Effect of Freezing/Thawing Temperature on the Viscoelastic and Nutritional Qualities of Carrots

Figures & data

TABLE 1 Texture properties of raw and carrots stored at –20^oC for 30 d

Item	Hardness 1(N)	Hardness 2(N)	Fracturability(N)	Springiness	Cohesiveness	Chewiness(N)	Resilience
4-20	44.98^a ± 6.02	39.04^a ± 3.72	39.12^a ± 9.12	0.41^b ± 0.04	0.18^b ± 0.03	3.44^a ± 0.79	0.07^a ± 0.02
4-70	57.50^b ± 5.85	46.38^ab ± 7.04	63.04^b ± 8.21	0.41^b ± 0.05	0.25^c ± 0.03	4.46^b ± 0.41	0.09^b ± 0.01
4-196	63.80^c ± 4.93	54.81^b ± 9.80	77.83^c ± 9.01	0.27^a ± 0.03	0.08^a ± 0.01	2.86^a ± 0.52	0.04^a ± 0.01
18-20	54.10^a ± 8.70	47.35^ab ± 8.29	44.57^a ± 7.71	0.37^b ± 0.03	0.17^b ± 0.03	3.39^a ± 0.83	0.06^a ± 0.01
18-70	66.11^b ± 8.04	51.33^ab ± 8.37	55.49^b ± 7.27	0.38^b ± 0.03	0.23^c ± 0.02	5.53^b ± 1.35	0.09^b ± 0.02
18-196	97.75^d ± 9.70	70.76^c ± 8.74	94.42^d ± 8.95	0.31^a ± 0.03	0.10^a ± 0.04	3.55^a ± 1.54	0.05^a ± 0.03
Control	129.82^e ± 13.95	109.45^d ± 12.67	176.75^e ± 5.25	0.46^c ± 0.06	0.14^b ± 0.02	7.81^c ± 2.16	0.06^a ± 0.01

^a–eMean ± SD;

Different superscripts within a column represent significant differences (p < 0.05);

Control: raw carrots; 4–20, 70, and 196: carrots frozen at –20, –70, and –196^oC, respectively, and thawed at 4^oC; 18–20, 70, and 196: carrots frozen at –20, –70, and –196^oC, respectively, and thawed at 18^oC.

FIGURE 1 Scanning electron microscope images at 100 × magnification of raw and treated carrot tissues. a: Raw tissues; b, c, and d: tissues frozen at –20, –70, –196, respectively, and thawed at 18^oC. P: pore; H: hole; C: crack.

FIGURE 2 Frequency spectra for storage modulus (G′) of raw and treated carrots. Raw: raw carrot; 4–20, 70, and 196: carrots frozen at –20, –70, and –196^oC, respectively, and thawed at 4^oC; 18–20, 70, and 196: carrots frozen at –20, –70, and –196^oC, respectively, and thawed at 18^oC.

FIGURE 3 Frequency spectra for loss modulus (G″) of raw and carrots. Raw: raw carrot; 4–20, 70, and 196: carrots frozen at –20, –70, and –196^oC, respectively, and thawed at 4^oC; 18–20, 70, and 196: carrots frozen at –20, –70, and –196^oC, respectively, and thawed at 18^oC.

FIGURE 4 Frequency spectra for loss tangent (Tanδ) of raw and treated carrots. Raw: raw carrot; 4–20, 70, and 196: carrots frozen at –20, –70, and –196^oC, respectively, and thawed at 4^oC; 18–20, 70, and 196: carrots frozen at –20, –70, and –196^oC, respectively, and thawed at 18^oC.

TABLE 2 The average elastic modulus of all points on the frequency sweep curve of raw and carrots stored at –20^oC for 30 d

Item	Storage modulus (Pa × 10^4)	Loss modulus (Pa × 10^4)	Loss tangent
4–20	24.37^a ± 3.09	7.59^a ± 0.72	0.36^d ± 0.04
4–70	52.93^b ± 3.09	15.54^b ± 2.07	0.31^cd ± 0.03
4–196	84.96^b ± 4.09	24.33^c ± 3.05	0.27^bc ± 0.02
18–20	50.42^b ± 2.70	14.24^b ± 1.82	0.32^cd ± 0.05
18–70	62.00^b ± 3.12	16.61^b ± 2.20	0.29^bc ± 0.03
18–196	122.17^c ± 7.90	33.56^d ± 3.76	0.23^b ± 0.03
Control	809.93^d ± 19.66	143.58^e ± 9.03	0.18^a ± 0.01

^a-eMean ± SD;

Different superscripts within a column represent significant differences (p < 0.05);

Control: raw carrots; 4–20, 70, and 196: carrots frozen at –20, –70, and –196^oC, respectively, and thawed at 4^oC. 18–20, 70, and 196: carrots frozen at –20, –70, and –196^oC, respectively, and thawed at 18^oC.

TABLE 3 Carotenoid contents of raw and carrots stored at –20^oC for 30 d (expressed as mg kg^–1 d.b.)

Item	α-carotene	β-carotene	Lycopene	Lutein
4–20	205.71^a ± 6.83	396.32^a ± 22.22	2.21^a ± 0.52	0.11^a ± 0.11
4–70	217.45^a ± 11.40	418.17^a ± 26.05	2.67^b ± 0.83	0.65^b ± 0.10
4–196	317.22^c ± 20.12	602.10^c ± 41.11	2.78^b ± 0.36	1.17^c ± 0.18
18–20	259.16^b ± 12.57	514.24^b ± 30.43	2.13^a ± 0.22	1.31^c ± 0.22
18–70	261.08^b ± 15.33	536.18^b ± 40.34	3.10^b ± 0.55	1.22^c ± 0.29
18–196	338.27^c ± 15.41	598.20^c ± 36.28	3.18^b ± 0.12	1.78^d ± 0.34
Control	355.03^c ± 17.69	663.49^c ± 44.70	5.09^c ± 0.76	0.75^b ± 0.21

^a–dMean ± SD;

Means within a column without a common superscript differ (p < 0.05);

Control: raw carrots; 4–20, 70, and 196: carrots frozen at –20, –70, and –196^oC, respectively, and thawed at 4^oC. 18–20, 70, and 196: carrots frozen at –20, –70, and –196^oC, respectively, and thawed at 18^oC.

TABLE 4 Soluble sugar contents of raw and carrots stored at –20^oC for 30 d (expressed as mg g^–1 d.b.)

Item	Fructose	Glucose	Sucrose
4–20	181.85^a ± 9.91	149.27^a ± 13.40	485.46^a ± 16.01
4–70	204.42^b ± 8.03	225.23^b ± 8.07	606.70^b ± 17.21
4–196	218.78^c ± 11.91	250.98^b ± 14.11	783.37^e ± 23.71
18–20	183.41^a ± 10.11	212.27^a ± 10.91	643.71^c ± 12.01
18–70	206.89^b ± 11.30	234.24^b ± 11.40	686.08^d ± 15.02
18–196	220.45^c ± 7.44	255.16^b ± 15.56	779.61^e ± 20.11
Control	236.35^c ± 12.34	290.37^c ± 13.58	875.43^f ± 19.47

^a–fMean ± SD;

Means within a column without a common superscript differ (p < 0.05);

Control: raw carrots; 4–20, 70, and 196: carrots frozen at –20, –70, and –196^oC, respectively, and thawed at 4^oC. 18–20, 70, and 196: carrots frozen at –20, –70, and –196^oC, respectively, and thawed at 18^oC.

TABLE 5 Standard partial regression coefficients between mechanical and nutritional attributes

Coefficient	α-carotene	β-carotene	Lycopene	Lutein	Fructose	Glucose	Sucrose
Hardness1	0.212	0.212	0.154	0.321	0.153	0.141	0.161
Hardness2	0.118	0.127	0.132	0.035	0.131	0.119	0.133
Fracturability	0.126	0.136	0.135	0.054	0.147	0.134	0.152
Springiness	–0.224	–0.218	0.0.31	–0.606	–0.181	–0.185	–0.240
Cohesiveness	–0.073	–0.093	–0.018	–0.060	–0.121	–0.114	–0.136
Gumminess	0.110	0.107	0.130	0.153	0.114	0.105	0.120
Chewiness	0.024	0.023	0.121	–0.053	0.019	0.010	0.001
Resilience	–0.079	–0.096	–0.008	0.008	–0.054	–0.050	–0.056
Storage modulus	0.008	0.020	0.121	–0.242	0.043	0.031	0.022
Loss modulus	0.034	0.046	0.127	–0.176	0.062	0.049	0.045
Loss tangent	–0.234	–0.236	–0.148	–0.365	–0.225	–0.213	–0.253
R^2	0.911*	0.956*	0.997*	0.923*	0.980*	0.949*	0.933*

*Linear correlation was significant at p < 0.01;

R²: correlation coefficient square of regression equation.