Freshness of deep frozen mackerel and croaker during long-term storage

Figures & data

Figure 1. Freezing curves of mackerel (a) and croaker (b) with various freezing temperatures

Figure 2. Thawing curves of mackerel (a) and croaker (b) with various storage temperatures

Figure 3. Changes in drip loss of thawed mackerel (a) and croaker (b) depending on various freezing temperatures and storage periods. ^a-dMeans with different lowercase letters within the same storage temperature are significantly different (p< .05). ^A-CMeans with different uppercase letters within the same storage month are significantly different (p< .05)

Figure 4. Changes in water-holding capacity (WHC) of thawed mackerel (a) and croaker (b) depending on various freezing temperatures and storage periods

Table 1. Changes in the color of thawed mackerel depending on various freezing temperatures and storage periods

Color
	Storage temperature (°C)	Storage periods (months)
		Control			1			3			5			6
CIE L*	−18	34.99	±	2.05 ^c	37.44	±	1.80^bcA	42.80	±	2.19^aA	39.82	±	1.46^abA	38.81	±	2.37 ^bA
	−50	34.99	±	2.05^b	38.74	±	1.21^abA	38.76	±	0.78^abB	36.64	±	2.65^abAB	39.74	±	2.82^aA
	−60	34.99	±	2.05^ab	36.58	±	1.06^abA	37.91	±	0.91^aB	34.62	±	1.66^bB	38.06	±	2.19^aA
CIE a*	−18	3.46	±	0.54^a	0.31	±	0.32^cB	1.59	±	0.31 ^bA	1.08	±	0.33^bB	−0.29	±	0.43^cB
	−50	3.46	±	0.54^ab	2.96	±	0.34^bcA	2.05	±	0.30^cdA	3.94	±	0.42^aA	2.71	±	0.22 ^dA
	−60	3.46	±	0.54^a	0.91	±	0.29^cB	2.00	±	0.18 ^bA	0.05	±	0.18^dC	1.98	±	0.57 ^bA
CIE b*	−18	1.68	±	0.40 ^c	4.58	±	0.68 ^bA	7.55	±	0.28^aA	6.56	±	0.67^aA	5.22	±	0.99 ^bA
	−50	1.68	±	0.40^b	5.33	±	0.66^aA	5.37	±	0.38^aB	4.77	±	0.44^aB	4.68	±	0.21^aA
	−60	1.68	±	0.40^b	4.40	±	0.40^aA	4.19	±	0.26^aC	2.39	±	0.29^bC	3.70	±	0.79^aA
ΔE	−18				5.13	±	1.13 ^bA	10.02	±	1.78^aA	7.37	±	1.00^abA	6.65	±	1.81 ^bA
	−50				5.33	±	0.94^aA	5.47	±	0.75^aB	3.94	±	1.94^aB	5.96	±	2.01^aA
	−60				4.16	±	0.57^aA	4.18	±	0.48^aB	3.80	±	0.48^aB	4.24	±	1.70^aA

^a-cMeans with different lowercase letters within the same storage temperature are significantly different (p< .05).

^A-CMeans with different uppercase letters within the same storage month are significantly different (p< .05).

The CIE L*, a* and b* are the color space defined by the International Commission on Illumination.

Table 2. Changes in the color of thawed croaker depending on various freezing temperatures and storage periods

Color
	Storage temperature (°C)	Storage periods (months)
		Control			1			3			5			6
CIE L*	−18	59.59	±	2.50^a	45.46	±	2.74^cA	52.41	±	3.57^bB	59.34	±	2.50^aA	55.44	±	2.53^abA
	−50	59.59	±	2.50^a	46.42	±	1.37 ^dA	50.96	±	0.81^cB	56.32	±	2.88^abA	54.72	±	1.89 ^bA
	−60	59.59	±	2.50^a	43.70	±	1.33^cA	57.50	±	1.72^abA	55.00	±	2.40 ^bA	55.88	±	2.51^abA
CIE a*	−18	−0.69	±	0.57^b	−0.39	±	0.22^abA	0.19	±	0.49^aA	−0.55	±	0.22 ^bAB	−0.61	±	0.12 ^bA
	−50	−0.69	±	0.57^ab	−0.63	±	0.34^abA	−0.25	±	0.21^aA	−1.00	±	0.27^bB	−1.20	±	0.20^bB
	−60	−0.69	±	0.57^b	−0.73	±	0.22^bA	−0.60	±	0.41^abA	0.06	±	0.42^aA	−1.05	±	0.16^bB
CIE b*	−18	4.50	±	1.61^a	2.98	±	0.96^abA	1.24	±	1.45^bB	2.10	±	0.81 ^bA	−1.17	±	0.44^cB
	−50	4.50	±	1.61^a	3.23	±	0.54^aA	3.53	±	1.49^aAB	3.58	±	1.40^aA	2.70	±	1.21^aA
	−60	4.50	±	1.61^ab	4.18	±	0.53^abA	6.10	±	0.81^aA	2.11	±	0.88^cA	3.26	±	0.93^bcA
ΔE	−18				14.23	±	2.82^aA	8.11	±	3.41 ^bA	3.55	±	0.81^cA	7.36	±	0.84^bcA
	−50				13.24	±	1.38^aA	8.80	±	0.78 ^bA	4.31	±	1.41^cA	5.42	±	1.62^cA
	−60				15.90	±	1.34^aA	3.00	±	1.09^bB	5.42	±	2.05 ^bA	4.16	±	2.20 ^bA

^a-dMeans with different lowercase letters within the same storage temperature are significantly different (p< .05).

^A-BMeans with different uppercase letters within the same storage month are significantly different (p< .05).

Figure 5. Changes in the appearance of thawed mackerel (a) and croaker (b) depending on various freezing temperatures and storage periods. Mon, month

Figure 6. Changes in thiobarbituric acid reactive substances (TBARS) of thawed mackerel (a) and croaker (b) depending on various freezing temperatures and storage periods

Figure 7. Changes in total volatile basic nitrogen (TVBN) of thawed mackerel (a) and croaker (b) depending on various freezing temperatures and storage periods

Table 3. F-values for parameters of mackerel and croaker depending on various freezing temperatures and storage periods

Parameter	Mackerel						Croaker
	Time		Temperature		Time × Temperature		Time		Temperature		Time × Temperature
	F-value	P-value	F-value	P-value	F-value	P-value	F-value	P-value	F-value	P-value	F-value	P-value
Drip loss	312.520	<0.001	228.240	<0.001	8.009	<0.005	407.858	<0.001	74.078	<0.001	13.359	<0.001
WHC	178.724	<0.001	5.204	<0.05	0.739	NS	331.311	<0.001	2.794	NS	2.459	NS
CIE L*	5.034	<0.01	3.860	NS	0.352	NS	39.714	<0.001	0.920	NS	4.342	<0.05
CIE a*	16.498	<0.001	91.082	<0.001	27.325	<0.001	3.465	<0.05	1.186	NS	3.283	<0.05
CIE b*	49.103	<0.001	43.290	<0.001	5.241	0.005	3.405	<0.05	1.492	NS	2.360	NS
ΔE	1.052	NS	4.332	NS	0.416	NS	55.831	<0.001	1.696	NS	20.415	0.001
TBARS	114551	<0.001	14242	<0.001	5720	<0.001	389578	<0.001	714424	<0.001	255492	<0.001
TVBN	118.082	<0.001	70.165	<0.001	5.051	<0.001	277.116	<0.001	21.279	<0.001	7.645	0.001

NS, Not significant; ΔE, color difference; Time × Temperature, Influence of both time and temperature; TBARS, Thiobarbituric acid reactive substances; TVBN, Total volatile basic nitrogen; WHC, Water holding capacity.