An aqueous enzymatic extraction method was developed to obtain free oil and protein hydrolysates from dehulled rapeseeds. The rapeseed slurry was treated by the chosen combination of pectinase, cellulase, and b-glucanase (4:1:1, v/v/v) at concentration of 2.5% (v/w) for 4 h. This was followed by sequential treatments consisting of alkaline extraction and an alkaline protease (Alcalase 2.4L) hydrolysis to both produce a protein hydrolysate product and demulsify the oil. Response surface methodology (RSM) was used to study and optimize the effects of the pH of the alkaline extraction (9.0, 10.0 and 11.0), the concentration of the Alcalase 2.4L (0.5, 1.0 and 1.5%, v/w), and the duration of the hydrolysis (60, 120, and 180 min). Increasing the concentration of Alcalase 2.4L and the duration of the hydrolysis time significantly increased the yields of free oil and protein hydrolysates and the degree of protein hydrolysis (DH), while the alkaline extraction pH had a significant effect only on the yield of the protein hydrolysates. Following an alkaline extraction at pH 10 for 30 min, we defined a practical optimum protocol consisting of a concentration of 1.25-1.5% Alcalase 2.4L and a hydrolysis time between 150 and 180 min. Under these conditions, the yields of free oil and protein hydrolysates were 73-76% and 80-83%, respectively. The hydrolysates consisted of approximately 96% of peptides with a MW less than 1500, of which about 81% had a MW less than 600 Da.
The antioxidant and antithrombotic activities of crude rapeseed peptides (CRPs) and peptide fractions (RP25 and RP55) prepared from aqueous enzymatic extraction (AEE) of rapeseed were determined. The reducing power of RP55 and CRPs was higher than that of RP25 at the same concentrations. Rapeseed peptides exhibited marked antioxidant activities. The median effective dose (ED 50 ) values of CRPs, RP25 and RP55 for a,a-diphenyl-b-picrylhydrazyl (DPPH) radical scavenging were 72, 499 and 41 lg/mL, respectively. The ED 50 values for RP25 and RP55 for hydroxyl radicals scavenging were 2.53 and 6.79 mg/mL, respectively while the ED 50 values of RP55 and CRPs for inhibition of lipid peroxidation in a liposome model system were 4.06 and 4.69 mg/mL, respectively. The inhibitory effect on lipid oxidation of RP55 was similar to that of ascorbic acid at a concentration of 5.0 mg/mL. A good positive correlation existed between the peptide concentration and antioxidant activity. RP55 generally showed more potent antioxidant activities except for hydroxyl radicals scavenging ability than RP25 and CRPs at the same concentrations, which was thought to relate to the significantly higher contents of hydrophobic amino acid, tannin, and the brown color substances in RP55. Rapeseed peptides possessed marked inhibitory activities on the thrombin-catalyzed coagulation of fibrinogen, however, their inhibitory effects were not comparable to that of heparin.
To evaluate the effects of the roasting process on the extraction yield and oil quality, peanut seeds were roasted at different temperatures (130-220°C) for 20 min prior to the aqueous extraction of both oil and protein hydrolysates with Alcalase 2.4 L. Roasting temperatures did not significantly affect the yields of free oil, whereas the temperature of 220°C led to a reduced recovery of protein hydrolysates. The color and acid values of peanut oils did not change significantly with roasting temperatures. The enzyme-extracted oil with roasting at 190°C had a relatively low peroxide value, a strong oxidative stability, and the best flavor score. Using the same seedroasting temperature (190°C), quality attributes such as color, acid and peroxide values, phosphorus content and oxidative stability of the enzyme-extracted oil were better than those of the oil obtained by an expeller. After the peanut seeds were roasted at 190°C for 20 min, with a seeds-to-water ratio of 1:5, an enzyme concentration of 2%, and an incubation time of 3 h, the yields of free oil and protein hydrolysates were 78.6 and 80.1%, respectively. After demulsification of the residual emulsion by a freezing and thawing method, the total free oil yield increased to 86-90%.
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