Secondary structures and their effects on antioxidant capacity of antioxidant peptides in yogurt

Figures & data

Table 1. Estimated secondary structures of yogurt antioxidant peptides.

	Secondary structure percentage (%)
Samples	α-Helix	β-Sheet	β-Turn	Random coil	α-Helix/β-Structure Ratio
Control	32.99 ± 1.31	28.74 ± 0.95	14.36 ± 0.73	15.88 ± 0.65	0.77 ± 0.03
pH Treatment
6.0	32.28 ± 0.99	37.99 ± 1.11	14.23 ± 0.21	15.48 ± 0.48	0.62 ± 0.03
7.0	32.99 ± 1.21	28.95 ± 0.98	14.66 ± 0.15	15.63 ± 0.53	0.76 ± 0.04
8.0	32.77 ± 1.01	29.10 ± 1.02	14.46 ± 0.24	15.63 ± 0.44	0.75 ± 0.02
Thermal Treatment (°C)
38	32.33 ± 1.22	37.95 ± 1.29	13.89 ± 0.37	15.8 ± 0.39	0.62 ± 0.04
50	32.88 ± 1.17	28.94 ± 1.18	14.46 ± 0.25	15.75 ± 0.55	0.76 ± 0.04
65	16.61 ± 0.75	35.51 ± 1.41	24.19 ± 0.87	17.75 ± 0.47	0.28 ± 0.01
Urea Concentration (mol/L)
1	15.19 ± 0.34	36.88 ± 1.27	27.46 ± 0.92	14.9 ± 0.33	0.24 ± 0.01
3	28.28 ± 0.45	32.62 ± 1.04	26.42 ± 0.75	12.67 ± 0.15	0.48 ± 0.01
5	29.35 ± 0.88	31.77 ± 1.16	25.29 ± 1.00	13.57 ± 0.22	0.51 ± 0.02
7	27.71 ± 0.63	33.43 ± 1.12	26.42 ± 0.73	12.42 ± 0.19	0.46 ± 0.03
8	29.18 ± 1.00	31.78 ± 1.20	25.64 ± 0.68	13.39 ± 0.15	0.51 ± 0.02
Trifluoroethanol (v/v)
10%	29.91 ± 0.77	35.88 ± 1.38	9.38 ± 0.08	17.86 ± 0.57	0.66 ± 0.03
30%	30.65 ± 1.05	35.11 ± 1.26	9.98 ± 0.05	17.71 ± 0.60	0.68 ± 0.04
50%	29.98 ± 1.01	35.71 ± 1.37	9.54 ± 0.07	17.75 ± 0.46	0.66 ± 0.03

Data are mean ± standard deviation of triplicate tests.

Figure 1. Antioxidant capacity of yogurt antioxidant peptides under the following treatments: (A) pH6, pH7, and pH8; (B) heat treat with 38°C, 50 ^oC, and 65 ^oC; (C) urea on the concentration of 1mol/L, 3mol/L,5mol/L,7mol/L, and 8mol/L; (D) trifluoroethanol on the concentration of 10%, 30%, and 50% (v/v). Different label letters indicate significant differences among samples at a significant level of 0.05, and the same label alphabet means insignificant.

Figure 2. Fluorescence spectrum of yogurt antioxidant peptides under the following treatments: (A) pH6, pH7, and pH8; (B) heat treat with 38°C, 50 ^oC, and 65 ^oC; (C) urea on the concentration of 1mol/L, 3mol/L,5mol/L,7mol/L, and 8mol/L; (D) trifluoroethanol on the concentration of 10%, 30%, and 50% (v/v). Different label letters indicate significant differences among samples at a significant level of 0.05, and the same label alphabet means insignificant.

Figure 3. FTIR spectrum of yogurt antioxidant peptides under the following treatments: (A) pH6, pH7, and pH8; (B) heat treat with 38°C, 50 ^oC, and 65 ^oC; (C) urea on the concentration of 1mol/L, 3mol/L,5mol/L,7mol/L, and 8mol/L; (D) trifluoroethanol on the concentration of 10%, 30%, and 50% (v/v). Different label letters indicate significant differences among samples at a significant level of 0.05, and the same label alphabet means insignificant.

Figure 4. Spectrum of amide I (1700–1600 cm⁻¹) in of yogurt antioxidant peptides: (A) Control, (B) pH 6.0 yogurt peptide, (C) pH 7.0 yogurt peptide, (D) pH 8.0 yogurt peptide, (E) 38°C treated yogurt peptide, (F) 50°C treated yogurt peptide, (G)65°C treated yogurt peptide, (H) 1.0 mol/L urea treated yogurt peptide, (I) 3.0 mol/L urea treated yogurt peptide, (J) 5.0 mol/L urea treated yogurt peptide, (K) 7.0 mol/L urea treated yogurt peptide, (L) 8.0 mol/L urea treated yogurt peptide, (M) 10% (v/v) trifluoroethanol treated yogurt peptide, (N) 30% (v/v) trifluoroethanol treated yogurt peptide, and (O) 50% (v/v) trifluoroethanol treated yogurt peptide. Different label letters indicate significant differences among samples at a significant level of 0.05, and the same label alphabet means insignificant.

Figure 5. Circular dichromatic spectrogram of yogurt antioxidant peptides under the following treatments: (A) pH6, pH7, and pH8; (B) heat treat with 38°C, 50 ^oC, and 65 ^oC; (C) urea on the concentration of 1mol/L, 3mol/L,5mol/L,7mol/L, and 8mol/L; (D) trifluoroethanol on the concentration of 10%, 30%, and 50% (v/v). Different label letters indicate significant differences among samples at a significant level of 0.05, and the same label alphabet means insignificant.