| Rapeseed meal is a by-product of oil extraction ,which is formed after the squeezing and defatting process.The content of total protein reaches 35%-45% and can be exploited as food additive because of its good quality.Bioactive peptides can be obtained from protein hydrolysate. However, the meal hasn't been utilized completely.It is only used for animal feed and fertilizer ,thus leading to the waste of resources. Therefore,it's significant to work on the value-added process of rapeseed meal.On the basis of alkali-extraction and acid-precipitation combining with ultra-filtration, the preparation of rapeseed protein isolate(RPI) from high-temperature double-low meal was studied and the respective reaction conditions were optimized. Then the product's drying conditions and central properties were investigated. A kinetic model equation simulating the enzymatic hydrolysis with alkaline protease was obtained.The main conclusions of the experiments were as follows:(l)With the extraction rate of protein as the index and through the optimization of single factor and orthogonal experiments,the optimum conditions of the protein extraction were: pH =13, 3 times extraction,the ratio of material and solution(g/ml) were 1:10,1:8,1:6 respectively ,the temperature was 40℃and the time of extraction was 40 minutes.The extraction rate of protein was 61.9%.(2)The optimum technical conditions of acid-precipitation and ultra-filtration process were: precipitation of protein at pH4.5.For the ultra-filtration of the separated solution, the temperature was 40℃,the velocity of flow was 2m/s, the pressure was 0.10Mpa.The precipitation rate of protein was 63.2% . In the ultra-filtration process ,the capture rate of protein was 68.5% and it still retain 67% after enlargement test.The volume flow of solution through membrane recover 90% of original by washing.(3)The intake and exit temperature of the spray dryer were 180℃and 80℃respectively.Through centrifugal spray drying to the homogenized protein solution,the flaxen RPI powder was obtained and the content of protein was 70.5%.The final recovery rate of protein was 54.7%. Compared with the product from low-temperature meal, the RPI has the similar amino acid composition.(4)Water binding capacity,foaming capacity,emulsification capacity and stability of RPI were studied.Compared with the soybean protein isolate(SPI), the foaming capacity of RPI is better and its emulsification capacity and stability are equivalent to SPI, but its water binding capacity is worse.(5)The substrate RPI was hydrolyzed by alkaline protease and the degree of hydrolysis(DH) was best under the hydrolysis condition as follows: temperature was 55℃, pH=9.0, concentration of substrate and enzyme were 4.32g/100ml and 0.50g/100ml respectively. The DH ascended as the increase of enzyme concentration and descended as the increase of substrate concentration. Under the condition of pH9.0 and 40℃, a kinetic model equation simulating the enzymatic hydrolysis of RPI was obtained on the basis ofmany experiments: The equation can be used to instruct andoptimize the hydrolysis process when the DH≤40%.(6)Under the best condition of high DH, the activity of alkaline protease reduced gradually in the hydrolysis process and the enzyme activity reduced to 36% of original after 120min.The evaluation of bitterness produced by the peptides was best between 30min to 60min.
|
PDF Full Text Request