| 1. |
- Chen, Guo, 1969, et al.
(författare)
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A Porosimetric Mapping of Breadcrumb Structures by Differential Scanning Calorimetry and Nuclear Magnetic Resonance
- 2013
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Ingår i: Food Biophysics. - : Springer Science and Business Media LLC. - 1557-1858 .- 1557-1866. ; 8:3, s. 209-215
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Tidskriftsartikel (refereegranskat)abstract
- Ice crystals in frozen bread are substantially shaped by the complex pore structures of crumb. In this study we inspected the breadcrumb porosity of ice-filled pores from the profiles of ice crystals mapped by differential scanning calorimetry and nuclear magnetic resonance. Two types of wheat bread containing different amounts of dietary fiber and sugar were studied after frozen storage at -18 A degrees C for 3 weeks. Both pore sizes and pore size distributions were derived via comparing the measurements to those of water-saturated mesoporous silica (MCM-41 C18) with a well-defined pore size distribution. Good consistency was shown for the crumb pore structures obtained using the two techniques. Both bread types featured broad nanometer ranges of pore sizes characterized with largely bimodal size distributions. Besides, the frozen high-fiber bread displayed a higher proportion of large pores and a broader pore size distribution than the high-sugar bread. By comparing such pore size distributions with those obtained previously for the corresponding fresh bread, it can be concluded that structural differences between the two bread types were produced during the frozen storage, manifesting the disparate freezing performances of bread with different formulations.
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| 2. |
- Chen, Guo, 1969, et al.
(författare)
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Formation and distribution of ice upon freezing of different formulations of wheat bread
- 2012
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Ingår i: Journal of Cereal Science. - : Elsevier BV. - 1095-9963 .- 0733-5210. ; 55:3, s. 279-284
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Tidskriftsartikel (refereegranskat)abstract
- The formation and distribution of ice upon the freezing of fresh breadcrumb were investigated using differential scanning calorimetry. Three types of wheat bread containing different amounts of sugar and dietary fiber were measured. Various frozen states were produced through freezing with different cooling rates (0.5, 1, 2, 5, 10, 20 and 30 degrees C/min) to -30 degrees C; they were then analyzed and compared by thawing with the same heating rate (10 degrees C/min) to 20 degrees C. All DSC heating traces exhibited dual endotherms in the temperature range for the melting of ice: The major transition was attributed to the ice formed in the large crumb pores (gas cells) and the minor event, which preceded the major endotherm, was assigned primarily to the ice formed in the nanometer-sized pores within the gluten-starch matrix. The size of ice crystals in the two classes of pores was estimated using the modified Gibbs-Thompson relation. The distributions of ice in these pores depended on the bread compositions. It is concluded that the complex crumb porosity plays an essential role in shaping the activities of water and ice in the breadcrumb.
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| 3. |
- Chen, Guo, 1969, et al.
(författare)
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Glassy Dynamics of Proteins
- 2012
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Ingår i: Structural Glasses and Supercooled Liquids: Theory, Experiment, and Applications. - : Wiley. - 9780470452233 ; , s. 319-339
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Chen, Guo, 1969, et al.
(författare)
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Impact of long-term frozen storage on the dynamics of water and ice in wheat bread
- 2013
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Ingår i: Journal of Cereal Science. - : Elsevier BV. - 0733-5210 .- 1095-9963. ; 57:1, s. 120-124
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Tidskriftsartikel (refereegranskat)abstract
- Frozen storage of bread has a substantial impact on the dynamics of water and ice in the crumb and crust. In this study, the impact was characterized using wheat bread stored at -18 °C for a long term of ?4 months. The frozen bread incurred a considerable loss of the crumb water that migrated out and formed ice crystals on the bread surface. Such a moisture decrease underwent more rapidly for the bread stored without intact crust, suggesting the specific role of crust during frozen storage. Moisture also redistributed significantly within the frozen crumb, resulting in an elevated crumb heterogeneity of freezable water. This redistribution of freezable water was accompanied by a progressive recrystallization of the crumb-borne ice crystals, which were measured to grow into bulk sizes using a modified calorimetric procedure for analyzing the crumb samples at their as-frozen states.
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| 5. |
- Eckardt, Johanna, et al.
(författare)
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Long-term frozen storage of wheat bread and dough : Effect of time, temperature and fibre on sensory quality, microstructure and state of water
- 2013
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Ingår i: Journal of Cereal Science. - : Elsevier BV. - 0733-5210 .- 1095-9963. ; 57:1, s. 125-133
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to determine effect of storage time, storage temperature and addition of fibre on sensory quality, state of water, microstructure and texture of bread and dough. Samples with and without fibre, were stored frozen for 2, 3.5 and 6 months at temperatures of -19, -16 and -8 °C as dough and bread. Sensory quality was evaluated by a trained analytical panel. Microstructure was analysed by light microscopy. Texture measurements were performed on bread, and the state of water was measured by differential scanning calorimetry. Bread without fibre stored as dough at -19 °C was the sample most like freshly baked bread. Sensory evaluation also confirmed that quality of the final bread was improved if samples were stored as dough compared to stored as bread. The microstructure had larger gaps between the starch and gluten phases when stored at warmer temperatures, due to retrogradation of starch, dehydration of gluten and water migration. DSC measurements showed that bread stored at -19 °C gained extra amount of freezable water, but lost ice after storage at -8 °C. Texture measurements showed that firmness increased with extended storage time. Bread stored at -8 °C had lowest quality in all measurements.
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| 6. |
- Meng, X. X. Y., et al.
(författare)
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Humidity-Dependent Phase State of Gasoline Vehicle Emission-Related Aerosols
- 2021
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 55:2, s. 832-841
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Tidskriftsartikel (refereegranskat)abstract
- The phase states of primarily emitted and secondarily formed aerosols from gasoline vehicle exhausts were investigated by quantifying the particle rebound fraction (f). The rebound behaviors of gasoline vehicle emission-related aerosols varied with engines, fuel types, and photochemical aging time, showing distinguished differences from biogenic secondary organic aerosols. The nonliquid-to-liquid phase transition of primary aerosols emitted from port fuel injection (PFI) and gasoline direct injection (GDI) vehicles started at a relative humidity (RH) = 50 and 60%, and liquefaction was accomplished at 60 and 70%, respectively. The RH at which f declined to 0.5 decreased from 70 to 65% for the PFI case with 92# fuel, corresponding to the photochemical aging time from 0.37 to 4.62 days. For the GDI case, such RH enhanced from 60 to 65%. Our results can be used to imply the phase state of traffic-related aerosols and further understand their roles in urban atmospheric chemistry. Taking Beijing, China, as an example, traffic-related aerosols were mainly nonliquid during winter with the majority ambient RH below 50%, whereas they were mostly liquid during the morning rush hour of summer, and traffic-related secondary aerosols fluctuated between nonliquid and liquid during the daytime and tended to be liquid at night with increased ambient RH.
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| 7. |
- Peng, X., et al.
(författare)
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Photodissociation of particulate nitrate as a source of daytime tropospheric Cl2
- 2022
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Chlorine atoms (Cl) are highly reactive and can strongly influence the abundances of climate and air quality-relevant trace gases. Despite extensive research on molecular chlorine (Cl2), a Cl precursor, in the polar atmosphere, its sources in other regions are still poorly understood. Here we report the daytime Cl2 concentrations of up to 1 ppbv observed in a coastal area of Hong Kong, revealing a large daytime source of Cl2 (2.7 pptv s−1 at noon). Field and laboratory experiments indicate that photodissociation of particulate nitrate by sunlight under acidic conditions (pH < 3.0) can activate chloride and account for the observed daytime Cl2 production. The high Cl2 concentrations significantly increased atmospheric oxidation. Given the ubiquitous existence of chloride, nitrate, and acidic aerosols, we propose that nitrate photolysis is a significant daytime chlorine source globally. This so far unaccounted for source of chlorine can have substantial impacts on atmospheric chemistry. © 2022, The Author(s).
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| 8. |
- Swenson, Jan, 1966, et al.
(författare)
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Anomalous dynamics of aqueous solutions of di-propylene glycol methylether confined in MCM-41 by quasielastic neutron scattering
- 2014
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 141:21
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Tidskriftsartikel (refereegranskat)abstract
- The molecular dynamics of solutions of di-propylene glycol methylether (2PGME) and H2O (or D2O) confined in 28 angstrom pores of MCM 41 have been studied by quasielastic neutron scattering and differential scanning calorimetry over the concentration range 0-90 wt.% water. This system is of particular interest due to its pronounced non-monotonic concentration dependent dynamics of 2PGME in the corresponding bulk system, showing the important role of hydrogen bonding for the dynamics. In this study we have elucidated how this non-monotonic concentration dependence is affected by the confined geometry. The results show that this behaviour is maintained in the confinement, but the slowest diffusive dynamics of 2PGME is now observed at a considerably higher water concentration; at 75 wt.% water in MCM-41 compared to 30 wt.% water in the corresponding bulk system. This difference can be explained by an improper mixing of the two confined liquids. The results suggest that water up to a concentration of about 20 wt.% is used to hydrate the hydrophilic hydroxyl surface groups of the silica pores, and that it is only at higher water contents the water becomes partly mixed with 2PGME. Hence, due to this partial micro-phase separation of the two liquids larger, and thereby slower relaxing, structural entities of hydrogen bonded water and 2PGME molecules can only be formed at higher water contents than in the bulk system. However, the Q-dependence is unchanged with confinement, showing that the nature of the molecular motions is preserved. Thus, there is no indication of localization of the dynamics at length scales of less than 20 angstrom. The dynamics of both water and 2PGME is strongly dominated by translational diffusion at a temperature of 280 K.
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