Controlled enzymatic hydrolysis on characteristic and antioxidant properties of soybean protein isolate-maltodextrin conjugates

Figures & data

Figure 1. External fluorescence spectrum of SPI, SPI-Md, and hydrolysates of SPI-Md conjugates.

Figure 2. FT-IR spectrum of SPI, Md, SPI/Md mixture, SPI-Md conjugates, and hydrolysates of SPI-Md conjugates (DH 2.9%).

Table 1. Changes in free amino acid content (mg/100 ml) of SPI, SPI-Md, and hydrolysates of SPI-Md conjugates.

AA	SPI	SPI-Md	DH 1.8	DH 2.9	DH 4.6	DH 5.7	DH 6.2
Asp	1.41 ± 0.12^f	1.31 ± 0.08^e	1.22 ± 0.03^d	1.03 ± 0.04^b	1.19 ± 0.03^c	1.33 ± 0.10^e	0.95 ± 0.07^a
Glu	1.95 ± 0.05^d	1.05 ± 0.18^a	1.47 ± 0.16^bc	1.52 ± 0.07^c	1.41 ± 0.01^bc	1.48 ± 0.06^bc	1.32 ± 0.03^b
Ser	0.09 ± 0.02^c	0.02 ± 0.01^a	0.02 ± 0.00^a	0.06 ± 0.02^b	0.07 ± 0.01^b	0.06 ± 0.02^b	0.03 ± 0.01^a
His	0.23 ± 0.05^c	0.13 ± 0.02^b	0.05 ± 0.02^a	0.16 ± 0.01^b	0.05 ± 0.01^a	0.06 ± 0.02^a	0.06 ± 0.01^a
Gly	1.56 ± 0.13^c	0.29 ± 0.02^b	0.35 ± 0.03^b	0.25 ± 0.04^b	0.08 ± 0.01^a	0.07 ± 0.02^a	0.27 ± 0.04^b
Thr	0.35 ± 0.04^e	0.20 ± 0.03^cd	0.24 ± 0.02^d	0.02 ± 0.01^a	0.13 ± 0.02^b	0.17 ± 0.03^bc	0.02 ± 0.00^a
Arg	6.56 ± 0.16^d	5.96 ± 0.24^ab	6.10 ± 0.09^bc	5.84 ± 0.13^ab	5.61 ± 0.28^a	5.65 ± 0.20^a	6.32 ± 0.15^cd
Ala	1.56 ± 0.15^d	0.99 ± 0.21^c	0.99 ± 0.10^c	0.89 ± 0.01^bc	0.81 ± 0.10^abc	0.75 ± 0.11^ab	0.65 ± 0.05^a
Tyr	0.78 ± 0.26^b	0.07 ± 0.02^a	0.13 ± 0.04^a	0.22 ± 0.02^a	0.12 ± 0.03^a	0.24 ± 0.01^a	0.18 ± 0.03^a
Cys	0.24 ± 0.02^a	0.03 ± 0.01^a	0.20 ± 0.05^a	0.85 ± 0.14^b	1.19 ± 0.19^c	1.82 ± 0.22^d	2.06 ± 0.16^d
Val	0.87 ± 0.07^b	0.34 ± 0.04^a	0.24 ± 0.02^a	0.78 ± 0.22^b	0.81 ± 0.10^b	0.96 ± 0.06^b	0.84 ± 0.13^b
Met	0.11 ± 0.01^b	0.13 ± 0.03^b	0.04 ± 0.00^a	0.03 ± 0.01^a	0.04 ± 0.02^a	0.03 ± 0.00^a	0.03 ± 0.01^a
Phe	0.69 ± 0.18^a	0.54 ± 0.12^a	1.33 ± 0.33^b	1.84 ± 0.24^c	2.00 ± 0.15^cd	2.60 ± 0.09^e	2.29 ± 0.19^de
Ile	0.26 ± 0.02^a	0.30 ± 0.06^a	0.67 ± 0.16^bc	0.80 ± 0.13^cd	0.54 ± 0.10^b	1.86 ± 0.15^e	0.89 ± 0.19^d
Leu	0.83 ± 0.13^cd	0.32 ± 0.02^a	0.53 ± 0.03^b	0.77 ± 0.07^c	0.94 ± 0.06^de	1.36 ± 0.10^f	1.07 ± 0.10^e
Lys	0.59 ± 0.09^c	0.21 ± 0.03^b	0.03 ± 0.01^a	0.05 ± 0.02^a	0.02 ± 0.00^a	0.02 ± 0.00^a	0.04 ± 0.02^a
Total	18.10 ± 0.40^e	11.90 ± 0.25^a	13.63 ± 0.23^b	15.13 ± 0.33^c	15.01 ± 0.16^c	18.45 ± 0.35^e	17.02 ± 0.52^d

Asp = aspartic acid, Glu = glutamic acid, Ser = serine, His = histidine, Gly = glycine, Thr = threonine, Arg = arginine, Ala = alanine, Tyr = tyrosine, Cys-s = cysteine, Val = valine, Met = methionine, Phe = phenylalanine, Ile = isoleucine, Leu = leucine, Lys = lysine, Pro = proline.

Values are mean ± standard deviation (n = 3). Means with different letters within the same row are significantly different (p < 0.05).

Table 2. Correlation coefficient of DH and antioxidant activity.

Correlation Index	DH	A700	DPPH	Fe^2+	Inhibiting
DH	1
A700	−0.271	1
DPPH	0.371	−0.923**	1
Fe^2+	−0.636	−0.486	0.432	1
Inhibiting	−0.958**	0.462	0.600	0.421	1

Statistical analysis was performed assuming a significance level of P＜0.05.

Figure 3. DPPH radical scavenging capacity of SPI, SPI-Md, and hydrolysates of SPI-Md conjugates at pH = 7.0.

Figure 4. Fe²⁺ chelation activity of SPI, SPI-Md, and hydrolysates of SPI-Md conjugates at pH = 7.0.

Figure 5. Reducing power of SPI, SPI-Md, and hydrolysates of SPI-Md conjugates at pH = 7.0.

Figure 6. Lipid oxidation resistance of SPI, SPI-Md, and hydrolysates of SPI-Md conjugates at pH = 7.0.