Research On Aqueous Extraction Of Oil And Protein From Flaxseed

Flaxseed or linseed(Linum usitatissimum L.), which is a member of the Linaceae family, is an important oilseed crop in the world. Besides its traditional oleochemical uses, it is currently gaining recognition as a functional food ingredient for the human diet due to its high nutritional value and health functions. In terms of making the best use of flaxseed, the mucilage was removed firstly and then ethanol or enzyme was employed to assist the aqueous extraction of oil from demucilaged flaxseed, followed by the extraction of protein. The main results were as following:Firstly, effect of flaxseed mucilage on the enzyme-assisted aqueous extraction of flaxseed oil and factors influencing flaxseed demucilaging with hot water were studied. It was found that the oil yield of the demucilaged flaxseed was much higher than the raw flaxseed and increased with the decrease of residual mucilage. The oil yields of raw flaxseed and demucilaged flaxseed at 100°C were 69.20±1.51% and 84.26±0.63% respectively. In order to increase the oil yield, it was necessary to eliminate the mucilage before enzymatic treatment. The optimum conditions for flaxseed demucilaging were: soaking temperature 85°C, p H 3, flaxseed-water ratio 1: 7(w/v), extraction twice and duration 60 min. Under these conditions, the oil yield of the demucilaged flaxseed could be 84.47±0.53%.Content of cyanogenic glycosides in different fractions was also determined under the optimum demucilaging conditions. It was found that the cyanogenic glycoside was substantially removed with its content lowered from 242.6±0.8 mg/kg flaxseed to 7.1±0.6 mg/kg flaxseed. No cyanogenic glycoside was detected in the crude gum.The oil yields of different oil extraction methods including aqueous extraction(AE), enzyme-assisted(En AE) and ethanol-assisted aqueous extraction(Et AE) were compared and effect of grinding methods on the oil yield were also studied. The results showed that particle size of the flaxseed powder grinded by high-speed grinder and cylindrical roll crusher were 133.4 μm and 65.77 μm respectively. The oil yield of flaxseed powder grinded by cylindrical roll crusher was much higher. The hightest oil yields of AE, En AE and Et AE were 84.27±0.54%, 84.81±1.58% and 92.73±0.20% respectively. When extracted by Et AE, the oil yields of flaxseed powder grinded by dry and wet processes were 92.50±0.28% and 68.91±0.57% respectively.Therefor, it was necessary to dry the flaxseed after demucilaging.Factors influencing the oil yield of Et AE were optimized and the oil obtained was compared with cold-pressed flaxseed oil and commercial oil. Optimum conditions for Et AE were: ratio of flaxseed powder to 15%(w/w) ethanol-water solution 1: 4.5(w/v), 65°C, p H 8.0 and duration 2 h. Under these conditions, the oil yield could reach to 92.82±0.58%. The contents of tocopherol, linolenic acid and trans-fatty acids of the oil obtained were 79.62 mg/100 g, 45.97%, 0.22% respectively. The oil was comparable with cold-pressed oil made in the lab, as indicated by the indexes such as tocopherol and phosphatide content.Finally, factors influencing extraction of protein from the insoluble phase of the Et AE process were studied. The insoluble phase protein(IPP) was obtained and compared with aqouse phase protein(APP) during Et AE process, pressed defatted protein(PDP) and demucilaged pressed defatted protein(DPDP). The results showed that the optimum conditions for extracting protein from insoluble phase were: 70°C, p H 10.5, solid-water ratio 1: 10(w/v), and duration 90 min. Under these conditions, the protein yield could reach to 64.79±0.89%. Essential amino acids content and hydrophobicity of APP were lower than that of others. Demucilage process could reduce the polysaccharide content in the protein.