Optimization of Physical Refining to Produce Rice Bran Oil with Light Color and High Oryzanol Content

Crude rice bran oil (RBO) is rich in valuable minor components such as tocotrienols, phytosterols and γ-oryzanol. These compounds are well preserved during physical refining, but in current industrial practice, RBO is mostly refined chemically because this results in a lighter color. However this process removes most of the γ-oryzanol. The challenge is to develop a refining process which combines a high γ-oryzanol retention with the commercially desired light color. A modified physical refining process was developed, consisting of an acid degumming, prebleaching, dewaxing, physical removal of free fatty acids using packed column technology, a modified washing step, conventional bleaching and deodorization. A RBO with acceptable oryzanol retention of 39% had a Lovibond red color value (measured with a 5.25-inch cell) of 2.8, approaching very close the color of a chemically refined RBO (red = 2). At the process step where high (94%) retention of γ-oryzanol was achieved, a somewhat darker Lovibond red value of 5.2 was obtained.     

Minor constituents of vegetable oils during industrial processing

We report the effects of individual steps of industrial refining, carried out in Brazil, on the alteration of selected minor constituents of oils, such as corn, soybean, and rapeseed oils. Total sterols, determined by capillary gas chromatography (GC), decreased by 18–36% in the fully refined oils, compared with the crude oils. The total steradienes, dehydration products of sterols, were determinedvia a simple clean-up on a short silica gel column, followed by high-performance liquid chromatography (HPLC) with ultraviolet detection. The level of steradienes, normally not present in crude oils, increased after each refining step, especially after deodorization. Thus, the content of steradienes increased after deodorization by about 15- to 20-fold in corn and soybean oils, and by about 2-fold in rapeseed oil. The total steryl esters were also determinedvia clean-up on a short silica gel column, followed by HPLC with evaporative light scattering mass detection. A minor decrease in the level of steryl esters was observed after complete refining. The individual tocopherols and tocotrienols were determined by HPLC with a fluorescence detector. The level of total tocopherols and tocotrienols decreased by about 2-fold after complete refining of corn oil and by about 1.5-fold in soybean and rapeseed oils. In all three cases, maximum reduction of tocopherols was observed after the deodorization step. The level of polymeric glycerides, determinedvia clean-up on a short silica gel column followed by size-exclusion HPLC, increased to some extent (0.4–1%) during refining. The level oftrans fatty acids, determined by capillary GC, also increased to a substantial extent (1–4%) after refining. Part of doctoral thesis of Roseli Ap. Ferrari to be submitted to Faculdade de Engenharia de Alimentos, Universidade de Campinas, Campinas, Brazil.     

Effect of Industrial Chemical Refining on the Physicochemical Properties and the Bioactive Minor Components of Peanut Oil

The effect of the industrial chemical refining process on the physicochemical properties, fatty acid composition, and bioactive minor components of peanut oil was studied. The results showed that the moisture and volatile matter content, acid value, peroxide value, and p‐anisidine value were significantly changed (P < 0.05) after the complete refining process. No significant variation (P > 0.05) in the iodine value was observed among all the peanut oil samples. Similar changes were observed in the DPPH radical scavenging activity and the total tocol content during chemical refining. In addition, chemical refining did not have much effect on the fatty acid composition, except for certain changes of several individual fatty acids. Moreover, the chemical refining resulted in 23.6, 23.1, and 9.5 % losses of squalene, total phytosterols, and total tocols (α, β, γ, δ‐tocopherols and α, β, γ, δ‐tocotrienols), respectively. The degumming–neutralization step caused the greatest overall reduction of these bioactive minor components. However, the concentrations of α‐tocotrienol and γ‐tocotrienol increased after full refining. Furthermore, chemical refining slightly changed the relative proportions of individual phytosterols and individual tocols.     

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.     

Comparative study on the stability of crude and refined rice bran oil during long‐term storage at room temperature

The effect of the full refining process on the stability of rice bran oil during storage at room temperature was studied. Crude and refined rice bran oil were kept in the dark and were exposed to light for 240 days, and every 10 days samples were drawn and analysed. The storage stability of crude and fully refined rice bran oil was determined and compared with respect to fatty acid composition, tocopherols, tocotrienols, sterols and γ‐oryzanol content. In addition, the oxidative status was evaluated by determining the concentration of polar compounds and the oil stability index (OSI). A good correlation between the decrease of total tocopherols and the OSI was found. α‐Tocopherol had the highest correlation coefficient (r² = 0.9653) in crude rice bran oil kept in the dark, and γ‐tocopherol showed the lowest in the refined sample (r² = 0.4722). The order of stability of tocopherols and tocotrienols in crude oil was completely different from that in refined oil. In comparison to tocopherols, sterols showed a better stability during the entire storage period. The exposure to daylight heavily affected the composition and the stability of both crude and refined rice bran oil.     

Fatty Acid,Phytosterol, and Polyamine Conjugate Profiles of Edible Oils Extracted from Corn Germ,Corn Fiber,and Corn Kernels

This study compared the profiles of fatty acids, phytosterols, and polyamine conjugates in conventional commercial corn oil extracted from corn germ and in two “new-generation” corn oils: hexane-extracted corn fiber oil and ethanol-extracted corn kernel oil. The fatty acid compositions of all three corn oils were very similar and were unaffected by degumming, refining, bleaching, and deodorization. The levels of total phytosterols in crude corn fiber oil were about tenfold higher than those in commercial corn oil, and their levels in crude corn kernel oil were more than twofold higher than in conventional corn oil. When corn kernel oil was subjected to conventional degumming, refining, bleaching, and deodorization, about half of the phytosterols was removed, whereas when corn fiber oil was subjected to a gentle form of degumming, refining, bleaching, and deodorization, only about 10% of the phytosterols was removed. Finally, when the levels of polyamine conjugates (diferuloylputrescine and p-coumaroyl feruloylputrescine) were examined in these corn oils, they were only detected in the ethanol-extracted crude corn kernel oil, confirming earlier reports that they were not extracted by hexane, and providing new information that they could be removed from ethanol-extracted corn kernel oil by conventional degumming, refining, bleaching, and deodorizing.     

Factors affecting refining losses in rice (Oryza sativa L.) bran oil

Components of rice bran oil have been assessed for their effect on refining losses. Rice bran oil used in the study had the following (percent) analysis: free fatty acids, 6.8; phosphatides, 1.25; wax, 2.85; monoglycerides, 1.67; diglycerides, 4.84, and oryzanol, 1.85; the rest (80.74) was mostly triglycerides. The phosphatides and mono- and diglycerides had no noticeable effect on refining losses at levels of up to 2% in the oil. Waxes and oryzanol increased the refining losses substantially. In model experiments where these were incorporated into peanut oil individually and in combination, the wax at as low a level as 1% increased the refining losses by about 80% more than control and the refining losses increased with concentration of wax. Oryzanol had a similar effect. When wax and oryzanol were present together in the oil, the effect was synergistic—the refining losses were higher than the sum of their individual effects. Phosphatides, mono- and diglycerides tended to reduce the adverse effect of wax and oryzanol. The main components responsible for higher than normal refining losses in rice bran oil have been identified as wax and oryzanol.     

Trans fatty acid content and positional distribution in refined and heated rice bran oil

The objective of this study was to evaluate the impact of the refining process and of heating at frying temperature (180 °C, 8 h) on the content of trans fatty acids and their positional distribution in sn-positions of triacylglycerols (TAG) of rice bran oil. Tr-18:2 was an artifact specific to the deodorization step, which additionally changed its distribution at the 2-MAG and 1,3-DAG positions. No correlation between the formation of polymer TAG and trans fatty acids could be observed.     

Antioxidant Activity of Phytochemicals from Distillers Dried Grain Oil

A distillate was obtained by molecular distillation of oil extracted from distillers dried grains (DDG). The distillers dried grain oil distillate (DDGD) contained phytosterols, steryl ferulates, tocopherols, tocotrienols, and carotenoids. DDGD was tested for its impact on the oxidative stability index (OSI) at 110 °C of soybean, sunflower, and high-oleic sunflower oils, as well as the same oils that were stripped of their natural tocopherols and phytosterols. In addition, the impact of added DDGD on the stability of stripped sunflower oil during an accelerated storage study conducted at 60 °C was also determined. DDGD (0.5–1% w/w) had little impact on the OSI of soybean, sunflower, and high-oleic sunflower oil, but at levels of 0.1–1% it significantly increased the OSI for stripped soybean, sunflower, and high-oleic sunflower oil in a dose-dependent manner. DDGD also delayed peroxide value, conjugated diene, and hexanal formation during accelerated storage of stripped sunflower oil. The antioxidant activity is probably due to the combination of tocopherols, tocotrienols, and steryl ferulates.     

Effects of ferric chloride on thermal degradation of γ‐oryzanol and oxidation of rice bran oil

The kinetics of γ‐oryzanol degradation in antioxidant‐stripped rice bran oil were investigated at 180°C for 50 h. Ferric chloride was added to the oil at different concentrations (0, 2.5, 5.0, and 7.5 mg/kg‐oil) to determine the degradation reaction rate of γ‐oryzanol and the extent of lipid oxidation (peroxide value and p‐anisidine value). It was found that the losses of γ‐oryzanol and its four components (cycloartenyl ferulate, 24‐methylene cycloartanyl ferulate, campesteryl ferulate, and β‐sitosteryl ferulate) could be described by a first‐order kinetics model. The degradation rate constant, k, linearly increased (p < 0.05) with the ferric chloride concentration, and increased about 1.5 times when 7.5 mg/kg‐oil ferric chloride was added. Ferric chloride addition also accelerated the lipid oxidation of rice bran oil significantly (p < 0.05). Practical applications: This paper describes the kinetic analysis of the degradation of γ‐oryzanol, a major phytochemical in rice bran oil, at its frying temperature. The results indicated that iron in the form of ferric chloride accelerated both the degradation of γ‐oryzanol and lipid oxidation.     

Geometrical isomerization of polyunsaturated fatty acids in physically refined rapeseed oil during plant‐scale deodorization

The effect of the operating temperature (between 220 and 270 °C) on the formation of trans isomers of linoleic and linolenic acids in physically refined rapeseed oil during deodorization in a plant‐scale semicontinuous tray‐type deodorizer (capacity 10 t/h) was investigated. The industrial procedures of physical refining consisted of a two‐step bleaching and deodorization process. The degree of isomerization of linoleic acid ranged from 0.33 to 4.77% and that of linolenic acid from 4.43 to 45.22% between 220 and 270 °C, respectively. A relation between the logarithm of the degree of isomerization and the deodorization temperature can be approximated by statistically highly significant linear functions for both linoleic and linolenic acids. Oleic acid was resistant to the heat‐induced geometrical isomerization. The values found for the ratio between the degrees of isomerization of linolenic and linoleic acids, slightly decreasing with increasing temperature, were equal to 13.6 and 12.9 at 230 and 240 °C, respectively. Two trans isomers of linoleic acid, exclusively with one double bond isomerized into trans configuration, and four trans isomers of linolenic acid, mostly with one double bond isomerized into trans configuration, were determined in deodorized rapeseed oils. Linolenic acid was observed to be the main source responsible for the formation of nearly all trans fatty acids in physically refined rapeseed oil. At 235 °C, a deodorization temperature considered as a reasonable technological compromise, the content of trans fatty acids in plant‐scale physically refined rapeseed oil was less than 1% of total fatty acids, which would be acceptable for further application.     

Minor components in oils and their effects on frying performance

Minor components are the non‐triacylglycerol constituents of oil and constitute up to 5% of the total lipid composition. Though minor in composition, they can exert major influence on the performance of oil during frying. The effect of the minor components on frying performance depends on their chemical nature, composition and amount in the oil. Among these minor components tocopherols, phytosterols, phospholipids, γ‐oryzanol, lignans, phenolics, and carotenoids are the most important. Here, their effect on the frying performance of edible oils is discussed.     

Effect of the full refining process on rice bran oil composition and its heat stability

The effects of the chemical refining process on the minor compounds of rice bran oil and its heat stability were investigated. After 8 h of heating, about 50% and 30% of total tocopherols remained in crude and refined rice bran oil, respectively. The individual tocopherols were differently affected by the refining process. The order of heat stability of tocopherols and tocotrienols in crude oil was found to be different from that in fully refined oil. A similar tendency was observed for sterols. After 8 h of heating, 65% and 72% of total sterols, and 14% and 46% of sterol esters, of crude or fully refined rice bran oil, respectively, disappeared. The heating process led to a 4% and 10.3% increase in polymer contents in crude and refined rice bran oil, respectively. Although refined rice bran oil showed good heat stability, when compared to crude oil its heat stability was decreased to some extent.     

Influence of the vegetable oil refining process on free and esterified sterols

The influence of the refining process on the distribution of free and esterified phytosterols in corn, palm, and soybean oil was studied. Water degumming did not affect the phytosterol content or its composition. A slight increase in the content of free sterols was observed during acid degumming and bleaching due to acid-catalyzed hydrolysis of steryl esters. A significant reduction in the content of total sterols during neutralization was observed, which was attributed to a reduction in the free sterol fraction. Free sterols probably form micelles with soaps and are transferred into the soapstock. The steryl ester content remained constant during all neutralization experiments, indicating that hydrolysis of steryl esters did not take place during neutralization. During deodorization, free sterols are distilled from the oil, resulting in a gradual reduction in the total sterol content as a function of the deodorization temperature (220–260°C). A considerable increase in the steryl ester fraction was found during physical refining, probably owing to a heat-promoted esterification reaction between free sterols and FA.     

Deodorization of vegetable oils: Prediction of trans polyunsaturated fatty acid content

Kinetics of the formation of trans linoleic acid and trans linolenic acid were compared. Pilot plant-scale tests on canola oils were carried out to validate the laboratory-scale kinetic model of geometrical isomerization of polyunsaturated fatty acids described in our earlier publication. The reliability of the model was confirmed by statistical calculations. Formation of the individual trans linoleic and linolenic acids was studied, as well as the effect of the degree of isomerization on the distribution of the trans fatty acid isomers. Oil samples were deodorized at temperatures from 204 to 230°C from 2 to 86 h. Results showed an increase in the relative percentage of isomerized linolenic and linoleic acid with an increase in either the deodorization time or the temperature. The percentage of trans linoleic acid (compared to the total) after deodorization ranged from <1 to nearly 6%, whereas the percentage of trans linolenic acid ranged from <1 to >65%. Applying this model, the researchers determined the conditions required to produce a specially isomerized oil for a nutritional study. The practical applications of these trials are as follows: (i) the trans fatty acid level of refined oils can be predicted for given deodorization conditions, (ii) the conditions to meet increasingly strict consumer demands concerning the trans isomer content can be calculated, and (iii) the deodorizer design can be characterized by the deviation from the theoretical trans fatty acid content of the deodorized oil.     

Thermal degradation of long‐chain polyunsaturated fatty acids during deodorization of fish oil

Long‐chain polyunsaturated fatty acids (LC‐PUFA) of the n‐3 series, particularly eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid, have specific activities especially in the functionality of the central nervous system. Due to the occurrence of numerous methylene‐interrupted ethylenic double bonds, these fatty acids are very sensitive to air (oxygen) and temperature. Non‐volatile degradation products, which include polymers, cyclic fatty acid monomers (CFAM) and geometrical isomers of EPA and DHA, were evaluated in fish oil samples obtained by deodorization under vacuum of semi‐refined fish oil at 180, 220 and 250 °C. Polymers are the major degradation products generated at high deodorization temperatures, with 19.5% oligomers being formed in oil deodorized at 250 °C. A significant amount of CFAM was produced during deodorization at temperatures above or equal to 220 °C. In fact, 23.9 and 66.3 mg/g of C20 and C22 CFAM were found in samples deodorized at 220 and 250 °C, respectively. Only minor changes were observed in the EPA and DHA trans isomer content and composition after deodorization at 180 °C. At this temperature, the formation of polar compounds and CFAM was also low. However, the oil deodorized at 220 and 250 °C contained 4.2% and 7.6% geometrical isomers, respectively. Even after a deodorization at 250 °C, the majority of geometrical isomers were mono‐ and di‐trans. These results indicate that deodorization of fish oils should be conducted at a maximal temperature of 180 °C. This temperature seems to be lower than the activation energy required for polymerization (intra and inter) and geometrical isomerization.     

Kinetics of the cis‐trans isomerization of linoleic acid in the deodorization and/or physical refining of edible fats

The cis‐trans isomerizations undergone by linoleic acid during industrial deodorization and/or physical refining of edible fats were studied in an experimental discontinuous pilot plant of 250 kg using nitrogen as stripping gas in place of steam. For each oil, the expression of the analytical results has been made as molar fraction, which is kinetically equivalent to making an abstraction from the other components in the reaction bulk and assumes they do not take part in the isomerization. The kinetic constants for the formation of the acids C18:2(9c,12t), C18:2(9t,12c) and C18:2(9t,12t) were determined. The equations and values obtained justify that the reaction orders studied are zero (or can be considered zero) for the time taken in an industrial deodorization and/or physical refining of edible fats. The analytical method used is appropriate for direct application of the results in industry.     

Stability of Minor Lipid Components with Emphasis on Phytosterols During Chemical Interesterification of a Blend of Refined Olive Oil and Palm Stearin

Minor compounds such as tocopherols and phytosterols in vegetable oils play an important role in their stability and nutritional value. This study monitored the effects of chemical interesterification on the levels of tocopherols, tocotrienols, phytosterols and phytosterol oxidation products (POPs) in an olive oil and palm stearin blend (50/50 w/w). Tocopherols and tocotrienols were dominated by α-tocopherol (192 ppm) and γ-tocotrienol (70 ppm) and decreased during interesterification. Among the tocopherols, δ-tocotrienol had the highest decrease (35%) at 120 °C. During interesterification at 90 and 120 °C, total sterol content in the oil blend (509 ppm) declined slightly, by 3 and 5%, respectively. Phytosterols were esterified at a higher level at 120 °C (7%) than at 90 °C (4%) during this process. Distribution of fatty acids in the esterified sterols followed the fatty acid composition of the oil blend. Total POP content was 4.3 ppm, and remained generally unchanged during interesterification. Among the nine POPs tentatively identified by their mass spectra, 6-hydroxysitostanol and 6-hydroxycampestanol dominated in the oil blend and in the interesterified product. The formation pathways of these saturated di-hydroxyphytosterols have yet to be identified. Although the interesterification process comprised several treatments, there were only minor losses of tocopherols and phytosterols and virtually no increases in the POPs.     

Optimization of industrial‐scale deodorization of high‐oleic sunflower oil via response surface methodology

Optimization of industrial‐scale deodorization of high‐oleic sunflower oil (HOSO) via response surface methodology is presented in this study. The results of an experimental program conducted on an industrial‐scale deodorizer were analyzed statistically. Predictive models were derived for each of the oil quality indicators (QI) in dependence on the studied variable deodorization process parameters. The deodorization behavior of some minor components was analyzed on a pilot‐scale deodorizer. For comparison, a similar experimental program was also performed on the laboratory‐scale. The results of this study demonstrate that optimization of the deodorization process requires a suitable compromise between often mutually opposing demands dictated by different oil QI. The production of HOSO with top‐quality organoleptic and nutritional values (high tocopherol and phytosterol contents and low free and trans fatty acid contents) and high oxidative stability demands deodorization temperatures in the range between 220 and 235 °C and a total sparge steam above 2.0% (wt/wt in oil). The response surface methodology provides the tools needed to identify the optimum deodorization process conditions. However, the laboratory‐scale experiments, while showing similar response characteristics of QI in dependence on the process parameters and thus helpful as a guide, are of limited value in the optimization of an industrial‐scale operation.     

Minor Constituents in Canola Oil Processed by Traditional and Minimal Refining Methods

The minimal refining method described in the present study made it possible to neutralize crude canola oil with Ca(OH)₂, MgO, and Na₂SiO₃ as alternatives to NaOH. After citric acid degumming, about 98 % of the phosphorous content was removed from crude oil. The free fatty acid content after minimal neutralization with Ca(OH)₂ decreased from 0.50 to 0.03 %. Other quality parameters, such as peroxide value, anisidine value, and chlorophyll content, after traditional and minimal neutralization were within industrial acceptable levels. The use of Trisyl silica and Magnesol R60 made it feasible to remove the hot-water washing step and decreased the amount of residual soap to <10 mg/kg oil. There were no significant changes in chemical characteristics of canola oil after using wet and dry bleaching methods. During traditional neutralization, the total tocopherol loss was 19.6 %, while minimal refining with Ca(OH)₂, MgO, and Na₂SiO₃ resulted in 7.0, 2.6, and 0.9 % reductions in total tocopherols. Traditional refining removed 23.6 % of total free sterols, while after minimal refining free sterols content did not change. Both traditional and minimal refining resulted in almost complete removal of polyphenols from canola oil. Total phytosterols and tocopherols in two cold-pressed canola oils were 774 and 836 mg/100 g, and 366 and 354 mg/kg, respectively. The minimal refining method described in the present study was a new practical approach to remove undesirable components from crude canola oil meeting commercial refining standards while preserving more healthy minor components.