Mariana Montenegro

Singlet Molecular Oxygen Quenching Ability of Carotenoids in a Reverse-micelle Membrane Mimetic System¶

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(1Δg) 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(1Δg) 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 O2(1Δg) 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(kq) and the energy E(S) of the longest wavelength transition π→π* 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 β‐carotene with O2(1Δg) indicated the formation of the β‐carotene‐5,8‐endoperoxide as the primary oxidation product.

Gum Arabic: More Than an Edible Emulsifier

Gum Arabic (GA) or Acacia gum is an edible biopolymer obtained as exudates of mature trees of Acacia senegal and Acacia seyal which grow principally in the African region of Sahe in Sudan. The exudate is a non-viscous liquid, rich in soluble fibers, and its emanation from the stems and branches usually occurs under stress conditions such as drought, poor soil fertility, and injury (Williams & Phillips, 2000).

Characterization and singlet oxygen quenching capacity of spray-dried microcapsules of edible biopolymers containing antioxidant molecules.

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.

Gum arabic microcapsules as protectors of the photoinduced degradation of riboflavin in whole milk

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 1.37mg/mL of MC without βc (MC-GA) and with 0.54μg/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.

Caracterización de acelga fresca de Santiago del Estero (Argentina). Comparación del contenido de nutrientes en hoja y tallo. Evaluación de los carotenoides presentes

An integrated characterization study of Swiss chard grown in Santiago del Estero, Argentina, was carried out. As Swiss chard is a vegetable of important regional consumption, the determination of its basic constituents, minerals and pigments was done to appraise the nutritional value offered by this food in our area. Moisture, ash content, proteins, fats, available carbohydrates, total dietary fiber, chlorophylls and carotenoids were analysed, comparing the leaves and the stems. As to minerals, calcium, magnesium, sodium, manganese, zinc, iron, phosphorous, potassium, and boron were determined. Differences in the concentration of minerals, proteins, fats and fiber between the leaves and the stems were found, as well as the carotenoid content mainly in the leaves. These findings revealed important differences in energy content and provitamin A value, showing that the stem is a usable part of this vegetable to be recommended in diets with low calories.

The Employment of a Removable Chitosan‐Derivatized Polymeric Sensitizer in the Photooxidation of Polyhydroxylated Water‐Pollutants

The known O2(1∆g)‐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(1∆g)‐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(1∆g) 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(1∆g) in acidic solution was evaluated. The polymer quenches the oxidative species with a rate constant 2.4 × 108 M−1 s−1 being the process mostly attributable to a physical interaction. This fact promotes the photoprotection of the bonded dye in the CH‐RB polymer.

Physicochemical characterization of water-soluble chitosan derivatives with singlet oxygen quenching and antibacterial capabilities

New water-soluble chitosan derivatives (WSCh) were obtained by Maillard reaction (MR) between glucosamine (GA) with both low and medium molecular weight chitosans (Ch). The WSCh showed larger solubility than the respective Ch, while their deacetylation degree (DD) decreased by approximately 12%. Infrared spectroscopy experiments of WSCh confirmed the formation of imine bonds after MR with intensified pyranose structure, and sugar molecules as polymer branches. However, a 6-times reduction of the molecular weight of WSCh was measured, indicating the breakdown of the polysaccharide chain during the MR. The polysaccharides quenched singlet molecular oxygen (1O2), with rate quenching constants correlating with the DD value of the samples, suggesting the important role of amino groups (-NH2) in the deactivation of 1O2. Additionally, all polysaccharides presented antimicrobial activity against pathogenic bacteria, e.g. Staphylococcus aureus, Escherichia coli, Salmonella sp., Enterococcus faecalis and Listeria ivanovii, as tested by their minimum inhibitory concentration (MIC). This way we obtained new water-soluble polysaccharides, with similar functional properties to those presented by native Ch, enhancing its potential application as carrier material for bioactive compounds.

Encapsulated whey–native yeast Kluyveromyces marxianus as a feed additive for animal production

ABSTRACT Whey is the main byproduct of the cheese industry. While the composition is variable, it retains up to 55% of milk nutrients. The beneficial features of whey indicates a promising source of new potentially probiotic strains for the development of food additives destined for animal production. The aim of this study was to identify Kluyveromyces spp. isolated from whey, to study some probiotic properties and to select the best strain to be encapsulated using derivatised chitosan. Kluyveromyces marxianus strains (VM003, VM004 and VM005) were isolated from whey and identified by phenotypic and molecular techniques. These three yeast strains were able to survive under gastrointestinal conditions. Moreover, they exhibited weak auto-aggregation and co-aggregation with pathogenic bacteria (Salmonella sp., Serratia sp., Escherichia coli and Salmonella typhimurium). In general the K. marxianus strains had a strong antimicrobial activity against pathogenic bacteria. The potential probiotic K. marxianus VM004 strain was selected for derivatised-chitosan encapsulation. Material treated with native chitosan exhibited a strong antimicrobial activity of K. marxianus, showing a total growth inhibition at 10 min exposure. However, derivatised-chitosan encapsulation showed a reduced antimicrobial activity. This is the first study to show some probiotic properties of whey–native K. marxianus, in vitro. An encapsulation strategy was applied using derivatised chitosan.

On the natural fate of maleic hydrazide. Kinetic aspects of the photochemical and microbiological degradation of the herbicide

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.

Soy genistein administered in soluble chitosan microcapsules maintains antioxidant activity and limits intestinal inflammation

We used water-soluble Chitosan obtained by Maillard reaction with glucosamine to microencapsulate soy genistein (Ge) and preserve its biological activity for oral administration. Release of Ge was pH dependent with a super Case II mechanism at pH 1.2 and an anomalous transport with non-Fickian kinetics at pH 6.8. Microencapsulated Ge retained its antioxidant properties in vitro and its daily administration to mice attenuated clinical signs of acute colitis, limited inflammatory reaction and reduced oxidative stress and tissue injury as well. Remarkably, after feeding microencapsulated Ge the production of IL-10 in colonic tissue was restored to levels of untreated controls. According to statistical multivariate analysis, this cytokine was the parameter with the highest influence on the inflammatory/oxidative status. Microencapsulation of Ge with derivatized Chitosan becomes an interesting alternative to develop therapeutic approaches for oxidative inflammatory diseases; our findings suggest that the soy isoflavone could be incorporated into any functional food for application in intestinal inflammation.