Enzyme-assisted aqueous extraction

Solvent extraction using hexane is the widely practised extraction process in the oil industry. While very efficient in terms of oil recovery, it has several drawbacks. The process is costly, involving high capital equipment and operational expenditures. It is dangerous due to the perpetual potential of fire and explosion. The residual solvent in the oil and the meal is a potential health hazard suspect. The high temperatures used in desolventizing the meal, to some extent, reduces the nutritional and functional properties of the proteins in the meal. 

Several factors make the process particularly appealing to the rape-seed/canola industry. As such, most of the developmental work on the process has been done with canola/rapeseed. Although seed varieties with low levels of glucosinolates are now in use in the rapeseed/canola industry, other compounds such as tannins, sinapine and phytic acids are still significantly abundant in the seeds and remain in the meal produced by conventional extraction processes. The enzymatic aqueous process yields a final meal with significantly reduced levels of these compounds (Table 12.4). 

The quality characteristics of the oil produced by the enzyme-assisted aqueous extraction process is comparable to that of conventional extraction procedures except in its phosphorus content (Table 12.5). The enzymatic process yields oil with less phosphorus which requires no or limited degumming. The crude oil from this process can be physically refined without further treatment (Laiho et al., 1991). Despite this improved quality of the crude oil which is an apparent cost saving in subsequent downstream processing, the enzymatic process has not been commercially exploited due to problems with yields. Considerable degree of emulsification occurs during the process. Approximately 18-25% of the available oil in the seed remains unrecovered in a standard operation. The discovery that the versatile protein, oleosin, binds approximately 20% of the oil in oil-bearing seeds (Tzen et al., 1990) has implicated this protein in the low yields associated with this process. Thus, the recoveries could be improved by the use of proteases. It has, however, been observed that successful application of proteases to improve oil recovery produces excessively bitter meals, repressing the potential utilization of the meal as feed or food. 

The emulsion problems encountered in enzyme-assisted aqueous extraction of vegetable oils is of less concern in processing fish oils. Pretreatment of macerated fish with papain or bromelain is said to increase oil yield (Godfrey, 1983). For papain, an incubation temperature of 65°C for 30min and for bromelain, incubation at 50-55°C for 1-2 h is found to be effective. Dosages of 1-5 kg per tonne of fish weight are needed in both cases. 

The use of thermostable microbial proteases operating at temperatures of 70-75°C are much preferred due to the less dosage needed and less likelihood to contribute to microbial contamination due to the relatively high incubation temperatures. 

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Aqueous enzymatic oil extraction is another ecofriendly extraction procedure. It is based on simultaneous isolation of oil and protein from oilseed by dispersing finely ground seed in water and separating the dispersion by centrifugation into oil, solid, and aqueous phases. The presence of certain enzymes during extraction enhances oil recovery by breaking cell walls and oil bodies (22). For peanuts, a multistep aqueous extraction process has been described with a recovery of about 98% (23). More recently, the relatively new technique of enzyme-assisted aqueous extraction has been applied to peanuts with a reported oil recovery of 86-92% (24). 

Lamsal, B.P. P.A. Murphy L.A. Johnson. Flaking and extrusion as a mechanical treatment for enzyme-assisted aqueous extraction of oil from soybeans, /. Am. Oil Chem. Soc. 2006, 83, 973-979. 

Latif, S., Diosady, L.L. and Anwar, F. (2008) Enzyme-assisted aqueous extraction of oil and protein from canola (Brassica napus L.) seeds. European Journal of Lipid Science and Technology, 110(10), 887-892. Proctor, R. (1997) Soybean oil extraction and processing, in Soybeans Chemistry, Technology and Utilization (ed. K. Li), Chapman HaU, New York, pp. 297-346. 

Lamsal B, Murphy P, Johnson L. 2006. Flaking and Extrusion as Mechanical Treatments for Enzyme-Assisted Aqueous Extraction of Oil from Soybeans. J. Am. Oil Chem. Soc. 83 973-979. 

Latif S, Diosady LL, Anwar F. 2008. Enzyme-Assisted Aqueous Extraction of Oil and Protein from Canola (Brassica Napus L.) Seeds. Eur. J. Lipid Sci. Technol. 110 887-892. 

Conventional methods for extracting oils involve three basic approaches physical, chemical and a combination of both. In all cases the fundamental mechanism is to rupture the cell structure of the oil-bearing plant or animal materials and subsequently or simultaneously remove the oil. Enzymes have found use in oil extraction and their applications can be categorized as enzymes that assist pressing, enzymes that enhance solvent extraction and enzymes that assist aqueous extraction. 

The polysaccharide contents of seaweeds vary according to the species. Generally, these polysaccharides have been extracted using water or aqueous organic solvents (Albuquerque et ah, 2004). However, as the cell wall consists of complex polymers, it is not easy to extract active polysaccharides using solvent extraction process. The production of different bioactive polysaccharides with lyases is required in order to increase the extraction efficiency of more functional ingredients from seaweeds. Therefore, enzyme-assisted extraction technique can be employed as an alternative method to improve the extraction efficiency of bioactive polysaccharides for industrial use (Athukorala et ah, 2009 Kang et ah, 2011). 

Investigations into avoid this danger have taken place. Extended anionic surfactants have been employed to extract corn oil instead of hexane [17]. These extractions were shown to extract 83% of the oil available and also maintained the composition of the corn oil when compared to extractions carried out using hexane. A mixture of enzymes to extract oil from Irvingia gabonensis kernels was employed controlled, ordered addition of the enzymes optimized the extraction of the oil up to 90% efficiency [18]. Similar protocols were applied to the extraction of canola oil [19] and showed that the enzymatically assisted extractions were more efficient than by using water alone and produced better oil quality than both aqueous and solvent extractions. The efficiency of the process in this instance was significantly increased from those previously stated (circa 25%). 

Li et al., [20] studied the enzymatic treatment for aqueous extraction of the total phenolic contents of five eitrus peels (Yen Ben lemon, Meyer lemon, grapefinit, mandarin and orange). The highest reeovery using Celluzyme MX (cellulase) in the enzyme-assisted extraction process was up to 65.5% (about 87.9% of the solvent extraction). 

Tano-Debrah, K., Ohta, Y., (1997). Aqueous extraction of coconut oil by an enzyme-assisted process. J. Sci. Food Agric. 74,497-502. 

Domingues et al. (160), in their comprehensive review of enzymatic improvement of oil extraction, included discussion of various processes that also used hexane as a solvent. They reported aqueous enzyme processes that used hexane in a 1 2 hexane-water ratio. Additional hexane was added to the enzyme-treated and dried materials. Although enzymatic-assisted extraction is presently only economical in olive processing, because of the milder conditions used and, in most cases, higher quality oils obtained, it does have potential for future use. 

Enzymes have also been used to increase oil and protein release. Reports on rapeseed, sunflower, coconut, olive, and cottonseed have shown a high oil extraction yield using enzymes in the aqueous medium. Enzymes can be used to assist in the extraction of oils. It has been shown that a mixture of cell wall-degrading enzymes such as hemicellulases, cellulases, and pectinases can materially assist in oil extraction, particularly under mild conditions, by liquefying the structural ceU waU components of the oilseed. 

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