Partial extraction method for the rapid analysis of total lipids and γ-oryzanol contents in rice bran

Total lipids and γ-oryzanol in rice bran were determined by a partial extraction method. The results agreed well with the conventional total extraction methods. The proposed method uses fewer hazardous organic solvents, takes a shorter extraction time and requires no special extraction apparatus. Total lipids and γ-oryzanol in nine rice bran varieties were analysed by the developed technique. Daw Dum 5647 had the highest total lipids and γ-oryzanol while the lowest content was found in KD XBT 313-19-1-1 and SP XBT 43-7, respectively. The adsorption coefficient (K_d) of the lipids and γ-oryzanol, between hexane and bran, at 30 °C are between 1.16 and 2.00 and 2.02 and 2.65, respectively (depending on the moisture content of the bran). From the K_d values, it was estimated that about 92–95% of the lipids and 95–96% of the γ-oryzanol were extracted into hexane at a 10:1 (v/w) ratio of hexane to bran. The effect of solvents on the extraction of γ-oryzanol from rice bran was also studied. It was found that isopropanol was the most suitable solvent for extraction and determination of γ-oryzanol in rice bran. It showed better agreement with the total extraction method.     

Gas Chromatographic Separation and Identification of Jacaric and Punicic 2-Ethyl-1-Hexyl Esters

The present study demonstrates the separation of a critical pair of conjugated linolenic acid (CLN) isomers—jacaric acid (JA; c8, t10, c12-18:3) and punicic acid (PA; c9, t11, c13-18:3)—on a 60-m conventional Supelcowax 10 column. The alkyl esters of different alcohols (C₁–C₈) of JA and PA were prepared and analyzed isothermally at 220, 230 and 240 °C. The adequacy of their separation was determined from the separation factors (α) and peak resolutions (R _s). Acceptable resolution (R _s = 1.01) of JA and PA was obtained with their 2-ethyl-1-hexyl ester derivatives at a column temperature of 230 °C. In addition, the Gibbs energy of transfer from solution to gas of the three double bonds \((\Delta_{\text{sln}}^{\text{g}} G_{\text{u}}\)) could be used to describe the interactions of the double bond with the stationary phase. Characterization of 2-ethyl-1-hexyl esters of Jacaranda mimosifolia seed oil at 230 °C demonstrates that the oil contains JA and α- and β-calendic acid as a CLN without the presence of PA. The results suggested that JA could be resolved from PA on a 60-m Supelcowax 10 column as the ethyl hexyl ester.     

Separation and Determination of Wax Content Using 100-Å Phenogel Column

Rice bran wax (RBW) is a by product of rice bran oil refinery. Crude RBW from refineries in Thailand had only 20–40% of the wax ester. The major impurity was triglyceride (TG). Purification of RBW requires a rapid and reliable method of analysis. In this study, a modified size exclusion HPLC column (100-Å Phenogel) was reported. Degree swellings of the gel matrix were controlled by isooctane–toluene mobile phase ratio. With pure toluene as the mobile phase, the gel matrix is fully swollen. Wax and TG could not be separated. With 65:35 (v/v) of isooctane–toluene, wax and TG as well as other lipids were baseline separated. The resolution (Rs) between wax and TG was greater than 1.5. Acetic acid (0.1% or higher) in the mobile phase could suppress peak tailing and improved separation of the lipid containing active hydroxyl groups such as free fatty acid, diglyceride and monoglyceride without affecting retention times of the wax and the TG. Separation of lipids in crude RBW could be completed in a single run on the modified Phenogel column (100 Å) with the total analysis time less than 15 min. The relationship between the amount of wax in the sample and the peak area was linear with the R ² greater than 0.98.     

A Mathematical Model for Estimating Molecular Compressibility of Fatty-Acid Methyl Ester and Biodiesel

In this study, the molecular compressibility (k_m) of a fatty-acid methyl ester (FAME) or a biodiesel is correlated with ΔG, , via the Gibbs energy additivity method, where MW is the molecular weight of the FAME or the average MW of the biodiesel. The Gibbs energy associated with molecular compressibility () is further correlated with the structure of FAME. Thus, the relationship between the structure (of a FAME or a biodiesel) and the physical property (k_m) is established. Thus, k_m of a FAME at different temperatures can be easily estimated from the carbon numbers of fatty acid (z) and the number of double bonds (n_d) with good accuracy. For biodiesel, k_m is calculated from the same equation with the average z (z_(ave)) and average n_d (n_d(ave)). k_m is not temperature independent and a slight change in k_m depends on the structure of the FAME and biodiesel. For FAME having 14 carbon atoms or less in the fatty acid, k_m decreases as temperature is increased. On the other hand, for FAME with a longer chain length (16 or higher), k_m increases as temperature is increased. Similarly, a double bond in the long-chain FAME is more sensitive to temperature than the saturated FAME.     

Correlating the Speed of Sound with the Gibbs Energy and Estimating the Speed of Sound in Fatty Acid Methyl Ester and Biodiesel

The relationship between the speed of sound (u) in biodiesel and the change in Gibbs energy (ΔG) has not been described in the literature. With the Gibbs energy additivity method, the relationship between u and ΔG can be expressed as ln(u²) = ΔG/RT + A, where R is the universal gas constant, T is the absolute temperature, and A is a constant. The molecule of fatty acid methyl ester (FAME) was arbitrarily sub-divided into groups of atoms and a ΔG was assigned to each group of atoms. A new model correlating the speed of sound to the structure of fatty acid was derived. The proposed model was good for estimation of the speed of sound in both FAME and biodiesel at various temperatures with good accuracy. The absolute average deviations for the speed of sound in FAME (65 data points) and in biodiesel (175 data points) were 0.23% and 0.36%, respectively. Only the number of double bonds and carbon atoms of the fatty acid are required for the calculation.     

Reducing Oil Losses in Alkali Refining

Neutralization is an important step in the chemical refining of edible oils. Free fatty acids (FFA) are generally removed in neutralization as sodium soaps but neutral oil is also entrapped in the emulsion and removed with the soap during centrifugation. Thus, alkali neutralization causes a major loss of neutral oil in the chemical refining of edible oils. The effects of demulsifiers (NaCl, KCl, Na₂SO₄ and tannic acid) on reducing alkali refining losses of refined palm, soybean, and sunflower oils (used as model oils) incorporated with FFA from rice bran oil were investigated. Adding small amounts of demulsifiers to the alkali neutralization step significantly reduced neutral oil loss of these model oils. All demulsifiers except for tannic acid had similar effects on refining losses in all oil model systems. The optimum demulsifier content was 1.0 % (w/w of oil).     

Effects of Crude Rice Bran Oil Components on Alkali-Refining Loss

The effects of minor components in crude rice bran oil (RBO) including free fatty acids (FFA), rice bran wax (RBW), γ-oryzanol, and long-chain fatty alcohols (LCFA), on alkali refining losses were determined. Refined palm oil (PO), soybean oil (SBO) and sunflower oil (SFO) were used as oil models to which minor component present in RBO were added. Refining losses of all model oils were linearly related to the amount of FFA incorporated. At 6.8% FFA, the refining losses of all the model oils were between 13.16 and 13.42%. When <1.0% of LCFA, RBW and γ-oryzanol were added to the model oils (with 6.8% FFA), the refining losses were approximately the same, however, with higher amounts of LCFA greatly increased refining losses. At 3% LCFA, the refining losses of all the model oils were as high as 69.43–78.75%, whereas the losses of oils containing 3% RBW and γ-oryzanol were 33.46–45.01% and 17.82–20.45%, respectively.     

An empirical approach for predicting kinematic viscosities of biodiesel blends

Kinematic viscosity (η) is an important property of diesel fuels, including biodiesels, which are marketed mostly as the blends in many countries around the world. In this study, the free energy of viscous flow (ΔG_vis) for a non-associated liquid mixture is assumed to be the summed of ΔG_vis of individual components. Hence, the Eyring’s equation, η = Ae(−ΔG_vis/RT), is transformed to ln η_blend = a + bn₁ + c/T + dn₁/T (where, a, b, c and d, T and n₁ are thermodynamically related constants, absolute temperature and mole fraction of biodiesel, respectively). The transformed equation is used to predict kinematic viscosity of biodiesel blends (η_blend) of different degree of blending at any temperatures from pour point to 100 °C. The predicted kinematic viscosities are in good agreement with those reported in literatures at all temperatures. The highest deviation is ±5.4% and the average absolute deviation (AAD) is less than 2.86%. The transformed equation can also be used to predict kinematic viscosities of pure fatty acid methyl esters in diesel fuel. Methyl ricinoleate is an exception. The AAD is 4.50% and the deviation is as high as 12.80%. The high deviation suggests that molecular interactions between methyl ricinoleate and diesel fuel is high and cannot be ignored.     

Effect of Selected Polyhydric Alcohols on Refining Oil Loss in the Neutralization Step

Alkaline neutralization is a classical method for removal of free fatty acids (FFA) in crude oil. It is generally accompanied by neutral oil loss. Thus, reduction of refining losses associated with alkaline neutralization is very desirable. Refined, bleached and deodorized (RBD) palm oils with different FFA contents were used as oil models in this study. FFA in the oil models were neutralized with sodium hydroxide in polyhydric alcohols as neutralization media. Glycerol, propylene glycol and ethylene glycol in water were effective neutralization media. FFA in the oil models were totally removed in one step of neutralization, while percentages of refining losses were different. The losses were increased in the order of water > propylene glycol > ethylene glycol > glycerol used as neutralization media. Also, a higher concentration of polyhydric alcohol in the neutralizing media significantly reduced the percentage of refining loss (p < 0.05). Glycerol (90% in water) was the most effective neutralization media (p < 0.05). When neutralization was carried out on crude palm oil (containing 7.53% FFA), refining loss was reduced from 36.1% (in water) to 20.0% (in 90% glycerol in water).     

Energy Additivity Approaches to QSPR Modeling in Estimation of Dynamic Viscosity of Fatty Acid Methyl Ester and Biodiesel

Viscosity is an important physical property of fatty acid methyl esters (FAME) and biodiesel (mixture of FAMEs). In this work, quantitative structure–property relationship (QSPR) for estimation of dynamic viscosity of FAMEs and biodiesel is approached via the Gibbs energy additivity method. The Gibbs energy of dynamic viscous flow is simply derived from the sum of the Gibbs energy of kinematic viscous flow and Gibbs energy of volumetric expansion. The derived model can be used for estimation of dynamic viscosity of saturated and unsaturated FAMEs commonly found in nature. Also, the proposed model can be extended to a mixture of FAMEs or biodiesel as well as biodiesel blends. Thus, the dynamic viscosity of FAMEs as well as neat and blended biodiesels can be estimated by the same equation from the carbon number (z) and number of double bonds (n_d) at different temperature (T). The average absolute deviation (AAD) values for saturated, unsaturated FAMEs, biodiesels, and biodiesel blends (at 20–100 °C) are approximately the same as the original model for estimation of kinematic viscosity.