Aqueous Ethanol Extraction Of Corn Germ Oil And Protein Assisted By Steam Explosion

Corn germ is an abundant oil-bearing byproduct of corn machining industries. In the case of China, the output is about 3.8 million tons every year. Corn germ contains 35~56%(w/w) oil, in which has high level of linoleic acid, tocopherol and phytosterols; protein content is about 17~28%, in which has high level of albumin and globulin, the nutritional value is close to egg protein. Currently, the main usage of corn germ is to recover corn oil through the prepress-solvent extraction method, the produced sediment could only be used for animal feed, in which the superior protein resource is not value-added utilized. In order to improve oil quality and enhance protein resource utilization, some researchers developed the aqueous enzymatic extraction in recent years. Aqueous enzymatic extraction method has the virtue of mild extraction conditions, quality oil and recoverable byproducts. However, the high price of enzyme and the long production cycle mean aqueous enzymatic method is difficult to achieve large-scale industrial production. In order to preserve the superiority of aqueous enzymatic method on oil quality, decrease production price and shorten production time, in this dissertation, aqueous ethanol assisted by steam explosion was used to extract corn germ oil and protein. The main research results are as follow.First, influence of different extraction method(aqueous extraction, aqueous enzymatic extraction and aqueous ethanol extraction) on free oil yield and total yield was researched, and the process of extraction corn germ oil was definited. Results showed: either the free oil yield or total yield, aqueous ethanol method was highest, next was aqueous enzymatic method, the last was aqueous method. Hence, the aqueous ethanol method was employed as extraction process in this study.Second, the difference between steam explosion and high-temperature cooking pretreatment was compared on every phase oil content, shape change, microstructure change and crude oil quality. Results showed: the effect of steam explosion was better on oil yield and crude oil quality. Hence, steam explosion was applied to be pretreatment method.Based on this concrete process, the conditions of aqueous ethanol extraction assisted by steam explosion were optimized. The optimal conditions of steam explosion: steam pressure 1.3 MPa, resident time 30 s; the optimal conditions of particle size: finely-groud 4 times(particle size 33.72 μm); the optimal conditions of aqueous ethanol extraction: extraction temperature 70°C, ethanol concentration 30%(v/v), extraction pH 9.0, solid-to-liquid ration 1:7(w/v), extraction time 2 h. Under above optimal conditions, the free oil yield reached 93.74 %±0.25%, the residual oil content of water phase was 3.78%±0.52%, the residual oil content of sendiment phase was 2.48%±0.16%.In addition, the oil quality extracted by aqueous ethanol assisted by steam explosion was analysed. Results showed: the extracted oil reached the national first grade standard; from the view of characteristic indexes, grade quality indexes, trans-fatty acid indexes etc, the oil quality of aqueous ethanol assisted by steam explosion was superior to the commercial oil quality of traditional prepress-solvent extraction assisted by high-temperature cooking.Finally, the extraction process conditions of steam-exploded sediment phase were optimized. The protein properties were also investigated. Results showed that the optimal sediment protein extraction conditions were: extraction temperature 70°C, solid-to-liquid ratio 1:15(w/v), extraction pH 10.5, extraction time 90 min, under these conditions, the highest sediment protein yield reached 44.97%, the total protein yield of raw metarial reached 74.02%. The steam explosion pretreatment was favourable for enhancing protein purity. The total sugar content of water pahse proteins were significantly higher than sediment phase protein, indicating that aqueous ethanol extraction would promote sugar dissolved. Except for foaming capacity, other properties of water phase protein and sediment phase protein like solubility of oil holding capacity and emulsification were fine, which displayed corn germ protein was a widely used ingredient.