Study on the composition of rice bran oil and its higher free fatty acids value

The compositions of rice bran oils (RBO) and three commercial vegetable oils were investigated. For refined groundnut oil, refined sunflower oil, and refined safflower oil, color values were 1.5–2.0 Lovibond units, unsaponifiable matter contents were 0.15–1.40%, tocopherol contents were 30–60 mg%, and FFA levels were 0.05–0.10%, whereas refined RBO samples showed higher values of 7.6–15.5 Lovibond units for color, 2.5–3.2% for unsaponifiable matter, 48–70 mg% for tocopherols content, and 0.14–0.55% for FFA levels. Of the four oils, only RBO contained oryzanol, ranging from 0.14 to 1.39%. Highoryzanol RBO also showed higher FFA values compared with the other vegetable oils studied. The analyses of FA and glyceride compositions showed higher palmitic, oleic, and linoleic acid contents than reported values in some cases and higher partial glycerides content in RBO than the commonly used vegetable oils. Consequently, the TG level was 79.9–92% in RBO whereas it was >95% in the other oils studied. Thus, refined RBO showed higher FFA values, variable oryzanol contents, and higher partial acylglycerol contents than commercial vegetable oils having lower FFA values and higher TG levels. The higher oryzanol levels in RBO may contribute to the higher FFA values in this oil.     

Experimental data and modeling of rice bran oil extraction kinetics using ethanol as solvent

The extraction kinetics of rice bran oil (RBO), free fatty acids (FFA), and oryzanol using ethanol (0 and 6.3 mass % of water) at 40°C–70°C were investigated. High extraction temperatures increased the yields of RBO and oryzanol by increasing the diffusivity of the solvent, regardless of its water content. Two models that permitted the estimation of mass transfer and diffusion coefficients were fitted to the oil extraction data with low average relative deviations (≤5.92%). The diffusion coefficient (1.93–7.46 × 10^–10 m²?s^–1) increased with increasing temperature and decreasing hydration of the solvent.     

Identification of oil palm breeding lines producing oils with low acid values

In the oil palm (Elaeis guineensis Jacq.), an active endogenous lipase is responsible for the massive release of free fatty acids (FFA) in the mesocarp of fruits at maturity. This can lead to the production of oils with unacceptable acid values. We have investigated the lipase activities in 39 genotypes of oil palm presently used in breeding programs. While most E. guineensis genotypes exhibited high lipase activity values, four of them with negligible activities were identified. We analyzed in situ lipolysis in the mesocarp upon severe wounding of fruits. The FFA content of high‐lipase fruits ranged from 17 to 55%, while all low‐lipase fruits contained less than 7.5% FFA. The analysis of oil from fallen overripe fruits indicated that all low‐lipase genotypes contained less than 1.2% FFA (oil acidity <5% FFA, FAO‐WHO international norms), while all but one high‐lipase genotypes had FFA contents much higher than the acceptable standards. Because the identified low‐lipase lines are of high agronomical value and at least one of them is an elite genotype, it will soon be possible to provide farmers with new low‐lipase oil palm lines allowing significant savings on labor costs, without any need for further breeding.     

Deacidification of high-acid rice bran oil by reesterification with monoglyceride

Autocatalytic esterification of free fatty acids (FFA) in rice bran oil (RBO) containing high FFA (9.5 to 35.0% w/w) was examined at a high temperature (210°C) and under low pressure (10 mm Hg). The study was conducted to determine the effectiveness of monoglyceride in esterifying the FFA of RBO. The study showed that monoglycerides can reduce the FFA level of degummed, dewaxed, and bleached RBO to an acceptable level (0.5±0.10 to 3.5±0.19% w/w) depending on the FFA content of the crude oil. This allows RBO to be alkali refined, bleached, and deodorized or simply deodorized after monoglyceride treatment to obtain a good quality oil. The color of the refined oil is dependent upon the color of the crude oil used.     

Effect of refining of crude rice bran oil on the retention of oryzanol in the refined oil

The effect of different processing steps of refining on retention or the availability of oryzanol in refined oil and the oryzanol composition of Indian paddy cultivars and commercial products of the rice bran oil (RBO) industry were investigated. Degumming and dewaxing of crude RBO removed only 1.1 and 5.9% of oryzanol while the alkali treatment removed 93.0 to 94.6% of oryzanol from the original crude oil. Irrespective of the strength of alkali (12 to 20° Be studied), retention of oryzanol in the refined RBO was only 5.4–17.2% for crude oil, 5.9–15.0% for degummed oil, and 7.0 to 9.7% for degummed and dewaxed oil. The oryzanol content of oil extracted from the bran of 18 Indian paddy cultivars ranged from 1.63 to 2.72%, which is the first report of its kind in the literature on oryzanol content. The oryzanol content ranged from 1.1 to 1.74% for physically refined RBO while for alkali-refined oil it was 0.19–0.20%. The oil subjected to physical refining (commercial sample) retained the original amount of oryzanol after refining (1.60 and 1.74%), whereas the chemically refined oil showed a considerably lower amount (0.19%). Thus, the oryzanol, which is lost during the chemical refining process, has been carried into the soapstock. The content of oryzanol of the commercial RBO, soapstock, acid oil, and deodorizer distillate were in the range: 1.7–2.1, 6.3–6.9, 3.3–7.4, and 0.79%, respectively. These results showed that the processing steps—viz., degumming (1.1%), dewaxing (5.9%), physical refining (0%), bleaching and deodorization of the oil—did not affect the content of oryzanol appreciably, while 83–95% of it was lost during alkali refining. The oryzanol composition of crude oil and soapstock as determined by high-performance liquid chromatography indicated 24-methylene cycloartanyl ferulate (30–38%) and campesteryl ferulate (24.4–26.9%) as the major ferulates. The results presented here are probably the first systematic report on oryzanol availability in differently processed RBO, soapstocks, acid oils, and for oils of Indian paddy cultivars.     

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.     

Influence of chemical refining on the major and minor components of rice brain oil

The effects of each individual step of the chemical refining process on major and minor components of rice bran oil were examined. In comparison with common vegetable oils, rice brain oil contains a significantly higher level of several bioactive minor components such as γ-oryzanol, tocotrienols, and phytosterols. Alkali treatment or neutralization results in a significant loss of oryzanol. In addition, it gives rise to a change in the individual phytosterol composition. After bleaching, some isomers of 24-methylenecycloartanol were detected. Because of their relatively high volatility, phytosterols and tocotrienols are stripped from the rice brain oil during deodorization and concentrated in the deodorizer distillate. At the same time, oryzanol is not volatile enough to be stripped during deodorization; hence, the oryzanol concentration does not change after deodorization. Complete refining removed 99.5% of the FFA content. Depending on the applied deodorization conditions, trans FA can be formed, but the total trans content generally remains below 1%.     

Storage stability evaluation of some packed vegetable oil blends

The physicochemical characteristics and minor component contents of blended oils packed in pouches in relation to starting oils used for blending were studied over a period of 6 mon at two storage temperatures and humidity conditions: 27°C/65% RH and 40°C/30–40% RH. Color, PV, FFA value, β-carotene content, tocopherol content, and oryzanol content of the oils were monitored at regular intervals. The color, PV (0.6–20.7 meq O₂/kg, FFA value (0.08–2.1%), tocopherol content (360–1700 ppm%), oryzanol content (460–2,000 mg%), and sesame oil antioxidants (400–2,000 mg%) were not changed in either the starting oils or their blends. Oils and oil blends containing a higher initial PV (18.9–20.7 meq O₂/kg) showed a slight reduction in value at 40°C, whereas oils having lesser PV of 5–10 showed a slight increase during the storage period. Among the minor components studied, only β-carotene showed a reduction, 8.9–60.2% at 27°C and 48–71% at 40°C, for the different oil blends studied. The observed results indicated that the packed oil blends studied were stable under the conditions of the study, and the minor components, other than β-carotene, remained unaltered in the package even at the end of 6 mon of storage.     

Effect of minimal neutralization at optimal conditions on minor components and oxidation stability of sunflower oil

In this study, oxidatively stable minimal neutralized sunflower seed oils were produced using three chemicals (Ca(OH)₂, MgO, and Na₂SiO₃) under previously determined optimal process conditions. Lipid oxidation rates at these optimum conditions were compared to the oils neutralized with NaOH (0.20%, 40°C, 15 min). It was concluded that the oils neutralized by NaOH had the shortest hydroperoxide and hexanal lag phases, thus were the least stable oils. Oils neutralized by Ca(OH)₂, MgO, and Na₂SiO₃ had lower FFA and higher oxidative stability than oil neutralized by NaOH. The study focused on which weak alkaline has higher oxidation stability and minimum FFA content and maximum acceptable tocopherol content. The oil neutralized by Ca(OH)₂ had the lowest FFA value and highest total phenolics and α-tocopherol contents and it had better oxidative stability than oil neutralized by NaOH. It suggests that Ca(OH)₂ could be more effective in producing a high quality oil.     

Reduction of Free Fatty Acids in Acidic Nonedible Oils by Modified K10 Clay

Biodiesel is a biofuel obtained from vegetable oils. The oils used as raw materials are usually refined edible vegetable oils. Nonedible acidic oils are unsuitable for biodiesel production unless reduction of the high content in free fatty acids (FFA) of these materials had been achieved. Obtaining a good raw material from unprofitable oils becomes an important research field. Additionally clays have a long history in industrial sorption and catalysis, some being commercially available and with properties that can be modified. In this work we present the results of the use of the montmorillonite clay K10 and two acid modified clays K10(I) and K10(II), in the esterification of stearic acid with methanol and 95 % of methyl stearate was obtained with K10(II). These clays were then used for the first time to reduce the acidity of enhanced FFA sunflower oil and they show to be very effective. Reduction of FFA from 11 to 4 % was obtained with K10(II) mainly due to 94 % conversion of FFA into fatty acid methyl esters (FAME). These clays were also tested with two waste oils, one from domestic use and the other gathered from different restaurants, and showed their ability to lower the acidity of these oils. Reactions were followed by ¹H NMR as well as quantitative determination of FFA and FAME. Clays were characterized by FTIR and XRD.     

A modified method for determining free fatty acids from small soybean oil sample sizes

A modification of the AOCS Official Method Ca 5a-40 for determination of free fatty acids (FFA) in 0.3 to 6.0-g samples of refined and crude soybean oil is described. The modified method uses only about 10% of the weight of oil sample, alcohol volume, and alkali strength recommended in the Official Method. Standard solutions of refined and crude soybean oil with FFA concentrations between 0.01 and 75% were prepared by adding known weights of oleic acid. The FFA concentrations, determined from small sample sizes with the modified method, were compared with FFA percentages determined from larger sample sizes with the Official Method. Relationships among determinations obtained by the modified and official methods, for both refined and crude oils, were described by linear functions. The relationship for refined soybean oil had an R ² value of 0.997 and a slope of 0.99±0.031. The values for crude soybean oil are defined by a line with R ²=0.9996 and a slope of 1.01±0.013.     

Extrusion deactivation of rice bran enzymes by pH modification

Rice bran is considered in Mexico as “waste”, useful only for feeds. As considerable amounts of oil are available in rice bran, it might be worthwhile to stabilize it and extract the edible oil before using it for feedstuffs. Precisely these oils are responsible for rice bran rapid deterioration, particularly in climatic conditions such as those prevalent in Mexico's tropical areas (high humidity and high temperature). This paper deals with the study of the effect of pH during extrusion of fresh rice bran in order to inactivate lipid‐breaking enzymes. Hydrochloric acid or calcium hydroxide, Ca(OH)₂, were added at 0, 1, 5, 10% (dry basis), and moisture content of the bran samples was varied (20, 30, 40%, dry basis) in a 3² factorial design to corroborate its effect at acid and alkaline pH range. Free fatty acids (FFA) increase was the control variable. Extruded samples were stored at room temperature (between 20 and 28 °C) using a non‐extruded sample as control to assess the shelf life effects. Results indicate that in acid‐extruded samples, the increase in FFA concentration after 98 days was much less than in the unmodified‐pH or alkaline samples. The lowest FFA increase after 3 months of storage time was <10 mg FFA/g rice bran using extrusion with no water or chemicals added or using extrusion adding HCl, irrespective of the moisture content of rice bran.     

In‐process monitoring in industrial olive mill by means of FT‐NIR

A total of 287 olive lots and 161 olive oil samples were analyzed for fat content, moisture and free acidity, using a Fourier transform near‐infrared (FT‐NIR) instrument located in an industrial mill. Samples having a wide range of both reference values and olive lot sizes (from <0.5 to >4 t) were collected at three industrial mill plants, located in the same Italian region, which utilize different technological equipment for virgin olive oil production. Olive paste spectra were acquired in diffuse reflectance, while oil samples were measured in transmission. Calibration models for oil content and moisture of olives as well as free acidity of virgin olive oils were developed using partial least squares (PLS) regression, first derivative and straight line subtraction. Results of calibration and validation of the PLS models selected were good. The PLS results indicate good similarity between data obtained from FT‐NIR and reference laboratory methods, allowing a rapid and less expensive screening analysis. Unfortunately, the correlation between the oil yield values recorded for all olive lots at the industrial mills and the oil content predicted by FT‐NIR was not satisfactory (R² = 0.605).     

Influence of triacylglycerol characterics on the determination of free fatty acids in vegetable oils by fourier transform infrared spectroscopy

A rapid and direct Fourier transform infrared (FTIR) spectroscopic method using a 25-μm NaCl transmission cell was developed for the determination of free fatty acids (FFA) in six important vegetable oils (corn, soybean, sunflower, palm, palm kernel, and coconut oils) that differ in fatty acid profile. The calibrations were established by adding either standard FFA (oleic, lauric acids) or a representative mixture of FFA obtained after saponification of the refined oils. For all oils, up to a FFA level of 6.5% for coconut oil, the best correlation coefficient was obtained by linear regression of the free carboxyl absorption at 1711 cm⁻¹. All correlation coefficients were greater than 0.993, and no significant difference between the calibration methods could be detected. Upon validation of the calibration, no significant difference (α=0.05) between the “actual” and the “FTIR predicted” FFA values could be observed. The calibration models developed for the six oils differed significantly and indicate the need to develop a calibration that is specific for each oil. In terms of repeatability and accuracy, the FTIR method developed was excellent. Because of its simplicity, quick analysis time of less than 2 min, and minimal use of solvents and labor, the introduction of FTIR spectroscopy into laboratory routine for FFA determination should be considered.     

Impact of Free Fatty Acids and Phospholipids on Reverse Micelles Formation and Lipid Oxidation in Bulk Oil

Association colloids such as phospholipid reverse micelles could increase the rate of lipid oxidation in bulk oils. In addition to phospholipids, other surface active minor components in commercial oils such as free fatty acids may impact lipid oxidation rates and the physical properties of reverse micelles. In this study, the effects of free fatty acids on changes in the critical micelle concentration (CMC) of 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) in stripped corn oil (SCO) were determined by using the 7,7,8,8-tetracyanoquinodimethane solubilization technique. Different free fatty acids including myristoleic, oleic, elaidic, linoleic and eicosenoic were added at 0.5 % by wt along with the DOPC into the bulk oils. There was no significant effect of free fatty acids with different chain length, configuration and number of double bonds on the CMC value for DOPC in bulk oil. However, increasing concentrations of oleic acid (0.5 to 5 % by wt) caused the CMC value for DOPC in bulk oils to increase from 400 to 1,000 μmol/kg oil. Physical properties of DOPC reverse micelles in the presence of free fatty acids in bulk oils were also investigated by the small angle X-ray scattering technique. Results showed that free fatty acids could impact on the reverse micelle structure of DOPC in bulk oils. Moreover, free fatty acid decreased pH inside reverse micelle as confirmed by the NMR studies. The oxidation studies done by monitoring the lipid hydroperoxide and hexanal formation revealed that free fatty acids exhibited pro-oxidative activity in the presence and absence of DOPC. Different types of free fatty acids had similar pro-oxidative activity in bulk oil.     

Prediction of crude sunflower oil deterioration after seed drying and storage processes

The effects of air-drying temperature and storage time on several characteristics of crude sunflower oil were evaluated in terms of FFA and PV. Long storage affected oil content to a greater extent than air-drying temperature. FFA and PV varied between 0.53 and 1.22% and between 10.7 and 23.3. meq O₂/kg, respectively, when samples of uniform initial moisture content (approximately 28%) were dried at various temperatures between 25 and 90°C to approximately 7% moisture content, stored for 8 mon, and then analyzed. Both oil quality characteristics increased exponentially with air-drying temperature (T) and linearly with storage time (t). Mathematical functions of the form A·exp(B·T)+C·t (where A, B, and C are parameters adjusted from experimental data) most closely predicted the experimental loss of quality of sunflower oil in terms of FFA and PV with variations in T and t. Statistical analysis showed SE of the estimated parameters of 0.08 and 1.19 and coefficients of determination, R ², of 0.922 and 0.939 for FFA and PV, respectively, which were significant at 95% confidence. High-oleic seeds from a similar experiment were used to validate the proposed equation. The results of applying the mathematical function proposed above showed a reasonable ability to predict the experimental values with SE of 0.037 and 0.808 and R ² of 0.983 and 0.972 for FFA and PV, respectively, which were significant at 95% confidence. Plots of residuals showed random distribution. The results obtained suggested that the equation proposed could be used as a quality-loss model in sunflower drying simulations.     

Activated Kaolin Minerals as Bleaching Clays for Prolonging the Useful Life of Palm Oil in Industrial Frying Operations

During frying operations, vegetable oils break down and compounds with undesirable flavors are produced. Various procedures have been developed to extend the useful life of frying oils, including treatment with bleaching clays. In this article, we describe the activation of kaolin minerals by a combination of grinding and chemical treatments, and report their performance in removing breakdown products generated in palm oil that had been used for 20 hours continuous frying. There was little influence of the original kaolin mineral form on the ability to reduce the free fatty acid (FFA) contents, and grinding only changed FFA reduction from ∼32% to ∼36%. However, much greater FFA reductions were obtained after chemical treatment of the ground clays, and the best performing kaolin product gave similar FFA reduction to a commercial bleaching clay (∼76% and ∼77%, respectively). This activated kaolin also produced a reduction in viscosity at 40 °C from ∼73 to 48.4 cSt (compared to 45.5 cSt in the unused oil), and in the peroxide value from 30.0 to 22.0 meq/kg (compared to 10.0 meq/kg in the initial oil). Thus, activated kaolin samples represent a cheap and convenient alternative to conventional bleaching clay for improving common quality parameters in used palm oil, although we also found that the optimum kaolin preparation conditions were different from those that have been reported for raw rice bran oil refining.     

FTIR estimation of free fatty acid content in crude oils extracted from damaged soybeans

A user-interactive computer-assisted Fourier transform infrared (FTIR) method has been developed for estimation of free fatty acids (FFA) in vegetable oil samples by deconvolution of the infrared (IR) absorbances corresponding to the triglyceride ester and FFA carbonyl bonds. Peak areas were used to determine FFA as a percentage of the total carbonyl areas in weighed standards of refined, bleached, deodorized soybean oil containing from 0 to 5% added oleic acid. These data for percent FFA by FTIR were compared to corresponding FFA data obtained by two titration methods-the AOCS Official Method Ca 5a-40 and the Official Method with a slight modification. Correlation coefficients were 0.999 for the Ca 5a-40, 0.999 for the modified and 0.989 for the FTIR methods. FFA in samples of crude soybean oils extracted from damaged beans (0.5 to 2.1% FFA) were measured by FTIR and compared to data obtained by titration of the same samples (correlation coefficient, 0.869). To whom correspondence should be addressed at National Center for Agricultural Utilization Research, Agriculture Research Service, U.S. Department of Agriculture, 1815 North University Street, Peoria, IL 61604. ¹The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

Deacidifying rice bran oil by solvent extraction and membrane technology

Crude rice bran oil containing 16.5% free fatty acids (FFA) was deacidified by extracting with methanol. At the optimal ratio of 1.8:1 methanol/oil by weight, the concentration of FFA in the crude rice bran oil was reduced to 3.7%. A second extraction at 1:1 ratio reduced FFA in the oil to 0.33%. The FFA in the methanol extract was recovered by nanofiltration using commercial membranes. The DS-5 membrane from Osmonics/Desal and the BW-30 membrane from Dow/Film Tec gave average FFA rejection of 93–96% and an average flux of 41 L/m²·h (LMH) to concentrate the FFA from 4.69% to 20%. The permeate, containing 0.4–0.7% FFA, can be nanofiltered again to recover more FFA with flux of 67–75 LMH. Design estimates indicate a two-stage membrane system can recover 97.8% of the FFA and can result in a final retentate stream with 20% FFA or more and a permeate stream with negligible FFA (0.13%) that can be recycled for FFA extraction. The capital cost of the membrane plant would be about $48/kg oil processed/h and annual operating cost would be about $15/ton FFA recovered. The process has several advantages in that it does not require alkali for neutralization, no soapstock nor wastewater is produced, and effluent discharges are minimized.     

Rapid Determination of Degradation in Frying Oils with Near-Infrared Spectroscopy

Measures of free fatty acids (FFA), total polar materials (TPM), and conjugated dienoic acids (CDA), typical indices of oil degradation, were analyzed in daily oil aliquots taken from soybean oils with different linolenic acid concentrations used to fry French fries. The oils also were scanned with a reflectance near-infrared spectrometer using a wavelength range of 350–2,500 nm. By using partial least squares and one-out cross validation, calibrations were developed to quantitatively determine FFA, TPM, and CDA by near-infrared spectroscopy (NIRS). The coefficients of determination (R ²) when compared to the standard methods were 0.973 for FFA, 0.984 for TPM, and 0.902 for CDA. NIRS was an accurate and fast method to determine FFA, TPM, and CDA in oxidized oils. The ability to obtain different parameters simultaneously makes NIRS a potentially valuable tool for food quality assurance.