Effects of ozone and oxygen on the degradation of carotenoids in an aqueous model system

The effects of ozone and oxygen on the degradation of carotenoids in an aqueous model system were studied. All-trans beta-carotene, 9-cis beta-carotene, beta-cryptoxanthin, and lycopene were adsorbed onto a C(18) solid phase and exposed to a continuous flow of water saturated with oxygen or ozone at 30 degrees C. Carotenoids were analyzed using HPLC with a C(30) column and a photodiode array detector. Approximately 90% of all-trans beta-carotene, 9-cis beta-carotene, and beta-cryptoxanthin were lost after exposure to ozone for 7 h. A similar loss of lycopene occurred in only 1 h. When exposed to oxygen, all carotenoids, except beta-cryptoxanthin, degraded at lower rates. The degradation of all the carotenoids followed zero-order reaction kinetics with the following relative rates: lycopene > beta-cryptoxanthin > all-trans beta-carotene > 9-cis beta-carotene. The major degradation products of beta-carotene were tentatively identified on the basis of their elution on the HPLC column, UV-Vis spectra, and electrospray LC-MS. Predominant isomers of beta-carotene were 13-cis, 9-cis, and a di-cis isomer. Products resulting from cleavage of the molecule were beta-apo-13-carotenone and beta-apo-14'-carotenal, whereas epoxidation yielded beta-carotene 5,8-epoxide and beta-carotene 5, 8-endoperoxide.     

Theoretical Analysis on the Removal of Cyclic Volatile Organic Compounds by Non-thermal Plasma

Volatile organic compounds (VOCs) from anthropogenic sources, especially cyclic organics with stable structure and strong toxicity (e.g., cyclohexane and benzene), exert hazards to atmospheric environment and human health, and need to be controlled urgently. As an emerging technology for VOC removal, non-thermal plasma (NTP) with low-energy consumption and high removal efficiency is widely studied. However, in contrary to the abundant experiments, theoretical studies are only few, and the degradation mechanisms and pathways of VOCs are still open questions, which hinders the effective VOC removal. Herein, the density function theory (DFT) calculations of NTP degradations for two typical cyclic organics, cyclohexane and benzene, are performed. The degradations of cyclic organics are mainly resulted by the dehydrogenation, decarburation, elimination, and ring-opening reactions and can be markedly promoted with radical ·OH, H·, and O· produced by background gas (H2O and O2). For cyclohexane degradations, the presence of O· decreases the energy barrier from 81.9 to 8.7 kcal/mol in the initial step, leading to an optimal degradation pathway with minimum plasma energy at around 0.5 eV. For benzene degradations, the presence of ·OH decreases the energy barrier from 118.4 to 5.5 kcal/mol in the initial step, triggering an optimal degradation pathway with minimum plasma energy at around 6 eV. The higher plasma energy required in degradation of benzene is due to its more stable structure than alkanes ring. Moreover, the O₂ concentration and plasma energy are suggested to increase for efficient degradation of cyclohexane and benzene, respectively.     

Model studies on the photosensitized isomerization of bixin

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.     

In-depth mechanistic study on the formation of acrylamide and other vinylogous compounds by the maillard reaction

The formation of acrylamide was studied in low-moisture Maillard model systems (180 degrees C, 5 min) based on asparagine, reducing sugars, Maillard intermediates, and sugar degradation products. We show evidence that certain glycoconjugates play a major role in acrylamide formation. The N-glycosyl of asparagine generated about 2.4 mmol/mol acrylamide, compared to 0.1-0.2 mmol/mol obtained with alpha-dicarbonyls and the Amadori compound of asparagine. 3-Hydroxypropanamide, the Strecker alcohol of asparagine, generated only low amounts of acrylamide ( approximately 0.23 mmol/mol), while hydroxyacetone increased the acrylamide yields to more than 4 mmol/mol, indicating that alpha-hydroxy carbonyls are much more efficient than alpha-dicarbonyls in converting asparagine into acrylamide. The experimental results are consistent with the reaction mechanism based on (i) a Strecker type degradation of the Schiff base leading to azomethine ylides, followed by (ii) a beta-elimination reaction of the decarboxylated Amadori compound to afford acrylamide. The beta-position on both sides of the nitrogen atom is crucial. Rearrangement of the azomethine ylide to the decarboxylated Amadori compound is the key step, which is favored if the carbonyl moiety contains a hydroxyl group in beta-position to the nitrogen atom. The beta-elimination step in the amino acid moiety was demonstrated by reacting under low moisture conditions decarboxylated model Amadori compounds obtained by synthesis. The corresponding vinylogous compounds were only generated if a beta-proton was available, for example, styrene from the decarboxylated Amadori compound of phenylalanine. Therefore, it is suggested that this thermal pathway may be common to other amino acids, resulting under certain conditions in their respective vinylogous reaction products.     

Kinetics of photoirradiation-induced synthesis of soy oil-conjugated linoleic acid isomers

Photoirradiation of soy oil with UV/visible light has been shown to produce significant amounts of trans,trans conjugated linoleic acid (CLA) isomers through conversion of various synthesized intermediate cis,trans isomers. The objective of this study was to determine the kinetics of CLA isomers synthesis to better understand the production of various isomers. Soy oil was irradiated with UV/visible light for 144 h in the presence of an iodine catalyst and CLA isomers analyzed by gas chromatography (GC). Arrhenius plots were developed for the conversion of soy oil linoleic acid (A) to form cis-, trans/trans-, cis-CLA (B), conversion of cis-, trans/trans-, cis-CLA to form trans,trans-CLA (C) with respect to B, and formation of trans,trans-CLA isomers with respect to C. The kinetics of consumption of linoleic acid (LA) to form cis-, trans/trans-, cis-CLA was found to be of second-order with a rate constant of 9.01 x 10-7 L/mol s. The rate of formation of cis-, trans/trans-, cis-CLA isomers depends on the rate of formation from LA and its rate of consumption to form trans,trans-CLA isomers. The conversion of cis-, trans/trans-, cis-CLA isomers to trans,trans-CLA isomers was found to be of first-order with a rate constant of 2.75 x 10-6 s-1. However, the formation of thermodynamically stable trans,trans-CLA isomers (C) with respect to C was found to be a zero-order reaction with a rate constant of 10.66 x 10-7 mol/L s. The consumption of LA was found to be the rate-determining step in the CLA isomers formation reaction mechanism. The findings provide a better understanding of the mechanism of CLA isomers synthesis by photoirradiation and the factors controlling the ratio of various isomers.     

Thermal stability of genistein and daidzein and its effect on their antioxidant activity

Soy isoflavones, present in many processed soy foods, are known for their phytoestrogenic and antioxidant activities. The aim of this work was to study the kinetics of genistein and daidzein degradation at elevated temperatures and to follow changes in their antioxidant activity. Daidzein and genistein in model solutions (pH 7 and 9) were thermally treated at 120 degrees C or incubated at 70, 80, and 90 degrees C. Isoflavone degradation was observed at all temperatures, with apparent first-order kinetics at 70-90 degrees C, and E(a) = 8.4 and 11.6 kcal/mol at pH 9, respectively. Microcalorimetric stability tests showed a similar pattern of degradation, however, with higher E(a) (genistein, 73.7 kcal/mol; daidzein, 34.1 kcal/mol) that may be attributed to the anaerobic conditions. The antioxidant activity of incubated isoflavone solutions, followed by the ABTS test, decreased rapidly at pH 9 for genistein, whereas only moderate reduction was observed for daidzein (pH 7 and 9) or genistein at pH 7. This may indicate different degradation mechanisms for genistein and daidzein.     

Effect of storage temperature on the degradation of dimethoate in fortified orange and peach juices

The effect of storage temperature on dimethoate degradation in fortified orange and peach juices was studied. The insecticide was aseptically injected into packed orange and peach juices and stored at 40, 15, and 0 degrees C. Samples were taken at regular time intervals and were examined for dimethoate residues. The residues were determined with a simple gas chromatographic method; the recoveries of dimethoate from orange and peach juices were found to be from 88 to 114% for both products. The limits of determination were 0.004 and 0.003 mg/kg, respectively. From the experimental data, rate constants, half-lives, and activation energies for the decomposition of dimethoate in orange and peach juices were evaluated. During the storage of fruit juices in refrigerated rooms (0 degrees C) half-lives of dimethoate were found to be largely extended, being 1733 days for orange juice and 2310 days for peach juice. Corresponding times for storage at 15 degrees C were 533 days for both juices and for storage at 40 degrees C 24 days for orange juice and 24.6 days for peach juice. The activation energy for dimethoate in orange juice was 22.3 kcal/mol and for peach juice, 21. 2 kcal/mol.     

Impact of high-pressure carbon dioxide combined with thermal treatment on degradation of red beet (Beta vulgaris L.) pigments

A combined high-pressure carbon dioxide (HP-CO 2) and thermal degradation reaction of betanin and isobetanin in aqueous solution was investigated and can be described by a first-order decay. At 45 degrees C, the degradation rate constant ( k) for each pigment component significantly increased (the half-life ( t 1/2) decreased, p < 0.05) with elevated pressure. Furthermore, HP-CO 2 treatment led to lower k values (higher t 1/2 values) than thermal treatment. However, k and t 1/2 values approached those of thermal treatment when the pressure was >30 MPa combined with temperatures exceeding 55 degrees C. Moreover, betanin was more stable than isobetanin under HP-CO 2. E a values ranged from 94.01 kJ/mol for betanin and 97.16 kJ/mol for isobetanin at atmospheric pressure to 170.83 and 142.69 kJ/mol at 50 MPa, respectively. A higher pressure and temperature as well as longer exposure time resulted in higher values of L*, b*, C*, and h degrees . HP-CO 2 induced more degradation products from betanin and isobetanin than thermal treatment with an identical temperature and exposure time.     

Physical stability of shikonin derivatives from the roots of Lithospermum erythrorhizon cultivated in Korea.

Five red shikonin pigments, deoxyshikonin, shikonin, acetylshikonin, isobutylshikonin, and beta-hydroxyisovalerylshikonin, were isolated from the roots of Lithospermum erythrorhizon cultivated in Korea. The purified pigments were red, purple, and blue at acidic, neutral, and alkaline pH values, respectively. Physical stability of the purified pigments against heat and light in an aqueous solution was examined for possible value-added food colorants. The thermal degradation reactions were carried out at pH 3.0 (50 mM glycine buffer) in 50% EtOH/H(2)O. Deoxyshikonin (t(1/2) = 14.6 h, 60 degrees C) and isobutylshikinin (t(1/2) = 19.3 h, 60 degrees C) are relatively less stable than other shikonin derivatives (t(1/2) = 40-50 h, 60 degrees C). Activation energies of thermal degradation of the isolated pigments were calculated. The activation energy of deoxyshikonin was the highest (12.5 kcal mol(-)(1)) and that of beta-hydroxyisovalerylshikonin was the lowest (1.71 kcal mol(-)(1)) value. Light stabilities of the pigments were similar to each other in that the half-life values of photodegradation for 20000 lx light intensity were 4.2-5.1 h.     

Kinetics of chlorophyll degradation and color loss in heated broccoli juice

Degradation of chlorophyll in broccoli juice occurred at temperatures exceeding 60 degrees C. Chemical analysis revealed that degradation of chlorophyll a and b to pheophytin a and b, respectively, followed first-order kinetics and that chlorophyll a was more heat sensitive than chlorophyll b. Temperature dependencies of chlorophyll a and b degradation rate constants could be described by Arrhenius equations with activation energies (E(a)) of 71.04 +/- 4.89 and 67.11 +/- 6.82 kJ/mol, respectively. Objective greenness measurements, using the -a value as the physical property, together with a fractional conversion kinetic analysis, indicated that green color degradation followed a two-step process. Kinetic parameters for the first degradation step were in accordance with the kinetic parameters for pheophytinization of the total chlorophyll content, as determined by chemical analysis (E(a) approximately 69 kJ/mol). The second degradation step, that is, the subsequent decomposition of pheophytins, was characterized by an activation energy of 105.49 +/- 4.74 kJ/mol.     

Carotenoid composition of marigold (Tagetes erecta) flower extract used as nutritional supplement.

Commercially prepared marigold flower (Tagetes erecta) extract was saponified and analyzed for carotenoid composition. HPLC analyses were performed on two normal-phase columns (beta-Cyclobond and silica) and on a C(30) reversed-phase column. The extract contained 93% utilizable pigments (detected at 450 nm), consisting of all-trans and cis isomers of zeaxanthin (5%), all-trans and cis isomers of lutein, and lutein esters (88%). All were identified by chromatographic retention, UV-visible spectra, and positive ion electrospray mass spectrometry in comparison to authentic standards. Contrary to previous findings, insignificant levels (<0.3%) of lutein oxidation products were detected in the saponified extract. This compositional determination is important for the application of marigold extract in nutritional supplements and increases its value as a poultry feed colorant because it contains more biologically useful lutein compounds than previously believed.     

Thermal degradation of anthocyanins from purple potato (cv. Purple Majesty) and impact on antioxidant capacity

Degradation parameters of purified anthocyanins from purple-fleshed potato (cv. Purple Majesty) heated at high temperatures (100-150 °C) were determined. Purified anthocyanins, prepared by removing salts, sugars, and colorless nonanthocyanin phenolics from the crude extract, were monitored and quantified using HPLC and spectrophotometry for heat-induced degradation products. Separation of colorless phenolics from the anthocyanins was confirmed using HPLC at two wavelengths, 280 and 520 nm. The degradation kinetics of purified anthocyanins followed a first-order reaction with reaction rate constants (k values) of 0.0262-0.2855 min(-1), an activation energy of 72.89 kJ/mol, thermal death times (D values) of 8.06-8789 min, and a z value of 47.84 °C over the temperature range of 100-150 °C. The enthalpy and entropy of activation were 59.97 kJ/mol and -116.46 J/mol·K, respectively. The antioxidant capacity in the purified anthocyanins, measured by DPPH and ABTS assays, was increased after the thermal treatment, indicating antioxidant activities of degradation products in the samples.     

Stability of isoflavones in soy milk stored at elevated and ambient temperatures

Soy isoflavones are widely recognized for their potential health benefits. The increased use of traditional and new food products calls for the assessment of their stability during processing and storage. The present study examines the stability of genistein and daidzein derivatives in soy milk. Soy milk was stored at ambient and elevated temperatures, and the change in isoflavone concentration was monitored with time. Genistin loss in time showed typical first-order kinetics, with rate constants ranging from 0.437-3.871 to 61-109 days(-1) in the temperature ranges of 15-37 and 70-90 degrees C, respectively. The temperature dependence of genistin loss followed the Arrhenius relation with activation energies of 7.2 kcal/mol at ambient temperatures and 17.6 kcal/mol at elevated temperatures. At early stages of soy milk storage at 80 and 90 degrees C, the 6' '-O-acetyldaidzin concentration increased, followed by a slow decrease. The results obtained in this study can serve as a basis for estimating the shelf life of soy milk as related to its genistin content.     

Thermodynamic parameters of beta-lactoglobulin-pectin complexes assessed by isothermal titration calorimetry

Isothermal titration calorimetry (ITC) was used to determine the binding constant, stoichiometry, enthalpy, and entropy of beta-lactoglobulin/low- and high-methoxyl pectin (beta-lg-LM- and HM-pectin) complexes at 22 degrees C and at pH 4. The binding isotherms revealed the formation of soluble intrapolymer complexes (C1) further followed by their aggregation in interpolymer complexes (C2). The interaction between beta-lg and LM- or HM-pectin in C1 and C2 occurred spontaneously with a Gibbs free energy around -10 kcal/mol. The C1 were enthalpically driven, whereas enthalpic and entropic factors were involved in the C2 formation. Because ITC did not allow the dissociation of different enthalpic contributions, the values measured as pectin and beta-lg interacted could partially be attributed to conformational changes. The C1 had a binding stoichiometry of 8.3 and 6.1 beta-lg molecules complexed per LM- or HM-pectin molecule, respectively. The C2 had about 16.5 and 15.1 beta-lg molecules complexed per LM- and HM-pectin, respectively.     

Thermal degradation of commercial grade sodium copper chlorophyllin

Sodium copper chlorophyllin (SCC), a water-soluble commercial derivative of chlorophyll, has gained importance as a food colorant and dietary supplement with apparent chemopreventive activities. The thermal stability of SCC was studied to assess the potential application of this chlorophyll derivative for use in thermally processed foods and supplements. Thermal degradation of an aqueous 500 ppm SCC solution was monitored between 25 and 100 degrees C by a loss of absorbance at 627 nm. Decomposition was also followed by reversed phase C18 HPLC with photodiode array detection to monitor the loss of Cu(II)Chlorin e4, the major component of commercial grade SCC. The rate of thermal degradation of SCC was found to follow first-order reaction kinetics. HPLC analysis confirmed the ultraviolet and visible absorbance data and also demonstrated loss of the major SCC component, Cu(II)Chlorin e4, at a rate faster than that of overall SCC. The activation energy was estimated using the Arrhenius equation and found to be 13.3 +/- 0.8 and 16.0 +/- 2.1 kcal/mol for the thermal degradation of SCC and Cu(II)Chlorin e4, respectively. The observed temperature sensitivity of SCC was determined to be similar to that of natural chlorophyll and raises the possibility of color deterioration when used in food products where mild to severe thermal treatment is applied. Furthermore, the implication of rapid loss of Cu(II)Chlorin e4, a reported bioactive component of SCC, upon heating may result in alteration of potential dietary benefits such as antimutagenic and antioxidant activity.     

Thermal processing of vegetables increases cis isomers of lutein and zeaxanthin

Carotenoids, lutein and zeaxanthin, found in fruits and vegetables, comprise the macula pigment of the eye. These carotenoids exist in plants as the all-trans geometric form; however, in human plasma, cis isomers of these carotenoids have also been identified. Thermal processing can induce carotenoid trans to cis isomerization. The aim of this research was to determine if thermal processing induces isomerization of lutein and zeaxanthin and to quantify the extent of this reaction. High-performance liquid chromatography was used to separate and quantitate geometric isomers of lutein and zeaxanthin. Isomers were tentatively identified by UV-visible absorbance spectra, comparison of retention times to those of isomerized standards using C(30) chromatography, and mass spectrometry. Thermal processing increased the percent cis isomers of lutein and zeaxanthin up to 22 and 17%, respectively. Further studies are needed to consider the physiological impact of consuming carotenoid isomers in processed vegetables.     

Hydrolysis kinetics of fenthion and its metabolites in buffered aqueous media

This study investigates the hydrolysis kinetics of fenthion and its five oxidation metabolites in pH 7 and pH 9 buffered aqueous media at 25, 50, and 65 degrees C. Five metabolites and three hydrolysis products were synthesized and purified. The reactant and the corresponding hydrolysis products were determined by HPLC. Rate constant and half-life studies revealed that fenthion and its metabolites were relatively stable in neutral media, and their stability decreased as pH increased. The half-lives at 25 degrees C ranged from 59.0 days for fenthion to 16.5 days for fenoxon sulfone at pH 7, and from 55.5 days for fenthion to 9.50 days for fenoxon sulfone at pH 9; half-lives were greatly reduced at elevated temperatures. The activation energy (E(a)) was found to range from 16.7 to 22.1 kcal/mol for the compounds investigated. The phenol hydrolysis product of fenthion and fenoxon, 3-methyl-4-methylthiophenol was not stable in pH 7 and pH 9 buffered solutions at 50 degrees C, whereas 3-methyl-4-methylsulfonylphenol and 3-methyl-4-methylsulfinylphenol were relatively stable under the same conditions. At pH 9, the primary hydrolysis mechanisms of fenthion and its oxidation metabolites were combination of hydroxide ion and neutral water molecule attacking on the P atom to form corresponding phenol derivatives. Under neutral conditions, the primary hydrolysis mechanisms of fenthion and its oxidation metabolites were assumed to be the combination of water molecule attacking on the P atom to form phenol derivatives and on the C atom to yield dealkylation products.     

ToF-SIMS characterization of thermal modifications of bixin from Bixa orellana fruit

Bixa orellana fruit extracts were studied by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The intensity of the peak at m/z 396, assigned to the bixin molecular ion plus two hydrogen atoms (C25H(32)O(4+), decreased as the extract was heated and nearly disappeared with heating above 150 degrees C. Simultaneously, the formation of dimers at m/z 790, 804, and 818 was observed. The ToF-SIMS spectrum is characterized by a large amount of peaks generated by the principal ions and their multiple fragmentation patterns. To extract maximum information from the data set, multivariate statistical analysis was applied. Principal component analysis revealed important structural changes of the bixin molecule upon heating at different temperatures. This information can be used by the food industry as by controlling the temperature of the heating process the red/yellow balance of this colorant can be tuned.     

Degradation kinetics of the antioxidant additive ascorbic acid in packed table olives during storage at different temperatures

The kinetics of ascorbic acid (AA) loss during storage of packed table olives with two different levels of added AA was investigated. Three selected storage temperatures were assayed: 10 degrees C, ambient (20-24 degrees C), and 40 degrees C. The study was carried out in both pasteurized and unpasteurized product. The effect of pasteurization treatment alone on added AA was not significant. In the pasteurized product, in general AA degraded following a first-order kinetics. The activation energy calculated by using the Arrhenius model averaged 9 kcal/mol. For each storage temperature, the increase in initial AA concentration significantly decreased the AA degradation rate. In the unpasteurized product, AA was not detected after 20 days in samples stored at room temperature and AA degradation followed zero-order kinetics at 10 degrees C, whereas at 40 degrees C a second-order reaction showed the best fit. In both pasteurized and unpasteurized product, the low level of initial dehydroascorbic acid disappeared during storage. Furfural appeared to be formed during storage, mainly at 40 degrees C, following zero-order kinetics.     

Interaction of curcumin and bixin with β-cyclodextrin: complexation methods, stability, and applications in food

This work aimed to compare methods for the formation of complexes of bixin and curcumin with β-cyclodextrin (β-CD) and to evaluate the stability of the complexes formed by these methods and their food applications. The stoichiometric relationship between curcumin and β-CD was 1:2 and that between bixin and β-CD was 1:1. Curcumin-β-CD and bixin-β-CD complexes formed by kneading, coprecipitation, and simple mixing were evaluated by differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), or nuclear magnetic resonance (NMR-H). For both curcumin and bixin, the best method of complexation was coprecipitation. Complexation of colorants with β-CD promoted an intensification of color and increased water solubility; however, stabilization in the presence of light occurred only for bixin. Application of curcumin-β-CD in cheese and yogurt and bixin-β-CD in the curd did not alter the initial characteristics of the products, which were sensorialy well accepted. Therefore, the complexation of these natural colorants with β-CD favors their use in low-fat foods, broadening the field of industrial application.