Characteristics of solvent extracted flaxseed (Linum usitatissimum L.) meals

Wanasundara, Janitha Priyakanthi Deepani (1992) Characteristics of solvent extracted flaxseed (Linum usitatissimum L.) meals. Masters thesis, Memorial University of Newfoundland.

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Abstract

Flaxseed meal was prepared by a two-phase solvent extraction system consisting of alkanol, ammonia, water and hexane. Methanol, ethanol and isopropanol were used as the alkanol and the prepared meals were evaluated with respect to their effect on nutrients, antinutrients and functional characteristics. Commercially available flaxseed meal was also studied. -- Approximately 46 to 49% meal and 46 to 50% oil were recovered from dry seeds depending on the extraction system employed. The removal of 4.2 to 5.7% polar substances from the seeds resulted in an increase of 13 and 10% in the content of crude protein and ash, respectively. The presence of ammonia in the polar phase had little effect on the non-protein nitrogen content. -- A method was developed to isolate and quantify individual cyanogenic glycosides of linseed using chromatographic techniques. The cultivar used for this study was free of linamarin and contained 4.42±0.08 mg/g of linustatin and 1.90±0.03 mg/g of neolinustatin in the defatted meal on a dry basis. The extraction system, consisting of 10% (w/w) ammonia in 95% (v/v) methanol, removed 57% of linustatin and neolinustatin present in the original samples. A higher content of water, up to 15% in the methanol-ammonia-water phase, removed 67 to 68% of cyanogenic glycosides but resulted in a sticky, dark-coloured meal. Increased contact time (30 min) and solvent-to-seed ratio (R, 13.3) were more effective as 78% to 8l% of cyanogenic glycosides were removed by this process. A two stage extraction with methanol-ammonia-water/hexane gave similar results, but, a three stage extraction removed approximately 92.5% of cyanogenic glycosides present in flaxseed. -- The content of total phenolic acids (220±13 mg/lOOg), condensed tannins (136±13 mg/lOOg) and soluble sugars (7.69±0.16%) of defatted meals were reduced by 10-48%, 26-74% and 5-46%, respectively. Defatted flaxseed meals contained 2.4±0.13 to 2.8±0.37% of phytic acid and solvent extraction resulted in a slight increase in its content in the products. Flaxseed meal was low in methionine, lysine and tryptophan compared to the FAO/WHO reference values. Methanol-ammonia-water/hexane extraction had little effect on the content of amino acids but resulted in lowering of the content of some of the fatty acids possibly due to the removal of some phopholipids by the polar phase. -- Flaxseed meal had a very high water absorption (9.7g H₂O/g) and water hydration capacity (5.2 g H₂O/g) and they were not altered by extraction with the two-phase solvent processing. The presence of ammonia in the extraction system enhanced the fat absorption of the meals 2.6-3.2 fold and increased the pH by almost one unit. Nitrogen solubility of the meals was fairly high (46-65%) and extraction with methanol-ammonia improved the nitrogen solubility of the products at their natural pH. Minimum value of the nitrogen solubility in the meals was observed at pH between 3.0-3.5. Emulsifying capacities of the meals were 64.5% to 80.6% and they were fairly stable to heat and retained 95 to 100% of the emulsifying activity. Whippability of the meals was between 55 to 70% and the foams were stable.

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