Adriana N. Mauri

UV-MALDI-TOF and ESI-TOF mass spectrometry characterization of silsesquioxanes obtained by the hydrolytic condensation of (3-glycidoxypropyl)-trimethoxysilane in an epoxidized solvent

Silsesquioxanes obtained by the hydrolytic condensation of (3-glycidoxypropyl)trimethoxysilane (GPMS) in diglycidyl ether of bisphenol A (DGEBA) were characterized by electrospray ionization time-of-flight mass spectrometry (ESI-TOF MS) and matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOF MS), employing two different matrices and both positive and negative ion modes. A bimodal distribution of molar masses, in the 1300-6400 m/z range, was observed in MALDI mass spectra. This distribution accounted for oligomers formed in two successive generations but did not include a cluster of higher molar-mass species present in SEC chromatograms. Most of the peaks present in ESI and MALDI mass spectra could be described by the generic formula T n -(OCH 3 ) m , with m = 0, 2, and 4 for n = even, m = 1, 3, 5 for n = odd, and T = RSiO (3n-m)/2n . This corresponds to completely condensed polydedra (m = 0), incompletely hydrolyzed polyhedra (m = 1 to 3), and their precursors (m = 4). Predominant species in the first cluster contained 10 to 14 Si atoms whereas those in the second cluster had 18 to 23 Si atoms. Small amounts of the following species: T 8 (OH)(OCH 3 ), T 9 (OH), T 10 (OH)(OCH 3 ), and T 11 (OH) could be identified in MALDI MS, using 9H-pyrido[3,4-b]indole (nor-harmane) as matrix in the negative ion mode. It was inferred that some of these species had a relevant participation in the generation of the second cluster of higher molar masses. The stability of the silsesquioxane solution in DGEBA was the result of the very small concentration of free SiOH groups available for further condensation.

Neat and silica-enriched polysilsesquioxanes in dispersed media

Fil: Mauri, Adriana Noemi. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Centro de Investigacion y Desarrollo en Criotecnologia de Alimentos. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Centro de Investigacion y Desarrollo en Criotecnologia de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigacion y Desarrollo en Criotecnologia de Alimentos; Argentina

Characterization of soy-protein based SO2-releasing pads for browning prevention in fresh-cut apples

ABSTRACT The use of polymeric matrices releasing active principles is a promising strategy to circumvent dipping treatments and reduce additive usage. Herein, we developed soy protein-based films containing 0, 10, 25 or 50% sodium sulfite on protein isolate basis (SPI), and determined the influence of the antioxidant on the color, thickness, opacity, solubility, moisture, water permeability and mechanical properties of the resulting materials. Raising sulfite concentration reduced the tensile strength, without affecting the Young’s modulus of the films. The formulation containing 50% sodium sulfite on SPI basis was selected based on the lighter color, lowest moisture and higher permeability of the resulting films to evaluate the efficacy of the materials to prevent apple browning. The incorporation of SO2-releasers in packages containing fresh-cut apples delayed fruit yellowing (increase of b* values) by 40%. This shows that sodium sulfite soy protein–based films may be useful to extend the postharvest life of fresh-cut apple.