Structure of the zein protein as treated with subcritical water

Figures & data

Figure 1. Effect of subcritical water treatment on solubility of zein. Bars represent standard deviations. Different letters indicate significant differences (p ≤ 0.05) according to Duncan’s multiple tests.

Figure 2. Effect of subcritical water treatment on molecular particle size of zein protein.

Table 1. Foam capacity and foam stability of zein samples.

	Foaming properties			Foaming properties
Sample	FC (%)	FS (%)	Sample	FC (%)	FS (%)
Control	22.5 ± 1.1^a	40.2 ± 1.3^a
20 min	25.5 ± 0.7^b	51.1 ± 1.0^b	110°C	24.8 ± 1.2^ab	49.6 ± 0.8^bc
40 min	27.2 ± 0.9^c	52.7 ± 0.9^bc	130°C	25.6 ± 0.8^b	51.3 ± 1.3^a
60 min	28.1 ± 0.9^cd	53.4 ± 0.9^d	150°C	23.6 ± 1.1^a	48.7 ± 0.9^b
80 min	28.8 ± 0.8^cd	55.5 ± 1.1^e	170°C	23.2 ± 0.9^a	46.2 ± 0.8^a
100 min	29.6 ± 1.2^d	56.4 ± 1.2^e
120 min	31.5 ± 1.0^e	58.5 ± 0.7^f

Different letters indicate significant differences (p ≤ 0.05) according to Duncan’s multiple tests.

Figure 3. (a, b): Effect of subcritical water treatment on the DSC of zein; (c, d): Effects of subcritical water treatment on the circular dichroism spectra of zein.

Table 2. The contents of secondary structure of zein after different time with subcritical water.

Secondary structure	α-Helix (%)	β-sheet (%)	β-Turn(%)	Random coil (%)
Control	18.91^a	35.62^e	20.84^e	24.63^ab
20 min	19.59^b	35.47^d	18.85^a	25.99^b
40 min	19.86^d	35.79^f	18.99^b	25.37^b
60 min	20.25^g	34.43^a	21.11^f	24.21^ab
80 min	19.90^e	35.07^b	20.69^d	24.34^ab
100 min	19.79^c	35.47^d	20.59^c	24.16^a
120 min	20.09^f	35.26^c	20.86^e	23.77^ab

Different letters indicate significant differences (p ≤ 0.05) according to Duncan’s multiple tests.

Table 3. The contents of secondary structure of zein after different temperatures with subcritical water.

Secondary structure	α-Helix (%)	β-sheet (%)	β-Turn (%)	Random coil (%)
Control	18.91^a	35.62^b	20.84^d	24.63^b
110°C	19.04^b	36.30^e	19.83^c	24.83^c
130°C	19.95^d	37.11^d	18.69^a	25.28^e
150°C	19.49^c	35.70^c	19.73^b	25.07^d
170°C	20.25^e	34.19^a	21.07^e	24.48^a

Different letters indicate significant differences (p ≤ 0.05) according to Duncan’s multiple tests.

Figure 4. Effect of subcritical water treatment on the physical structure of zein protein. Scanning electron microscopy images of untreated zein protein (a) and subcritical water-treated zein (b–f). Subcritical water treatment conditions: treatment sample 0.5 g/30 mL; subcritical water treatment times: 20 min (b) and 60 min (c) and 100 min (d). Subcritical water treatment temperatures: 130°C (e) and 170°C (f). And all magnifications are ×5,000.

Figure 5. Effects of subcritical water treatment on the atomic force microscopy (AFM). AFM images of untreated zein (a) and subcritical water-pretreated zein (b–f). Subcritical water treatment conditions: treatment sample (0.5 g/30 mL); subcritical water treatment time, 20 min (b), 60 min (c), and 100 min (d). Subcritical water-treated temperature 130°C (e) and 170°C (f).