Study On Producing Rapeseed Acei Peptides By Liquid-State Fermentation

Rapeseed angiotensin I-converting enzyme (ACE) inhibitory peptides,which was produced by hydrolyzing rapeseed protein into peptide with 3-6 amino acid residues. It could decrease the blood pressure by inhibiting ACE activity.Compare with potent synthetic ACE inhibitors, food-derived ACE inhibitors have safety advantages. Thus food-derived ACE inhibitors has been the hotspot in present research.The methods of debirtering existing now are not only laborious but of high cost. It cuts down production cost,and accelerates the industrialization of funetional peptide to produce peptide which drolyzing rapeseed protein in one step with food–grade Bacillus subtilis.Thus the production of rapeseed Angiotensin I-converting enzyme inhibitory peptides with Bacillus subtilis will have widely-use prospect.There are no relative internal and external reports so far.This thesis focused on the following four aspects:(1)Screening of srains used for producing rapeseed ACE nhibitory peptides through liquid-state fermentation;(2)Optimization of medium conditions used for producing rapeseed ACE inhibitory peptides through liquid-state fermentation;(3)Optimization of technology used for producing rapeseed ACE inhibitory peptides through liquid-state fermentation;(4)Separation and purification ACE inhibitory peptides from rapeseed protein. The results were as follows:(1) In order to get the best strain for producing rapeseed angiotensin I-converting enzyme inhibitory peptides through liquid-state fermentation.Strains Bacillussubtilis asoriginal, Bacillus licheniformis,Aspergillus niger, Geotrichum candidum, Candida utilis, Actinomucor elegans and Aspergillusoryzae were used for liquid-state fermentation with rapeseed meal.Peptide recovery ratio,soluble nitrogen, amino acid nitrogen, protease activity,ACE inhibition activity were used as evaluation indexes.The results shows that Bacillussubtilis asoriginal has the highest peptide recovery ratio and ACE inhobitory comparing with other strains.This is the best strain which can be used for producing rapeseed ACE inhibitory peptides through liquid -state fermentation.(2)Rapeseed meal was used to produce peptide with Bacillus subtilis by liquid -state fermentation. With rapeseed peptide yield and ACE inhibitory as indexes for single factor test, the medium conditions was optimized for producing rapeseed ACE peptides through Liquid-state fermentation by response surface analysis. Results shows that the optimal conditions are as follows: initial pH 7.0, solid-liquid ratio1:23, concentrations of glucose 0.45% and concentrations of KH2PO40.8%, Under the above conditions, the ACE inhibitory reached 69.3 %..(3) Rapeseed meal was used to produce peptide with Bacillus subtilis by liquid -state fermentation.With rapeseed peptide yield and ACE inhibitory as indexes for single factor test, The technology conditions was optimized for producing rapeseed ACE inhibitory peptides through liquid-state fermentation by response surface analysis. Results shows that the optimal conditions are as follows: fermentation time 20h, fermentation temperature38℃, and inoculum size1×108 ind/mL, under the above conditions, the ACE inhibitory reached 70.95 %.(4)Separate and purification rapeseed ACE inhibitory peptides by ultra filtration, gel filtration, ion exchange and HPLC,The results shows that rapeseed peptides wih the molecular weight below 3000D has the highest ACE inhibitory activity. 5 main peaks are acquired by gel filtration, R-D has the highest ACE inhibitory activity, 73.5%. Purification R-D by ion exchange, 3 main peaks are acquired, R-D-B has the highest ACE inhibitory activity, 78.2%. Purification R-D-B by HPLC, R-D-B-B is acquired, which is proved the pure peptide.