Study On Preparation Isolated Proteins And Active Peptides From Jerusalem Artichoke Stem

After Jerusalem artichoke is extracted inulin, Jerusalem artichoke stem is the major byproduct and its content is very large. In order to improve the comprehensive utilization of Jerusalem artichoke, this paper, taking Jerusalem artichoke stem as material, extracted protein from it and measured its functional properties. Applicable proteolysis was chosen to prepare peptide. After enzymatic hydrolysis, the antioxidant and antimicrobial activity, cleaning nitrite and blocking synthesis of nitrosamine were studied. The results were as follow:1. Protein was prepared by ultrasonic method and its partial functional properties were measured. The optimum extracting conditions were as following:pH 13.5, solid-to-liquid ratio 1:40(g/mL), the ultrasonic time 50min and the temperature of 60℃. At this point, the highest extraction ratio was (71.2±0.3)%. When the protein isoelectric point was 4.0, the emulsifying capacity was up to 80% under pH9.0, the foaming ability 92.86% under the protein concentration of 4% and the solubility 91.65% under the temperature of 70℃.2. Using the response surface methodology to optimize alkaline protease preparation and enzymatic hydrolysis for peptide. The determined best conditions:substrate concentration 0.08g/mL, hydrolysis time 9h, pH10.3, temperature 50℃ and enzyme dosage 6000U/g. Under those conditions, the degree of hydrolysis was up to 43.29%.3. Taking Jerusalem artichoke stem as raw protein, using the response surface methodology to optimize acid protease preparation and enzymatic hydrolysis for antioxidant peptide. The determined best conditions:enzyme dosage 8000U/g, temperature 50℃, pH5.0, hydrolysis time 3.5h and substrate concentration 0.16g/mL. Under those conditions, the scavenging activity of DPPH free radical was up to 88.10%. The reducing power and hydroxyl radical scavenging activity were the largest under the antioxidant peptide concentration of 4%, but both less than VC. It can be seen that antioxidant peptide of Jerusalem artichoke stem has a higher antioxidant.4. Through imitating human gastric juice environments, Jerusalem artichoke stem peptide can effectively clean and block synthesis of nitrosamine. When the peptide concentration was 5% and 2% respectively, the clearance and blocking rate was up to 94.18%,24.4%. To delaminate Jerusalem artichoke stem by ultrafiltration method and measure the peptide in each molecular weight, we can find that the nitrite scavenging was up to 66.15% under the molecular weight of 3-5K and the time of 60min. And the blocking synthesis of nitrosamine was up to 98.96% under the molecular weight of 5-10K.5. The hydrolysates of acid protease and alkaline protease had inhibition effects on staphylococcus aureus, Escherichia coli and Bacillus subtilis. Among them, the inhibitory effect of the alkaline protease hydrolysate was better. The optimized inhibitory concentration of acid protease and alkaline protease hydrolysate was 3mg/mL,4mg/mL, respectively. These two kinds of hydrolysis protease have the best inhibitory effect under the molecular weight of 5-10K and 3-5K, respectively.