[Show abstract][Hide abstract] ABSTRACT: The known O2(1Δg)-sensitizer system Chitosan bounded Rose Bengal (CH-RB), with Rose Bengal (RB) immobilized by irreversible covalent bonding to the polymer Chitosan (CH), soluble in aquous acidic medium, was employed in the photodegradation of three tri-hydroxy benzene water-contaminants (THBs). The system sensitizes the O2(1Δg)-mediated photodegradation of THBs by a process kinetically favored, as compared to that employing free RB dissolved in the same solvent. Additionally the free xanthene dye, degradable by O2(1Δg) through self-sensitization upon prolonged light-exposure, is considerably protected when bonded to CH-polymer. The polymeric sensitizer, totally insoluble in neutral medium, can be removed from the solution after the photodegradative cycle by precipitation through a simple pH change. This fact constitutes an interesting aspect in the context of photoremediation of confined polluted waters. In other words, the sensitizing system could be useful for avoiding to dissolve dyestuffs in the polluted waters, in order to act as conventional sunlight-absorbing dye-sensitizers.In parallel the interaction CH - O2(1Δg) in acidic solution was evaluated. The polymer quenches the oxidative species with a rate constant 2.4x108 M−1s−1 being the process mostly attributable to a physical interaction. This fact promotes the photoprotection of the bonded dye in the CH-RB polymer.This article is protected by copyright. All rights reserved.
Full-text · Article · Sep 2014 · Photochemistry and Photobiology
[Show abstract][Hide abstract] ABSTRACT: Microcapsules (MC) made with gum arabic (GA) as shell material without and with β-carotene (βc) as core material were prepared by the spray-drying technique. The effect of these MC on the photodegradation of riboflavin (Rf) in whole milk by fluorescent daylight lamp irradiation was evaluated at a storage temperature of 4°C. The additions of 1.37 mg/mL of MC without βc (MC-GA) and with 0.54 μg/mL of βc (MC-βc-GA) decreased the apparent first-order rate constant of Rf photodegradation by approximately 26 and 30%, respectively. A systematic kinetic and mechanistic analysis of the results indicates that the global protective effect of the MC is mainly due to the combination of quenching of the electronically excited triplet state of Rf and scavenging of the photogenerated reactive oxygen species, such as singlet molecular oxygen, superoxide radical anion and hydroxyl radical. A minor contribution to the photoprotective effect can be also associated with the inner-filter effect exerted by the MC, which partially blocks the direct excitation of Rf. These results allow us to conclude that photodegradation of Rf in milk can be considerably reduced by the addition of small amounts of MC, avoiding large losses in the nutritional value of milk.
Full-text · Article · Jun 2014 · Journal of Dairy Science
[Show abstract][Hide abstract] ABSTRACT: Kinetic and mechanistic aspects of the photochemical and microbiological degradation of the herbicide Maleic Hydrazide (MH) have been studied. Riboflavin (Rf, vitamin B2) was employed as a main photosensitizer whereas Humic Acid (HA) was included as a second sensitizer in order to more closely simulate natural environmental conditions. MH quenches excited singlet and triplet states of Rf, with rate constants close to the diffusion limit. The herbicide and dissolved molecular oxygen competitively quench triplet excited Rf. As a consequence the reactive oxygen species (ROS), superoxide radical anion (O2(-)), hydrogen peroxide (H2O2) and singlet molecular oxygen (O2((1)Δg)) are produced by electron- and energy-transfer processes, respectively, as demonstrated by auxiliary experiments employing selective auxiliary quenchers and the exclusive O2((1)Δg) generator Rose Bengal (RB). As a global result, the photodegradation of Rf is retarded, whereas MH is degraded by the generated ROS. The bacteria Pseudomonas aeruginosa (Ps) and Bacillus subtilis (Bs), recognized as contaminants surface-water and soil and microbial antagonists of phytopathogenic, were used in the microbiological experiments. Results of the individual incubation of both bacteria in in the presence of MH indicate a stimulation on the Ps growth, implying the biodegradation of the herbicide, whereas MH only exerted a bacteriostatic effect on Bs.
No preview · Article · Apr 2014 · Journal of photochemistry and photobiology. B, Biology
[Show abstract][Hide abstract] ABSTRACT: Microcapsules of gum arabic or maltodextrin 20DE containing antioxidant molecules (AOx), for example, carotenoids and tocopherol derivatives, were prepared by the spray-drying technique. The properties of these microcapsules were evaluated by several techniques, such as dynamic light scattering, scanning electronic microscopy, and steady-state and time-resolved fluorescence spectroscopy of microencapsulated pyrene. The quenching of photochemically generated singlet molecular oxygen ((1)O(2)) by the AOx in homogeneous solvents as well as in microcapsule solutions was evaluated using time-resolved phosphorescence detection of (1)O(2). The quenching rate constant of the process, k(Q)(AOx), was strongly dependent on the type of the AOx. These results are explained by compartmentalization effects of the AOx in the core of the microcapsules and the accessibility of (1)O(2). The contribution of the biopolymer as quencher of (1)O(2) was also investigated. The present results can be applied to the design of edible antioxidant microcapsules within the food and cosmetic industries.
Full-text · Article · Jul 2010 · Journal of Agricultural and Food Chemistry
[Show abstract][Hide abstract] ABSTRACT: The kinetic of the O2(1Δg)-photosensitized oxidation of the flavanone naringin (7-rhamnoglucosyl-4′,5-dihydroxyflavanone, FL) and its chalcone isomer (4′-rhamnoglucosyl-2′,6′,4-trihydroxychalcone, CH) in neutral and 1 mM NaOH ethanol solutions was studied using Rose Bengal as photosensitizer. The rate constants for the chemical quenching of O2(1Δg) by the flavonoids (kr) were determined using either UV–vis absorption spectroscopy or HPLC techniques, and for the total (physical + chemical) quenching (kt) were determined using time-resolved phosphorescence detection of O2(1Δg) at 1270 nm.A larger reactivity towards O2(1Δg) of CH than for FL in neutral ethanol solutions was observed, due to the extra conjugated double bond in CH. However, in alkaline media the reactivity of both isomers was larger than in neutral conditions. This behavior was associated to the increment of electron density by the formation of a carbanion in FL and to the presence of the extended conjugated π-system in the CH isomer by deprotonation of phenolic groups. In all cases, the formation of 4-hydroxybenzoic acid as ending product was detected by HPLC. Based on reported mechanisms of O2(1Δg)-mediated oxidation of flavonoids, the formation of 7-rhamnoglucosyl-5,4′-dihydroxyflavonol as primary photo-oxidation product was proposed.The reactivity towards O2(1Δg) of the aglycone of naringin (5,7,4′-trihydroxyflavanone or naringenin, NG) in alkaline conditions was lower than for the parent naringin, due to incapability of NG to form a carbanion species.These results are expected to have significance in biosynthesis, antioxidant properties and stability of naturally occurring flavonoids.
Full-text · Article · Feb 2007 · Journal of Photochemistry and Photobiology A Chemistry
[Show abstract][Hide abstract] ABSTRACT: Riboflavin (Rf)-mediated photosensitized degradation of vitamins A and D3 in skimmed milk under illumination with a white fluorescence lamp was studied by using the HPLC technique. The photosensitized degradation of both vitamins followed first-order kinetics, and the temperature effect on the observed photodegradation rate constant allowed the determination of the activation energy Ea as being 4 and 16 kcal/mol for vitamins A and D3, respectively. The addition of lycopene microencapsulated by spray-drying with a gum arabic-sucrose (8:2) mixture (MIC) produced a reduction of ca. 45% in the photosensitized degradation rate of both vitamins. Front-face fluorescence experiments showed the same photoprotection factor in the degradation of Rf itself, indicating that the photodegradation mechanism involved Rf-mediated reactive species, such as the excited triplet state of Rf, 3Rf*, and/or singlet molecular oxygen, 1O2. The interaction of both 3Rf* and 1O2 with MIC was evaluated in aqueous solutions by using laser-induced time-resolved absorption or emission spectroscopy, and the contribution of an inner-filter effect in the presence of MIC in skimmed milk was evaluated by diffuse reflectance spectroscopy. The main operating mechanism of photoprotection is due to the deactivation of 3Rf* by the proteic component of gum arabic; thus, gum arabic based microcapsules could be used to improve the photostability of milk during its storage and/or processing under light.
Full-text · Article · Feb 2007 · Journal of Agricultural and Food Chemistry
[Show abstract][Hide abstract] ABSTRACT: The photosensitized isomerization reaction of the natural cis carotenoid bixin (methyl hydrogen 9'-cis-6, 6'-diapocarotene-6, 6'-dioate) with rose bengal or methylene blue as the sensitizer in acetonitrile/methanol (1:1) solution was studied using UV-vis spectroscopy, high-performance liquid chromatography (HPLC), and time-resolved spectroscopic techniques, such as laser-flash photolysis and singlet oxygen phosphorescence detection. In both N(2)- and air-saturated solutions, the main product formed was all-trans-bixin. The observed isomerization rate constants, k(obs), decreased in the presence of air or with increase in the bixin concentration, suggesting the participation of the excited triplet state of bixin, (3)Bix, as precursor of the cis--> trans process. On the other hand, bixin solutions in the absence of sensitizer and/or light did not degrade, indicating that the ground state of bixin is stable to thermal isomerization at room temperature. Time-resolved spectroscopic experiments confirmed the formation of the excited triplet state of bixin and its deactivation by ground state bixin and molecular oxygen quenching processes. The primary isomerization products only degraded in the presence of air and under prolonged illumination conditions, probably due to the formation of oxidation products by reaction with singlet molecular oxygen. An energy-transfer mechanism was used to explain the observed results for the bixin transformations, and the consequences for food color are discussed.
Full-text · Article · Jan 2004 · Journal of Agricultural and Food Chemistry
[Show abstract][Hide abstract] ABSTRACT: Se realizaron estudios de caracterización integral de acelga (Beta vulgaris, var. cycla) cultivada en la Provincia de Santiago del Estero, Argentina. Por tratarse de un vegetal de importante consumo regional, se realizó la determinación de sus constituyentes básicos, minerales y pigmentos para conocer los valores nutricionales que aporta este alimento en nuestra región. Se analizaron comparando hoja y tallo: humedad, cenizas, proteínas, grasas, hidratos de carbono utilizables, fibra dietaria total, contenido de clorofila y carotenoides. En cuanto a minerales, se determinaron calcio, magnesio, sodio, potasio, manganeso, zinc, hierro, fósforo y boro. Se encontraron diferencias en los aportes de minerales, proteínas, grasas y fibra entre hoja y tallo, así como también el contenido de carotenoides exclusivamente en las hojas. Los resultados marcan importantes diferencias en el contenido energético y en su valor provitamínico A entre la hoja y el tallo de este vegetal, mostrando que este último es una parte aprovechable de la planta, recomendable en dietas hipocalóricas.
Full-text · Article · Apr 2003 · Ciência e Tecnologia de Alimentos
[Show abstract][Hide abstract] ABSTRACT: The influence of the medium heterogeneity upon the bimolecular rate constants for the physical quenching, kq, and chemical quenching, kr, of singlet molecular oxygen O2(1deltag) by seven natural and three synthetic carotenoids (CAR) with different substituent patterns was studied in a reverse micelle system of sodium bis(2-ethylhexyl)sulfosuccinate, hexane and water. Because O2(1deltag) was generated inside the water pools of the reverse micelles by photosensitization of the water-soluble dye rose bengal and the CAR are mainly located in the external hexane pseudophase, the quenching process was interpreted using a pseudophase model for the partition of 02(1deltag) between the water pools and the organic pseudophases. The kq values were mainly dependent on the extent of the double-bond conjugation of the CAR, as demonstrated by a good empirical relationship between log(k(q)) and the energy E(S) of the longest wavelength transition pi-->pi* of the CAR. In contrast, the kr values were almost independent of the extent of the double-bond-conjugated system and about four orders of magnitude lower than kq. However, in all cases, CAR photobleaching was observed with the formation of various oxidation products, depending on the photosensitization time. Chromatographic and spectroscopic product analysis for the reaction products of beta-carotene with O2(1deltag) indicated the formation of the beta-carotene-5,8-endoperoxide as the primary oxidation product.
Full-text · Article · May 2002 · Photochemistry and Photobiology
[Show abstract][Hide abstract] ABSTRACT: The carotenoid composition of butternut squash (Cucurbita moschata) cultivated in the province of Santiago del Estero, Argentina, was determined. The main carotenoids isolated were identified as beta-carotene (beta,beta-carotene), alpha-carotene (beta,epsilon-carotene), and lutein (beta,epsilon-carotene-3,3'-diol) and the minor carotenoids, as phytofluene (7,8,11,12,7',8'-hexahydro-psi,psi-carotene), zeta-carotene (7,8,7',8'-tetrahydro-psi,psi-carotene), neurosporene (7,8-dihydro-psi,psi-carotene), violaxanthin (5,6,5',6'- diepoxy-5,6,5',6'-tetrahydro-beta,beta-carotene-3,3'-diol) and neoxanthin (5,6-epoxy-6,7-didehydro-5,6,5',6'-tetrahydro-beta,beta- carotene-3,5,3'-triol). In some samples, 5,6,5',6'-beta-carotene diepoxide, (5,6,5',6'-diepoxy-5,6,5',6'-tetrahydro-beta,beta-carotene) and flavoxanthin (5,8-epoxy-5,8-dihydro-beta,epsilon-carotene-3,3'-diol) were detected. The presence of cis-isomers of beta,beta-carotene was also detected by HPLC. The vitamin A value obtained was 432 micrograms RE/100 g fresh sample, which indicates that this vegetable is an important source of provitamin A.
No preview · Article · Jan 2002 · Archivos latinoamericanos de nutrición