Changes in protein compositions and textural properties of the muscle of skate fermented at 10°C

Figures & data

Figure 1. Changes in pH (a), ammonia nitrogen (b), TVBN (c), TMAN (d) and TCA-soluble peptides (e) content of skate muscle during fermentation. Bars represent standard deviation from three determinations. ^a–hMeans followed by different letters are significantly different (p < 0.05)

Table 1. Textural profiles analysis in skate muscle during fermentation

Fermentation time (days)	Hardness (N)	Springiness	Gumminess (N)	Chewiness (N)	Cohesiveness
0	0.65 ± 0.01^a	0.26 ± 0.04^ab	0.76 ± 0.08^ab	0.24 ± 0.01^a	1.42 ± 0.01^a
2	0.48 ± 0.05^b	0.28 ± 0.03^a	0.70 ± 0.28^ab	0.18 ± 0.02^ab	1.28 ± 0.06^ab
4	0.53 ± 0.03^ab	0.24 ± 0.06^ab	0.62 ± 0.08^b	0.13 ± 0.02^b	1.19 ± 0.03^bc
6	0.59 ± 0.02^ab	0.21 ± 0.01^ab	0.59 ± 0.11^b	0.14 ± 0.06^b	1.02 ± 0.01^c
8	0.52 ± 0.05^b	0.20 ± 0.03^ab	0.62 ± 0.01^b	0.12 ± 0.03^b	0.65 ± 0.14^d
10	0.48 ± 0.07^b	0.17 ± 0.01^b	0.82 ± 0.07^a	0.14 ± 0.02^b	0.53 ± 0.13^d
12	0.47 ± 0.05^b	0.18 ± 0.04^b	0.68 ± 0.11^ab	0.16 ± 0.05^ab	0.63 ± 0.10^d
14	0.54 ± 0.07^ab	0.20 ± 0.04^ab	0.76 ± 0.06^ab	0.16 ± 0.06^ab	0.57 ± 0.03^d

^a-d Means with different superscripts in the same column indicate significant differences (p < 0.05).

Figure 2. Fractions of each protein in skate muscle during fermentation

^a–g Different letters at the tops of the bars indicated significant differences during fermentation (p < 0.05).

Figure 3. SDS-PAGE patterns of myofibrillar proteins (a), sarcoplasmic proteins (b), and alkali-soluble proteins (c) from skate muscle during fermentation

Table 2. Changes in free amino acid content of skate muscle during fermentation

Free amino acids (mg/100 g)	Fermentation time (day)
	0	5	10	14
Phosphoserine	3.80 ± 0.01^c	3.00 ± 0.15^d	7.52 ± 0.46^b	9.29 ± 0.07^a
Taurine	60.40 ± 0.16^a	60.18 ± 0.85^a	58.00 ± 0.66^b	43.84 ± 0.09^c
Aspartate	1.13 ± 0.05^b	2.06 ± 0.11^a	0.30 ± 0.04^d	0.49 ± 0.01^c
Threonine	25.23 ± 0.29^b	39.62 ± 1.37^a	15.47 ± 6.29^c	6.77 ± 0.10^d
Serine	37.27 ± 0.32^a	17.40 ± 0.44^b	3.21 ± 0.64^c	2.04 ± 0.04^d
Glutamate	33.46 ± 0.56^a	10.52 ± 0.28^b	10.49 ± 0.35^b	8.09 ± 0.01^c
Sarcosine	71.79 ± 0.26^b	83.00 ± 3.12^a	67.87 ± 0.88^c	64.83 ± 0.22^d
α-Aminoadipic acid	4.59 ± 0.01^a	2.39 ± 0.10^c	4.60 ± 0.11^a	4.23 ± 0.01^b
Glycine	32.84 ± 0.42^d	34.47 ± 0.86^c	40.24 ± 0.86^b	43.20 ± 0.08^a
Alanine	38.18 ± 0.42^b	35.81 ± 11.53^c	47.13 ± 1.54^a	31.01 ± 0.01^d
Citrulline	7.83 ± 0.01^b	8.67 ± 0.35^a	5.75 ± 0.13^c	5.19 ± 0.14^d
α-Aminobutyric acid	2.58 ± 0.01^b	1.48 ± 0.03^d	3.84 ± 0.16^a	2.70 ± 0.05^c
Valine	14.06 ± 0.28^a	11.95 ± 0.31^b	13.67 ± 0.93^a	11.18 ± 0.06^c
Cysteine	1.02 ± 0.03^b	0.68 ± 0.01^c	3.79 ± 0.18^a	3.89 ± 0.12^a
Methionine	9.73 ± 0.34^a	7.81 ± 0.25^b	5.79 ± 0.70^d	7.03 ± 0.11^c
Cystathionine	2.89 ± 0.01^a	2.95 ± 0.04^a	2.14 ± 0.04^b	1.99 ± 0.06^c
Isoleucine	9.82 ± 0.26^a	6.85 ± 0.13^b	4.60 ± 0.49^c	4.17 ± 0.06^c
Leucine	17.35 ± 0.54^a	12.63 ± 0.39^b	12.34 ± 1.62^b	12.46 ± 0.08^b
Tyrosine	6.91 ± 0.12^a	5.96 ± 0.16^b	3.14 ± 0.37^c	3.22 ± 0.02^c
Phenylalanine	11.56 ± 0.39^a	7.53 ± 0.25^b	6.90 ± 1.18^b	7.46 ± 0.02^b
β-Aminopropionic acid	164.40 ± 0.32^b	186.70 ± 6.33^a	147.38 ± 2.05^c	120.43 ± 0.08^d
β-Aminoisobutyric acid	1.00 ± 0.01^b	1.81 ± 0.08^a	0.88 ± 0.06^c	0.62 ± 0.01^d
γ-Aminobutyric acid	0.46 ± 0.01^c	0.58 ± 0.01^b	0.77 ± 0.10^a	0.47 ± 0.02^c
Ethanolamine	3.51 ± 4.27^d	6.39 ± 0.14^c	7.52 ± 0.26^b	8.28 ± 0.02^a
Ammonium	113.64 ± 1.55^c	183.52 ± 4.28^a	107.08 ± 0.63^d	116.60 ± 1.13^b
Hydroxylysine	0.46 ± 0.01^c	1.19 ± 0.02^b	0.43 ± 0.04^d	2.91 ± 0.09^a
Ornithine	26.13 ± 0.21^a	27.89 ± 0.91^a	19.50 ± 0.86^b	19.10 ± 0.08^b
Lysine	29.00 ± 0.47^a	28.78 ± 0.78^b	19.60 ± 1.03^d	21.98 ± 0.04^c
Histidine	5.52 ± 0.13^a	5.15 ± 0.17^b	2.36 ± 0.31^c	2.71 ± 0.01^c
3-Methylhistidine	0.24 ± 0.02^c	0.27 ± 0.01^c	0.42 ± 0.17^b	0.62 ± 0.35^a
Anserine	1.85 ± 0.11^b	1.80 ± 0.11^b	1.27 ± 0.11^c	3.18 ± 0.32^a
Carnosine	1.03 ± 0.07^d	1.73 ± 0.06^c	1.86 ± 0.16^b	1.93 ± 0.04^a
Arginine	1.33 ± 0.18^b	1.44 ± 0.09^b	2.20 ± 0.21^a	2.63 ± 0.21^a

^a Means with different superscripts in the same column indicate significant differences (p < 0.05).

Figure 4. Principal compound analysis of some parameters related to different protein fractions of skate muscle. MFN: Myofribrillar fraction nitrogen, SPN: Sarcoplasmic protein nitrogen, NPN: Non-protein nitrogen, ASN: Alkali-soluble protein nitrogen, TSP: TCA-soluble peptide