Microstructure and quality of cabbage slices (Brassica oleracea L. var. capitata L.) as affected by cryogenic quick-freezing treatment

Figures & data

Table 1. The freezing experiment parameters

Treatment	Amount of cabbage (g)	Instrument capacity (L)	Air speed (m/s)	Convective heat transfer coefficient (W/m^2 K)
−20°C quick-frozen	1000	10	0.4	14.63
Dry ice quick-frozen	500	5	0.25	11.57
−60°C quick-frozen	1000	10	0.65	18.65

Table 2. The freezing rate and drip loss of different quick-frozen cryogenic treatments

Treatment	Freezing rate (°C/min)	Drip loss (%)
Color protecting + blanching + −20°C quick-frozen	0.2^a±0.1	0.61^b±0.05
Color protecting + blanching + dry ice quick-frozen	7.6^c±0.3	0.26^a±0.05
Color protecting + blanching + −60°C quick-frozen	2.3^b	0.35^b±0.08

Figure 1. The freezing curves of different quick-frozen cryogenic treatments at 4°C

Figure 2. Morphology of cabbage slices treated by different freezing processing observed by SEM (a: fresh cabbage slices, b: color protecting+blanching, c: Color protecting + blanching + −20°C quick-frozen + stored at −18°C, d: Color protecting + blanching + dry ice quick-frozen + stored at −18°C, e: Color protecting + blanching + −60°C quick-frozen + stored at −18°C; a: 500×, b: 2000×)

Figure 3. Effects of different quick-frozen cryogenic preservation treatments on total chlorophyll, V_C and TA of purple cabbage slices during storage (■, Control; ●, Color protecting+blanching; ▲, Color protecting + blanching + −20°C quick-frozen + stored at −18°C; ▼, Color protecting + blanching + dry ice quick-frozen + stored at −18°C; ◆, Color protecting + blanching + −60°C quick-frozen + stored at −18°C)

Table 3. Effects of different quick-frozen cryogenic preservation treatments on the content of total sugars and reducing sugars of purple cabbage slices

Treatment	Total sugar/(g/100g)			Reducing sugar/(g/100g)
	Day 0	Day14	Day28	Day0	Day14	Day28
1	17.1^a ± 0.3	9.4^e ± 0.3	5.6^e± 0.2	11.6^a ± 0.1	7.5^c ± 0.3	3.4^e ± 0.4
2	16.5^b ± 0.4	12.0^d ± 0.5	7.5^d± 0.4	11.4^a ± 0.8	8.0^c ± 0.4	4.5^d± 0.5
3	15.9^bc ± 0.3	13.9^c ± 0.4	11.0^c ± 0.4	11.3^a ± 0.8	8.4^bc ± 0.8	6.4^c ± 0.1
4	15.5^c ± 0.3	15.4^a ± 0.3	13.6^a ± 0.2	11.3^a ± 1.2	10.7^a ± 0.5	8.3^a ± 0.1
5	16.4^b ± 0.2	14.7^b ± 0.3	12.5^b ± 0.1	11.4^a ± 1.1	9.3^b ± 0.5	7.3^b ± 0.1

mean ± standard deviation (n = 3), mean bars with different letters (a-e) in the same treatments at different incubation times differ significantly (P ≤ 0.05), “-” means that the sample was not measurable. Treatment: 1. Control; 2. Color protecting+blanching; 3. Color protecting + blanching + −20°C quick-frozen + stored at −18°C; 4. Color protecting + blanching + dry ice quick-frozen + stored at −18°C; 5. Color protecting + blanching + −60°C quick-frozen + stored at −18°C.

Figure 4. Effects of different quick-frozen cryogenic preservation treatments on TPA values of purple cabbage slices during storage (■, control; ●, color protecting + blanching; ▲, color protecting + blanching + −20 °C quick-frozen + stored at −18 °C; ▼, color protecting + blanching + dry ice quick-frozen + stored at −18 °C; ◆, color protecting + blanching + −60 °C quick-frozen + stored at −18 °C)

Table 4. Effects of different quick-frozen cryogenic preservation treatments on the total number of bacteria of cabbage slices

Treatment	Total bacteria count/(CFU/g)
	Day0	Day 14	Day 28
1	(3.2 ± 0.4)^a × 10^2	(6.0 ± 0.3)^a × 10^6	(5.1 ± 0.1)^a × 10^8
2	(2.9 ± 0.2)^a × 10^2	(5.1 ± 0.2)^b × 10^5	(3.5 ± 0.7)^b × 10^8
3	(2.0 ± 0.3)^b × 10^2	(8.4 ± 1.0)^c × 10^3	(8.5 ± 0.7)^c × 10^4
4	(9.7 ± 0.7)^d × 10	(4.8 ± 0.3)^c × 10^3	(2.0 ± 0.5)^c × 10^4
5	(1.5 ± 0.2)^c × 10^2	(6.2 ± 0.5)^c × 10^3	(4.4 ± 0.6)^c × 10^4

mean ± standard deviation (n = 3), mean bars with different letters (a-e) in the same treatments at different incubation times differ significantly (P ≤ 0.05); “-” means that the sample was not measurable. Treatment: 1. Control; 2. Color protecting + blanching; 3. Color protecting + blanching + −20°C quick-frozen + stored at −18°C; 4. Color protecting + blanching + dry ice quick-frozen + stored at −18°C; 5. Color protecting + blanching + −60°C quick-frozen + stored at −18°C.

Table 5. Effects of different quick-frozen cryogenic preservation treatments on the total number of yeast and mold of cabbage slices

Treatment	Total yeast and mold count/(CFU/g)
	Day 0	Day 14	Day 28
1	(4.3 ± 0.4)^a × 10	(5.0 ± 0.4)^a × 10^4	(8.8 ± 0.2)^a × 10^6
2	(3.9 ± 0.7)^a × 10	4.7^b ×10^4	(7.6 ± 0.4)^b × 10^5
3	(2.3 ± 0.4)^b × 10	(1.4 ± 0.2)^c × 10^3	(3.5 ± 0.6)^c × 10^3
4	<1.0^c ×10	(5.2 ± 1.3)^c × 10^2	(1.0 ± 0.05)^c × 10^3
5	<1.0^c ×10	(9.8 ± 1.3)^c × 10^2	(2.9 ± 0.6)^c × 10^3

mean ± standard deviation (n = 3), mean bars with different letters (a-e) in the same treatments at different incubation times differ significantly (P ≤ 0.05), “-” means that the sample was not measurable. Treatment: 1. Control; 2. Color protecting+blanching; 3. Color protecting + blanching + −20°C quick-frozen + stored at −18°C; 4. Color protecting + blanching + dry ice quick-frozen + stored at −18°C; 5. Color protecting + blanching + −60°C quick-frozen + stored at −18°C.

Figure 5. Effects of different quick-frozen cryogenic preservation treatments on sensory acceptability of Purple Cabbage Slices during storage (■, Control; ●, Color protecting+blanching; ▲, Color protecting + blanching + −20°C quick-frozen + stored at −18°C; ▼, Color protecting + blanching + dry ice quick-frozen + stored at −18°C; ◆, Color protecting + blanching + −60°C, quick-frozen + stored at −18°C)