Water Activity by Pavinee Chinachoti
Starch - Stärke, 2002
ABSTRACT The freeze-thaw stabilities of three different rice flour gels (amylose rice flour with ... more ABSTRACT The freeze-thaw stabilities of three different rice flour gels (amylose rice flour with 28% amylose, Jasmine rice flour with 18% amylose and waxy rice flour with 5% amylose) were studied by first freezing at –18 °C for 22 h and subsequent thawing in a water bath at 30 °C, 60 °C and 90 °C, or by boiling in a microwave oven. The freeze-thaw stability was determined for five cycles. Starch gels thawed at higher temperature exhibited a lower syneresis value (percent of water separation) than those thawed at lower temperature. Amylose rice flour gels gave the highest syneresis values (especially at the first cycle). The Jasmine rice flour gels gave a higher syneresis value than the waxy rice flour gel. Except for freezing by storage at –18 °C and thawing at 30 °C, there was no separation of water at any cycle when waxy rice flour gel was thawed at any temperature, irrespectively of the freezing methods used. Cryogenic Quick Freezing (CQF) followed by storage at –18 °C and then thawing (by boiling or by incubation at any other temperatures) gave lower syneresis values than all comparable samples frozen by storage at –18 °C. The order of syneresis values for the three types of rice flour was waxy rice flour < Jasmine rice flour < amylose rice flour. The syneresis values and the appearance of starch gels, which had gone through the freeze- thaw process, suggested that the order of freeze-thaw stability of gels for the three types of rice flour was waxy > Jasmine > amylose rice flour.
Journal of Food Science, 1986
... NBSA. Physics & Chem. A. ElA(1): 89. Heiss, R. 1955. ... echnol. 10: 385. Junk, WR an... more ... NBSA. Physics & Chem. A. ElA(1): 89. Heiss, R. 1955. ... echnol. 10: 385. Junk, WR and Pancoast, HM 1973. Handbook of Sugars. AVI Pub-lishing Company, Inc., Westport, CT. Karel, M. 1975. Physico-chemical modification of the state of water in foods-A speculative survey. ...
Water Mobility by Pavinee Chinachoti
Carbohydrate Polymers, 2001
Mobility of water in cellulose was studied by solid-state 1 H and high-resolution 2 H NMR as a fu... more Mobility of water in cellulose was studied by solid-state 1 H and high-resolution 2 H NMR as a function of moisture content within the unfreezable moisture range (0±19% dry basis). Measurements of relative mobilities were based on relative intensities, transverse and longitudinal relaxation times and lineshape analysis. At 2±16% moisture content (dry basis), water molecules reoriented anisotropically, suggesting an interaction with cellulose ®bers. At moisture content below the monolayer value (2.8%, dry basis), 90% of the protons were immobile and no liquid deuterium signal was detected. A sharp increase in liquid or mobile 1 H intensity (accompanied by a decreased LW) and increases in 2 H NMR T 1 and T 2 relaxation times were observed as moisture increased above 9% (dry basis). At this moisture content the molecular mobility approached the fast exchange regime. The data con®rmed earlier reports that unfreezable water could be highly mobile and not in a rigid state.
Carbohydrate Polymers, 2002
Molecular and structural mobility of xanthan and locust bean gum mixtures (with and without manni... more Molecular and structural mobility of xanthan and locust bean gum mixtures (with and without mannitol) were studied in relation to microbial stability. Molecular mobility was measured by solid state 1H and 2H NMR and by 2H high resolution NMR while differential scanning calorimetry and dynamic mechanical analysis were used to investigate structural mobility. The NMR mobile signal was found to increase significantly with increasing moisture content and, at above 30% moisture content, the solid component disappeared with observed structural collapse. Cell survival decreased with moisture content increasing from 6 to 15% corresponding with an increasing mobile proton and deuterium signals (i.e. increased mobility). Presence of mannitol protected the cells from death at increasing moisture content and a relationship with a lower mobile 1H signal (as compared with the control) seems to be present. A strong mannitol–water interaction, leading to a decreased mobility, is suggested to play a role. No evidence of a glassy to rubbery transition was observed from DSC and DMA analyses, suggesting that structural relaxation did not play a significant role in NMR solid-liquid transition, i.e. NMR molecular mobility.
International Journal of Food Science and Technology, 2003
ABSTRACT The role played by water activity, ‘mobility’ and physico-chemical properties of the med... more ABSTRACT The role played by water activity, ‘mobility’ and physico-chemical properties of the media in modulating microbial response has been the object of large debate in the scientific community. In this study, Staphylococcus aureus growth parameters (lag phase and cell density at 24 h) in brain heart infusion (BHI) and BHI:NaCl (1:1) were analysed in their correlation with physico-chemical/mobility parameters descriptive of the media [solid content, aw, kinematic viscosity, 17O NMR (R2, Pbw and )]. In these high moisture content, liquid and ‘homogeneous’ media S.aureus growth related to all the physico-chemical and molecular mobility parameters analysed in a similar manner and it was found to be influenced more significantly by added NaCl than by the physico-chemical and molecular mobility of the media. Staphylococcus aureus growth parameters correlated better with aw (relatively independent of NaCl concentration) than with any other parameter considered in this study.
Journal of Agricultural and Food Chemistry, 2000
The aim of this work was to characterize the glassy-rubbery transition in starch gels using molec... more The aim of this work was to characterize the glassy-rubbery transition in starch gels using molecular (NMR) techniques. Proton cross-relaxation ((1)H CR) NMR spectra of gelatinized starch ( approximately 50% mc) were obtained by cooling stepwise from 20 to -30 degrees C. A significant line broadening was observed in the CR spectra between 0 and -10 degrees C. Deconvolution of the spectra into its component curves (broad and narrow) yielded a peak amplitude, width at half-height, and peak area for each curve. Between 0 and -10 degrees C (temperatures around T(g)), a significant line width change in the broad component (rigid solid) was apparent. These observed qualitative changes may be evidence of a glassy-rubbery transition at a molecular (short-range) level which are strengthened by a similar transition temperature range found previously with (13)C CP-MAS and DMA tan delta(T) measurements. However, the increase in the relative quantity of rigid protons observed by (1)H CR NMR spectra could also be attributed to ice. The (1)H CR NMR method showed its potential application for probing solid components in gels using a simple and economical NMR spectrometer, without the need for a solid-state instrument.
Journal of Agricultural and Food Chemistry, 1991
Page 1. J. Agfic. FoodChem. iQQl, 39, 1915-1920 1911 170 Nuclear Magnetic Resonance Studies of Wa... more Page 1. J. Agfic. FoodChem. iQQl, 39, 1915-1920 1911 170 Nuclear Magnetic Resonance Studies of Water Mobility during Bread Staling Mal-Shick Kim-Shin,+ Frank Mar;,$ Pramila A. Rae,+ Thomas R. Stengle,* and Pavinee Chinachoti'>+ ...
Journal of Agricultural and Food Chemistry, 2003
Molecular mobility of water was studied in a microbiological media containing complex and heterog... more Molecular mobility of water was studied in a microbiological media containing complex and heterogeneous mixtures of cellulose, l-sorbose, and orange serum broth (OSB) using (2)H and (17)O high-resolution NMR. All mixtures showed Lorentian (17)O NMR spectra but complex (2)H NMR line shapes. Sorbose, when solubilized, caused line-narrowing where as cellulose-OSB mixtures showed wide peaks with flat plateaus. Presence of liquid or solvent water had a profound effect on a marked increase in T(2) relaxation time observed in sorbose-containing samples. (17)O NMR data were not composition dependent, while (2)H NMR data were highly sorbose dependent.
Journal of Agricultural and Food Chemistry, 1998
"Freezable" and "unfreezable" water in waxy corn starch were ... more "Freezable" and "unfreezable" water in waxy corn starch were characterized by thermal analysis, and the mobility in those states was characterized by solid state (2)H and (1)H NMR. Water was found to be isotropically mobile for samples over a range of water contents (6.3-47% by total weight) at room temperature. Mobility increased with increasing water content and temperature. According to (1)H and (2)H NMR data, a large fraction of "unfreezable" (DSC) was relatively mobile comparable to a liquid state even down to -32 degrees C. Some anisotropically immobile D(2)O at low temperatures exhibited a solid state Pake pattern in (2)H NMR spectra, which was similar to that of frozen D(2)O (ice) with a 144 kHz splitting. The decreasing fraction of mobile water with decreasing temperature suggested that only some of the so-called "unfreezable" water could be progressively immobilized as temperature decreased. However, much of the water (>50% of water present) remained very high in mobility, regardless of the relatively rigid starch molecules in the glassy solid state.
Journal of Food Science, 1989
ABSTRACT Proton pulsed NMR methodology was applied to correlate the observed spin-lattice (T1) an... more ABSTRACT Proton pulsed NMR methodology was applied to correlate the observed spin-lattice (T1) and spin-spin (T2) relaxation times with the amount of water associated to sucrose (SOL) and that to starch (POL) in a sucrose-starch model system containing both. Sucrose, starch and four mixtures were equilibrated to four water activities (aw, 0.86-0.97). Calculations for T2 were invalid due to an undeterminable amount of molecular diffusion caused by field inhomogeneity in the magnet. Model equations were developed for calculating SOL and POL from T1 and aw; These values showed high correlations (R2>0.97) with SOL and POL as determined from sorption data for sucrose and starch. This validated the use of this instrument with the mathematical models developed.
Cereal Chem. 73(6):736-743 Proton rotating frame relaxation times (Tlp(H)) were used to charac- o... more Cereal Chem. 73(6):736-743 Proton rotating frame relaxation times (Tlp(H)) were used to charac- of gluten decreased the Tjp(H), which was also dependent on moisture. terize the molecular dynamics and structural homogeneity in waxy corn When mixed at a 1:1 starch-to-gluten ratio and heated, the Tjp(H) starch, wheat gluten, and mixtures of both. Single-phase relaxation of associated with the gluten were
Bread Staling and Roles of Water by Pavinee Chinachoti
Cereal Chemistry, 2000
Cereal Chem. 77(4):484-488
Journal of Agricultural and Food Chemistry, 2001
The thermomechanical properties of breadcrumb were investigated using dynamic mechanical analysis... more The thermomechanical properties of breadcrumb were investigated using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The main transition (T(1), near 0 degrees C) shifted to lower temperature with added glycerol due to freezing point depression. The low-temperature transition (T(3), approximately -50 degrees C), found only in high-glycerol (8.8%) bread, suggested that of excess or phase-separated glycerol. The high-temperature transition (T(2), 60-85 degrees C) appeared only in aged breadcrumbs; its temperature range was correlated well with the amylopectin melting transition (DSC) but its tan delta amplitude did not correlate well with the amylopectin melting enthalpy (r(2) = 0.72). On the other hand, the change of E' ' (viscous behavior) suggested that T(2) might be related to the change in the amorphous region. Domain-to-domain (amorphous) and crumb-to-crust moisture migrations are two critical phenomenological changes associated with aging and could lead to significant local dehydration of some amorphous regions contributing to mechanical firming during storage.
Journal of Agricultural and Food Chemistry, 1998
Dynamic mechanical analysis (DMA) data indicated an increase in final glass transition temperatur... more Dynamic mechanical analysis (DMA) data indicated an increase in final glass transition temperature with storage time, with no increase in initial temperature. After deconvolution, the tan delta(T) curve for ice melting was identified as the main peak, whereas glassy-rubbery transition peak(s) occurred at lower temperatures. Accompanying increase in "unfreezable" water and degree of amylopectin recrystallization showed that increase in the glassy-rubbery transition involved more than just moisture loss, and it may be possible that some amorphous network may have progressed extensively.
Journal of Food Science, 1992
ABSTRACT
Journal of Food Science, 2002
Storage stability of standard white bread (SWB) and Meal, Ready-to-Eat (MRE) breads were studied ... more Storage stability of standard white bread (SWB) and Meal, Ready-to-Eat (MRE) breads were studied in terms of texture firming, amylopectin recrystallization, and water relations. SWB showed a more rapid increase in firmness during storage mainly due to the loss of moisture to the crust and surrounding environment. The MRE, a long shelf-life military bread, firmed much slower due to the moisture loss inhibition (hermetic pouch) and plasticization (by formulation). This work confirmed previous findings that in some cases, firming of a bread can be strongly influenced by factors other than amylopectin crystallization. This is possible through controlling changes in the amorphous domains earlier described from thermomechanical studies.
Journal of Texture Studies, 1992
Cylindrical specimens of bread crumbs were subjected to a compressiondecompression cycle using a ... more Cylindrical specimens of bread crumbs were subjected to a compressiondecompression cycle using a computer interfaced Universal Testing Machine during 11 days of storage at ambient temperature. lhe strain (% deformation) was set at various levels in the range of 20-80%. l h e overall work per unit volume, calculated from the area under the stress-strain curve, increased exponentially with the imposed strain while the percent recoverable work, calculated from the area under the decompression curve, decreased exponentially with the strain. m e loss of elasticity that accompanies bread aging was clearly manifested in the percent recoverable work, irrespective of the imposed strain, It declined in a manner that could be described by a power law or an exponential decay model at the same degree of fit as judged by statistical criteria.
Thermochimica Acta, 1994
Thermal and molecular analyses of cereal food systems have been considered as a new approach to c... more Thermal and molecular analyses of cereal food systems have been considered as a new approach to clarify these complex systems. The roles of glass transition, crystal melting, phase separation, and molecular mobility and interaction, are of great interest. The starch melting and glass-rubber transition, for instance, are complex, biphasic phenomena. NMR, X-ray diffraction, and many other methods have brought out new evidence and arguments for different models. Glass-rubber transitions of gluten and its components have been reported by various techniques. Thermal events in bread at various moisture levels observed by DSC, DMA and TMA are compared in terms of rheological properties, volume expansion, and melting behavior. The staling of bread is described as a function of storage time and moisture loss.
Health impact of Food and Food ingredients by Pavinee Chinachoti
Microbial Activity and Water by Pavinee Chinachoti
Molecular Physics, 2001
... ELENA VITTADINI', SHELLY J. SCHMIDT' and PAVINEE CHINACHOT13 * ' Opta Food Ing... more ... ELENA VITTADINI', SHELLY J. SCHMIDT' and PAVINEE CHINACHOT13 * ' Opta Food Ingredients, Inc, 25 Wiggins Avenue, Bedford, MA 01730, USA Department of Food Science and Human Nutrition, 367 Bevier Hall, 905 South Goodwin Avenue, University of Illinois, Urbana ...
Journal of Agricultural and Food Chemistry, 1999
A sugar transport defected strain of Aspergillus nidulans (biA-1 sorA-2) was tested for spore ger... more A sugar transport defected strain of Aspergillus nidulans (biA-1 sorA-2) was tested for spore germination in nutrient media containing various water activity (a(w)) values and varying amounts of non-nutritive, nontoxic carbohydrates (L-sorbose and cellulose). Freeze-dried media [containing the same nutrient level but different in sorbose/cellulose (s:c) ratio] were adjusted to 0.75-0.97a(w) at 25 degrees C before inoculation. Minimum a(w) for germination varied with s:c ratio. Because both sorbose and cellulose were not metabolizable and unable to be transported into the cells, the results reflected the molecular mobility of water. (2)H NMR T(2) relaxation time correlated well with spore germination time, and it distinguished the difference between water sorbed to cellulose and water in a solution associated with dissolved sorbose. On the other hand, mold germination time correlated poorly with a(w). It was highly dependent on the s:c ratio. Water mobility was found to correlate better with biological activity than a(w) because it differentiated the availability between water in dissolved sorbose and adsorbed water in cellulose.
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Water Activity by Pavinee Chinachoti
Water Mobility by Pavinee Chinachoti
Bread Staling and Roles of Water by Pavinee Chinachoti
Health impact of Food and Food ingredients by Pavinee Chinachoti
Microbial Activity and Water by Pavinee Chinachoti