Research On Extraction Sesame Protein From Subcritical Meal And Its Enzymatic Hydrolysis To ACE Inhibitory Peptide

Sesame is one of ’Chinese four major edible oil crops, a large amounts of sesame cake are produced during oil processing. Although the sesame cake is abundant, its processing and utilization are low because of backward processing technology. As a result, sesame protein in the sesame cake is not fully utilized. Moreover, research on extracting protein from subcritical sesame cake and preparation of ACE inhibitory peptides from sesame protein are still in the early stages. In order to promote the development in the processing and application of sesame protein, this study are mainly about isolation of sesame protein from subcritical cake by alkali-solution and acid-precipitation method, reducing the browning of sesame protein during drying processing through various methods, analyzing the difference in structure, composition and functionality among SPSI, NSPA SPHS which originated different raw material, exploring the conditions of preparation of sesame ACE inhibitory peptide by enzymatic hydrolysis, separation and purification of the high activity ACE inhibitory peptide. The main results are as follows:The protein was extracted from subcritical sesame cake by means of alkali-solution and acid-precipitation method. Based on the results of single factor experiment, the optimum alkali-extraction conditions were obtained by orthogonal experiments as follows: temperature 45 ℃, pH 10.5, solid-to-liquid ratio 1:18, extraction time 20 minutes. Under the optimum conditions, the sesame protein extraction rate reached(91.79±0.24)%. The optimum acid precipitation condition was pH5.0; and the recovery of sesame protein and the protein content in the product were up to(73.53±0.32)% and(82.33±0.24)% respectively. In addition, dialysis and pre-freezing at-70 ℃ were applied to effectively inhibit browning of sesame protein during lyophilization. The secondary alkali-solution and acid-precipitation method could improve the purity of sesame protein to(84.32±0.56)%, but the protein recovery decreased to(61.01±0.41)%, so that this method was not suitable for the purification of sesame protein. Thus, because of saving time and operating easily the process of alkali-solution and acid-precipitation, is suitable for industrialization.The difference between structure and function of the SPSI, the NSPA and the SPHS were compared. The result of SDS-PAGE electrophoresis is shown, there were no differences between SPSI and NSPA in the composition and distribution of sesame protein subunits; while the typical subunits of the sesame protein in the SPHS were lost because of thermal decomposition, which would affect their properties and application. The results of Fourier transform infrared spectroscopy analysis show that: the amide III band absorption peak of SPSI, NSPA and SPHS were at 1235 cm-1, 1237 cm-1 and 1240 cm-1 respectively. Amino acid composition analysis results show that the amino acid composition of SPSI was similar with that of NSPA, and their amino acids ratio was higher than that of the SPHS in line with the FAO recommended values. Compared with functionality of the three sesame proteins, SPSI had good solubility, water absorption, oil absorption, emulsification and foam stability. It had proved that there were differences in the structure and composition of the sesame protein extracted from different raw materials, which affecting the functional and nutritional properties. The influence of subcritical extraction on sesame protein was so weak that sesame protein originated from subcritical sesame meal was more suitable as a food ingredient because of the highly nutritious and functional.SPSI was used as raw material to prepare angiotensin-I converting enzyme(ACE) inhibitory peptides by enzymatic method. According to the hydrolysis results of Alcalase、alkaline protease 2709、Trypsinase、Bromelain and Nuetrase, Alcalase was screened out as a tool enzyme to prepare ACE inhibitory peptides. Based on the results of single factor experiments, the optimum hydrolysis conditions were obtained by response surface design as follows: time 147 min, pH 8.21, temperature 55 ℃, at these conditions the peptide generation rate, the degree of hydrolysis and ACE inhibition rate were obtained to 75.27%, 20.06% and 70.80% respectively, the IC50 was 1.004 mg/mL.Finally, using ultrafiltration and Sephadex G-25 purified the ACE inhibitory peptides. After ultrafiltration, the IC50 value was 0.899 mg/mL and peptide recovery rate was 50.74%. Using Sephadex G-25 to desalt and separate the permeate liquid which was after ultrafiltration, the results showed that the peak III had the highest ACE inhibitory activity and the IC50 value was 0.531 mg/mL, desalination rate reached 95.17% and peptide recovery rate was 39.89%. The F-III might contain three short peptides speculated by using LC-MS techniques, whose molecular weight were 1416.6, 1746.5 and 2017.6 respectively.