Browsing by Subject "Polyols"

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    Aqueous solution and vapor phase adsorption of oxygenates onto zeolites
    (2012-11) Mallon, Elizabeth Emma
    The ability of zeolites to discriminate between molecules on the basis of size and functionality gives them the potential to be effective adsorbents and membrane materials for purification of biomass-derived chemicals and fuels. Since molecules from biomass are polyfuntional and non-volatile, it is necessary to decouple the interactions that drive aqueous adsorption of oxygenates onto zeolites in order to develop efficient zeolite-based separations for biomass processing. In this dissertation, the roles of adsorbent structural and chemical composition and adsorbate functionality are explored through the systematic development of aqueous and vapor adsorption isotherms of C2-C6 oxygenates on small (FER), medium (MWW, MFI, BEA), and large (MOR, FAU) pore zeolites as well as on hierarchical microporous-mesoporous materials (MCM-36, 3DOm-MFI, and SBA-15). Ambient temperature Henry’s constants (Kads) for aqueous diol and triol adsorption on silicalite-1 (aluminum-free MFI) increase exponentially with carbon number demonstrating that confinement of the adsorbate in the zeolite pores is a primary driving force for adsorption. This conclusion is supported by a monotonic decrease in propylene glycol Kads values with an increase in adsorbent pore size, and by a comparison of propylene glycol Kads values on MWW and MFI and their hierarchical counterparts (MCM-36 and 3DOm-MFI, respectively) that shows that propylene glycol preferentially adsorbs in the micropores of hierarchical materials. A comparison of diol and triol adsorption on silicalite-1 demonstrates that increasing the number of hydroxyl groups causes a decrease in adsorption affinity, and this phenomenon is probed by comparing Henry’s constants for aqueous adsorption of C3 polyfunctional molecules onto zeolites with their octanol-water partition coefficients, Kow, which were calculated using the prevalent ClogP group contribution method. It was found that Kads increases linearly with Kow for these adsorbates on H-ZSM-5 (aluminum-containing MFI), FAU, BEA, and ITQ-1 (MWW) at 278 K regardless of interactions in the bulk phase as measured by the solution activity coefficient. Exceptions to the correlation established between Kads and Kow are the adsorption of 1,2,!-triols with carbon number greater than three on H-ZSM-5 and adsorption of all oxygenates studied on FER, which we postulate is due to a shift in the adsorption configuration with adsorbate/zeolite structure which cannot be captured by Kow alone. The effect of zeolite defects on oxygenate adsorption was isolated through the development of vapor and aqueous adsorption isotherms on silicalite-1 materials that vary in structural and surface properties. Silicalite-1 crystals prepared through alkaline-synthesis, alkaline synthesis with steaming post-treatment, and fluoride synthesis routes are confirmed as crystalline MFI by SEM and XRD and are shown to contain ∼8.5 to 0 silanol defects per unit cell by 29Si MAS, 1H MAS, and 1H-29Si CPMAS NMR. A hysteresis in the Ar 87 K adsorption isotherm at 10−3 P/P0 evolves with a decrease in silanol defects, and, through features in the XRD and 29Si MAS NMR spectra, it is postulated that the hysteresis is the result of an orthorhombic-monoclinic symmetry shift with decreasing silanol defect density. Gravimetric and aqueous solution measurements reveal that propylene glycol adsorption at 333 K is promoted by silanol defects, with a maximum 20-fold increase observed for aqueous adsorption in the Henry’s Law regime with an increase from ∼0 to 8.5 silanols per unit cell. A comparison of vapor and aqueous propylene glycol adsorption on defect-free silicalite-1 at 333 K, both of which exhibit the Type V character, indicates that water enhances adsorption by a factor of 2 in the Henry’s Law regime, which is in agreement with simulations reported in the literature. Kads values for aqueous C2-C4 polyol adsorption at 298 K are shown to have a linear dependence on the silanol defect density, which indicates that these molecules preferentially interact with silanol defects. i
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    Effect of polyols on flavor release during mastication of sugar-free confections
    (2012-10) Raithore, Smita
    Flavor is one of the most important attributes influencing food choice. In confectionery products, a major focus on product innovation involves developing more desirable flavor attributes for maximum impact and duration as well as providing healthier products. In addition to advances in flavor technology, the confectionery industry has moved towards products that are sugar-free by utilizing polyols (sugar alcohols) instead of traditional sugar ingredients, such as sucrose or glucose. Polyols, like sugar, provide sweetness to a confectionery product and can also impact the product performance in multiple ways such as the texture and the flavor release properties. Currently there is limited knowledge on how polyols alter flavor delivery and ultimately impedes product innovation. The overall objective of this thesis was to investigate the influence of polyols on delivery of flavor components, volatiles (aroma) and non-volatiles (taste), in confectionery products. As an initial study (presented in Chapter 3) a model confectionery product was formulated with different polyols: xylitol, mannitol or sorbitol that ranged in physical-chemical properties. Release of volatile and non-volatile flavor components was monitored close to the respective biological receptors of three trained panelists over a 12 min mastication period. Real-time release of volatile flavor compounds (aroma) were measured in exhaled breath by APCI-MS analysis, and non-volatile flavor compounds (taste, polyols and high intensity sweeteners, HIS: acesulfame K and aspartame) were monitored in expectorated saliva by LC/MS/MS analysis. In general, the rate of delivery of both aroma and taste components were inversely related to the water solubility of the polyol utilized. The flavor release profiles for both the aroma and HIS compounds were highest for the sample formulated with the least water-soluble polyol (mannitol) and lowest for sample with the most water-soluble polyol (sorbitol). Time-intensity sensory evaluation of these samples was also in agreement with the instrumental data supporting the observed chemical changes in flavor delivery resulted in changes in flavor perception. Based on the observation that water solubility of polyols influenced flavor delivery, we further hypothesized that surface area of the polyol material would also influence the flavor release profile. In chapter 4, the influence of polyol-type and particle size on the flavor release profile in a sugar-free confection was investigated in vivo. Four samples with an average particle size of 62 or 246μm (sorbitol) and 57 or 184μm (mannitol) were analyzed. Two trained panelists masticated the samples at a controlled chewing rate for 12 minutes period. APCI-MS analysis of the expired breath reported the samples formulated with mannitol, in general, had a higher aroma release profile than when formulated with sorbitol. LC/MS analysis of the expectorated saliva reported the HIS had a significantly higher release profile for the smaller polyol particle size samples; the release rate of polyol was not significantly changed by the particle size. Sensory time-intensity analysis of the sorbitol samples was also in agreement with the HIS delivery, the smaller particle size sorbitol gum was significantly higher in perceived sweetness intensity (compared to the larger particle sized sample). In summary, unique polyol-flavor interactions were reported to alter flavor delivery; the aroma compounds were mainly influenced by the polyol-type whereas the HIS by particle size (surface area). In the final research phase the mechanisms of flavor delivery in confections were further investigated by conducting a mass balance analysis of the volatile and non-volatile flavor compounds during a 12 min mastication of samples formulated with sorbitol of two particle sizes (Chapter 5). The mass and release rate of the volatile compounds (ethyl butyrate, benzaldehyde, menthol, menthone and limonene) were monitored in the exhaled breath, in the saliva and the sample bolus; whereas the non-volatiles compounds (sorbitol or mannitol, aspartame and acesulfame K) were monitored in the expectorated saliva and the sample bolus. In general, the percent recovery of the volatile compounds released during mastication was lower or was less quantifiable in comparison to the more polar non-volatile compounds. For the volatile compounds analyzed, the medium hydrophobicity region showed the lowest % recovery (< 10%) and suggested biological absorption was the main quantitative route of delivery in the oral cavity. The aroma release profile in the exhaled breath was reported not to be influenced by the compound concentration in the saliva or sample bolus during mastication but was suggested to be mainly controlled by residual levels of these compounds in the oral cavity or the lungs. Conversely, the percent recovery of the non-volatile compounds released from the samples during mastication was relatively high (> 90%). The release profile of both the polyol (sorbitol) and HIS compounds were reported not to be concentration dependent during the first 4 minutes of mastication. This suggested the polyol and HIS were physically entrapped in the sample matrix and the release mechanism was related to the surface exposure rate these compounds to the oral cavity during chewing (mechanical stress) for release to occur during mastication. In summary, we have reported novel mechanisms by which polyols influence the delivery of the aroma and taste compounds in sugar-free confectionery products as well as oral processing mechanisms that govern flavor delivery (absorption in the oral cavity). This information provides new knowledge for the food (and pharmaceutical) industry to tailor product quality.