| The waste solution produced in sweet potato processing contains large amounts of sweet potato protein. Recycling sweet potato protein from waste solutions can reduce the waste of resources and the pollution to the environment. Furthermore, sweet potato protein has significant bioactive functionality and it is a high-quality plant protein with good processing characteristics. Therefore, it is of great theoretical and practical value to study the antihypertensive activity on the hydrolyzates of sweet potato protein. The objective of this work was to obtain ACE inhibitory peptide from sweet potato protein using pepsin as well as to research its isolation, purification and structural analysis, at the same time explored the effect on the SBP of SHRs from sweet potato protein peptide.Isolation of ACE inhibitory peptide from sweetpotato protein was performed by utilizing pepsin. The effect of concentration of substrate, enzyme to substrate concentration ratio, pH value and temperature on the ACE inhibition ratio was studied by one- factor experiment and optimum design of quaternary quadratic rotation orthogonality experiment to get the best enzymatic hydrolysis condition. Results indicate that the optimal processing conditions for preparing ACE inhibitory peptides with pepsin are as follows: concentration of substrate 2.3 %, enzyme to substrate concentration ratio 3.7 %, pH value 2.3, temperature 37℃, time 8 h.Sweet potato protein peptide was separated into three fractions by ultra - filtration technology, and the range of molecular weight of the peptides are 0 - 3 kDa, 3 - 5 kDa, 5 - 10kDa. With the increase in concentrations of peptides, the ACE inhibition ratio had a marked increase, indicating dose dependent. In addition, ACE inhibitory activity of the peptide below 3 kDa, of which IC50 value ratio was 0.6661mg/ml, standed out very much, while the peptide whose molecular weight distribution was between 5– 10 kDa showed the lowest activity. After further demineralization and purify, the molecular weight range of sweet peptides below 3 kD was 212 Da - 2551 Da based on the data of MALDI - TOF - MS, of which the peptides with molecular weight 1384 Da, 1131 Da, 985 Da and 815 Da occupied most. By RP - HPLC, the composition of amino acids in sweet potato peptide was measured. The result showed sweet potato peptide has high contents of hydrophobic, aromatic and branched-side chains amino acids, the content were 29.8g/100g Peptide, 8.41 g/100g Peptide and 12.94 g/100g Peptide, respectively.The result showed that sweet potato peptide could steadily reduce SBP of SHRs both once and long - term dose. And it also turns out the heart rate, weight and blood lipids levels of SHRs were not influenced by both once and long - term dose. Furthermore, the content of ET -1 in SHR serum was significantly reduced after administration for 24 days. The once - oral administration animal experiments showed that the highest blood pressure of SHR drop was 23.59 mmHg, 16.91 mmHg, 16.18 mmHg at a dosage of 600 mg/kg·bw, 1500 mg/kg·bw and 2000 mg/kg·bw, respectively, after 1h administration. With time increased, the SBP of SHRs rose again, and nearly returned to the original level after 12 h. The long term oral administration design was conducted for 24 days. There were significant differences of SBP of SHRs for 6 days'administration when comparing the three dose groups with the control group. And the blood pressure of SHR drop was 13.01 mmHg, 10.54 mmHg, 8.46 mmHg, respectively. Moreover, There was no remarkable difference between the medium-dosage group and the low one.Regardless once administration or long - term administration, with a mixture of sweet potato peptide and captopril ( 1500 mg/kg·bw + 5 mg/kg·bw) had a synergistic effect on the SBP of SHRs. And its effect was superior to that of using captopril alone. And there was no adverse impact on the growth condition , heart rates and lipid levels of SHRs. Meanwhile, the content of ET - 1 and Ang II in SHR serum was significantly reduced after administration for 24 days. Sweet potato peptides mixed with captopril and captopril alone filled in stomach by mouth both kept step-down activity between 3h and 6h (P < 0.05). The highest blood pressure of two groups'SHR drop both appeared after 3h administration, which were 15.08 mmHg and 9.55 mmHg. Simultaneously, the hypertension effect of sweet potato peptides mixed with captopril was better than that of captopril used alone. The results of long-term oral administration indicated that a mixture of sweet potato peptides and captopril had significant antihypertensive action. The blood pressure of the combination group was 164.16mmHg significantly dropped 20.03 mmH, and if continuing to give medicine, the blood pressure of combination group and the positive control group both had significant variation compared with blank control (P < 0.05). And the blood pressure drop of SHR was 28.87 mmHg after 24 days'administration.The present study showed that, Sweet potato peptide has good antihypertensive effect, and is an ideal source for development and utilization. |
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