J9382

ABSTRACT: δ-Stearolactone was prepared from oleic acid using concentrated sulfuric acid under various conditions in the presence of polar, nonparticipating solvents. δ-Stearolactone was formed in as high as 15:1 ratios over the thermodynamic product, γ-lactone, in the presence of methylene chloride, 100% wt/vol, at room temperature with two equivalents of sulfuric acid for 24 h. This procedure is applicable to other olefinic fatty acids such as estolides and fatty acid methyl esters. Temperature plays a role in the regioselectivity of the cyclization for δ-lactone, as lower temperatures (20°C) gave higher δ/γ ratios. At higher temperatures (50°C) in the presence of sulfuric acid and methylene chloride the yield of lactone was 75% but with a δ/γ ratio of only 0.3:1. Cyclization of oleic acid to lactone also occurred with other acids. Oleic acid underwent reaction with perchloric acid, one equivalent, in the absence of solvent at 50°C, which yielded δ-lactone in a modest yield with a 3.1 δ/γ ratio. The same temperature effect was observed with perchloric acid that was observed in the case of sulfuric acid. Because δ-stearolactone is much more reactive than the corresponding fatty acid, fatty acid ester, or γ-lactone, we believe that it will be a useful synthon for many new industrial products including new biodegradable detergents

J8898

ABSTRACT: Phenolic compounds are the most important antioxidants of virgin olive oil. This paper reports on the application of solid phase extraction (SPE) in the separation of phenolic compounds from olive fruit, olive oil, and by-products of the mechanical extraction of the oil and the complete spectroscopic characterization by nuclear magnetic resonance of demethyloleuropein and verbascoside extracted from olive fruit. SPE led to a higher recovery of phenolic compounds from olives than did liquid/liquid extraction. SPE also was used to separate phenolic compounds from pomaces and vegetation waters. Phenylacid and phenyl-alcohol concentrations in extracts obtained from SPE and liquid/liquid extraction were not significantly different (P < 0.05). The recovery of the dialdehydic form of elenolic acid linked to 3,4-(dihydroxyphenyl)ethanol and an isomer of oleuropein aglycon, however, was low. Paper no. J8898 in JAOCS 76, 873-882 (July 1999). KEY WORDS: HPLC analysis, NMR, phenols, secoiridoids, solid phase extraction, virgin olive oil. Phenolic compounds of olive fruit and virgin olive oil have been found to correlate with the pungent and bitter taste of the oil (1); they also inhibit blood platelet aggregation, are involved in the synthesis of thromboxane in human cells (2), and inhibit phospholipid oxidation (3). The most important classes of phenolic compounds of olive fruit include phenyl acids, phenyl alcohols, flavonoids, and secoiridoids (4). The main phenyl alcohols of olive are 3,4-(dihydroxyphenyl)ethanol (3,4-DHPEA) and p-(hydroxyphenyl)ethanol (p-HPEA) (5,6). The flavonoids include the flavonol glycosides, luteolin-7-glucoside, and rutin, and the anthocyanins, cyanidin, and delphinidin glycosides Phenyl acids and phenyl alcohols have also been found in virgin olive oil Various analytical methods have been studied to evaluate phenolic compounds in olive fruit and olive oil MATERIALS AND METHODS Sample preparation. Olive fruits (Olea europaea L.) from frantoio and coratina cultivars were used. To extract phenolic compounds from olive fruit, 500 g of olives were destoned. To study phenolic compounds in oil, vegetation waters, and pomaces, 3 kg of olives were crushed with a hammer mill and slowly mixed (malaxed) at 30°C for 60 min. The oil was extracted using a laboratory hydraulic press (maximum pressure 220 bar). Destoned fruit, stones, vegetation waters, and pomaces were immediately frozen in liquid nitrogen to inhibit enzymatic activity, freeze-dried, and stored at −30°C before analysis. Reference compounds. The 3,4-DHPEA was synthesized in the laboratory according to the procedure of Baraldi et al. (29). The 3,4-DHPEA-EDA and 3,4-DHPEA-EA were extracted from virgin olive oil and the chemical structures were Phenolic compounds from olive fruit and pomaces. The extraction, purification, and separation procedure of phenolic compounds was optimized using freeze-dried olives from the frantoio cultivar, and optimal conditions were applied to the extraction and separation of phenolic compounds from the pomaces Freeze-dried stones were crushed and added to the destoned olives in the same ratio as the original olive. Whole fruits (10 g) were mixed at −25°C with 50 mL of 80% methanol added containing 20 mg/L sodium diethyldithiocarbamate (DIECA) (30), to inhibit polyphenoloxidase and lipoxygenase activities. The mixture was homogenized in an Omni-mixer (Sorvall) for 30 s at 1050 × g and filtered using a Buchner funnel apparatus. The extraction was repeated six times. The extracts were collected and the methanol was evaporated in vacuum under nitrogen flow at 35°C. The remaining aqueous extract is referred to as the water extract. Phenolic compounds may be oxidized during methanol evaporation and successive separation of the water extract in the C 18 cartridge. For this reason, different combinations of antioxidants, such as SO 2 (90 mg/g), SO 2 (25 mg/g) + ascorbic acid (2 mg/g), and ascorbic acid (2 mg/g) were added to the extract before methanol evaporation. SPE was used to separate the phenolic compounds present in the water extract. Two milliliters of water extract was added to a 5 g/20 mL Extract-Clean highload C 18 cartridge (Alltech Italia Srl, Milan, Italy) and the following two sequences of organic solvents were used to recover phenolic compounds: ethyl ether (300 mL), ethyl acetate (100 mL) and methanol (200 mL) or methanol (600 mL). To reduce phenol oxidation, elution from the C 18 cartridge under a flow of nitrogen also was tested. The eluate was collected and the organic solvent evaporated in vacuum under nitrogen flow at 35°C. The residue was dissolved in 1 mL of methanol and injected into the high-performance liquid chromatograph (HPLC). The results obtained from the olive fruit by SPE were compared with those from the liquid/liquid extraction performed according to Amiot et al. (27). Phenolic compounds from vegetation waters. Freeze-dried vegetation waters were rehydrated with water containing DIECA (20 mg/L), and 2 mL was loaded on a 5 g/20 mL Extract-Clean highload C 18 cartridge (Alltech Italia Srl). To recover and fractionate phenolic compounds the following three sequences of organic solvents were studied: ethyl acetate (500 mL) and methanol (100 mL), or ethyl ether (100 mL) and ethyl acetate (500 mL), or ethyl ether (600 mL). The eluate concentration and HPLC injection were carried out as above The HPLC system was composed of a Varian 9010 solvent delivery system (Varian Associates, Inc., Walnut Creek, CA) with a 150 × 4.6 mm i.d. Inertsil ODS-3 column (Alltech Italia Srl) coupled with a Varian Polychrom 9065 ultraviolet (UV) diode array detector, operating in the UV region. The samples were dissolved in methanol, and a sample loop of 20 µL capacity was used. The mobile phase was a mixture of solution A (0.2% acetic acid, pH 3.1) and methanol (B), and the flow rate was 1.5 mL/m. The total run time was 55 min and the gradient changed as follows: 95% A/5% B for 2 min; 75% A/25% B for 8 min; 60% A/40% B for 10 min; 50% A/50% B for 10 min; 0% A/100% B for 10 min; the mixture was maintained for 5 min, then returned to 95% A/5% B for 10 min. Phenolic compounds from virgin olive oil. Phenols were extracted from virgin olive oil using a 5 g/20 mL ExtractClean highload C 18 cartridge (Alltech Italia Srl). Twenty milliliters of either hexane or hexane/ethyl ether (98:2 vol/vol) was used to condition the cartridge, 5 g of oil was introduced, and the sample was washed with 100 mL of the particular conditioning solvent to remove the nonpolar fraction. To elute phenolic compounds, 80 mL of the following solvents were tested: methanol, methanol/water (80:20 vol/vol), and acetonitrile. The solvents from the eluent were evaporated to dryness in vacuum under nitrogen flow at 35°C. The dried residue was dissolved in 1 mL of methanol and analyzed by HPLC using the same chromatographic conditions reported in a previous paper (23). Results were compared with the liquid/liquid extraction performed according to Montedoro et al. (23). To study the effect of nonionic surfactants in phenol extraction, Tween ® 20, Tween ® 80 (BDH Co.) and Triton ® X-100 (LKB Bromma, Sweden) were tested. The nonionic surfactants (2% wt/vol) were added to the extraction (methanol/water 80:20, vol/vol) and the elution (methanol) solvents for liquid/liquid extraction and SPE, respectively. Separation and NMR characterization of verbascoside and demethyloleuropein. Verbascoside and demethyloleuropein were extracted from the freeze-dried destoned olives (coratina cultivar), using the extraction procedure reported above. The separation and purification of these compounds were achieved using preparative HPLC. A Varian liquid chromatograph Model 5000 equipped with a 500 × 9.4 mm i.d. Whatman Partisil 10 ODS-2 semipreparative column (Alltech Italia Srl), coupled with a Varian Polychrom 9065 diode array detector was used. The phenolic extract was injected in the column using a sample loop of 1 mL, and compounds were detected at 278 nm. The peaks corresponding to the demethyloleuropein and verbascoside were recovered using a Gilson Model 201 fraction collector (Gilson Medical Electronics, Inc., Middleton, WI). The mobile phase was a mixture of solution A (0.2% acetic acid, pH 3.1) and methanol (B) (flow rate 5.6 mL/m). The total running time of the analysis was 65 min and the gradient was changed as follows: 80% A/20% B at time 0 min, 60% A/40% B realized in 20 min; the mixture was maintained for 20 min, 0% A/100% B for 5 min, and the mixture was maintained for 10 min, and returned to 80% A/20% B for 5 min. Each phenolic extract injection corresponded to about 10 mg of total phenols, expressed as 3,4-DHPEA equivalent, as determined with the Folin-Ciocalteau reagent (23). The collected compounds were recovered according to the procedure described in a previous paper (15). The NMR spectra were recorded on Bruker AC 200 and Bruker DRX 500 spectrometers (Bruker, Karlsruhe, Germany) (operating at 200.13 and 500.13 MHz for 1 H and 50.13 and 125.77 MHz for 13 C) using TMS as the external standard. About 20 mg of sample was dissolved in 0.6 mL in methanold 4 . 1 H, 13 C{ 1 H}, 13 C-1 HJ Modulated, 1 H-COSY (with gradients), 1 H-NOESY phase-sensitive, 1 H-{ 13 C}-correlation (with gradients), and 1 H-{ 13 C}-long range correlation experiments (with gradients) were performed (31). The 1 H-NOESY phase-sensitive spectrum was obtained with a mixing time of 800 ms. The H-{ 13 C}-correlation and 1 H-{ 13 C}-long range correlation experiments were obtained using the Bruker pulse programs inv4gs and inv4gslnd, respectively, setting the delays for evolution of couplings at 3.3 ms and 50 ms, respectively. The 1 H-COSY experiment was obtained with the cosygs Bruker pulse program. Structural assignments Statistical analysis. All chemical and instrumental measurements were replicated three times. Means ± standard deviations are reported in the tables. To evaluate the significance of differences between mean values among three or more different experimental groups the one-way analysis of variance using the Tukey test was performed. To compare two groups of values the paired t-test was employed. Statgraphics Version 6.1 (Statistical Graphics Corp., 1992, Manugistics, Inc., Rockville, MD) was used to perform all statistical analyses. RESULTS AND DISCUSSION Phenolic compounds from oive fruit and pomace. The effect of antioxidants on the recovery of phenols was studied. As shown in SO 2 strongly reduced the concentration of 3,4-DHPEA-EDA, probably due to the nucleophilic addition of HSO 3 − to the dialdehydic groups of 3,4-DHPEA-EDA causing its precipitation from the aqueous solution (33). The elution under nitrogen significantly improved only the recovery of p-hydroxybenzoic, caffeic, and vanillic acids (P < 0.05). Phenyl alcohols, phenyl acids, flavonoids and secoiridoids are characterized by different affinities with different organic solvents (4). For this reason the elution of phenolic compounds from SPE was carried out using a sequence of ethyl ether, ethyl acetate, and methanol to study the selective recovery of phenolic compounds from the water extract. Results reported in Phenolic compounds from vegetation waters. To separate phenolic compounds from vegetation waters using SPE, a sequence of organic solvents was tested. The highest phenolic recovery was obtained using ethyl ether Methanol was also tested but did not provide good results (data not shown) due to the high background noise in the UV detector during HPLC analysis. It is likely that the high concentrations of quinones and melanoidins occurring in the vegetation waters (33), and soluble in methanol, may interfere with the detector response. Vegetation waters showed a phenolic composition very different from that of olive fruit. In fact, secoiridoid glucosides, such as oleuropein and demethyloleuropein, were greatly concentrated in olives, whereas the vegetation waters had high concentrations of secoiridoid derivatives, such as 3,4-DHPEA and 3,4-DHPEA-EDA. Phenolic compounds from virgin olive oil. As reported in previous papers (15,16) virgin olive oil showed low amounts of phenyl acids and phenyl alcohols and high concentrations of secoiridoid derivatives such as 3,4-DHPEA-EDA, 3,4-DHPEA-EA, and p-HPEA-EDA, which originate from oleuropein, demethyloleuropein, and ligstroside during the oil me- chanical extraction process. SPE also was tested in the extraction of phenols from virgin olive oil and different organic solvents were studied to remove the nonpolar fraction and to elute phenolic compounds. Methanol led to the highest recovery in total phenols when the cartridge was conditioned with hexane (data not shown). An HPLC chromatogram of phenolic extract obtained by SPE is reported in NMR characterization of demethyloleuropein and verbascoside. The 1 H and 13 C NMR data for demethyloleuropein (1) and verbascoside (2) are reported in Despite the fact that demethyloleuropein has been known for more that two decades (11) we believe its NMR characterization has not been reported. The assignment of the carbon and proton resonances was achieved by comparing proton and carbon data with those reported for oleuropein (15). The NMR characterization of verbascoside has been reported (12), but we revised the assignment using the results of several two-dimensional experiments. respectively. C-9 correlated with H-8 and H-4 of the glucose, thus, the caffeic moiety is connected to glucose. C-3 of glucose correlated with H-1 of rhamnose and C-1 of rhamnose with H-3 of glucose, indicating that the two moieties are connected in these positions. A strong cross peak between C-8 of aglycon and H-1 of glucose ensures that the fragments are connected. The 1 H-NOESY experiment confirmed the assignment discussed above. Oil Chem. Soc. 69:394-395 (1992 117:25-32 (1995). 4. Macheix, J.J., J. Billot, Fruit Phenolics, CRC Press, Boca Raton, 1990, pp. 1-126. 5. Vazquez Roncero, A., C. Janer Del Valle, and L. Janer Del Valle, Determination of Total Polyphenols in Olive Oils, Grasas Aceites 24:350-357 (1973 ACKNOWLEDGMENTS 2 Identification of Some Phenolic Acids and Their Antioxidant Capacity, Sci. Tecnol. Alimenti. 2:177-186 (1972 Food Chem. 44:2040-204

J8918.lej

ABSTRACT: We prepared stable oil-in-water emulsions of argan oil with two different types of mixtures of nonionic emulsifiers. Three different types of oil (Israeli argan oil, Moroccan argan oil, and soybean oil) were emulsified with mixtures of Span 80 and Tween 80. The optimum HLB value for argan oil was 11.0 (±1.0). The argan oil-in-water emulsions were stable for more than 5 mon at 25°C. Synergistic effects were found in enhancing stability of emulsions prepared with sucrose monostearate. The origin of the oil and the internal content of natural emulsifiers, such as monoglycerides and phospholipids, have a profound influence on its interfacial properties and on the stability of the argan oil-in-water emulsions. Paper no. J8918 in JAOCS 76, 15-18 (January 1999)

J8703

ABSTRACT: A new method for analysis of Sorbitan Tristearate (STS) in vegetable oils and fats has been developed. The method is based on isolation and hydrolysis of STS compounds in a silica cartridge. The polyalcohols are eluted from the silica cartridge and the final separation and quantitation are done by high-performance liquid chromatography and refractive index detection. Linearity, precision, and recovery satisfy general demands on quantitative methods. The detection limit and the quantitation limit are well below the concentrations normally used to attain functional effects of STS in vegetable oils and fats

J9262

ABSTRACT: A second-order kinetic model for hydrogenation of fatty acids in series has been developed and analyzed. The model is applied to the data obtained for sodium formatecatalyzed hydrogenation of soybean, peanut, corn, and olive oils. There is good agreement between the experimental data and predicted values obtained from the model as evidenced by the analysis of r 2 and F-test values. The effect of individual fatty acid composition of various edible oils on the rate of hydrogenation has been explained in view of the mathematical model developed. The individual rate constants seem to obey the Arrhenius rate law. The second-order kinetic analysis discussed is found to be suitable for mathematically describing hydrogenation of vegetable oils by hydrogen donors as compared to the traditional first-order kinetic analysis

J8485

ABSTRACT: We report the results of our study on Rhizomucor miehei lipase-catalyzed lauric acid-glycerol esterification in a foam reactor. A satisfactory yield of glyceride synthesis can be achieved with an unusually high initial water content (50% w/w). We found that product formation could be regulated by controlling foaming. Foaming was a function of the air flow rate, reaction temperature, pH value, ionic strength, and substrate molar ratio. Monolaurin and dilaurin, which constituted nearly 80% of the total yield, were the two dominant products in this reaction; trilaurin was also formed at the initial stages of the reaction. A study of pH and ionic strength effects on an independent basis revealed that they affect the interfacial mechanism in different manners. On varying the ratio of lauric acid and glycerol, only a slight change in the degree of conversion was detected and the consumption rate of fatty acid was approximately the same. JAOCS 75, 643-650 (1998). KEY WORDS: Esterification, foams, glyceride synthesis, HPLC, lipase, Rhizomucor miehei, substrate inhibition. Lipases have been successfully employed in catalyzing many organic reactions (1-5). Among those reactions, lipase-catalyzed esterifications are of most commercial interest (6-8). For instance, esterification of sugar with fatty acids produces sugar esters, which are potentially important as food and cosmetic emulsifiers (9). A substitute for a natural wax ester, jojoba oil, can be derived from the transformation of high-erucic acid rapeseed oil and erucyl alcohol (10). The main products of the reaction discussed in this paper, mono-and diglycerides, are extensively used in food and cosmetic additives to increase the flavor and enhance emulsifying as well as texturizing functions. The use of lipases has broadened over the last decades to include the synthesis of biosurfactants, cloning of a detergent lipase (11), and biorefining of oils (12). Enzyme-catalyzed reactions, as an alternative to traditional chemical synthesis, have become increasingly important in the food, cosmetics, and pharmaceutical industries because, in general, no toxic materials are involved, and reaction conditions are mild and have high stereoselectivity (13-15) as well as enantioselectivity, which is advantageous for the production of fine chemicals. Though lipase is active at oil/water interfaces, immiscibility of oil (substrates and products) and water (essential for enzymatic function) complicates the esterification process. As a result, a lot of effort has been spent to enhance the oil/water contact area (and therefore the catalytic efficiency of the lipase) by designing an optimal reaction environment to carry out this reaction. Generally, reaction media for esterification by lipases can be classified into two categories, organic and solvent-free media (in aqueous solutions, the equilibrium is shifted far to the hydrolysis side; thus, aqueous solutions are not suitable for esterification). When an organic medium is employed, organic solvents have to be used to dissolve the reactants. By magnetic stirring (14,15), using immobilized lipase (16) or substrate support (17,18), or adding surfactants to form micelles (19-21), the interfacial area between lipids and the aqueous phase can be increased considerably. However, drawbacks include mass transfer limitations, need for toxic solvents and surfactants in the separation step, and difficulty of operating reactions in a continuous mode. In contrast, reactions carried out in a solvent-free medium do not cause contamination, but have other disadvantages. When incubating substrates and lipase together in a nonaqueous medium As a consequence, there still exists a need to develop a reaction environment for lipase that optimizes the catalytic efficiency at oil/water interfaces. It is well known that the incubation conditions as well as the reaction microenvironment have a governing effect on enzymatic mechanisms, in that the catalyzing pattern may differ as the interfacial property changes. In this paper, we report the effects of various factors on the enzymatic glyceride synthesis in a foam reactor. Because lipase and most of the reactants possess sufficient surface activity, there is no requirement of adding surfactants or solvents, thereby vastly reducing the cost of down-stream processing. In this work, we report our results obtained with a new reaction medium, foams, to host the fatty acid-glycerol (GLY) esterification catalyzed by lipase from Rhizomucor miehei. Several methods are available to make foams (31). All of them involve a large amount of gas being introduced into a *To whom correspondence should be addressed. E-mail: [email protected]. liquid, during which more and more gas bubbles are produced and several changes start to occur (31): (i) Disproportionation or Ostwald ripening: as time increases, bigger bubbles grow in size by diffusion of the gas through the liquid continuous region at the expense of smaller bubbles; Enzymatic Glyceride Synthesis in a Foam (ii) Creaming: because air bubbles are buoyant and fairly large, they cream rapidly by forming a separate foam layer on top of the bulk liquid; (iii) Polyhedral geometry: as more bubbles are formed, the bubble cells come in contact with and deform one another, leading to foam cells of polyhedral shape, which minimizes the total surface area. Each of these cells has 12 neighbors. At this stage, the structure of the foams consists mainly of a large number of thin liquid films (lamellae), which make an angle of 120°with one another. The line where the thin films meet is called the Plateau border, which encloses most of the liquid in the foams (31,32); (iv) Drainage: owing to gravitational effects, the central liquid between the foam cells starts to drain from the Plateau borders to bulk liquid; (v) Rupture or formation of stable black film: at the final stage of foam drainage, the film thickness reaches an approximate equilibrium value of several hundred Ångstroms. At more than a minimum concentration of the solute, a black film is formed after drainage, which indicates that its thickness is less than the wavelength of light. Alternatively, the films often become more brittle with draining and can resist no more stress, resulting in film rupture and bubble coalescence. By bubbling air through a reaction mixture that contains lipase, GLY, water, and a fatty acid, foaming can be induced. It is our goal to relate the hydrodynamics of the foam system to the catalytic performance of the lipase. The formation of numerous air/liquid thin films increases the contact area between the oil and aqueous phases significantly. Furthermore, with most of the liquid phase (mainly GLY and buffer) and excess substrates being in the Plateau borders, the reaction equilibrium on foam films can be driven toward glyceride synthesis. EXPERIMENTAL PROCEDURES Materials. All reactants, such as lauric acid (LA) and GLY, were obtained from Sigma Chemical Co (St. Louis, MO). Monolaurin (ML), dilaurin (DL), and trilaurin (TL), as standards for high-performance liquid chromatography (HPLC) calibration, were purchased from Sigma at the highest purities available. The solvents (Fisher Scientific, Pittsburgh, PA) for HPLC analysis (chloroform, acetone, and acetonitrile) were used without further purification. Lipozyme, a fungal lipase in liquid form (activity 10 LU/mg of solution), from R. miehei, was a generous gift from Novo Industry (Copenhagen, Denmark). Various buffer solutions with different ionic concentrations and the phosphate salts used in preparing phosphate buffers of different pH values were all obtained from Sigma Chemical Co. Product analysis. To achieve a good separation of fatty acid and glycerides, HPLC was used (33) with a Waters (Milford, MA) ALC 200 Series, WISP sample injector, and Data Module. The stationary phase was the Supelcosil™ LC-18 column from Supelco Company (Bellefonte, PA). The mobile phase was a mixture of acetone and acetonitrile at a 1:1 volume ratio at a constant flow rate of 0.8 mL/min. For each analytical run, a 15-µL sample was injected. The duration for one analysis was 45 min, with an additional 10 min needed to resume the stability of the chromatographic system. In this work, the reverse-phase method was employed. An evaporative light-scattering detector (ELSD IIA; Varex Corporation, Rockville, MD) was installed on the HPLC to monitor the eluting components from the chromatographic column (34,35). ELSD operating conditions were as follows: drift tube temperature and exhaust temperatures of 100 and 80°C, respectively, and a carrier gas flow of 1 L/min dry nitrogen. The selectivities are expressed as mol% of the starting fatty acid contained in each specific product (ML, DL, unreacted fatty acid, etc.) at the time of sampling. Direct measurement of the LA concentration with the light-scattering detector was not reliable, and all lauric concentrations reported are calibrated by mass balance from the measured concentrations of the mono-, di-, and triglycerides. Foam reactor. Enzymatic reactions. An initial 50% (w/w) of nonionic or buffered solution and reactants (fatty acid and GLY), at different molar ratios, was first incubated in the reactor for 0.5 h to allow the fatty acid to melt and the whole system to be thermally equilibrated. To avoid overflow of foam, the total liquid volume was adjusted to approximately 6 mL. In all experiments, the GLY was present in excess, and its amount was held constant. The most common molar ratio used was LA/GLY = 0.1, corresponding to a molar concentration of 0.56 M for LA at the beginning of the reaction. The starting molar concentration of GLY was kept constant at 5.6 M. The starting water concentration was also constant at 27 M; however, this dramatically decreased toward the end of the reaction. The final water contents of the reaction mixtures were determined by a Mettler-Toledo (Worthington, OH) DL18 Karl Fischer auto titrator. After the start of air flow, esterification reactions were initiated by addition of 0.04 mL of unpurified lipase-containing protein solution for each mL of the starting reactant mixture. The amount of lipase in the protein solution is given as 10 LU/mg of liquid by the manufacturer. We did not check this independently. Owing to the surface activity of both fatty acid and enzyme molecules, bubbles of uniform size were immediately formed. At regular intervals, 200 µL of foam materials was sampled in a capillary tube and diluted with chloroform to 644 Y.-C. YEH AND E. GULARI JAOCS, Vol. 75, no. 5 (1998) a concentration range appropriate for HPLC analysis. To determine the reproducibility of our results, we performed several duplicate runs. Overall, the results were reproducible to better than ± 10%. GLY, initially added in excess, was not monitored during the reaction. Hence, chloroform, a good solvent for all other reactants except GLY, was the ideal candidate as a solvent for the following HPLC analysis. All reactions were stopped after 24 h owing to reduction in foam density. The concentrations of the products were calculated and are reported in terms of fatty acid equivalents (i.e., the total amount of the fatty acid converted to a monoglyceride is equal to the molar concentration of the monoglyceride; for a diglyceride, the fatty acid equivalent is twice the molar concentration of the diglyceride, and for a triglyceride it is three times). RESULTS AND DISCUSSION Effect of flow rate. We speculate that foaming is a controlling factor for glyceride synthesis. The primary reason is that, with good foaming, the interfacial area is increased and lipase and the reactants have a larger probability of interaction to form the acylenzyme intermediate. Temperature effect. The effect of temperature on the esterification reaction at different substrate molar ratios is illustrated in The cessation of conversion (mainly of TL) at higher temperatures could be due to two factors. First, as water was lost to dry air, the reaction mixture became so viscous that the reaction mixture did not foam anymore. As a result of the decreased interfacial area, the probability of interfacial interaction between ML and the enzyme was less, and further conversion of ML stopped. This was in accordance with the observation reported above for the flow rate effect. Second, some limited lipase denaturation may happen, especiall

J8378

ABSTRACT: Catalytic transfer hydrogenation of corn, peanut, olive, soybean, and sunflower oils has been studied with aqueous sodium formate solution as hydrogen donor and palladium on carbon as catalyst. Kinetic constants and selectivity have been determined under intensive stirring in the presence of stabilizing agents. Hydrogenation reactions followed first-order kinetics with respect to fatty acids. Besides good selectivity and short reaction time, this method offers safe and easy handling. The presence of linolenic acid retards the migration of double bonds, which explains why soybean oil is the most appropriate for this hydrogenation process. JAOCS 75, 629-633 (1998). KEY WORDS: Catalytic transfer hydrogenation, corn oil, isomerization selectivity, olive oil, peanut oil, saturation selectivity, soybean oil, sunflower oil. Oils used for edible purposes are produced from natural sources. Sometimes, oils are used without modification, but the requirements for edible oils are often considerably different from those of the natural products, so they have to be modified to reach the appropriate properties. Hydrogenation of vegetable oils is one of the earliest and most common commercial modifying methods. Hydrogenation changes the melting and solidification characteristics of the oils treated and is usually employed to reduce the degree of unsaturation of the naturally occurring triglycerides. Vegetable oils that are hydrogenated contain trienoic and dienoic fatty acids (FA) in a mixture with monoenoic and saturated acids. The main purpose of partial hydrogenation is to obtain monounsaturated from polyunsaturated FA, to obtain new, attractive organoleptic properties and greater chemical stability, especially with regard to oxidation. The first industrial application of hydrogenation of oils in the liquid phase was Normann's patent (1), in which finely dispersed nickel particles were used for the gas-phase hydrogenation of organic compounds. The use of other metals, such as copper, platinum and palladium, as catalysts is an extension of the possibilities. The industry keeps searching for catalysts that operate under milder conditions and produce lower levels of trans isomers. In this respect, palladium catalysts seem to be the most promising (2). In the search for an optimal hydrogenation procedure, an alternative new method for hydrogenation of edible oils and fats-catalytic transfer hydrogenation (CTH)-is being developed. Differing from the classical techniques with molecular hydrogen, hydrogen donors are used as a source of hydrogen in a catalytic transfer reduction. The generalized Equation 1 represents this process: Saturation selectivities can be calculated from the rate constants as Albright and Wisniak (6) suggested. Saturation selectivities are defined as ratios of the relevant rate constants in Equations 3 and 4: High-linoleic selectivity (S L ) yields oils with the lowest melting points for a given unsaturation. High-linolenic selectivity (S Le ) increases the oxidative stability of oil without changing its liquidity. These ratios should be as high as possible to reach high saturation selectivity. To obtain the products with desired properties, the amount of trans isomers formed during the hydrogenation process is also an important factor. Coenen (7) defined the specific isomerization (cis-trans isomerization) as the ratio of produced trans double bonds and all eliminated double bonds. As mentioned above, CTH uses some molecules as hydrogen donors. For sodium formate solution, it is believed that sodium formate is not the only hydrogen donor and that water also contributes hydrogen to the reaction. Equation 5 illustrates this process (8): In this paper, the kinetics of CTH of olive EXPERIMENTAL PROCEDURES Materials. Hydrogenation was carried out with different commercial vegetable oils: soybean and olive oils were supplied by GEA-Slovenska Bistrica (Slovenka Bistrica, Slovenia), and sunflower, peanut, and corn oils were supplied by Oljarica Kranj (Kranj, Slovenia For analysis, an SP-2560 fused-silica capillary column (100 m × 0.25 mm inside diameter, 0.20 µm film thickness; Supelco, Bellefonte, PA) was used in a Varian 3400 (Walnut Creek, CA) gas chromatograph, equipped with an all-glass splitter system and flame-ionization detector. The gas chromatograph was operated at 150-200°C, with a heating rate of 3°C/min and a helium carrier gas flow rate of 1.2 mL/min. Hydrogenation procedures. Oil with emulsifier, donor solution, and catalyst were agitated in a 250-mL round-bottomed flask. A mechanical stirrer with a 3-cm round-shaped Teflon blade was used. The thermostated water bath was used for the flask. Progress of the hydrogenation reaction was monitored by determining the FA composition of the samples that were periodically removed during the process. Analysis was carried out by gas chromatography. Operating conditions. The following composition and conditions were used for the process: oil, 50.00 g; donorHCOONa, 9.44 g; water, 50.00 g; catalyst-10% Pd/C, 1.00 g; stabilizer-Mayodan M-612, 0.20 g; temperature, 80°C; agitation, 600 min −1 ; pressure, atmospheric. RESULTS AND DISCUSSION CTH of oils with sodium formate solution as hydrogen donor and palladium on activated carbon as catalyst proceeds in a complex three-phase system (oil-water-solid catalyst); so, the appropriate amounts of each component should be present for a successful hydrogenation. Based on previous studies and the reports of other authors Higher concentrations slow down the reaction. This happens probably because the reaction proceeds through competitive adsorption of water and formate to identical active sites on the catalytic surface (8-10). In the three-phase system, reaction can only proceed in the oil-water interface where catalyst must also be present. Because of this, the liquid-liquid interface is one of the most important factors to influence the reaction rate and has to be large enough. The use of a stabilizer reduces the surface tension, thus enlarging the interface (11). With simultaneous solving of differential equations, which are derived from the simplified Bailey's reaction equation (Eq. 2), the rate constants are calculated in Equations 6-8 from the experimental data Based on the calculated saturation selectivities, some conclusions could be made; k Le and k L are quite similar in comparison with k Ol . This behavior may indicate that conjugated double bonds are formed by migration of double bonds (12) in polyunsaturated compounds (triunsaturated and diunsaturated) during hydrogenation. This results in a higher reactivity of dienes and especially trienes in comparison with monounsaturated compounds. The hydrogenation of monoenoic compounds is much slower. During the hydrogenation process, both geometrical and positional isomerizations take place. As a result of these processes, the number of chromatographic peaks [9] Si = "iso"-forms all hydrogenated double bond

J8735

ABSTRACT: Twenty-one compounds, which had been screened in preceding experiments as potent odorants of french fries prepared in palm oil (PO), were quantified by stable isotope dilution assays. Nineteen odorants were dissolved in sunflower oil in concentrations equal to those in PO. The flavor profile of the model obtained was close to that of a real sample of PO. A comparison of the complete model with models lacking one or more compounds indicated the following key odorants of PO: 2-ethyl-3,5-dimethylpyrazine, 3-ethyl-2,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, 3-isobutyl-2-methoxypyrazine, (E,Z)-and (E,E)-2,4-decadienal, trans-4,5-epoxy-(E)-2-decenal, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, methylpropanal, 2-and 3-methylbutanal, and methanethiol. Replacement of palm oil by coconut fat led to a coconut note in the profile of french fries. γ-Octalactone was identified as a major contributor to this note. JAOCS 75, 1385-1392 (1998)

J9087

ABSTRACT: Melt crystallization of anhydrous milk fat and subsequent filtration of the slurry is a common process for obtaining milk fat fractions with different physical and chemical properties. The crystallization mechanism is very complex and little is known about how the crystallizer conditions and the crystal size distribution (CSD) affect the filtration process. The objective of this study was to characterize the fractionation process and determine which geometric parameters of the crystallizer affect the filtration step. Two scales of fractionation were studied, 0.6 L and 3.6 L, with crystallization at 28°C. The slurry was pressure-filtered after 24 h at 500 kPa in a 1-L chamber. Impeller diameters and speeds were varied for both scales. Photomicroscopy and spectrophotometry were used to characterize the crystallization process, and filtration rates were measured by weighing the amount of filtrate passing through the filter. Filtration resistance values, calculated using the constant pressure filtration equation, as well as photomicroscopy results indicated that the agglomerates and crystals that formed had different morphological characteristics for the different mixing and flow regimes in the crystallizer. Crystallization conditions that provide an optimal filtration time, a solid fraction with minimal liquid entrainment, and a CSD with an intermediate range of sizes (80-500 µm) having good packing properties for filtration were found. Paper no. J9087 in JAOCS 76, 585-594 (1999)

J9192

ABSTRACT: The transformations of tristearin were examined by modulated temperature differential scanning calorimetry (MTDSC) in order to examine the utility of this technique. Tristearin has been used as a model polymorphic system, showing metastable phases and complicated transformation routes occuring at relatively slow rates. The β′-forms generated by thermal treatment under modulation do not differ significantly from those generated by the corresponding treatment without modulation. While the total heat flow thermograms are similar, the deconvoluted reversing component shows that annealing, especially at 63°C, has a significant effect on the crystal size and perfection of the solid phases formed. MTDSC also enables the melting of β′ to be separated from the simultaneous crystallization of the β form as evidenced in the c p component. Quantitative interpretations about such systems cannot be drawn from MTDSC at this point in time. Paper no. J9192 in JAOCS 76, 507-510 (April 1999)