An investigation of rice bran oil tank settling

A wax-like settling is observed in tanks in which rice bran oil is stored. “Soft” and “hard” wax fractions have been isolated from this settling by solvent Crystallization. Previous investigation has shown that the settling consists mainly of wax esters of long chain alcohols and long chain fatty acids. The present work describes the column chromatographic analysis of unhydrolyzed tank settling. The presence of an aromatic moiety is indicated in the infra red spectrum. Comparison of data obtained by analysis of the tank settling before and after hydrolysis shows that it contains only 33% of monomeric esters; the remainder may be present as a polymeric ester, as found in carnauba wax. Investigation of different samples of rice bran oil has shown that the ratio of monomeric to polymeric fraction varies with the history of the bran.     

The expansion and extraction of rice bran

Expansion of rice bran as a pretreatment for solvent extraction was studied. It was found that the expanded bran showed no rise in free fatty acid (FFA) even when stored at room temp, in open containers, for a period of three months, and a slight rise after one year storage; and that the bran was agglomerated into large particles which eliminated the “fines” and channeling problems characteristic of rice bran; and that the retention time for good extraction was on the order of 45 min; and that the percolation rate for a four ft depth of expanded bran was on the order of 35 gpm/ft².     

Extraction of rice bran oil using aqueous media

Aqueous extraction of oil from rice bran was studied on a laboratory scale and the resulting product was examined. The following process parameters influencing oil extraction were individually investigated: pH of aqueous media, extraction temperature, extraction time, agitation speed and rice bran‐to‐water ratio. Extraction temperature and pH were found to be the main factors influencing oil extraction. The highest oil yield was obtained at pH 12.0, extraction temperature 50 °C, extraction time 30 min, agitation speed 1000 rpm, and rice bran‐to‐water ratio 1.5‐to‐10. The quality of aqueous‐extracted oil in terms of free fatty acid, iodine value and saponification value was similar to a commercial sample of rice bran oil and hexane‐extracted oil, but the peroxide value was higher. Furthermore, the colour of aqueous‐extracted oil was paler than solvent‐extracted oil. © 2000 Society of Chemical Industry     

Stabilization of rice bran via different moving-bed drying methods

Stabilization of rice bran after milling is a necessary step to avoid subsequent oxidation of lipids in the bran. Selected moving-bed drying methods, i.e., hot-air fluidized bed drying (HAFBD), superheated-steam fluidized bed drying (SSFBD), and infrared vibrated bed drying (IRVD), were used to reduce the moisture content of the bran and, at the same time, inactivate deleterious enzymes, which are the cause of oxidation. Drying kinetics, oxidative stability parameters (i.e., lipase activity, free fatty acid content, and peroxide value), oil extraction yield, and contents of phenolic compounds and γ-oryzanol as well as color changes of the bran were determined. SSFBD could reduce the drying time by 8–22 and 76–79% in comparison with HAFBD and IRVD, respectively. Drying method significantly affected the total phenolic content (TPC) and total color changes but did not significantly affect the γ-oryzanol content of the bran. SSFBD resulted in the lowest levels of all oxidative stability parameters and to the highest TPC and oil extraction yield. SSFBD at 140°C resulted in the bran with the longest shelf life of 55 days and is suggested as an alternative method to shorten the stabilization process and maintain the stability of rice bran.     

The rate of development of acidity in stored tung seeds and kernels

Summary Whole tung seeds, whole kernels, and chopped kernels of high, medium, and low moisture contents were sealed in tin cans and stored in incubators maintained at 25°, 31°, and 38°C. At intervals samples were removed and the acid value of the oil determined. The different temperatures used had slight effect on the rate of development of free fatty acids in the oil of the whole seeds and kernels, but the higher temperatures greatly increased the rate of development of free acid in the chopped kernels. Whole seeds containing 7% and 12% moisture were stored for 4 weeks and seeds containing 17% moisture were stored for 2 weeks, during which periods the oils developed free fatty acids equivalent to acid values of 2.0 or less. Under none of the conditions used did the acid values of the oils exceed 8.0 after storage for 13 weeks. Whole kernels developed even less free fatty acids than seeds stored under similar conditions. Kernels containing 4% and 6% moisture were stored for 12 weeks during which period the acid value of the oil never exceeded 1.5. Even in kernels containing 12% moisture the acid value of the oil did not exceed 6.0 at the end of 12 weeks. Chopped kernels with moisture contents of 5% and 7% could be stored for 12 days without developing an acid value in the oil of more than 8.0. However chopped-kernels with a moisture content of 12% developed an acid value in the oil in excess of 8.0 in less than a week. Whole seeds with as much as 15% moisture could probably be stored for several weeks without developing an objectionable amount of free fatty acids. Since commercial hulled “nuts” practically always contain some broken kernels, to avoid development of free fatty acids in storage they should be dried to 10% or less moisture before storage. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

Rapid equilibrium extraction of rice bran oil at ambient temperature

Rapid equilibrium extraction of soybean flour has been effective in obtaining an oil with reduced phospholipid content. This technique was examined to obtain a low phospholipid and low free fatty acid rice bran oil (RBO). The amount of RBO extracted with hexane from 1 g of rice bran at 22°C was measured over a 10-min period. The amount of oil extracted from variable amounts of bran with a fixed volume of solvent was also studied. Ninety percent of the oil was extracted in one minute, with 93% of the total RBO being extracted after ten minutes. This compares with the 98% yield obtained from soy flour, but increasing the amount of bran used did not reduce the extraction rate. This extraction method produced a good quality RBO with low phospholipid, low free fatty acid and low peroxide values.     

EFFECT OF DRYING ON THE FORMATION OF FREE FATTY ACIDS IN RICE BRAN

It is a commonly known fact that the amount of moisture has a direct influence on the rate of formation of free fatty acids in Rice bran. During storage of rice bran, the free fatty acids in bran increase more rapidly with higher moisture content. The formation of free fatty acids increase with the increase of storage temperature in the presence of moisture.This chemical reaction has been found to be due to the reaction of bran oil with moisture in the presence of enzymes acting as catalysts. In addition to many methods used to arrest the formation of free fatty acids in rice bran, heat treatment is one of the popular methods. Here bran is subjected to heat treatment prior to storage. Even though empirical conditions have been evaluated for the treatment, no satisfactory mathematical model exists in order to estimate the formation of free fatty acids in rice bran. This study presents a mathematical model for the prediction of the formation of free fatty acids in rice bran during drying. The analysis of the mathematical model agreed with the general behaviour of enzyme with temperatures. The theoretical results are compared with the experimental observations. It was found that the model can be used satisfactorily for the prediction of formation of free fatty acids in rice bran with the time and temperature.     

Utilization of rice bran oil to produce an antifoamer

Crude rice bran oil was dewaxed by chilling to 17°C, followed by centrifuging. The wax sludge obtained was 68% free fatty acids and 32% waxes, whereas the oil phase was 65.65% fatty acids and 34.35% glycerides. The dewaxed oil was evaluated as an antifoaming agent for aqueous media and compared to commercial oleic acid. It was thought that dewaxed rice bran oil has an antifoaming power greater than oleic acid, especially when used in small proportions. Dewaxed rice bran oil was also applied to break and control the foam formation in a phosphoric acid production unit.     

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.     

Lipase‐catalyzed production of biodiesel from rice bran oil

Biodiesel has attracted considerable attention as an alternative fuel during the past decades. The main hurdle to the commercialization of biodiesel is the cost of the raw material. Use of an inexpensive raw material such as rice bran oil is an attractive option to lower the cost of biodiesel. Two commercially available immobilized lipases, Novozym 435 and IM 60, were employed as catalyst for the reaction of rice bran oil and methanol. Novozym 435 was found to be more effective in catalyzing the methanolysis of rice bran oil. Methanolysis of refined rice bran oil and fatty acids (derived from rice bran oil) catalyzed by Novozym 435 (5% based on oil weight) can reach a conversion of over 98% in 6 h and 1 h, respectively. Methanolysis of rice bran oil with a free fatty acid content higher than 18% resulted in lower conversions (<68%). A two‐step lipase‐catalyzed methanolysis of rice bran oil was developed for the efficient conversion of both free fatty acid and acylglycerides into fatty acid methyl ester. More than 98% conversion can be obtained in 4–6 h depending on the relative proportion of free fatty acid and acylglycerides in the rice bran oil. Inactivation of lipase by phospholipids and other minor components was observed during the methanolysis of crude rice bran oil. Simultaneous dewaxing/degumming proved to be efficient in removing phospholipids and other minor components that inhibit lipase activity from crude rice bran oil. Copyright © 2005 Society of Chemical Industry     

Effect of method of stabilization on aqueous extraction of rice bran oil

Rice bran oil is widely used in pharmaceutical, food and chemical industries due to its unique properties and high medicinal value. In this study aqueous extraction of rice bran oil from rice bran available in Sri Lanka, was studied. Key factors controlling the extraction and optimal operating conditions were identified. Several methods of bran stabilization were tested and the results were analyzed. The yield and quality of aqueous extracted oil was compared with hexane extracted oil.Aqueous extraction experiments were conducted in laboratory scale mixer–settler unit. Steaming, hot air drying, chemical stabilization and refrigeration better controls the lipase activity compared to solar drying. Steaming is the most effective stabilization technique. The extraction capacity was highest at solution pH range 10–12. Higher oil yield was observed at higher operating temperatures (60–80 °C). Kinetic studies revealed that extraction was fast with 95% or more of the extraction occurring within first 10–15 min of contact time. Parboiling of paddy increases the oil yield. Highest oil yield of 161 and 131 mg/g were observed for aqueous extraction of parboiled bran and raw rice bran respectively. The aqueous extracted oil was low in free fatty acid content and color compared to hexane extracted rice bran oil and other commonly used oils. Major lipid species in rice bran oil were oleic, linoleic and palmitic.     

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 DRYING ON THE FORMATION OF FREE FATTY ACIDS IN RICE BRAN

It is a commonly known fact that the amount of moisture has a direct influence on the rate of formation of free fatty acids in Rice bran. During storage of rice bran, the free fatty acids in bran increase more rapidly with higher moisture content. The formation of free fatty acids increase with the increase of storage temperature in the presence of moisture.This chemical reaction has been found to be due to the reaction of bran oil with moisture in the presence of enzymes acting as catalysts. In addition to many methods used to arrest the formation of free fatty acids in rice bran, heat treatment is one of the popular methods. Here bran is subjected to heat treatment prior to storage. Even though empirical conditions have been evaluated for the treatment, no satisfactory mathematical model exists in order to estimate the formation of free fatty acids in rice bran. This study presents a mathematical model for the prediction of the formation of free fatty acids in rice bran during drying. The analysis of the mathematical model agreed with the general behaviour of enzyme with temperatures. The theoretical results are compared with the experimental observations. It was found that the model can be used satisfactorily for the prediction of formation of free fatty acids in rice bran with the time and temperature.     

Physical refining of rice bran oil in relation to degumming and dewaxing

Physical refining of rice bran oil (RBO) with acidity between 4.0 and 12.4% has been investigated in relation to degumming and dewaxing pretretments. It appears that physical refining after combined low-temperature (10°C) degumming-dewaxing produces good-quality RBO with respect to color, free fatty acid, oryzanol, and tocopherol content.     

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.     

A novel process for physically refining rice bran oil through simultaneous degumming and dewaxing

A new process for the physical refining of rice bran oil through combined degumming and dewaxing was developed on a laboratory scale and then demonstrated on a commercial scale. The simultaneous degumming and dewaxing of the crude oil with a solution of water and CaCl₂, followed by crystallization at a low temperature (20°C), facilitated precipitation of the hydratable and nonhydratable phosphatides along with the wax, which enabled its separation and reduction to a greater extent. Bleaching and subsequent winterization (20°C) of this oil further reduced the phosphorus content to less than 5 ppm. Thus, these pretreatment steps enabled the physically refined rice bran oil to meet commercially acceptable levels for color, FFA content, and cloud point values (10–12 Lovibond units in a 1-in, cell, <0.25%, and 4–5°C, respectively) with very low neutral oil loss; this has not been observed hitherto. Rice bran oil is known for its high levels of bioactive phytochemicals, such as oryzanol, tocols, and sterols. The process reported here could retain more than 80% of these micronutrients in the end product. This paper was previously presented at the 95th AOCS Annual Meeting and Expo, Cincinnati, Ohio, May 9–12, 2004     

INFLUENCE OF DRYING ON THE STORAGE ABILITY OF RICE BRAN

It is known that the rate of formation of free fatty acids in rice bran is dependant on the history of temperature and moisture content experienced by the bran since its formation. A mathematical model is already available to predict the rate of formation of free fatty acids in rice bran for heat treatment conditions. This paper attempts to apply the model for storage conditions in order to predict the storage ability of rice bran which has undergone varying drying conditions. Experimental results already available were found to be in agreement with the predicted theoretical values based on the model.     

INFLUENCE OF DRYING ON THE STORAGE ABILITY OF RICE BRAN

It is known that the rate of formation of free fatty acids in rice bran is dependant on the history of temperature and moisture content experienced by the bran since its formation. A mathematical model is already available to predict the rate of formation of free fatty acids in rice bran for heat treatment conditions. This paper attempts to apply the model for storage conditions in order to predict the storage ability of rice bran which has undergone varying drying conditions. Experimental results already available were found to be in agreement with the predicted theoretical values based on the model.     

Effect of stirring on the thermooxidative stability of refined rice bran oil

The aim of this study was to find out how the refining process affects the susceptibility of rice bran oil to oxygen of air at high temperature. Samples of crude and refined rice bran oil were heated at 180 °C for 8 h with and without stirring in laboratory‐scale experiments. After every 30 min, samples were taken for analysis. The influence of stirring on rice bran oil heat stability was related to the loss of tocopherols and sterols, and to the thermooxidative state of the samples, which was evaluated according to polymer formation and changes occurring in fatty acid composition and triacylglycerol (TAG) structure. The results demonstrated a significant loss of natural antioxidants during the heating process with stirring, accompanied by a decrease in the levels of linoleic acid (18:2) and TAG (LLO, LLP and OLO) which resulted in a substantial increase of polymer TAG. The unsaturated fatty acids in the sn‐2 and sn‐1,3 positions were differently affected during the heating process.     

Supercritical fluid extraction of oil from millet bran

Proso millet bran [Panicum miliaceum (L.)], variety Dakota White, was extracted with supercritical carbon dioxide (SC-CO₂) to yield crude oil. The effects of operating parameters (pressure, temperature, and specific solvent flow) and of features of the raw material (moisture content and particle size) on oil extraction were investigated. Complete de-oiling of ground millet bran pellets was achieved under 300 bar at 40°C with a specific solvent flow of 2–10 h⁻¹ within 200 to 500 min. Solvent requirements were 20–30 kg CO₂/kg raw material. Composition of crude SC-CO₂ oil extracted under optimal conditions, i.e., fatty acid profile, amount of unsaponifiables, tocopherols, free fatty acids, sterols, sterol esters, waxes, hydrocarbons, and phospholipids, was compared to that of crude oil obtained by petroleum ether extraction. These two oils were similar in terms of fatty acid profile and amount of free fatty acids, unsaponifiables, peroxides, and tocopherols. They differed in respect to phospholipids (present in petroleum etherextracted oil and absent in SC-CO₂ extracted oil), metals, and waxes (lower levels in SC-CO₂ extracted oil). The effects of extraction procedures on oxidative stability of crude SC-CO₂ oil were studied. Ensuring that all pieces of the extractor in contact with the oil were in stainless steel; cleaning the separator, i.e., washing with KOH, rinsing, purging with N₂ and CO₂, and heating; performing a couple of extractions before the main extraction; and achieving the extraction without interruption all positively influenced the oxidative stability of the oil. Conversely, increasing CO₂ purity above 99.5% had no effect. Oxidative stability of the SC-CO₂ oil extracted under these conditions was only slightly lower than that of the oil extracted with petroleum ether.