Progress 01/01/09 to 12/31/13
Outputs
Target Audience: Scientists who study the molecular basis for storage and shelf-life of amorphous solid (dried and frozen) foods. Food technologists who study and develop strategies to extend the shelf-life of amorphous solid foods. Students who are being educated in the latest techniques for extending the shelf-life of amorphous solid foods. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? This project provided opportunities for scientific development to one graduate and several undergraduate students. The post-doctoral fellow hired to work on this project not only gained experience and expertise in biophysical analysis of the amorphous solid state using a variety of spectroscopic and imaging techniques (including optical luminescence, FTIR, and atomic force microscopcy) but this individual also pursued a second Ph.D. degree in food science in our graduate program; he is writing his dissertation and should defend it in summer/fall 2014. Several undergraduate students also worked on aspects of this project, either assisting the post-doc directly or working under the PI doing independent research projects. How have the results been disseminated to communities of interest? This work has been published in or submitted to the appropriate international scientific journals and the work presented at scientific conferences. What do you plan to do during the next reporting period to accomplish the goals? This is the final report on the project.
Impacts
What was accomplished under these goals?
The effect of glycerol on molecular mobility and hydrogen bonding in amorphous solid glucose was studied using Erythrosin B (Ery B) phosphorescence to spectrally characterize the temperature dependence of mobility in glucose/glycerol films from 100°C down to −10°C. Analysis of emission peak frequency, band width (full width at half-maximum), and time-resolved intensity decay parameters from Ery B provided information about activated modes of matrix mobility that enhanced the rate of dipolar relaxation around the triplet state and the rate of intersystem crossing to the ground state (kTS0). When normalized to glass-transition temperature (Tg) over the range of T-Tg from −50°C to 91°C both the average rate of matrix mobility and the width of the distribution of matrix mobility rates were comparable for glucose matrixes at all glycerol contents. An increase with temperature in the hydrogen bond peak frequency indicated the transformation of associated hydroxyl to free hydroxyl. The IR hydrogen bond bandwidth increased at higher glycerol content, suggesting that the strength of the bond became more widely distributed with the added glycerol. These results support a model in which glycerol plasticizes the glucose matrix across a wide range of concentrations with little change in the hydrogen bonding network while providing no evidence for the antiplasticization effect of glycerol seen in other carbohydrate matrixes. The effect of the antioxidants gallic acid and methyl, propyl and octyl gallate on the molecular mobility and hydrogen bond network in sucrose amorphous was studied. Solid amorphous sucrose films with and without the addition of antioxidants at a mole ratio of 1:5 (antioxidant:sucrose) were cast from solution onto quartz slides. Local molecular mobility from 0 to 70°C was measured using tryptophan amino acid as a luminescent probe dispersed in the films. Phosphorescence from the tryptophan probe provides spectroscopic characteristics—emisssion spectrum and lifetime—that are sensitive to changes in molecular mobility induced by the addition of antioxidants. Local molecular mobility detected by tryptophan increased in the following order: sucrose < sucrose-octyl gallate < sucrose-propyl gallate ≤ sucrose-methyl gallate ≤ sucrose-gallic acid. The antioxidants also modulated the activation energy for matrix motions that quench the tryptophan phosphorescence in a structure-dependent manner. IR measurements as a function of temperature indicated that hydrogen bond strength in these amorphous films followed a rank order (sucrose-methyl gallate > sucrose-gallic acid > sucrose-propyl gallate > sucrose > sucrose-octyl gallate) that was nearly the reverse of that seen in matrix mobility. Analysis of the differential effects of the antioxidants suggests that the presence of the hydroxyl benzoyl head group increased matrix molecular mobility and hydrogen bond strength while the saturated carbon chain decreased mobility and bond strength. The influence of the carboxyl group on matrix properties was comparable to that of the formyloxy group. These results indicate that the addition of specific functional ingredients such as antioxidants may significantly affect the physical properties and consequently functional properties of amorphous sedible films in ways that might condition their use. The observed changes are closely related to the chemical structure of the added species. The effects of glycerol on molecular mobility, oxygen diffusion and microstructure in amorphous zein matrix were studied using phosphorescence and atomic force microscopy (AFM). Films containing various amounts of glycerol (0, 5, 10, 20 and 30 wt%) were formulated by rapid dehydration from solutions of 0.5% (w/v) zein in 70% ethanol/water (v/v) containing corresponding contents of glycerol. Erythrosin B (Ery B) phosphorescence was used to monitor the molecular mobility of these matrices over the temperature range from 0 to 100°C. Analysis of Ery B emission peak frequency and bandwidth and intensity decay provided information about thermally-activated modes of molecular mobility in the matrices. Dipolar relaxation around the triplet state of Ery B was weakened and the extent of relaxation was decreased by adding glycerol at low concentration (≤ 10%), indicating the role of antiplasticizer in zein films at this concentration range. Consistently, measurements of the rate of non-radiative decay from the Ery B triplet state indicated that glycerol only performed as a plasticizer and increased the local mobility of the zein matrix at and above ~20 wt %, while for the films with glycerol at the content ≤20 wt %, the local mobility remained nearly constant or only slightly increased compared with that in the pure zein. Though there is a transition from antiplasticizer to plasticizer at higher content, glycerol dramatically suppressed the oxygen permeability of the film in the whole concentration range tested, even in the antiplasticizer region at low concentrations (≤ 10%). AFM images indicated that glycerol induced aggregation of zein complexes, which could lead to a more condensed film. These results indicate how the addition of glycerol to zein films could affect the physical properties, structure and thus functional properties in ways that influence their eventual use. The effect of non-reducing sugars or methylcellulose on the physical properties and rates of non-enzymatic browning (NBR) in starch-based glassy matrices were studied using the methods of luminescence and FTIR. Amorphous starch-based matrices were formulated by rapidly dehydrating potato starch gel mixed with additives at weight ratios of 7:93 (additive:starch). Data on the phosphorescence emission energy and lifetime from erythrosin B dispersed in the matrices indicated that sugars decreased starch matrix mobility in a Tg-dependent manner, except for trehalose that interacted with starch in a unique mode, while methylcellulose, the additive with the highest Tg, increase the molecular mobility. Using FTIR we found that methylcellulose decreased the strength of hydrogen bond network and sugars enhanced the hydrogen bond strength by the rank: trehalose > maltitol > sucrose. Comparing those changes with the rate of NBRs, we suggest that NBRs are primarily influenced by matrix mobility, which is modulated by the hydrogen bond network, and interactions among components.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2012
Citation:
Liang, Jun & Ludescher, Richard D. (2012) Influence of Glycerol on Molecular Mobility and Hydrogen Bond Network in Amorphous Glucose Matrix. Carbohydrate Research 361, 120-126.
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Liang, Jun, Corradini, Maria G. & Ludescher, Richard D. (2014) Influence of Antioxidant Structure on Local Molecular Mobility in Amorphous Sucrose. Carbohydrate Research 383, 14-20.
- Type:
Journal Articles
Status:
Under Review
Year Published:
2014
Citation:
Liang, Jun, Wang, Simon, Li, Ji, Huang, Qingrong, & Ludescher, Richard D. (2014) Influence of Glycerol on the Molecular Mobility, Oxygen Permeability and Microstructure of Amorphous Zein Films. Food Hydrocolloids, in review.
- Type:
Journal Articles
Status:
Under Review
Year Published:
2014
Citation:
Liang, Jun, Wang, Simon, Ludescher, Richard D. (2014) "Effect of Additives on Physical Properties in Amorphous Starch Matrices." Food Chemistry, in review
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Progress 01/01/11 to 12/31/11
Outputs
OUTPUTS: This project uses a variety of physical techniques including luminescence spectroscopy of intrinsic and introduced probes, Fourier Transfer Infrared spectroscopy, atomic force microscopy, confocal microscopy, and differential scanning calorimetry to investigate the relationship between composition, physical state, molecular mobility and chemical reactivity in amorphous solid food model systems. This work is directed to understanding and thus controlling the rates of specific chemical reactions and physical processes that influence the stability of amorphous solid and semi-solid foods. During the period being reported, a number of studies of the relation between composition and state were done. These studies investigations of the following: 1) The effect of antioxidants on the physical state and molecular mobility of amorphous solid films composed of the food protein zein isolated from maize. 2) The influence of the low molecular weight plasticizer glycerol on the temperature-dependence of the molecular mobility in amorphous solid glucose. 3) The influence of the low molecular weight plasticizer on the temperature-dependence of the the molecular mobility in amorphous solid starch. 4)The influence of composition, physical state and molecular mobility on the browning reaction in amorphous solid carbohydrates. PARTICIPANTS: Richard D. Ludescher, Ph.D., Project Director; Jun Liang, Ph.D., Post-doctoral Fellow TARGET AUDIENCES: The target audience for this project are fellow scientists in the food and pharmaceutical field who are interested in how the physical state of amorphous solid biomaterials influences the rates of chemical reactions and physical processes, and food technologists who are interested in formulating foods for increased stability and long-term quality. Efforts to reach this audience include presentations at national meetings and publication of research in established, high quality scientific journals in the field. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Progress was made in each area. 1) The effect of octyl and propyl gallate on zein/glycerol films was studied. Although both antioxidants increased the local mobility of the zein matrix to about the same extent, octyl gallate, and to a lesser extent propyl gallate, dramatically increased the permeability of the film to oxygen. AFM imaging indicated that propyl gallate induced aggregation of zein complexes, which could lead to a more condensed film. These results indicate that antioxidants in edible films may significantly affect the physical properties and structure and thus functional properties in ways that influence their eventual use. 2) Effect of glycerol on the molecular mobility and hydrogen bond network in glucose matrix was studied. When normalized to Tg, the mobility over the range of T-Tg from -50 to 91C were comparable for glucose with varying content of glycerol. These data demonstrate that both the average rate of matrix mobility and the width of distribution of matrix mobility rates around the glass transition were almost unchanged, despite different amount of glycerol. The IR hydrogen bond bandwidth increased at a higher glycerol content, suggesting that the strength of the bond became more widely distributed with the added glycerol. An increase with temperature in the hydrogen bond peak frequency indicated the transformation of associated hydroxyl to free hydroxyl. 3) Potato starch films containing varying weight content of glycerol (0-60%) were formulated. Glycerol affected the mobility of amorphous starch matrix primarily through plasticization when glycerol was above 20%. At weight content 10% and at temperature above 80C, glycerol exhibited an "antiplastization" effect. The IR hydrogen bond bandwidth increased with increasing content of glycerol, suggesting that the strength of the bond became more widely distributed with added glycerol. Shift to the high frequency of the hydrogen bond peak indicated the transformation of associated hydroxyl to free hydroxyl following the increase of temperature. AFM images revealed phase separation in the microstructure of films and increasing dispersion of starch complex with the increasing of glycerol content. 4) Non-enzymatic browning due to the reaction of lysine with glucose and starch was studied in dehydrated matrices based on starch mixed with non-reducing sugars or methylcellulose. Data on Ery B indicated that sugars decreased starch matrix mobility in a Tg-dependent manner, except for trehalose that interacted with starch in a unique mode. Whole methylcellulose increased the starch matrix mobility though its Tg was higher than any of the sugars used. Using FTIR we found that sugars enhanced the hydrogen bond network in an order of trehalose > maltitol > sucrose over a temperature range from 30-100C. By comparing the non-enzymatic browning rates (NBRs) with the matrix mobility, hydrogen bond network and Tg in relation to composition, we concluded that NBRs in starch-based matrices below Tg are determined by the matrix mobility, which is influenced by Tg, hydrogen bond network, and interactions among compounds.
Publications
- Liang, Jun & Ludescher, Richard D. (2011) Antioxidants Modulate Molecular Mobility, Oxygen Permeability, and Microstructure in Zein Films. Journal of Agricultural and Food Chemistry 59, 13173-13180.
- You, Yumin & Ludescher, Richard D. (2011) Effect of Starch on Molecular Mobility of Amorphous Sucrose. Journal of Agricultural and Food Chemistry, 59, 3340-3347.
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Progress 01/01/10 to 12/31/10
Outputs
OUTPUTS: Studied the effect of glycerol on the thermal dependence of the local molecular mobility of amorphous glucose in thin films using phosphorescence from the triplet probe erythrosin B (red dye #3) over the temperature range -10 to 100C. These studies were supplemented with FTIR studies of the effect on the hydrogen bonding in the films. Studied the effect of antioxidants on the thermal dependence of the local molecular mobility and oxygen permeability of amorphous zein/glycerol films using phosphorescence from erythrosin B (red dye #3); studied the microstructure of the films using atomic force microscopy. PARTICIPANTS: Richard D. Ludescher, Ph.D., principal investigator, provided oversight to the entire project. Jun Liang, Ph.D., post-doctoral research associate, conducted all scientific studies, data collection and analysis, generated first draft of two publications summarizing the work done. TARGET AUDIENCES: The target audience for this project is the universe of scientific researchers involved in studies of the amorphous solid state of biomaterials; this includes food scientists, material scientists, and chemical engineers. We began preparation of two scientific manuscripts for submission to appropriate internationally recognized journals. PROJECT MODIFICATIONS: We have expanded our studies to include work on the role that molecular mobility plays in modulating the function of antioxidants in amorphous solid biomaterials.
Impacts
Glycerol in amorphous sucrose acts as an antiplasticizer at low concentrations and as a plasticizer at higher concentrations. We thus examine whether the same phenomena occurred in amorphous glucose. Data on both the extent of dipolar relaxation (from analysis of emission peak energy with temperature) and the rate of matrix molecular mobility (from analysis of rate of non-radiative decay rate as function temperature), however, indicate that glycerol does not act as an antiplasticizer at low but does act as a plasticizer of the glassy glucose matrix at high concentrations. This difference from sucrose may reflect the closer similarity in molecular mass and structure of the glycerol/glucose with respect to the glycerol/sucrose system. Measurements of the extent of dipolar relaxation (from analysis of emission peak energy with temperature) and the rate of matrix molecular mobility (from analysis of rate of non-radiative decay as function of temperature) indicate that the antioxidants propyl gallate and octyl gallate further plasticize amorphous films of zein/glycerol (wt. ratio of 4/1). The effects of both antioxidants were dose dependent, but octyl gallate had a larger effect on mobility than propyl gallate. Measurements of the effect of the antioxidants on the rate of oxygen quenching (which reflects the permeability of oxygen) were consistent with the mobility results: octyl gallate had a major impact on the oxygen permeability at all temperatures above 0C while propyl gallate had a minor impact. These results illustrate the significant effect the additional of functional ingredients can have on the physical properties of edible films.
Publications
- No publications reported this period
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Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: This project investigates how the rates of chemical reactions are modulated by molecular mobility and local structure within the amorphous solid matrix composed of sugars and carbohydrates and how modulating the composition of these matrixes can influence the rates of these reactions. This work will provide the fundamental basis for developing molecular-level rules for increasing the shelf-life and quality of dried and frozen foods. Much of the research to date has been directed to developing a molecular level understanding of the local structure in amorphous sucrose. We have specifically investigated using Fourier transform Infrared (FTIR) spectroscopy how composition affects the local hydrogen bonding interactions in a variety of amorphous sugar matrixes of different composition. These matrixes included sucrose with the additives glycerol, NaCl and other salts, gelatin, or xanthan gum; maltodextrin DE18 with lactitol, and pure samples of the homologous series of maltooligosaccharides G2, G3, G4, G5, G6, and G7. Samples were prepared as pure or with variable compositions and FTIR spectra were collected at 25C over the range from 400-4000 1/cm; the region from 3000-3600 was selected for analysis. All samples were equilibrated over phosphorus pentoxide for 7 days to remove residual water. The OH stretching frequency, the basis for our analysis of the effect of additive on sucrose matrix interactions. was analyzed using software provided by the instrument manufacturer (Nicolet, Madison, WI). Our results were as follows: Glycerol has a complex dose-dependent effect on the sucrose matrix as the OH stretching frequency. The frequency decreased with glycerol over the range from 0-0.2 mole glycerol/mole sucrose and then increases over the range from 0.2-0.9 mol/mol. NaCl caused a linear decrease in OH stretching frequency of the sucrose matrix over the range from 0-0.6 mol/mol and then is constant to 0.9 mol/mol. Other salts (CaCl2, MgCl2, NaAcetate, Na3Citrate, Na2HPO4, and NaH2PO4) at fixed ratio of 0.2 mol/mol all caused a decrease in the OH stretching frequency compared to sucrose, with all salts showing a greater decrease at this mole fraction than NaCl. Gelatin at wt. ratios (g gelatin/g sucrose) of 0.00022, 0.00073, 0.0073, and 0.073 caused a slight increase in the OH stretching frequency of the sucrose matrix while at wt. ratio of 0.265 it caused a decrease. Xanthan gum had no significant effect on the OH stretching frequency of the sucrose matrix over the wt. ratios 0.0001-0.001 but caused a decrease at higher wt. ratio (to 0.01). Lactitol caused a linear decrease in the OH stretching frequency of the maltodextrin DE18 matrix over the range from 0-50 wt. % lactitol. Maltooligosaccharides OH stretching frequency showed a progressive increase in wavenumber over that seen in sucrose with oligosaccharides with higher molecular weight showing higher frequency from G2 to G4, and higher polymers showing the same frequency as the G4. PARTICIPANTS: Richard Ludescher, PhD Yumin You, PhD Jun Liang, PhD TARGET AUDIENCES: Target audience is the community of food scientists and food technologists in academia and industry. This audience will be reached by peer reviewed publications, talks and posters at national meetings, and informal communications. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Our conclusions are based on analysis of the OH stretching vibrations of the amorphous molecules. Previous results in the literature indicate that the wavenumber of the OH stretch decreases as more, or more optimal, hydrogen bonds are made by the molecule. Analysis of the trends in OH stretching frequency thus provide an indicator of changes in the extent of hydrogen bonding in the amorphous matrix. Such an analysis leads to the following conclusions in these amorphous sugar matrixes. Glycerol appears to increase the extent of hydrogen bonding at low mol ratios (0-0.4), suggesting that the presence of the small hydrogen bonding trihydroxy alcohol actually increases the integrity of the hydrogen bonded solid. This finding is consistent with and provides a structural explanation for our findings that glycerol actually decreases the molecular mobility of the sucrose matrix. NaCl appears to increase the extent of hydrogen bonding over the range from 0-0.5 mol/mol, suggesting that the salt increases the integrity of the hydrogen bonding solid. This finding is consistent with and provides a structural explanation for our findings that NaCl over this same concentration range actually decreases the molecular mobility of the sucrose matrix. Other salts at the mol ratio of 0.2 also increase the extent of hydrogen bonding in a manner consistent with our molecular mobility results. Gelatin and xanthan gum have no significant effects on local hydrogen bonding patterns in the matrix at low and cause a slight increase in hydrogen bonding integrity only at high wt. ratios. These results thus do not provide insight into the increases in molecular mobility seen at low wt. ratios of these polymers. Lactitol caused a linear increase in the extent of hydrogen bonding in the maltodextrin DE18 matrix in a manner entirely consistent with and explanatory of our findings that lactitol decreased the mobility of this matrix. In the homologous series of maltooligosaccharides the extent of hydrogen bonding decreased with increase in molecular weight up to the G4 molecule maltotetraose; this result is consistent with our finding that the molecular mobility within the glass state of these maltooligosaccharides decreases with increase in molecular weight.
Publications
- No publications reported this period
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