Triplet state energy of the carotenoid bixin determined by photoacoustic calorimetry

The triplet state energy level of the natural cis-carotenoid bixin (methyl hydrogen 9'Z-6,6-diapocarotene-6,6'-dioate) was determined using laser-induced photoacoustic calorimetry (PAC) in acetonitrile/methanol (1: 1) solution. An energy-transfer process with anthracene as sensitizer in O-2-saturated solution was used to populate the carotenoid triplet state. The energy balance of the system allowed the calculation of the triplet energy content of bixin as E-T = 18 +/- 2 kcal/mol. The result is discussed in relation with both its singlet molecular oxygen quenching and cis trans isomedzation abilities. The quantum yield, Phi = 0.69, for the formation of either the triplet state or the singlet molecular oxygen by the sensitizer anthracene was also determined. (c) 2006 Elsevier Ltd. All rights reserved.74356156

Thermal degradation kinetics of bixin in an aqueous model system

The kinetics of the thermal degradation of the natural cis carotenoid bixin in a water/ethanol (8:2) solution was studied as a function of temperature (70-125 degrees C), using high-performance liquid chromatography. The curves for the decay of bixin and formation of products (e.g., di-cis and all-trans isomers and a C17 degradation compound) did not adjust well to a first-order rate law, but very good fits were obtained using a biexponential model. This mathematical modeling gave the rate OF constant values for the formation of the primary products from bixin, and the energy barrier for each step was obtained. The di-cis isomers were formed immediately (15 kcal/mol) together with the decay of bixin, followed by a slow consumption, indicating their role as reaction intermediates. In fact, the di-cis isomers could easily revert to bixin (E-a approximate to 3 kcal/mol) or yield the primary C17 degradation product, with an energy barrier of 6.5 kcal/mol. In turn, 24 kcal/mol was necessary for the Bix -> all-trans step, explaining its slower formation.5362307231

Photoprotection of vitamins in skimmed milk by an aqueous soluble lycopene-gum arabic microcapsule

Riboflavin (Rf)-mediated photosensitized degradation of vitamins A and D-3 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 E-a as being 4 and 16 kcal/mol for vitamins A and D-3, 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, (3)Rf*, and/or singlet molecular oxygen, O-1(2). The interaction of both (3)Rf* and O-1(2) 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 (3)Rf* 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.55232332

Characterization and Singlet Oxygen Quenching Capacity of Spray-Dried Microcapsules of Edible Biopolymers Containing Antioxidant Molecules

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)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 (O-1(2)) by the AOx in homogeneous solvents as well as in microcapsule solutions was evaluated using time-resolved phosphorescence detection of O-1(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 O-1(2). The contribution of the biopolymer as quencher of O-1(2) was also investigated. The present results can be applied to the design of edible antioxidant microcapsules within the food and cosmetic industries.581380048011CICyT-UNSECONICETANPCyTFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Alexander von Humboldt FoundationFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Thermal Degradation Kinetics of Carotenoids in a Cashew Apple Juice Model and Its Impact on the System Color

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The thermal degradation kinetics of the main carotenoids of cashew apple in a juice model system was studied by HPLC and related to the changes of its CIELAB color parameters. Similar isomerization equilibrium constants and activation energies were observed for both all-trans-beta-carotene and all-trans-beta-cryptoxanthin. The curves for the decay of the main carotenoids and color changes showed a biphasic behavior that was best fitted by a biexponential equation. For the same heating conditions (60 or 90 degrees C), similar rate constants for the fast (gamma(1)) and slow (gamma(2)) decays were obtained for both the chemical (carotenoids) and physical (color) parameters monitored in the present research. This fact indicates that color parameters, such as Delta E*, are good predictors of both all-trans-beta-cryptoxanthin and all-trans-beta-carotene thermal degradation. A mechanism for thermal carotenoid degradation was proposed, involving parallel irreversible and reversible coupled reactions of both the initial all-trans-beta-cryptoxanthin and all-trans-beta-carotene to yield, respectively, degradation compounds and mono-cis isomers.571778417845Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CICyT-UNSE and CONICET (Argentina)Research Career of CONICETFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Singlet oxygen quenching and radical scavenging capacities of structurally-related flavonoids present in Zuccagnia punctata Cav.

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The singlet oxygen ((1)O(2)) quenching and free radical (DPPH(center dot), ABTS(center dot+) and O(2)(center dot-)) scavenging ability of three structurally-related flavonoids (7-hydroxyflavanone HF, 2',4'-dihydroxychalcone DHC and 3,7- dihydroxyflavone DHF) present in the Argentinean native shrub Zuccagnia punctata Cav. were studied in solution by combining electrochemical and kinetic measurements, mass spectroscopy, end-point antioxidant assays and computational calculations. The results showed that the antioxidant properties of these flavonoids depend on several factors, such as their electron- and hydrogen atom donor capacity, the ionization degree of the more acidic group, solvatation effects and electrostatic interactions with the oxidant species. The theoretical calculations for both the gas and solution phases at the B3LYP level of theory for the Osanger reaction field model agreed with the experimental findings, thus supporting the characterization of the antioxidant mechanism of the Z. punctata flavonoids.436553U14CONICETANPCyTCICyT-UNSECIUNTFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP