Degradation studies of hydrophilic, partially degradable and bioactive cements (HDBCs) incorporating chemically modified starch

The degradation rate in Hydrophilic, Degradable and Bioactive Cements (HDBCs) containing starch/cellulose acetate blends (SCA) is still low. In order to increase degradation, higher amounts of starch are required to exceed the percolation threshold. In this work, gelatinization, acetylation and methacrylation of corn starch were performed and assessed as candidates to replace SCA in HDBCs. Formulations containing methacrylated starch were prepared with different molar ratios of 2-hydroxyethyl methacrylate and methyl methacrylate in the liquid component and the amount of residual monomer released into water was evaluated. The concentration of reducing sugars, percentage of weight loss and morphologic analyses after degradation all confirmed increased degradation of HDBC with alpha-amylase, with the appearance of pores and voids from enzymatic action. Methacrylated starch therefore is a better alternative to be used as the solid component of HDBC then SCA, since it leads to the formation of cements with a lower release of toxic monomers and more prone to hydrolytic degradation while keeping the other advantages of HDBCs.The authors acknowledge to Foundation for Science and Technology (FCT), who supported this study through funds from project Concept2Cement (POCTI/CTM/60735/2004)

Thermomechanical Behavior of Wheat Gluten Films: Effect of Sucrose, Glycerin, and Sorbitol

Glass transition temperature (Tg) and mechanical and water vapor barrier properties of wheat gluten films containing glycerin, sucrose, glycerin-sucrose, and glycerin-sorbitol were studied. Glycerin and sucrose were immiscible; the wheat gluten film containing both solutes showed two separate thermal transitions (-58°C and -5°C, respectively). The low temperature (low-T) transition (-58°C) was due to a glycerin-rich region. The low-T tan δ peak height influenced the tensile strength and elongation linearly and the water vapor permeability (WVP) curvilinearly. However, the Tg failed to change with solute composition and exhibited low correlation with barrier and mechanical properties. Initial addition of glycerin increased the WVP dramatically. Sucrose decreased the WVP (only slightly), but resulted in a rigid and fragile film. The gluten-glycerin-sorbitol film at a ratio of 15:3:3 (w/w), 16.7% moisture (wb), showed a single effective Tg (-42°C) and intermediate values for tensile strength, percent elongation, and WVP, which were between those of the 15:6:0 and 15:4:2 gluten-glycerin-sucrose films

Solute-Polymer States of Water and the Physico-Chemical Properties of Food Model Systems (Crystallinity, Sorption, Hysteresis, Starch)

239 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1986.The objective was first to study physico-chemical properties of solute-polymer mixtures as related to water binding, solute content and water activity (a(,w)). It was hypothesized that these properties were due to the presence of solute (SOL) and polymer (POL) water. The second objective was to develop a non-invasive analytical method for SOL and POL.Interactions in freeze dried systems were found in sucrose-starch, NaCl-starch and sucrose-protein mixtures over the intermediate moisture range of a(,w). Interactions for sucrose-starch and NaCl-starch were determined by the reduction in water sorption from the expected values. Interacted solutes rose sharply with increasing solute-starch ratio to a maximum and decreased to zero with further increase. Interaction was highest at saturation a(,w) and higher in gelatinized than raw starch. Less interaction was found on desorption. In contrary, sucrose protein interactions resulted in higher water sorption than expected, i.e., they increased the water binding by the proteins.The crystallinity of waxy maize starch and sucrose by X-ray diffraction was found accurate. (1) Starch crystallinity increased with increasing a(,w) and moisture content. In gelatinized starch, a critical moisture content was required for recrystallization. Crystallinity hysteresis loop was over the same a(,w) range as water sorption hysteresis. On desorption, sucrose present caused a sharp decrease in starch crystallinity at 0-10% sucrose while, at higher sucrose content, the crystallinity increased. (2) Sucrose crystallinity in a mixture was about 80% at 0.33 and 0.75 a(,w) and 50% at 0.84 a(,w) on absorption. However, on desorption, all samples showed zero crystallinity. Moisture hysteresis for sucrose and waxy maize starch was insignificant. Sucrose-starch mixtures showed marked hysteresis, only at a(,w) below 0.86, the saturation a(,w) for sucrose. Hysteresis showed a close linear correlation with the amount of amorphous sucrose present.('1)H pulsed NMR was used to characterize the quantify SOL and POL in mixtures of sucrose and starch. T(,1) relaxation time increased with increasing sucrose content and a(,w). Model equations were developed for calculating SOL and POL from T(,1) and a(,w). These values showed high correlations (R('2) > 0.97) with SOL and POL from sorption data, validating the method.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Effect of physico-chemical and molecular mobility parameters on Staphylococcus aureus growth

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 inline image)]. 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