Size as a parameter for solvent effects on Candida antarctica lipase B enantioselectivity.

Changes in solvent type were shown to yield significant improvement of enzyme enantioselectivity. The resolution of 3-methyl-2-butanol catalyzed by Candida antarctica lipase B, CALB, was studied in eight liquid organic solvents and supercritical carbon dioxide, SCCO(2). Studies of the temperature dependence of the enantiomeric ratio allowed determination of the enthalpic (Delta(R-S)Delta H(++)) as well as the entropic (Delta(R-S)Delta S(++)) contribution to the overall enantioselectivity (Delta(R-S)Delta G(++)= -RTlnE). A correlation of the enantiomeric ratio, E, to the van der Waals volume of the solvent molecules was observed and suggested as one of the parameters that govern solvent effects on enzyme catalysis. An enthalpy-entropy compensation relationship was indicated between the studied liquid solvents. The enzymatic mechanism must be of a somewhat different nature in SCCO(2), as this reaction in this medium did not follow the enthalpy-entropy compensation relation.

New sample preparation technique for the determination of avoparcin in pressurized hot water extracts from kidney samples.

A new approach is presented for the determination of avoparcin in tissue. Complete recovery from spiked swine kidney was achieved with hot water modified with 30% ethanol (v/v). The samples were extracted at 75 degrees C and 50 atm by accelerated solvent extraction. In situ sample clean-up was achieved by using matrix solid-phase dispersion utilizing the acrylic polymer XAD-7 HP, and by adding triethylammonium phosphate (TEAP) to the extraction solvent. The aqueous extracts were concentrated by solid-phase extraction (SPE) on the hydrophilic interaction chromatography (HILIC) material polyhydroxyethyl aspartamide. Complete analyte retention was possible during SPE when the kidney extracts were modified with 70% ethanol. A 200 A, 5 microm HILIC column with UV225 detection was used for the separation of avoparcin. The retention time was less than 15 min with 47% aqueous component in acetonitrile and 15 mM TEAP as eluent. The average recovery of avoparcin from kidney samples was 108%.

Modeling of hydrogenation kinetics from triglyceride compositional data.

A mathematical model was developed to describe the reduction of soybean oil triglycerides during hydrogenation. The model was derived from reaction and transport mechanisms and formulated into a system of first-order irreversible rate expressions that included terms for temperature, hydrogen pressure, and catalyst concentration. The model parameters were estimated from experimental data, and the model was used to simulate the results of hydrogenation performed over the pressure range of 0.069-6.9 MPa. The model could be extended to include geometrical isomers formed during hydrogenation.

Selected uses of enzymes with critical fluids in analytical chemistry.

The use of enzymes coupled with supercritical fluid (SF)-based analytical techniques, such as supercritical fluid extraction (SFE), provides a safer environment platform for the analytical chemist and reduces the use of organic solvents. Incorporation of such techniques not only reduces the use of solvent in analytical laboratories, but it can also lead to overall method simplification and time savings. In this review, some of the fundamental aspects of using enzymes in the presence of SF media are discussed, particularly the influence of extraction (reaction) pressure, temperature, and water content of the extracting fluid and/or the sample matrix. Screening of optimal conditions for conducting reactions in the presence of SF media can be readily accomplished with automated serial or parallel SFE instrumentation, including selection of the proper enzyme. Numerous examples are cited, many based on lipase-initiated conversions of lipid substrates, to form useful analytical derivatives for gas chromatography, liquid chromatography, or SF chromatography analysis. In certain cases, enzymatic-aided processing of samples can permit the coupling of the extraction, sample preparation, and final analysis steps. The derived methods/techniques find application in nutritional food analyses, assays of industrial products, and micro analyses of specific samples.

Modern supercritical fluid technology for food applications.

This review provides an update on the use of supercritical fluid (SCF) technology as applied to food-based materials. It advocates the use of the solubility parameter theory (SPT) for rationalizing the results obtained when employing sub- and supercritical media to food and nutrient-bearing materials and for optimizing processing conditions. Total extraction and fractionation of foodstuffs employing SCFs are compared and are illustrated by using multiple fluids and unit processes to obtain the desired food product. Some of the additional prophylactic benefits of using carbon dioxide as the processing fluid are explained and illustrated with multiple examples of commercial products produced using SCF media. I emphasize the role of SCF technology in the context of environmentally benign and sustainable processing, as well as its integration into an overall biorefinery concept. Conclusions are drawn in terms of current trends in the field and future research that is needed to secure new applications of the SCF platform as applied in food science and technology.

Design and optimization of a semicontinuous hot-cold extraction of polyphenols from grape pomace.

Grape pomace contains appreciable amounts of polyphenolic compounds such as anthocyanins and procyanidins which can be recovered for use as food supplements. The extraction of these polyphenols from the pomace is usually accomplished at slightly elevated temperatures, frequently employing hydroethanolic solvents. Due to governmental regulations and the cost involved in using ethanol as a solvent, as well as the loss in polyphenolics due to thermal degradation, improved extraction techniques are required. In this study, a semicontinuous extraction apparatus employing only water was developed to maximize the recovery of anthocyanins and procyanidins from red grape pomace (Vitis vinifera). Water is preheated prior to its entry to the extraction cell containing the grape pomace sample, where it is allowed to then flow continuously through the unheated extraction vessel prior to its collection at ambient conditions. Extraction variables that impacted the polyphenolic recovery included pomace moisture content (crude or dried), sample mass, water flow rate, and extraction temperature. A response surface method was used to analyze the results from the extraction, and the optimal conditions were found to be 140 °C and 9 mL/min water flow rate. These conditions can produce an extract containing 130 mg/100 g DW of anthocyanins and 2077 mg/100 g DW of procyanidins. Higher yields of polyphenolics were observed using crude (wet) rather than dried pomace, hence avoiding the need to dry the pomace prior to extraction. The described semicontinuous extraction method using only water as the extraction solvent under subcritical conditions allowed the efficient extraction of polyphenols from red grape pomace without the attendant loss of polyphenolic content due to having to heat the extraction vessel prior to commencement of extraction.

Physicochemical characterization of dilute n-alcohol/biodiesel mixtures by inverse gas chromatography.

Inverse gas chromatography (IGC) has been used to determine the physicochemical parameters that characterize solution thermodynamic interactions in biodiesel-n-alcohol solute systems. Such data is of value to chemical engineers and separation scientists in optimizing separation processes to separate alcoholic solutes at low concentrations in soybean oil methyl ester mixtures (biodiesel). The derived activity and Henry's Law coefficient data can be used to rationalize the interaction of four members of an n-alcoholic homologous series and the soya-based methyl ester solvent in terms of such esters as "green" renewable solvents. Sorption isotherm data confirm linear behavior in most cases between the solute (alcohol) vapor state concentrations and their uptake into the biodiesel phase. Overall, the experimentally determined activity coefficients agree well with those predicted by solution thermodynamic theories as well as correlative chemical engineering equations.

Subcritical solvent extraction of procyanidins from dried red grape pomace.

Procyanidins in dried Sunbelt ( Vitis labrusca L.) red grape pomace were extracted using accelerated solvent extraction (ASE) with pressure (6.8 MPa), one extraction cycle, and temperature (40, 60, 80, 100, 120, and 140 degrees C). Six ethanol/water solvents (0, 10, 30, 50, 70, and 90%, v/v) were compared to conventional extraction with acetone/water/acetic acid (70:29.5:0.5, v/v/v). Procyanidins in the extracts were identified by HPLC-ESI-MS/MS and contained degrees of polymerization (DP) of 1-5 (monomers through pentamers) and polymers (DP > 10). Generally, 50% ethanol/water (v/v) extracted more total procyanidins than other ethanol/water compositions, and contained up to 115% of total procyanidins extracted by the acetone-based conventional solvent. Additionally, 50% ethanol/water (v/v) extracted 205, 221, and 113% more epicatechin, catechin, and dimers, respectively, than conventional extraction. Results indicated greater extraction of low oligomeric procyanidins using 50% ethanol/water (v/v) solvent between 80 and 140 degrees C.

Subcritical solvent extraction of anthocyanins from dried red grape pomace.

Accelerated solvent extraction (ASE) was used to optimize and determine the effectiveness of an alternative, environmentally friendly extraction procedure using subcritical solvents to recover anthocyanins from freeze-dried, ground Sunbelt red grape pomace. Anthocyanins were extracted from pomace using the following ASE variables: pressure (6.8 MPa), one extraction cycle, and temperature (40, 60, 80, 100, 120, and 140 degrees C). Conventional solvent extraction with methanol/water/formic acid (60:37:3 v/v/v) was compared to four hydroethanolic solvents (10, 30, 50, and 70% ethanol in water, v/v). Anthocyanins in the extracts were identified and quantified by HPLC-MS and HPLC. There was an insignificant interaction between solvent and temperature (p = 0.0663). Solvents containing 70 and 50% ethanol in water extracted more total anthocyanins (463 and 455 mg/100 g of DW, respectively) than other solvents. The total amounts of anthocyanins extracted at 100 degrees C (450 mg/100 g of DW), 80 degrees C (436 mg/100 g of DW), and 120 degrees C (411 mg/100 g of DW) were higher than at the other temperatures. Solvents containing 70 and 50% ethanol in water extracted similar amounts of anthocyanins as conventional extraction solvent.

Extraction of co-products from biomass: example of thermal degradation of silymarin compounds in subcritical water.

In an effort to increase revenues from a given feedstock, valuable co-products could be extracted prior to biochemical or thermochemical conversion with subcritical water. Although subcritical water shows significant promise in replacing organic solvents as an extraction solvent, compound degradation has been observed at elevated extraction temperatures. First order thermal degradation kinetics from a model system, silymarin extracted from Silybum marianum, in water at pH 5.1 and 100, 120, 140, and 160 degrees C were investigated. Water pressure was maintained slightly above its vapor pressure. Silymarin is a mixture of taxifolin, silichristin, silidianin, silibinin, and isosilibinin. The degradation rate constants ranged from 0.0104 min(-1) at 100 degrees C for silichristin to a maximum of 0.0840 min(-1) at 160 degrees C for silybin B. Half-lives, calculated from the rate constants, ranged from a low of 6.2 min at 160 degrees C to a high of 58.3 min at 100 degrees C, both for silichristin. The respective activation energies for the compounds ranged from 37.2 kJ/gmole for silidianin to 45.2 kJ/gmole for silichristin. In extracting the silymarin with pure ethanol at 140 degrees C, no degradation was observed. However, when extracting with ethanol/water mixtures at and 140 degrees C, degradation increased exponentially as the concentration of water increased.

Derivatization reactions of carbamate pesticides in supercritical carbon dioxide.

Supercritical fluid carbon dioxide (SC-CO(2)) has been used to dissolve derivatizing agents (e.g. heptafluorobutyric anhydride, HFBA, and pyridine), which also act as a modifier in the fluid phase, for simultaneous extraction and derivatization of carbamates from the sample matrix. The derivatized carbamate pesticides (carbaryl, 3-hydroxycarbofuran, carbofuran, aldicarb, methiocarb) were then analyzed by GC-ECD or GC-MS with excellent sensitivity. Extraction and conversion of the carbamates was complete, as indicated by HPLC with post-column hydrolysis and o-phthalaldehyde derivatization then fluorescence detection. GC-MS (ion trap) was also used to confirm the formation of the carbamate derivatives. Compared with the same HFBA reaction in an organic solvent the derivatization reaction time was considerably shorter in SC-CO(2.) The described approach, combining both extraction and derivatization, simplifies the analysis of carbamate pesticides and eliminates the use of organic solvents associated with the derivatization step.

Supercritical Fluid Extraction of Aflatoxin M1 from Beef Livert †.

Supercritical fluid extraction (SFE) and a pressurized-fluid-extraction process were applied for the removal of aflatoxin M1 from beef liver samples. Various pressures, temperatures, quantity of supercritical carbon dioxide, and organic modifiers were investigated to optimize the extraction methods. Organic modifier was found to be essential for quantitative recovery of aflatoxin M1. Extracts were cleaned up by solid-phase extraction and were analyzed via high-performance liquid chromatography coupled with fluorescence detection of the trifluoroacetic acid derivative. Solvent-modified carbon dioxide SFE achieved recoveries comparable to an AOAC-approved method involving organic solvent extraction. SFE allowed the traditional amounts of sample and organic solvent to be reduced. Also, the supercritical-fluid extraction permitted the use of carbon dioxide modified with acetonitrile: methanol (2:1) to replace methylene chloride as the organic solvent for the extraction step.