Active naringin-chitosan films: impact of UV irradiation.

Bioactive citrus extract-chitosan films were prepared through solvent casting-evaporation method. The impact of near UV irradiation was studied to reach a better understanding of the film behavior. The antimicrobial activity of films against Listeria innocua was maintained after UV irradiation. To study the interaction between chitosan and citrus extract components, naringin (main component) was selected as the model compound. UV treatment caused modifications of the flavanone regardless of the solvent used for its dissolution, depending on the concentration of naringin in the film: the greater the concentration the lower the modification. DSC results suggested cross-links due to UV irradiation and interactions between naringin and chitosan. This was confirmed by a decrease in the naringin release from the irradiated samples. Naringin- and citrus extract-chitosan films showed an increased absorbance in the UV region compared to pure chitosan films, showing potentiality for decreasing the lipid oxidation induced by UV light in foodstuffs.

Styrene-spaced copolymers including anthraquinone and ß-O-4 lignin model units: synthesis, characterization and reactivity under alkaline pulping conditions.

A series of random copoly(styrene)s has been synthesized via radical polymerization of functionalized anthraquinone (AQ) and ß-O-4 lignin model monomers. The copolymers were designed to have a different number of styrene spacer groups between the AQ and ß-O-4 lignin side chains aiming at investigating the distance effects on AQ/ß-O-4 electron transfer mechanisms. A detailed molecular characterization, including techniques such as size exclusion chromatography, MALDI-TOF mass spectrometry, and (1)H, (13)C, (31)P NMR and UV-vis spectroscopies, afforded quantitative information about the composition of the copolymers as well as the average distribution of the AQ and ß-O-4 groups in the macromolecular structures. TGA and DSC thermal analysis have indicated that the copolymers were thermally stable under regular pulping conditions, revealing the inertness of the styrene polymer backbone in the investigation of electron transfer mechanisms. Alkaline pulping experiments showed that close contact between the redox active side chains in the copolymers was fundamental for an efficient degradation of the ß-O-4 lignin model units, highlighting the importance of electron transfer reactions in the lignin degradation mechanisms catalyzed by AQ. In the absence of glucose, AQ units oxidized phenolic ß-O-4 lignin model parts, mainly by electron transfer leading to vanillin as major product. By contrast, in presence of glucose, anthrahydroquinone units (formed by reduction of AQ) reduced the quinone-methide units (issued by dehydration of phenolic ß-O-4 lignin model part) mainly by electron transfer leading to guaiacol as major product. Both processes were distance dependent.

Unexpected matrix interactions in liquid secondary ion mass spectrometry of two pyranosyl mercaptans.

An unexpected interaction with a thioglycerol matrix appeared in the liquid secondary ion mass spectrometry (LSIMS) spectra of two pyranosyl mercaptans [2,3,4,6-tetra-O-acetyl-1-thio-ß-D-glucopyranose (1a) and 2,3,4,6-tetra-O-acetyl-1,5-dithio-ß-D-glucopyranose (1b)] often used to prepare glucosinolates, important thiosaccharidic metabolites found in all plants of the order Brassicales. The reactions, probably occurring in the solvent cage, seem to involve radical mechanisms.

In vitro inhibitory effect of tetrahydrocurcuminoids on Fusarium proliferatum growth and fumonisin B1 biosynthesis.

Many plant pathogens produce toxic metabolites when growing on food and feed. Some antioxidative components seem to prevent fungal growth and mycotoxin formation. Recently, we synthesized a new class of powerful antioxidative compounds, i.e. tetrahydrocurcuminoids, and its structure/antioxidant activity relationships have been established. The South West of France produces large amounts of corn, which can be infected by Fusarium species, particularly F. proliferatum. In this context, the efficiency of tetrahydrocurcuminoids, which can be obtained from natural curcuminoids, was investigated to control in vitro the growth of F. proliferatum and the production of its associated mycotoxin, fumonisin B1. The relation between structure and antifungal activity was studied. Tetrahydrocurcumin (THC1), with two guaiacyl phenolic subunits, showed the highest inhibitory activity (measured as radial growth on agar medium) against the F. proliferatum development (67% inhibition at a concentration of 13.6 µmol ml⁻¹). The efficiencies of THC2 (36% at a concentration of 11.5 µmol ml⁻¹), which contains syringyl phenolic units, and THC3 (30% at a concentration of 13.6 µmol ml⁻¹), which does not have any substituent on the aromatic rings, were relatively close. These results indicate that the simultaneous presence of guaiacyl phenols and the enolic function of the ß-diketone moiety play an important role in the inhibition mechanisms. The importance of this combination was confirmed using n-propylguaiacol and acetylacetone as molecular models. Under the same conditions, ferulic acid and eugenol, other natural phenolic antioxidants, were less efficient in inhibiting fungal growth. THC1 also reduced fumonisin B1 production in liquid medium by approximately 35, 50 and 75% at concentrations of 0.8, 1.3, and 1.9 µmol ml⁻¹, respectively. These very low inhibitory concentrations show that tetrahydrocurcuminoids could be one of the most promising biobased molecules for the control of mycotoxinogen fungal strains.

Valorization of an industrial organosolv-sugarcane bagasse lignin: Characterization and use as a matrix in biobased composites reinforced with sisal fibers.

In the present study, the main focus was the characterization and application of the by-product lignin isolated through an industrial organosolv acid hydrolysis process from sugarcane bagasse, aiming at the production of bioethanol. The sugarcane lignin was characterized and used to prepare phenolic-type resins. The analysis confirmed that the industrial sugarcane lignin is of HGS type, with a high proportion of the less substituted aromatic ring p-hydroxyphenyl units, which favors further reaction with formaldehyde. The lignin-formaldehyde resins were used to produce biobased composites reinforced with different proportions of randomly distributed sisal fibers. The presence of lignin moieties in both the fiber and matrix increases their mutual affinity, as confirmed by SEM images, which showed good adhesion at the biocomposite fiber/matrix interface. This in turn allowed good load transference from the matrix to the fiber, leading to biobased composites with good impact strength (near 500 J m(-1) for a 40 wt% sisal fiber-reinforced composite). The study demonstrates that sugarcane bagasse lignin obtained from a bioethanol plant can be used without excessive purification in the preparation of lignocellulosic fiber-reinforced biobased composites displaying high mechanical properties.

Biobased composites from glyoxal-phenolic resins and sisal fibers.

Lignocellulosic materials can significantly contribute to the development of biobased composites. In this work, glyoxal-phenolic resins for composites were prepared using glyoxal, which is a dialdehyde obtained from several natural resources. The resins were characterized by (1)H, (13)C, 2D, and (31)P NMR spectroscopies. Resorcinol (10%) was used as an accelerator for curing the glyoxal-phenol resins in order to obtain the thermosets. The impact-strength measurement showed that regardless of the cure cycle used, the reinforcement of thermosets by 30% (w/w) sisal fibers improved the impact strength by one order of magnitude. Curing with cycle 1 (150 degrees C) induced a high diffusion coefficient for water absorption in composites, due to less interaction between the sisal fibers and water. The composites cured with cycle 2 (180 degrees C) had less glyoxal resin coverage of the cellulosic fibers, as observed by images of the fractured interface observed by SEM. This study shows that biobased composites with good properties can be prepared using a high proportion of materials obtained from natural resources.

Sisal fibers: surface chemical modification using reagent obtained from a renewable source; characterization of hemicellulose and lignin as model study.

Sisal fibers have one of the greatest potentials among other lignocellulosic fibers to reinforce polymer matrices in composites. Sisal fibers have been modified to improve their compatibility with phenolic polymer matrices using furfuryl alcohol (FA) and polyfurfuryl alcohols (PFA) that can be obtained from renewable sources. The modification corresponded first to oxidation with ClO 2, which reacts mainly with guaiacyl and syringyl units of lignin, generating o- and p-quinones and muconic derivatives, followed by reaction with FA or PFA. The FA and PFA modified fibers presented a thin similar layer, indicating the polymer character of the coating. The untreated and treated sisal fibers were characterized by (13)C CP-MAS NMR spectrometry, thermal analysis, and scanning electron microscopy. Furthermore, for a better understanding of the reactions involved in the FA and PFA modifications, the sisal lignin previously extracted was also submitted to those reactions and characterized. The characterization of isolated lignin and hemicellulose provides some information on the chemical structure of the main constitutive macrocomponents of sisal fibers, such information being scarce in the literature.

Renewable resources as reinforcement of polymeric matrices: composites based on phenolic thermosets and chemically modified sisal fibers.

Lignocellulosic materials can significantly contribute to the development of composites, since it is possible to chemically and/or physically modify their main components, cellulose, hemicelluloses and lignin. This may result in materials more stable and with more uniform properties. It has previously been shown that chemically modified sisal fibers by ClO(2) oxidation and reaction with FA and PFA presented a thin coating layer of PFA on their surface. FA and PFA were chosen as reagents because these alcohols can be obtained from renewable sources. In the present work, the effects of the polymeric coating layer as coupling agent in phenolic/sisal fibers composites were studied. For a more detailed characterization of the fibers, IGC was used to evaluate the changes that occurred at the sisal fibers surface after the chemical modifications. The dispersive and acid-base properties of untreated and treated sisal fibers surfaces were determined. Biodegradation experiments were also carried out. In a complementary study, another PFA modification was made on sisal fibers, using K2Cr2O(7) as oxidizing agent. In this case the oxidation effects involve mainly the cellulose polymer instead of lignin, as observed when the oxidation was carried out with ClO(2). The SEM images showed that the oxidation of sisal fibers followed by reaction with FA or PFA favored the fiber/phenolic matrix interaction at the interface. However, because the fibers were partially degraded by the chemical treatment, the impact strength of the sisal-reinforced composites decreased. By contrast, the chemical modification of fibers led to an increase of the water diffusion coefficient and to a decrease of the water absorption of the composites reinforced with modified fibers. The latter property is very important for certain applications, such as in the automotive industry.

Studies on the photochemistry of 1,7-diphenyl-1,6-heptadiene-3,5-dione, a non-phenolic curcuminoid model.

The comparative photostability of curcumin 1, and two non-phenolic curcuminoids: 1,7-diphenyl-1,6-heptadiene-3,5-dione 2 (unsubstituted curcumin) and dimethylcurcumin 3 in non-degassed dilute solutions (approximately 3-5 x 10(-5) mol l(-1)) has been established by UV-visible absorption spectroscopy; disappearance quantum yields were measured. The similar behavior of the three studied curcuminoids is indicative of only a moderate role of phenol groups in the photodegradation process. Structural analysis of the photodegradation products of compound 2 in more concentrated solution (approximately 3.6 x 10(-3) mol l(-1)) shows formation of benzaldehyde, cinnamaldehyde, 2'-hydroxy-5',6'-benzochalcone 4, flavanone 5 and some other unidentified photoproducts. Flavanone 5 is formed by irradiation of chalcone 4. It represents a unique example of photochemical conversion of a diarylheptanoid molecule into a flavonoid, another very important class of natural products.