RESUMEN
Corn starch dispersions (CSD) were hydrolyzed with citric acid and compared with CSD co-treated with citric acid combined with ultrasonication for 1 to 18 days, which are designated as single modification (CSD-SM) and dual modification (CSD-DM), respectively. The logistic functions monitor the dynamics of the hydrolysis advance (%) of the CSD-SM and CSD-DM as a function of time, where the zones most vulnerable to the single-treatment and/or co-treatment of the corn starch granules (CSG) are the amorphous or disordered regions. The characterization results of CSD-DM suggest that the structural changes caused by dual modification affected the morphology, sequence, and microstructure of the CSG. The heterogeneous changes caused by the dual modification changed the configuration of the CSG, generating a kind of destemming of the amorphous lamellae (depolymerization), an increase in the percentage of relative crystallinity of the CSD-DM and an active rearrangement of the intralamellar chains that promoted the relative amount of double helix for 18 days of double modification. The synergistic effect of the dual modification for CSD by the sequential combination of a chemical treatment followed by a physical one improved the hydrolyzed advance by 12 %, the relative crystallinity by 10 %, and the promotion of double helices by 25 % during 18 days of co-treatment.
Asunto(s)
Almidón , Zea mays , Almidón/química , Hidrólisis , Zea mays/química , Ácido Cítrico/química , CinéticaRESUMEN
In the present study, graphite oxide, graphite oxide doped with 0.8 g AgNO3 named GrO-0.5Ag, and graphite oxide doped with 1.25 g AgNO3 named GrO-1.0Ag (silver-doped graphitic materials) were synthesized by the modified Hummers and chemical doping methods. Subsequently, its antimicrobial activity against Bacillus subtilis, Candida albicans, Escherichia coli, and Staphylococcus aureus microorganisms was evaluated by agar well diffusion test with 1 and 2 mg·ml-1 of material concentrations. The silver-doped graphitic materials were characterized by X-Ray Diffraction, Fourier-Transform Infrared, Raman, X-Ray Photoelectron spectroscopies, and Scanning Electron Microscopy. The GrO-0.5Ag material showed a percentage of inhibition effect of 86, 82, 48, and 45% with respect to the positive control for Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Candida albicans microorganisms, respectively. Otherwise, the GrO-1.0Ag material showed a percentage of inhibition effect of 54% with respect to the positive control for Bacillus subtilis and less than 50% for the other microorganisms. The material concentrations showed a slight change in the percentage of inhibition effect for all microorganisms. Graphite oxide functional groups, small crystal size, free silver ions, and silver carbonate formation in silver-doped graphitic materials presented a viable alternative to inhibit bacterial growth.
Asunto(s)
Antiinfecciosos , Grafito , Nanopartículas del Metal , Agar , Bacillus subtilis , Candida albicans , Escherichia coli , Óxidos/farmacología , Plata/farmacología , Staphylococcus aureusRESUMEN
Maize starch was lime-cooked at 92 °C with 0.0-0.40% w/w Ca(OH)2. Optical micrographs showed that lime disrupted the integrity of insoluble remnants (ghosts) and increased the degree of syneresis of the gelatinized starch dispersions (GSD). The particle size distribution was monomodal, shifting to smaller sizes and narrower distributions with increasing lime concentration. X-ray patterns and FTIR spectra showed that crystallinity decreased to a minimum at lime concentration of 0.20% w/w. Lime-treated GSD exhibited thixotropic and viscoelastic behaviour. In the linear viscoelastic region the storage modulus was higher than the loss modulus, but a crossover between these moduli occurred in the non-linear viscoelastic region. The viscoelastic properties decreased with increased lime concentration. The electrochemical properties suggested that the amylopectin-rich remnants and the released amylose contained in the continuous matrix was firstly attacked by calcium ions at low lime levels (<0.20% w/w), disrupting the starch gel microstructure.