Solvent extraction, rice bran

Comparisons between hexane and isopropyl alcohol as solvents for rice bran oil extraction have been undertaken by several investigators (Proctor and Bowen, 1996 Hu et at, 1996). In general, isopropyl alcohol compares favorably with hexane with regard to oil yield and quality. Hu et al. (1996) reported that a 3 1 solvent bran ratio and a 60°C extraction temperature were optimal regardless of the solvent used. Preheating the solvent prior to extraction significantly enhanced oil, tocol and oryzanol yields. An increase in temperature from dO C to hO C resulted in 4% and 6% increases in crude oil yield for hexane and isopropyl alcohol, respectively similar trends were found for... 

Rice-Bran Wax. Rice-bran wax [8016-60-2] is extracted from cmde rice-bran oil. It can be degummed, the fatty acid content reduced by solvent extraction, and bleached. The wax is primarily composed of esters of lignoceric acid (43 wt %), behenic acid (16 wt %), and 22 02 alcohols (28 wt %). Rice-bran wax may be used in some food apphcations under the regulations described in 21 CFR 172.890. 

Xu, Z. Godber, J.S. 2000. Comparison of supercritical fluid and solvent extraction methods in extracting gamma-oryzanol from rice bran. J. Am. Oil Chem. Soc. 77 547-551. 

Limonene has recently been used in rice bran oil extraction as an alternative to hexane, which is commonly used in such processes.The yield and quality of crude rice bran oil obtained from the limonene extraction were almost equivalent to those obtained using hexane. Interestingly, although antioxidants were not present in the limonene, only a very small amount (<1 wt%) of oxidation product was found in the recovered limonene, and therefore the solvent is potentially recyclable in such a process. This also suggests that... 

The X-M process combines solvent extraction and milling of the rice (41). Brown rice is pretreated with warm rice oil (0.5%) for 2-3 hours to soften the bran. The rice is then milled in the presence of a rice oil miscella. The solvent slurry is then removed from the rice and the rice oil is recovered. Advantages are that stabilization is not required and the resultant oil had a minimum FFA level. This process is no longer used. 

Mechanical expression of rice bran yields less oil, 10-12%, than solvent extraction, 16-18%. Rice bran is treated with steam and dried prior to pressure expression. Prepressing is usually carried out at 70 kg/cm followed by oil expulsion at 105-316 kg/cm (9). As a result of the low yield of oil from mechanical extraction, residual oil in the bran is recovered with hexane. Hexane extraction can be performed by batch or a continuous operation. Continuous operation uses countercurrent flow to improve mass transfer. Solvent extraction at high temperatures results in higher crude oil yield, but the crude oil is of lower quality. A new oil-extraction process, which involves premolding of rice bran at 14% moismre content and <40°C followed by hexane extraction at <15°C, was reported to yield a light-colored crude oil with no wax (9). 

Yields are by mechanical expression for all except soybeans, cottonseed, and rice bran, which are by solvent extraction, and refer to whole or undecorticated seeds, unless otherwise stated. 

Figure 18. Collets made from pre-press canolo and rice bran by expander for solvent extraction. Courtesy of Anderson International, Cleveland, Ohio. (This figure is available in full color at http // www.mrw.interscience.wiley.com/biofp.)...

For oleaginous materials having a low oil content (18-20%), such as soybean and rice bran, solvent extraction is often applied for oil recovery. Hexane is widely accepted as the most effective solvent used today. Most of the extractors currently used are designed as countercurrent flow devices. The solid material flows in an opposite direction of solvent-oil miscella with an increasing oil concentration. The miscella containing around 25-30% oil after extraction is subjected to solvent distillation to recover the oil. The extracted solid material, commonly known as white flakes, is also conveyed to the desolventizing process. 

Solvent extraction is used extensively to recover chemicals from natural products. Solvents are used to extract and concentrate natural oils and products in the bioprocessing industries (nutraceu-tical, food, pharmaceutical, feed, cosmetic, biotechnology) in quantities from grams to metric tons. Biotechnology applications include the recovery of primary and secondary metabolites [4]. Extraction is used to recover vegetable oils and food products. It is used to process a variety of materials including groundnut, mustard seed, soybean, pahn kemal, sunflower, rice bran, copra, cottonseed, and minor oil seeds like neem, mahua, watermelon seed, castor seed, and so on. 

Seeds are one source of vegetable fibres, oils, and protein. Oil-bearing seeds are mechanically squeezed in a seed expeller or the oil is extracted with a solvent leaving behind the pulp and fibre syn. seed cake, oil cake, or meal. Seed cake retains some oils as does the seed expeller. Common seed cakes include cottonseed, peanut, linseed, maize, palm, rape seed, rice bran, soy beans, and sunflower. 

Kim, C, Byun, S, Cheigh, H and Kwon, T (1987a) Comparison of solvent extraction characteristics of rice bran pretreatment by hot air drying, steam cooking and extrusion. J. Am. Oil Chem. Soc., 64, 514—516. 

Rice bran, consisting of the pericarp, seed coat, germ, and aleurone tissues, accounts for 7%-10% of the rough rice weight. The bran is rich in protein, fat, minerals, and B-vitamins (Juliano and Bechtel 1985) (Chapter 18). In Asia, rice bran is used as a raw material for production of rice oil. Both mechanical expellers and hexane extraction systems are used. Solvent extraction usually yields 16%-18% oil and defatted rice bran with less than 1% residual oil, whereas mechanical pressing leaves around 10% oil, yielding partially defatted rice bran prone to oxidation. Recently, whole stabilized and defatted rice bran has been viewed as a source of important antioxidants and nutraceuticals with health-promoting effects. In Europe and America, rice bran is mainly used as poultry, cattle, and swine feed (Chapter 18). 

Ideally, bran should be stabilized within a few minutes after removal from the kernel. Stabilization process inactivates enzyme lipase that causes rapid hydrolysis of TAG. Three methods developed for brown rice stabilization are (1) heat dena-turation and inactivation of lipases, (2) extraction with an organic solvent to remove... 

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