg of product in unsealed DSC pans and exposing them to 55% and 65%RH at 25*C for 1440 minutes (1 day) using Dynamic Vapor Sorption. The pans were then sealed and Tg's were determined using the DSC model 2920. The Tg's (midpoint) of the
unhumidified samples ranged from 31.48 to 55.93 C. Increases in moisture content after 1440min at 55%RH and 65%RH were, on average, 7.29% and 11.11% (wb), respectively. Tg's (midpoint) after 55%RH ranged from -4.46 to 15.78 C, and after 65%RH ranged from -30.44 to -4.59 C. Thus, moisture sorption caused Tg's to drop below ambient temperature, resulting in products that were no longer glassy and hard, but sticky at room temperature.
Impacts
The glass transition temperature (Tg) is a pivotal temperature at which radical physical and chemical changes can occur in a food system. This study documents for the first time the effects of relative humidity on the Tg values of commercially available amorphous carbohydrate glasses.
Publications
- Effect of Relative Humidity on the Glass Transition Temperature of Commercially Available Amorphous Carbohydrate Glasses. July 2003, 64th Annual Institute of Food Technologists, Chicago, IL. M. Bohn and S. J. Schmidt (Submitted for presentation).
|
Progress 01/01/01 to 12/31/01
Outputs
The overall objective of this research project is to study the water and biopolymer mobility (as monitored by NMR relaxation rates and self-diffusion constant) and the glass transition temperature (Tg as monitored by differential scanning calorimetery) of model food systems. The focus of the research done during this past year was to explore the use of a new dynamic vapor sorption (DVS) technique to equilibrate samples to determine their glass transition temperature (Tg) by differential scanning calorimetery (DSC). The main two advantages of using the DVS technique for equilibrating samples compared to the traditional saturated salt solution method are: 1) any relative humidity between 0 and 98% can be selected at temperatures between 5 and 40 degrees C as opposed to specific RH values, and 2) continuous weight change data is collected over time as opposed to static weight change data at selected intervals. The model system selected for the development of this new DVS
technique was food grade crystalline sucrose. Crystalline sucrose was chosen since there are several previously published crystalline sucrose isotherms to which our DVS isotherm results could be compared. A 5.0 mg as is crystalline sucrose sample was evenly distributed on a 19mm quartz video DVS sample pan and placed in the DVS sample chamber. The sample was then equilibrated at 25 degrees C to RH values ranging from 0 to 95% RH in 5% RH increments, including two additional RH values of 78% and 83%. The change in mass versus time (dm/dt) criteria used by the DVS was set at 0.001% for all RH values. The air flow in the DVS was set at 500cc. Four replicate experiments were done. Good agreement was obtained between the DVS replicates and the DVS crystalline sucrose isotherms and those previously published in the literature. The isotherms obtained using the DVS technology were obtained in a considerably shorter period of time (26 hours) compared to the traditional saturated salt solution
method (15 to 30 days depending on the water activity of the salt solution used). These results suggest that the DVS is a quickly and reliable technique for sample equilibrate to any relative humidity desired between 0 and 98%. Future DVS and DCS research is underway in our laboratory to equilibrate and determine the Tg of freeze-dried sucrose at several RH values.
Impacts
The glass transition temperature (Tg) is a pivotal temperature at which radical physical and chemical changes can occur in a food system. What is needed is a method to equilibrate samples to various relative humidities in order to measure their Tg as a function of moisture content. The dynamic vapor sorption technique used in this research has been found to quickly and reliable equilibrate samples to any relative humidity desired between 0 and 98% at temperature between 5 and 40 degrees C.
Publications
- KAPPES, S.M. and SCHMIDT, S.J. 2001. Dynamic vapor sorption and differential scanning calorimetry of amorphous sucrose. June, 2001. 62nd Annual Institute of Food Technologists, New Orleans, LA.
- TEOH, H.M., SCHMIDT, S.J., DAY, G.A. and FALLER, J.F. 2001. Investigation of cornmeal components using dynamic vapor sorption and differential scanning calorimetry. Journal of Food Science, 66(3):434-440.
|
Progress 01/01/00 to 12/31/00
Outputs
The overall objective of this research project is to study the water and biopolymer mobility (as monitored by NMR relaxation rates and self-diffusion constant) and the glass transition temperature (Tg as monitored by differential scanning calorimetery) of model food systems, and to evaluate the ability of these parameters as predictors of food stability and safety by correlating these parameters with germination of Aspergillus niger conidia. The focus of the research done during this past year was to determine the nature of the step change in heat capacity (Cp) observed in native starches, attempting to answer whether the step change in Cp is a true Tg or rather a transition from an ordered to a disordered state. Modulated differential scanning calorimetery (MDSC; TA Instruments 2920) was used to measure the step change in heat capacity during gelatinization (dCp) of native corn, rice, and wheat starches and compared to the total change in heat capacity (tCp) before
and after gelatinization. Optimal conditions for MDSC scans were obtained: Amplitude of 0.5C; Oscillation period of 100 seconds; Heating rate of 1 degree C per minute; Helium as a purge gas at 25 cm3/minute; and a sample size of 10 mg. A step change in heat capacity between ungelatinized starch (dCp) was observed in the center of the gelatinization endotherm. The dCp was identical the tCp. For example, in a 40 percent native corn starch solution, the dCp was 0.66 J/g/C and the tCp was 0.067 J/g/C. The step change in heat capacity was attributed to a transition from an ordered to a disordered state because these quantities are similar and the dCp onset occurs after the onset of gelatinization. This does not preclude the possibility that a glass transition occurs at temperature(s) before gelatinization. The distribution of water in ungelatinized starch granules is not uniform before and during gelatinization. It is possible that small relaxations occur over a broad range of temperatures
as the distribution of water becomes more uniform. These small relaxations may be too small to be detected with MDSC. Additionally, the slow heating rate required for deconvolution of the modulated signal may cause annealing in the starch which may alter its structure and affect its glass transition temperature and measurement. Alternatively, the data may be indicative of a glass transition well below the starting point of the MDSC scans. The samples in this study were allowed to equilibrate at room temperature for a period of 12 to 18 hours before analysis and may have had enough time to hydrate and plasticize the amorphous regions of the starch. We are continuing this work equilibrating our samples to different relative humidities using a Dynamic Vapor Sorption (DVS) instrument and then running standard DSC.
Impacts
Water profoundly effects the textural, chemical, and microbial stability of food systems. What is needed is a reliable predictor of food stability that is not dependent on the composition of the food system. The approach of this research is to use a suite of techniques that probe the mobility of both the water and the solids of food systems at both the molecular and macroscopic level.
Publications
- Paeschke, T.M. and Schmidt, S.J. 2000. Changes in heat capacity associated with starch gelatinization. American Association of Cereal Chemists Annual Meeting, November 5-9, 2000, Kansas City, MO.
- Teoh, H.M., Schmidt, S.J., Day, G.A. and Faller, J.F. 2000. Investigation of cornmeal components using dynamic vapor sorption and differential scanning calorimetry. Journal of Food Science, September 2000 (Accepted).
|
Progress 01/01/99 to 12/31/99
Outputs
The overall objective of this research project is to study the water and biopolymer mobility (as monitored by NMR relaxation rates and self-diffusion constant) and the glass transition temperature (as monitored by DSC Tg values) of model food systems, and to evaluate the abilities of these parameters as predictors of food stability and safety by correlating these parameters with germination of Aspergillus niger conidia. A suite of NMR and DSC techniques will be used to fully characterize the water and solid mobility, and the Tg of these model food systems. Two specific objectives of this research project have been accomplished during this last year. The first objective was to apply the 2H NMR longitudinal (R1) and transverse (R2 and R2star) relaxation rates to three model food systems (sucrose, pregelatinized starch, and sucrose:starch mixture at a 1:1 ratio) equilibrated to ten different saturated salt solutions made with D2O with water activity (aw) values ranging
from 0.333 to 0.973 at 20 degrees C. For all three model food systems the 2H NMR relaxation rates increased with decreasing water content. This indicated that the molecular mobility of water in all three systems decreased with decreasing water content. The 2H NMR R1 and R2 relaxation rates were found not to predict mold conidia germination times. Whereas, the 2H NMR R2star relaxation rate, to a limited extent, was found to correlate to mold conidia germination times and may be a useful tool for predicting the stability and safety of foods. The second objective was to measure the molecular mobility of the solids in the pregelatinized starch model system at aw values ranging from 0.331 to 0.976 (made with H2O) using 13C NMR spin lattice relaxation time in the rotating frame (T1rho). According to the 13C T1rho studies, the T1rho values for all starch carbon atoms did not change appreciably in the aw range 0.331 to 0.910. However, the T1rho values decreased rapidly at aw values of 0.946
and 0.976, indicating that these two starch samples at room temperature were below the glass transition temperature (Tg) of the starch samples. These two high aw starch samples also exhibited mold germination, indicating that these samples were not stable at room temperature.
Impacts
Water profoundly effects the textural, chemical, and microbial stability of food systems. What is needed is a reliable predictor of food stability that is not dependent on the composition of the food system. The approach of this research is to use a suite of techniques that probe the mobility of both the water and the solids of food systems at both the molecular and macroscopic level.
Publications
- KOU, Y. and SCHMIDT, S.J. 1999. Vapor pressure and water activity measurements of saturated salt solutions made with D2O at 20 degrees C. Food Chemistry 66(2):253-256.
- KOU, Y., MOLITOR, P. and SCHMIDT, S.J. 1999. Mobility and stability of model food systems using NMR, DSC, and conidia germination techniques. Journal of Food Science 64(6):950-959.
|
Progress 10/01/97 to 09/30/98
Outputs
The overall objective of this research project is to study the water and biopolymer mobility (as monitored by NMR relaxation rates and self-diffusion constant) and the glass transition temperature (as monitored by DSC Tg values) of model food systems, and to evaluate the abilities of these parameters as predictors of food stability and safety by correlating these parameters with germination of Aspergillus niger conidia. A suite of NMR and DSC techniques will be used to fully characterize the water and solid mobility, and the Tg of these model food systems. Two specific objectives of this research project have been accomplished. The first objective was to refine and apply the Aspergillus niger conidia germination technique in model food systems as a microbial probe of food stability. The technique was successfully refined and has been applied to three model systems (sucrose, pregelatinized starch, and sucrose:starch mixture at a 1:1 ratio) equilibrated to ten different
saturated salt solutions with water activity (aw) values ranging from 0.11 to 0.98 at 20 degrees C. For the sucrose samples the conidia germinated in two days at aw values of 0.890 or greater; for the pregelatinized starch the conidia germinated in seven days or less at aw values of 0.946 or greater; and for the sucrose:starch mixture the conidia germinated in six days or less at aw values of 0.890 or greater. The second objective was to determine the aw values at 20 degrees C for ten saturated salt solutions made with deuterium oxide (D20) in place of H2O. These aw values are required for future experiments in which samples will be equilibrated to D20 saturated salt solutions for study by deuterium Nuclear Magnetic Resonance spectroscopy. Two methods were used to determine the aw: a vapor pressure manometer and an electronic chilled-mirror instrument. The D20 aw results are accepted for publication in Food Chemistry.
Impacts
(N/A)
Publications
- Kou, Y. and Schmidt, S. J. 1998. Vapor pressure and water activity measurements of saturated salt solutions made with D2O at 20 degrees C. Food Chemistry, Accepted December 7, 1998.
|
|