Small-angle X-ray scattering from sodium hyaluronate in aqueous sodium chloride

Summary Four narrow-distribution samples of sodium hyaluronate with weight-average molecular weights M _w of 3.8 × 10³ to 1.1 × 10⁴ in 0.02 and 0.1 M aqueous NaCl at 25°C have been studied by small-angle X-ray scattering. Data for their z-average radii of gyration <S²>_z ^1/2 and particle scattering functions P(θ), together with previous <S²>_z data from light scattering for high molecular weights, are compared with relevant theories for the wormlike chain with or without excluded volume, using the parameters estimated previously from intrinsic viscosity ([η]) data. It is shown that for M _w lower than 1.1 × 10⁴, <S²>_z, P(θ), and [η] of the polysaccharide in the aqueous salts are all consistently explained by this model without excluded volume. Received: 8 December 1997/Accepted: 26 December 1997     

Anomalous viscosity behavior of fatty acid esters in solution

Solution viscosity of oils of melonseed(Colocynthis vulgaris Schrad.), soyabean [Glycine max (L). Merr], and rubberseed [Hevea brasiliensis (Kunth) Muell.] were determined in different solvents at various concentrations. Reduced viscosity(_{η red}) vs concentration (C) plots showed three types of behavior:_{η red} increased linearly with C (2–30 g/dl);_{η red} levelled off with C (2–1.2 g/dl); and_{η red} rose steeply with decrease in C (below 1.2 g/dl), the latter behavior is anomalous. Similar viscosity behavior was observed for the methyl ester of melonseed oil, methyl palmitate and n-butyl acetate. Molecular cluster formation was believed to cause the observed anomalous viscosity behavior, the extent of which varied, depending on the nature of the fatty acid ester and the solvent.     

Synthesis and Polymerization of a Four-Arm Star with Pendent Cyclopentadienyliron Moieties

The synthesis of the title complex was achieved via the reaction of a η⁶-p-dichlorobenzene-η⁵-cyclopentadienyliron cation with an organic four-arm core to produce the tetrairon complex. This tetrairon-containing core was subsequently polymerized via nucleophilic aromatic substitution with various dinucelophiles such as 4,4′-thiobenzenethiol, bisphenol-A, 4,4′-(1-phenylethylidene)bisphenol, 4,4′-biphenol, bis(4-hydroxyphenyl)methane, producing five different cross-linked cationic organoiron polymers. Another cross-linked polymer was produced via direct polymerization of the four-arm organic core with the η⁶-p-dichlorobenzene-η⁵-cyclopentadienyliron cation. Due to the poor solubility of these cross-linked polymers, solid-state ¹³C CPMAS NMR was performed in order to verify that polymerization was successful. Thermogravimetric analysis (TGA) revealed that following the decoordination of the cyclopentadienyliron moieties, the polymers were thermally stable. Differential scanning calorimetry (DSC) showed that the polymers exhibited glass transition temperatures (T _g’s) ranging from 104 to 146°C. This article is dedicated to Professor Ian Manners for his outstanding contribution to the field of metal-containing polymers.     

Structure characterization of amorphous Al83Ni10Ce5Si2 under the relaxed annealing

In order to trace the structure evolution of amorphous Al₈₃Ni₁₀Ce₅Si₂ before crystallization, the alloy viscosity (η) was measured by methods after annealing treatment at various temperatures. It is found that the alloy viscosity decreases initially and then increases with the annealing temperature. The X-ray diffraction (XRD) patterns show that the variation of the height of the main peak with annealing temperature (H _max − T) is similar to that of the viscosity versus anncaling temperature (η − T), implying that the short-range order (SRO) in the amorphous alloy has changed. Additionally, the locations of the main peak and prepeak in the XRD curves move toward the high angle, implying that the characteristic spacing in the amorphous alloy decreases and that its volume decreases with the increase of the annealing temperature. The volume decrease is also confirmed by the development of the grooves on the free surface of the amorphous ribbon. The text was submitted by the authors in English.     

From 1-<Emphasis Type="SmallCaps">d</Emphasis> to 3-<Emphasis Type="SmallCaps">d</Emphasis> Supramolecular Structures Derived from Diphenic Acid and Auxiliary Ligands

Four novel compounds [Co(Hdpa) ₂(4,4′-bipy)₂]_n (1), {[Ni(dpa)(2,2′-bipy)(H₂O)](H₂O)}_n, (2), [Ni(dpa)(im)₃]_n (3) and [Zn(dpa)(im)]_n (4) [H₂dpa = 2,4′-diphenyl-dicarboxylic acid, 4,4′-bipy = 4,4′-bipyridine, 2,2′-bipy = 2,2′-bipyridine and im = imidazole] were synthesized and characterized by elemental analysis, IR and single-crystal X-ray diffraction. X-ray crystallography shows that the 2,4′-diphenic acid exhibits three coordination modes to link the metal ions: μ ₁ −η¹: η¹/μ ₀ −η⁰: η⁰, μ ₁−η ¹: η ⁰/μ ₂−η ¹: η ¹ and μ ₁−η ¹: η ⁰/μ ₁−η ¹: η ⁰. Compound 1 has a 1D supramolecular structure. Compounds 2 and 3 are 3D supramolecular structures. Compound 4 is a 2D supramolecular structure. All the compounds, 1–4, are self-assembled to form supramolecular structures through hydrogen bonding interactions.     

Synthesis and Crystal Structures of Two New Coordination Polymers Based on Diphenic Acid

Two new metal coordination polymers [Zn(dpa)(bim)] _n and [Ni(dpa)(bpp)] _n , (H₂dpa = 3,4′-Biphenyl-dicarboxylic acid, bim = Benzimidazole and bpp = 1,3-Di (4-pyridyl)-propane) have been synthesized and structurally characterized by elemental analysis, IR and X-ray diffraction. Single-crystal X-ray analyses reveal that the 3,4′-diphenic acids act as bridging ligands, exhibiting three coordination modes to link metal ions: μ ₂–η ¹: η ¹, μ ₁–η ¹: η ⁰ and μ ₁ –η¹: η¹. Compound 1 demonstrates a one-dimensional zigzag chain. There exists intermolecular hydrogen bonding interactions in compound 1 which lead to form supramolecular structure. Compound 2 is a two-dimensional (4,4) net, and further assembled twofold interpenetrating net. Furthermore, compound [Zn(dpa)(bim)] _n shows intense photoluminescence at room temperature.     

Influence of Extraction Processing on Rheological Properties of Rapeseed Oils

Rheological behavior of six crude rapeseed oils with different extraction methods including hot-pressing, solvent-extraction and cold-pressing were studied. Viscosities of the oils were measured with shear rates ranging from 0.1 to 200 s⁻¹ at three different temperatures. The Casson model was used to fit the experimental data and the Arrhenius equation was applied to estimate the energy of activation for viscosity (E _a). The extraction methods affected the total tocopherol, total phytosterols, total phenols, phosphorus and fatty acid composition. The hot-pressed medium-erucic rapeseed oil (HMRO) had the greatest viscosity, and the cold-pressed low-erucic rapeseed oil (CLRO) had the lowest viscosity among all the oils with shear rates >5 s⁻¹ at 10 °C. The crude rapeseed oils exhibited Newtonian behavior at higher shear rates. The significant difference of viscosity of the six oils was reduced with increasing temperature, and there was no significant change (P > 0.01) among the oils with a shear rate of 100 s⁻¹ at 50 °C. According to the values of E _a, the following order of a change in viscosity was obtained as follows: CMRO > SMRO > HMRO > CLRO > SLRO > HLRO(C, cold pressed; S, solvent extracted; H, hot pressed; M, medium erucic; L, low erucic; RO, rapeseed oil). Minor components may be the contributing factors for the values of E _a of rapeseed oils. The higher shear limiting viscosity (η_c) values calculated by the Casson model decreased as the temperature increased, but no significant change (P > 0.01) was observed for η_c by using different extraction methods at 50 °C.     

Chemistry and kinetics of LAS acid thermal decomposition

The emission of sulfur dioxide (SO₂) from linear alkylbenzene sulfonate (LAS) acid (LASH) at high temperatures has been studied. Rate constants and Arrhenius parameters have been determined, enabling estimation of the amount of SO₂ evolved under any time/temperature combination for risk assessment purposes. Further analysis of the kinetic data and comparison with earlier molecular modeling work on the mechanism of sulfonation of linear alkyl benzene (LAB) to make LASH provide insight into the reaction pathway of SO₂ formation by thermal decomposition of LASH. For risk assessment purposes, the calculation is as follows: Estimate k from k=3.9×10⁷·e^{−13,000/(273+T)}, where T is in degrees C and k is in s⁻¹. Estimate N(SO₂,t), the number of moles of SO₂ evolved when N(LASH₀) moles of LASH are heated for t s at T ^oC, from: N(SO₂,t)=N(LASH₀)×(1−e^−kt ).     

Molecular dynamics study on the viscosity of glass-forming systems near and below the glass transition temperature

Temperature-dependent viscosity is critical to decipher two profound questions in condensed matter physics, namely the glass transition and the relaxation of amorphous solids. However, direct measurement of viscosity over a large temperature range is extremely difficult. Here, using classical molecular dynamics (MD) simulations, we report a novel method to calculate the equilibrium viscosity of supercooled liquid both above and below the glass transition temperature (T_g) and to estimate the nonequilibrium viscosity of glass down to room temperature. Based on the shoving model, we derived an analytical formula showing that the shear viscosity in logarithmic scale changes linearly with the shear-induced variation in shear modulus or potential energy of the glass-forming system. The shear viscosity as a function of steady-state potential energy of liquid under different shear strain rates can be directly calculated in MD simulations; together with its equilibrium potential energy, one can extrapolate the zero-strain-rate equilibrium viscosity. We verified the proposed model by reliably calculating equilibrium viscosity near T_g of four glass-forming systems (Kob–Andersen system, silica, Cu_45.5Zr_45.5Al₉, and silicon) with different fragilities. Furthermore, our model can estimate the nonequilibrium viscosity of glass below T_g; the upper-bound nonequilibrium viscosity of amorphous silica and silicon at room temperature are calculated to be ~10³² and 10²⁵ Pa·s, respectively.     

Viscosity behavior and chain conformation of a (1→3)-α-glucan from Ganoderma lucidum

Summary Seven fractions of a (1→3)-α-D-glucan from Ganoderma lucidum have been studied by light scattering, sedimentation equilibrium, and viscometry in dimethylsulfoxide (DMSO) containing 0.25 M lithium chloride at 25°C. The intrinsic viscosity [η] - molecular weight relation for this glucan in the mixed solvent is found to be represented approximately by [η] = 0.071 M _w ^0.60 cm³ g⁻¹ in the range of weight-average molecular weight M _w studied, i.e., from 8 × 10³ to 4.4 × 10⁵. Its analysis based on current theories for wormlike chains shows that, without excluded volume effect, the (1→3)-α-D-glucan chain is characterized by a linear mass density of 380 nm⁻¹, a Kuhn segment length of about 3 nm, and a diameter of 1.2 nm and is somewhat more extended but more flexible than amylose, a (1→4)-α-glucan, in DMSO. Received: 28 July 1998/Accepted: 18 August 1998     

Rheological and mechanical properties of poly(lactic acid)/polystyrene polymer blend

Properties modification by blending polymers has been an area of immense interest. In this work, rheological and mechanical properties of poly(lactic acid)/polystyrene (PLA/PS) blends were investigated. PLA/PS blends in different ratios were prepared using a laboratory scale single screw extruder to obtain (3 mm) granules. Rheological properties were studied using a capillary rheometer and the Bagley’s correction was performed. True shear rate (γ _r ), true shear stress (τ _r ), and true viscosity (η _r ) were determined, the relationship between true viscosity and (1/T) was studied for PLA70 blend and the flow activation energy at a constant shear stress (E _τ ) and a constant shear rate (E _γ ) was determined. The mechanical property measurements were performed at room temperature. Stress at break and strain at break were determined. The results showed that PLA/PS blend exhibited a typical shear-thinning behavior over the range of the studied shear rates, and the viscosity of the blend decreased with increasing PLA content. Also it was found that no equal-viscosity temperature exists between PLA and PS. The mechanical results showed immiscibility between PLA and PS in the blend.     

Solution properties of polymacromonomers consisting of polystyrene

Summary Dynamic light scattering measurements have been made on 14 samples of a polymacromonomer consisting of polystyrene with 15 styrene side-chain units in cyclohexane at 34.5°C (the theta point) to determine the translational diffusion coefficient D as a function of molecular weight. The dependence of D on the main-chain length is analyzed on the basis of the wormlike chain by taking into account the end effect arising from side chains near the main-chain ends. The model parameters describing this dependence, i.e., the Kuhn segment length (11.5 ± 1.5 nm), the linear mass density (5600 ± 700 nm⁻¹), the diameter (5.2 ± 0.5 nm), and the end-effect parameter δ (2.5 ± 0.3 nm), are close to those determined previously from <S ²>_z (the z-average mean-square radius of gyration) and [η] (the intrinsic viscosity), leading to the conclusion that the wormlike chain model is capable of consistently explaining <S ²>_z, [η], and D of the polymacromonomer in the Θ solvent. Received: 8 February 2000/Accepted: 18 February 2000     

An efficient method for a numerical description of virgin olive oil color with only two absorbance measurements

Four polynomial expressions are obtained that provide a good approximation and an easy, rapid calculation of the chromatic coordinates and the chroma—L ^*, a ^*, b ^*, and C—for the illuminant C and the standard observer, for a virgin or extra virgin olive oil; absorbance is measured at only 480 and 670 nm. These are as follows: L ^*=0.556458(A₄₈₀)²−2.51145A₄₈₀+0.55504(A₆₇₀)²−8.53016A₆₇₀+98.4089; a ^*=0.177372(A₄₈₀)²+2.1363A₄₈₀+1.43254(A₆₇₀)²−0.789231A₆₇₀−13.9246; b ^*=−16.0277(A₄₈₀)²+79.8932A₄₈₀−5.06558(A₆₇₀)²+3.36169A₆₇₀+31.9405; C=−15.8439(A₄₈₀)²+78.9312A₄₈₀−5.26784(A₆₇₀)²+3.56917A₆₇₀+33.3927. These give acceptable results, making the method a practical alternative to the extremely laborious Commission Internationale d’Eclairage (CIE) L ^* a ^* b ^* system, by which 391 absorbance values must be measured individually, nanometer by nanometer, before applying more complex equations. The validity of the proposed method has been confirmed by comparison, using a set of 20 sample oils different from the set of 25 oils used to generate the order of the equations. The variations between the values provided by the proposed and standard methods, respectively, had a mean of 0.00 for each of the chromatic variables—L ^* , a ^* , b ^* , and C; SD were moderate (0.71, 0.52, 1.22, and 1.22, respectively); the root mean square and the R ²-terms also confirmed the validity of the method.     

Viscosity Adjustment of Aqueous Micellar Solutions of Gemini Surfactants by Interaction with Additional Surfactants

The viscosity of aqueous micellar solutions depends on the size and shape of the aggregates and thus can be adjusted by addition of another surfactant interacting with the original component, which alters the geometry of the molecule-pair consisting of two surfactants and influences strongly the size and shape of the mixed micelles. Ethanediyl-α,ω-bis(dimethyl dodecyl ammonium bromide), referred to as C₁₂-2-C₁₂·2Br, forms generally large micelles. Addition of a cationic surfactant (dodecyltrimethylammonium bromide, C₁₂TMABr) or a nonionic surfactant (alkyl polyoxyethylene ether, C _m E _n ), the mixed micelle size is reduced violently since the electrostatic repulsion between the same charged heads of C₁₂-2-C₁₂·2Br and C₁₂TMABr or the steric hindrance of the PEO chain of C _m E _n in the palisade layers of the mixed micelle, which leads to a decrease in the packing parameter P of the molecule-pair. As a result, the zero-shear viscosity (η ₀) of the mixed solution reduces rapidly. In contrast, on adding an oppositely charged surfactant, η ₀ of the mixed solution increases strongly since the P of the molecule-pair increases through electrostatic attraction between the oppositely charged heads. The typical cases occur in the mixtures of the anionic gemini surfactant, O,O′-bis(sodium 2-lauricate)-p-benzenediol C11pPHCNa, and the cationic surfactant C₁₂-2-C₁₂·2Br, C₁₂TMABr or its homologue with a different size of heads.     

Use of liquid chromatography-mass spectroscopy for studying the composition and properties of rhamnolipids produced by different strains of <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis>

Biosurfactants are produced as a mixture of different homologs. The application of liquid chromatography-electrospray mass spectrometry in negative mode for the analysis of rhamnolipid mixtures AT10 and 47T2 has been studied. Working at low (up to −35V) extraction voltages, the [M-H]⁻ for each compound was obtained. Increasing this potential to −75V produced an increase in the fragmentation of compounds and enabled the co-eluting isomers of rhamnolipids to be distinguished and their proportions in the sample to be calculated. In this work, the physicochemical and biological properties of two different rhamnolipid mixtures produced by two Pseudomonas strains RL_AT10 (Rha-Rha-C₁₀-C₁₀; Rha-Rha-C₁₀-C_12:1; Rha-Rha-C₁₀-C₁₂; Rha-C₁₀-C_12:1; Rha-C₁₀-C₁₀; RhaC₁₀-C_12:1; Rha-C₁₀-C₁₂; Rha-C_8:1; Rha-C_12:2) and RL_47T2 (Rha-Rha-C₈-C₁₀; Rha-Rha-C₈-C_12:1; Rha-Rha-C₁₀-C₁₀; Rha-Rha-C₁₀-C_12:1; Rha-Rha-C₁₀-C₁₂; Rha-Rha-C₁₂-C₁₀; Rha-Rha-C_12:1-C₁₂; Rha-Rha-C₁₀-C_14:1; Rha-C₈-C₁₀; Rha-C₁₀-C₈; Rha-C₁₀-C₁₀; Rha-C₁₀-C_12:1; Rha-C₁₀-C₁₂; Rha-C₁₂-C₁₀, where Rha=rhamnose moiety) are compared. The surface tensions found were 26.8 and 32.8 mN/m for RL_AT10 and RL_47T2, respectively. These two products differ in their antimicrobial properties, as based on their minimal inhibition concentrations (MIC). RL_AT10 was effective against the fungal species (MIC) Aspergillus niger (16 μg/mL); Gliocadium virens (16 μg/mL); Penicillium chrysogenum (32 μg/mL); Botrytis cinerea (18 μg/mL); and Rhizoctonia solani (18 μg/mL), whereas RL_47T2 was more effective against the bacteria (MIC) Enterobacter aerogenes (4 μg/mL); Serratia marcescens (8 μg/mL); Bacillus subtilis (16 μg/mL); and Staphylococcus aureus (32 μg/mL).     

Initiation of combustion processes in a hydrogen-oxygen mixture under the action of a low-energy strong-current electron beam

The process of combustion initiation in a hydrogen-oxygen mixture by a beam of electrons with an energy of ≈10 keV and a mean cross-sectional size of ≈10 cm is considered theoretically and experimentally. The initial pressure in the mixture is 500 Pa. The reaction was visualized by recording the time evolution of fluorescence intensity in the lines of molecular (λ = 310 nm) and atomic hydrogen and sodium doublet (λ = 589 nm). The calculations are performed on the basis of a semi-empirical model developed in a three-temperature (T ₀, T _e , and T _v) approximation. The induction and burning times determined in experiments and calculations are in good agreement. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 10–17, March–April, 2007.     

Sensory Thresholds of Selected Phenolic Constituents from Thyme and their Antioxidant Potential in Sunflower Oil

The odor detection thresholds of carvacrol (5-isopropyl-2-methyl-phenol), thymol (2-isopropyl-5-methyl-phenol) and p-cymene 2,3-diol (2,3-dihydroxy-4-isopropyl-1-methyl-benzene) in sunflower oil, determined by the three-alternative, forced-choice procedure, were 30.97, 124 and 794.33 mg kg⁻¹, respectively. Sunflower oil containing 13, 70, or 335 mg kg⁻¹ of carvacrol, thymol or p-cymene 2,3-diol, respectively, was judged to be similar (P < 0.01) in taste and odor to its antioxidant-free counterpart. The rate constant of sunflower oil oxidation, measured from the increase in peroxide value during storage at 25 °C, was 9.2 × 10⁻⁹ mol kg⁻¹ s⁻¹ while the rate constants were 9.3 × 10⁻⁹, 9.8 × 10⁻⁹, and 4.3 × 10⁻⁹ mol kg⁻¹ s⁻¹ in the presence of 13 mg kg⁻¹ carvacrol, 70 mg kg⁻¹ thymol, and 335 mg kg⁻¹ p-cymene 2,3-diol, respectively. At a level of 335 mg kg⁻¹, p-cymene 2,3-diol did not impart flavor taints and effected a 46.7% reduction in the rate of oxidation of sunflower oil. These findings indicate that the diphenolic p-cymene 2,3-diol could potentially replace synthetic antioxidants and is a valuable addition to the antioxidants used by the food industry in its quest to meet consumer demands for synthetic-additives-free and ‘natural’ foods.     

Physico-Chemical Characterization of <Emphasis Type="Italic">Moringa concanensis</Emphasis> Seeds and Seed Oil

The present work reports the characterization and comparison of Moringa concanensis seed oil from Tharparkar (a drought hit area), Pakistan. The hexane-extracted oil content of M. concanensis seeds ranged from 37.56 to 40.06% (average 38.82%). Protein, fiber, moisture and ash contents were found to be 30.07, 6.00, 5.88 and 9.00%, respectively. The extracted oil exhibited an iodine value of 67.00; a refractive index (40 °C) of 1.4648; its density (24 °C) was 0.8660 mg mL⁻¹; the saponification value (mg of KOH g⁻¹ of oil) was 179.00; unsaponifiable matter 0.78%; color (1 in. cell) 1.90R + 19.00Y; and acidity (% as oleic acid) 0.34%. Tocopherols (α, γ, and δ) in the oil accounted for 72.11, 9.26 and 33.87 mg kg⁻¹, respectively. Specific extinctions at 232 and 270 nm were 3.17 and 0.65, respectively. The peroxide and p-anisidine values of the oil were found to be 1.75 and 1.84 meq kg⁻¹, respectively. The induction periods (Rancimat, 20 L h⁻¹, 120 °C) of the crude oil was 10.81 h and reduced to 8.90 h after degumming. The M. concanensis oil was found to contain high levels of oleic acid (up to 68.00%) followed by palmitic, stearic, behenic, and arachidic acids up to levels of 11.04, 3.58, 3.44 and 7.09%, respectively. The results of the present analytical study, compared with those for other Moringa species and different vegetable oils, showed M. concanensis to be a potentially valuable non-conventional seed crop for high quality oil.     

Dietary lipid modification of myocardial eicosanoids following ischemia and reperfusion in the rat

Several different edible oils were compared for their ability to modify eicosanoid biosynthesis following experimentally-induced myocardial ischemia and reperfusion in the rat. Two types of palm oil [neutralized, bleached, and deodorized (NBDPO) and refined, bleached, and deodorized (RBDPO)] and partially hydrogenated soybean oil (SBO) were tested against a diet supplemented with sunflower seed oil (SSO) rich in n−6 polyunsaturated fatty acids (PUFA). Fish oil (FO) rich in n−3 PUFA, with its known cardioprotective actions, served as an internal reference point for the study. Test oils were fed as a 12% (w/w) supplement for nine months before the induction of myocardial ischemia and reperfusion. Palm oil diets exerted effects indistinguishable from the SBO group against cardiac arrhythmia, which occurred following alterations to coronary blood flow. Arrhythmic potentials, as expressed by a hierarchical scale (0–9) of arrhythmia score, were: SSO, 1.5±0.5; FO, 0.9±0.4; SBO; 3.1±0.5^*; NBDPO, 3.2±0.5^*; RBDPO, 3.3±0.6^*,^* P<0.05 vs. SSO. Following ischemia and reperfusion, both SSO and RBDPO groups tended to show an increase in myocardial prostacyclin, with the effect being more prominent in the RBDPO group (SSO, 10%; RBDPO, 25%). Thromboxane production was reduced in the FO group. Interestingly, cardiac muscle from both FO and palm oil groups displayed a reduced capacity to produce 12-hydroxyeicosatetraenoic acid SSO, 591.9±95.8; SBO, 375.5±48.9; NBDPO, 287.2±64.7^*; RBDPO, 230.9±80.2^**; FO, 203.7±81.4^** (ng/g dry wt,^* P<0.05,^** P<0.01). No clear relationship was seen between the availability of 20∶4n−6 in myocardial phospholipids and eicosanoid profile. Data suggests that fatty acid composition of edible oils is not the only determinant of arrhythmic vulnerability and eicosanoid production. Based on a paper presented at the PORIM International Palm Oil Congress, Kuala Lumpur, Malaysia, September 1993.