Microwave-assisted alkali hydrolysis for cellulose isolation from wheat straw: Influence of reaction conditions and non-thermal effects of microwave.

Microwave-assisted hydrolysis has been widely studied for cellulose fiber isolation, but the influence of reaction conditions and the microwave non-thermal effect are not well clarified. In this study, a series of well-designed experiments were carried out to measure the effects of reaction conditions including temperature, duration and alkali concentration. Compared to the other parameters, temperature was more relevant to the cellulose content in fiber. It could reach the maximum purity of 90.66 % when the temperature was up to 140 °C. Moreover, the existence of non-thermal effect of microwave has been confirmed through extensive determination and characterization of the fibers obtained from parallel controlled experiments conducted with or without microwave assistance. Approximately 50 %-75 % reduction in reaction time or 67 % of that in chemical costs would be realized under microwave with respect to traditional heating hydrolysis. Therefore, this work provides both deep insight and efficiency strategy into the microwave-assisted cellulose isolation.

Effect of Organic Solvents on Microalgae Growth, Metabolism and Industrial Bioproduct Extraction: A Review.

In this review, the effect of organic solvents on microalgae cultures from molecular to industrial scale is presented. Traditional organic solvents and solvents of new generation-ionic liquids (ILs), are considered. Alterations in microalgal cell metabolism and synthesis of target products (pigments, proteins, lipids), as a result of exposure to organic solvents, are summarized. Applications of organic solvents as a carbon source for microalgal growth and production of target molecules are discussed. Possible implementation of various industrial effluents containing organic solvents into microalgal cultivation media, is evaluated. The effect of organic solvents on extraction of target compounds from microalgae is also considered. Techniques for lipid and carotenoid extraction from viable microalgal biomass (milking methods) and dead microalgal biomass (classical methods) are depicted. Moreover, the economic survey of lipid and carotenoid extraction from microalgae biomass, by means of different techniques and solvents, is conducted.

Impact of lignin structure on oil production via hydroprocessing with a copper-doped porous metal oxide catalyst.

A copper-catalyzed depolymerization strategy was employed to investigate the impact of lignin structure on the distribution of hydroprocessing products. Specifically, lignin was extracted from beech wood and miscanthus grass. The extracted lignins, as well as a commercial lignin (P1000), were then fractionated using ethyl acetate to provide three different portions for each source of lignin [total of 9 fractions]. Each fraction was structurally characterized and treated with a copper-doped porous metal oxide (Cu-PMO) catalyst under 4MPa H2 and at 180°C for 12h. The reaction conditions provided notable yields of oil for each fraction of lignin. Analysis of the oils indicated phenolic monomers of commercial interest. The structure of these monomers and the yield of monomer-containing oil was dependent on the origin of the lignin. Our results indicate that hydroprocessing with a Cu-PMO catalyst can selectively provide monomers of commercial interest by careful choice of lignin starting material.

Structure impact of two galactomannan fractions on their viscosity properties in dilute solution, unperturbed state and gel state.

Two fractions of carob galactomannans (GM25 and GM80) were extracted at respectively 25°C and 80°C from crude locust bean gum. Those fractions having slightly different chemical structures, previously characterized, were studied for their viscosity properties over a wide range of concentrations: diluted solution, unperturbed state and gel state. For each of the physical properties, links to the chemical fine structure could be established, expanding knowledge on the topic: in dilute solution, GM25 is more soluble in water while GM80 seems to tend to self-association due to its structure as highlighted by intrinsic viscosity measurements ([η]GM25=9.96dLg-1 and [η]GM80=4.04dLg-1). In unperturbed state, initial viscosities η0 were more important for GM80 fractions at 1% and 2% due to greater hyperentanglements (η0(GM80,1%)=9.9Pas; η0(GM80,2%)=832.0; Pa.s η0(GM25,1%)=3.1Pas; η0(GM25,2%)=45.1Pas). In gel state, hydrogels obtained from GM80 were also stronger (hardness GM80 (2%)=0.51N and hardness GM25 (2%)=0.11N), suggesting a much more important number of junction areas within the gel network. The findings discussed herein demonstrate the potential for new applications.

Extraction by three processes of arabinoxylans from wheat bran and characterization of the fractions obtained.

Arabinoxylans (AXs) were extracted from destarched wheat bran (DWB) according to different processes, with a view to their production at industrial scale. Two fractions (F3a and F3b, respectively, purified on 10kDa and 100kDa ultrafiltration membranes) were obtained with low yields by treating DWB with an endoxylanase and this process left a solid residue exhausted in enzyme-extractable AXs (EDWB). F1 and F2 AX fractions were obtained by treatment with sodium hydroxide of, respectively, DWB and EDWB. The fraction F4 resulted from a hydrothermal treatment of EDWB in a pressure reactor, followed by ethanol precipitation. The different AX fractions were characterized and compared for the composition in monosaccharides, for the contents in fats and in ferulic, phytic and uronic acids, for the molecular mass distribution and the degrees of methylation and acetylation. The alkaline extractions gave one deesterified AX population with molecular mass (MM) higher than 670kDa and arabinose/xylose ratios (Ara/Xyl) around 1. The enzyme and thermal treatments yielded AXs with two main populations in size-exclusion chromatography (the largest one at 5-12.5kDa and a second one at 140-160kDa), having overall Ara/Xyl of, respectively, 0.7 and 0.5 for both processes. These data bring information about the influence of the process on the characteristics of AX fractions obtained from pretreated wheat bran. Here are also reported processes that enabled to recover enzyme-unextractable AXs from DWB, including an original and up-scalable hydrothermal extraction. Phytate contents of isolated AXs are described for the first time.

Characterization of sugar beet pectic-derived oligosaccharides obtained by enzymatic hydrolysis.

Three pectic oligosaccharides (POS) obtained by enzymatic hydrolysis of sugar beet pectin by combining endopolygalacturonase and pectinmethylesterase, were characterized using high performance liquid chromatography, thermogravimetric analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry and X-ray diffraction. According to chromatographic analyses, POS are composed of mixture of polymers with different molecular weights and different galacturonic acid contents. The thermal analysis showed no major variation in thermal behavior regarding POS composition but showed that POS were more sensitive to thermal degradation than the parent pectin as well as the deesterified pectin. No change in composition of the gaseous products was obtained through TGA-FTIR analysis. The X-ray pattern of POS clearly indicated a considerable decrease in crystallinity when compared to the native pectin. Thus, thermal characterization of POS may have practical repercussions if the formulation in which POS is incorporated is submitted to a high temperature treatment.

The use of Macronet resins to recover gamma-decalactone produced by Rhodotorula aurantiaca from the culture broth.

During the biotransformation of castor oil into gamma-decalactone, R. aurantiaca produced both the lactone form and its precursor (4-hydroxydecanoic acid). After six days of culture, a maximum yield of gamma-decalactone of 6.5 g/l was obtained. The parameters of gamma-decalactone adsorption on three Macronet resins (MN-202, MN-102 and MN-100) were investigated in water. Adsorption isotherms of gamma-decalactone for the three Macronet resins were linear. The trapping of gamma-decalactone produced by R. aurantiaca on these resins was then carried out. gamma-Decalactone was effectively retained by all the studied Macronet resins. The resin MN-202 trapped gamma-decalactone more efficiently than MN-102 and MN-100. The percentages of gamma-decalactone adsorbed on the resins MN-202, MN-102 and MN-100 were, respectively, 85, 75 and 81%, whereas around 70% of the adsorbed gamma-decalactone was then desorbed. We propose an industrial process that uses Macronet resins to extract gamma-decalactone from culture broth of R. aurantiaca.

The utilization of gum tragacanth to improve the growth of Rhodotorula aurantiaca and the production of gamma-decalactone in large scale.

The production of gamma-decalactone and 4-hydroxydecanoic acid by the psychrophilic yeast R. aurantiaca was studied. The effect of both compounds on the growth of R. aurantiaca was also investigated and our results show that gamma-decalactone must be one of the limiting factors for its production. The addition of gum tragacanth to the medium at concentrations of 3 and 4 g/l seems to be an adequate strategy to enhance gamma-decalactone production and to reduce its toxicity towards the cell. The production of gamma-decalactone and 4-hydroxydecanoic acid was significantly higher in 20-l bioreactor than in 100-l bioreactor. By using 20 g/l of castor oil, 6.5 and 4.5 g/l of gamma-decalactone were extracted after acidification at pH 2.0 and distillation at 100 degrees C for 45 min in 20- and 100-l bioreactors, respectively. We propose a process at industrial scale using a psychrophilic yeast to produce naturally gamma-decalactone from castor oil which acts also as a detoxifying agent; moreover the process was improved by adding a natural gum.

Enzymatic interesterification of anhydrous milk fat with rapeseed and/or linseed oil: oxidative stability.

Blends of anhydrous milk fat (AMF) and linseed oil (70:30) and of AMF, rapeseed oil (RO), and linseed oil (LO) (70:20:10) were submitted to enzymatic interesterification. The oxidative stabilities of the blends, the interesterified (IE) blends, and IE blends with 50 ppm of alpha-tocopherol added as antioxidant were studied. Samples were stored in open flasks at 60, 25, and 4 degrees C and periodically submitted to peroxide, p-anisidine, and TBA value determinations and UV measurement at 232 and 268 nm. The analysis of volatile compounds was carried out by SPME for the samples stored at 60 degrees C. Peroxides appeared to be the only significant oxidation products after 12 weeks of storage at 4 degrees C. As expected, the binary blends (BB) were more sensitive to oxidation than the ternary blends (TB). The BB were associated with increased volatile emission compared to the TB. Interesterification led to variable effects on the oxidation of fat mixtures, depending on composition and temperature (beneficial effect on BB, at both 25 and 60 degrees C, and a rather neutral effect on TB). The IE blends exhibited higher volatile release prior to aging. A pro-oxidant effect of alpha-tocopherol addition was observed at 25 degrees C on both BB and TB. At 60 degrees C, an antioxidant effect was observed on TB.

Production of gamma-decalactone by a psychrophilic and a mesophilic strain of the yeast Rhodotorula aurantiaca.

Among 18 psychrophilic strains isolated near the Antarctic Station, the psychrophilic strain Rhodotorula aurantiaca A19 was selected for its ability of growth and gamma-decalactone production at low temperatures. The effects of temperature, initial pH, and castor oil concentration on the growth and gamma-decalactone production by a psychrophilic and a mesophilic strain of R. aurantiaca were investigated. The highest gamma-decalactone production in flasks (5.8 g/l) was obtained with the strain A19 at 14 degrees C and initial pH 7.0 in medium containing 20 g/l castor oil. On the other hand, these factors did not affect the production of gamma-decalactone by the mesophilic strain. In fermentor, a gamma-decalactone concentration of 6.6 g/l was reached with the strain A19, whereas a maximum of 0.1 g/l was obtained with the mesophilic strain. Our results suggest that the ability to synthesize gamma-decalactone is a particularity of the strain A19, since the mesophilic strain (no. 30645) produced small amounts, and the other (no. 31354) did not exhibit this property. It is, to our knowledge, the first report of gamma-decalactone production by R. aurantiaca and furthermore by a psychrophilic yeast strain. Moreover, the amount of gamma-decalactone obtained in fermentor with the strain 19 was on the order of concentrations usually described in patents.

Enrichment of anhydrous milk fat in polyunsaturated fatty acid residues from linseed and rapeseed oils through enzymatic interesterification.

Lipozyme TL IM was used in a solvent-free batch and microaqueous system for enzymatic interesterification of anhydrous milkfat (AMF) with linseed oil (LO) in binary blends and with rapeseed oil (RO) in one ternary blend. The aim was to obtain and characterize physicochemically fats enriched with unsaturated C 18 fatty acids (oleic, linoleic, and, especially, linolenic acids) from natural vegetable oils. Binary blends of AMF/LO 100/0, 90/10, 80/20, 70/30, and 60/40 (w/w) were interesterified. The change in triacylglycerol (TAG) profiles showed that quasi-equilibrium conditions were reached after 4-6 h of reaction. Free fatty acid contents <1%. The decrease in solid fat content and in dropping point temperature obtained with increasing content of LO and interesterification resulted in good plastic properties for the products originating from the blends 70/30 and 60/40. This was confirmed by textural measurements. Melting profiles determined by differential scanning calorimetry showed complete disappearance of low-melting TAGs from LO and the formation of intermediary species with a lower melting temperature. Oxidative stability of the interesterified products was diminished with increasing LO content, resulting in low oxidation induction times. A ternary blend composed of AMF/RO/LO 70/20/10 gave satisfactory rheological and oxidative properties, fulfilling the requirements for a marketable spread and, moreover, offering increased potential health benefits due to the enriched content in polyunsaturated fatty acid residues.

Surface properties of Yarrowia lipolytica and their relevance to gamma-decalactone formation from methyl ricinoleate.

The surface of the lipid-degrading yeast, Yarrowia lipolytica, was characterized by contact angle and zeta potential (zeta) measurements. The cells were mainly hydrophilic with a negative charge that was only affected from pH 2 to 4. To study the effects of the surface charges on the biotransformation of methyl ricinoleate into the aroma compound, gamma-decalactone, the zeta values of the substrate droplets were modified by adding a cationic surfactant into the medium at concentrations that did not diminish cell viability: the adhesion of the lipid substrate to the cells was increased but not the overall performance of the process, therefore the adhesion is not the rate limiting here. Our methodology offers interesting perspectives for further applications.

Increased electron donor and electron acceptor characters enhance the adhesion between oil droplets and cells of Yarrowia lipolytica as evaluated by a new cytometric assay.

The adhesion of methyl ricinoleate droplets to cells of the yeast Yarrowia lipolytica was investigated. A new cytometric method, relying on the double staining of fatty globules with Nile Red and of cells with Calcofluor, enabled us to quantify methyl ricinoleate droplet adhesion to cells precultured on a hydrophilic or on a hydrophobic carbon source. In this last case, droplet adsorption was enhanced and a MATS (microbial adhesion to solvents) test revealed that this increase was due to Lewis acid-base interactions and not to an increase in the hydrophobic properties of the cell surface. These preliminary results demonstrate that the developed cytometric method is promising for various applications concerning the study of interactions between microorganisms and an emulsified hydrophobic substrates.

Interaction of an odorant lactone with model phospholipid bilayers and its strong fluidizing action in yeast membrane.

Some odorant lactones are naturally present in fruits or in fermented products; they can also be used as food additives and can be produced by microorganisms at the industrial scale by biotechnological processes. Gamma-decalactone was previously shown to have antimicrobial properties. We determined by infrared spectroscopy measurements that this compound rapidly diffused into model phospholipid bilayers (within 2 min), modifying the general physical state of a dimyristoyl-L-alpha-phosphatidylcholine (DMPC) film. In vivo, the lactone strongly increased membrane fluidity in the model yeast Yarrowia lipolytica, as evaluated by fluorescence anisotropy measurements. This effect was more important than that of benzyl alcohol, which is known as a fluidizing agent in living cells, and may explain the toxic action of gamma-decalactone in microorganisms.