Study On Enzymatic Hydrolysis Of Rapeseed Protein And Biological Activity Of Hydrolysates

Reports on the rapeseed peptides having biological activity prepared by enzymatic hydrolysis with one enzyme were more than that with the combination of two enzymes. The hydrolysis of rapeseed protein from double-low variety with the combination of two enzymes, the antioxidant activity of the hydrolysates, the separation and the purification of the hydrolysates, and the range of molecular weight of the fraction of hydrolysates with higher antioxidant activity, were studied. In addition, we had a study on the ability of the rapeseed peptides with different degree of hydrolysis(DH) to inhibit the activity of angiotensin-I-converting enzyme(ACE), and made a comparison to that of the drug Captopril. This paper aims to supply experimental evidence and theoretical base to the exploitation of rapeseed protein hydrolysates with antioxidant and antihypertensive activity.Two hydrolysates of rapeseed protein with alcalase only and with alcalase and flavourzyme in succession were prepared, and their antioxidant activity was studied. Results showed that DPPH radical-scavenging activity and reducing power were related to the variety of enzymes and DH. The hydrolysates prepared with two enzymes in succession had better DPPH radical-scavenging activity and reducing power than that of the hydrolysates prepared with alcalase only. The antioxidant capacity of hydrolyates was also related to their concentration. The antioxidant capacity could be improved if the concentration of the hydrolysates could be increased within a certain range.Effects of Na₂SO₃ on hydrolysis rates of rapeseed protein by neutrase, papain and flavourzyme were studied. The addition of sodium sulfite could significantly increase rate and degree of hydrolysis by neutrase, and the effect was much better than that by papain and flavourzyme. So effects of Na₂SO₃ on antioxidant activity of rapeseed protein hydrolysates with neutrase were studied, including effects on DPPH radical-scavenging activity, reducing power and inhibition of linoleic acid peroxidation of the hydrolysates. The pretreatment of rapeseed protein with Na₂SO₃ could increase the rate of hydrolysis of rapeseed protein with neutrase and the DPPH radical-scavenging activity of the hydrolysates, but could decrease reducing power and the inhibition of linoleic acid peroxidation of the hydrolysates.Hydrolysis of rapeseed meal with two enzymes in succession, such as neutrase with trypsin, alcalase, papain, flavourzyme or protamex respectively, and antioxidant activity of the hydrolysates were tested. Results indicated that all the hydrolysates by the above five combinations of enzymes had significant efficiency on DPPH radical-scavenging activity, reducing power and inhibition of linoleic acid peroxidation and the hydrolysates with the combination of neutrase and trypsin had the highest antioxidant activity.According to the above results, the hydrolysates with neutrase and trypsin in succession were further studied. The hydrolysates were separated with pellicon film and Sephadex G-25 gel column respectively and four fractions were obtained. The fraction with molecular weight between 6500Da and 1050Da had the highest DPPH radical-scavenging activity. It was clear that the antioxidant activity of hydrolysates was dependent on molecular structure, which was not only related to the variety of enzyme, but also to hydrolytic conditions and to the degree of hydrolysis.Hydrolysis of rapeseed protein with alcalase and the ability of the hydrolysates to inhibit the activity of angiotensin-I-converting enzyme(ACE), including the comparison of the hydrolysates with different hydrolytic time and the hydrolysates with commercial antihypertensive drug Captopril, were studied. Results indicated that in comparison with rapeseed protein, all the hydrolysates of rapeseed protein with different hydrolytic time had inhibiting effects to ACE, but DH had little effect on the inhibiting activity. The ability of the rapeseed protein hydrolysates to inhibit ACE was comparable to the drug Captopril, indicating the potential application of the hydrolysates as a new antihypertensive drug.