Assessment of the physico-chemical and sensory properties of frozen fillets of tuna and tuna-related fish species marketed along the Tanga and Mtwara coastlines, Tanzania

Figures & data

Table

Whereas;	Distillation parameters:
TVB-N = Total Volatile Basic Nitrogen (mg/100 g) NHCL = Normality of HCl (mol/1000 mL) Vs = Consumption mol/lHCl sample (mL) Vb = Consumption mol/lHCl blank (mL)	Variable	Specification	Requirement
	NaOH	40%	30mls
	Boric Acid	4%	25mls
	Steam	100%	4.5 minutes
	Water	Distilled	30mls

Figure 1. CIE L*a*b* color space: source: Konica Minolta.

Table 1. Tuna fillets sensory quality attributes (descriptors).

SPECIES	INDEX	1-HIGH QUALITY	2-GOOD QUALITY	3-POOR QUALITY
Yellow Fin	Color	Translucent pale reddish color	Brownish-yellow	Dark brown, very opaque green gray
	Texture	Firm and elastic (springs back quickly on pressing)	Firm, reduced elasticity, flesh soft (doesn’t spring back fully on pressing).	Very soft mushy, flesh falling away from the carcass, fingerprints leave impressions
	Odor	No fish smell, neutral, and fresh.	Definite fish smell, stale, slightly brine and fishy oxidized caramel	Very stale, very sour, putrid, very rancid and ammonia, fuel.
Skipjack	Color	Translucent, shiny	Dark red-brownish, Pale pink, light green, iridescent	Dark brown, gray-green, dark green, opaque, cooked appearance
	Texture	Firm and elastic (springs back quickly on pressing)	Firm, reduced elasticity, flesh soft (doesn’t spring back fully on pressing).	Very soft mushy, flesh falling away from the carcass, fingerprints leave impressions
	Odor	Game, meaty, seaweed neutral	Oxidized, stale, caramelized, slightly rancid, persistent sour. heavy brine, fruity	Putrid rancid, very stale, pungent, sour, fermented, fruity fecal, sweet cheesy acid, ammonia, fuel.
Bigeye	Color	Bright Red, reddish-pinkish fillets	Dark-red, Reddish-brown, brownish not translucent	Very opaque green-gray, red-pink, honeycomb, curdy (feverish) gray color
	Texture	Firm and elastic (springs back quickly on pressing).	Firm, reduced elasticity, flesh soft (doesn’t spring back fully on pressing).	Very soft mushy, flesh falling away from the carcass, fingerprints leave impressions
	Odor	No fish smell, fresh, neutral, slightly seaweedy.	Definite fish smell, light stinky, sweetish, sour, slightly rotten off-odors	Pronounced putrid, rotten, stinking, sulfide, strong off-odors
Kawakawa	Color	Brownish translucent, shiny	Pale pink, Dark red, slight green, iridescent pink-greenish	Dark-brown, gray-green, dark green opaque, honeycomb
	Texture	Firm and elastic (springs back quickly on pressing).	Firm, reduced elasticity, flesh soft (doesn’t spring back fully on pressing).	Very soft mushy, flesh falling away from the carcass, fingerprints leave impressions
	Odor	No fish smell, light, neutral, sourish, slight seaweedy fresh odor	Definite fish smell, light stinky, sweetish, sour and slightly rotten off-odors	Pronounced putrid, rotten, stinking, sulfide strong off-odors

Table 2. Average pH, TVBN, color, texture (hardness), and sensory results.

Fish Species	PH	TVBN	Color lightness properties			Texture (hardness) (N)	Sensory
			L*	a*	b*		Texture (hardness)	Color	Odor
Skipjack	6.10 ± 0.30	38.04 ± 10.50	24.33 ± 1.82	6.00 ± 1.20	3.20 ± 0.80	3.84 ± 1.20	2.40 ± 0.60	2.70 ± 0.50	2.50 ± 0.51
Bigeye	6.02 ± 0.33	34.00 ± 7.00	33.42 ± 2.81	4.70 ± 1.10	2.90 ± 1.40	5.40 ± 1.72	1.80 ± 0.60	1.54 ± 0.51	2.30 ± 0.50
Yellowfin	5.60 ± 0.08	36.01 ± 3.94	40.10 ± 1.50	4.80 ± 1.40	3.80 ± 1.20	8.60 ± 1.84	1.00 ± 0.00	1.00 ± 0.00	2.00 ± 0.00
Kawakawa	6.10 ± 0.20	37.00 ± 4.00	25.60 ± 1.84	7.50 ± 1.20	3.50 ± 0.91	5.01 ± 1.34	1.70 ± 0.50	2.40 ± 0.50	2.50 ± 0.51
Total	6.03 ± 0.30	36.11 ± 7.80	29.00 ± 6.00	5.80 ± 1.60	3.20 ± 1.11	5.00 ± 2.00	1.90 ± 0.64	2.10 ± 0.74	2.40 ± 0.50
Sampling Point
Fish landing site	6.12 ± 0.24	36.32 ± 8.50	26.74 ± 3.70	6.11 ± 1.60	3.20 ± 1.00	4.62 ± 1.60	2.00 ± 0.64	2.40 ± 0.60	2.50 ± 0.50
Market Samples	5.80 ± 0.30	35.50 ± 4.60	35.82 ± 4.51	5.00 ± 1.40	3.20 ± 1.50	6.20 ± 2.20	1.61 ± 0.61	1.20 ± 0.40	2.10 ± 0.23
Total	6.03 ± 0.30	36.11 ± 7.80	29.00 ± 5.51	5.83 ± 1.61	3.20 ± 1.11	5.00 ± 1.90	1.90 ± 0.64	2.10 ± 0.74	2.40 ± 0.50

Table 3. Tuna fillets Post Hoc Turkey’s b test results.

	PH		TVBN	Color lightness properties (L*)			Color a* Redness			Instrumental Texture (hardness)		Sensory Color			Sensory Texture (hardness)			Sensory Odor
Fish Species	Subset for alpha = 0.05		Subset for alpha = 0.05	Subset for alpha = 0.05			Subset for alpha = 0.05			Subset for alpha = 0.05		Subset for alpha = 0.05			Subset for alpha = 0.05			Subset for alpha = 0.05
	1	2	1	1	2	3	1	2	3	1	2	1	2	3	1	2	3	1
Yellowfin	5.6		36.01			40.09	4.82				8.60	1			1			2
Bigeye		6.02	33.90		33.42		4.70			5.40			1.54			1.80		2.30
Kawakawa		6.07	37.00	25.60					7.50	5.01				2.40		1.70		2.50
Skipjack		6.10	38.04	24.33				6.00		3.84				2.70			2.40	2.50

Table 4. Correlations physico-chemical and sensory quality properties.

		Color L*	Moisture	PH	Color a*	Sensory Color	Sensory Odor	Instrumental Texture	TVB-N	Sensory Texture
Color lightness properties (L*)	Pearson Correlation	1	0.001	−0.483**	−0.479**	−0.905**	−0.377**	0.434**	−0.196	−0.307**
	Sig. (2-tailed)		0.993	0.000	0.000	0.000	0.001	0.000	0.111	0.008
Moisture	Pearson Correlation	0.001	1	0.103	0.031	−0.001	0.006	0.073	0.043	−0.041
	Sig. (2-tailed)	0.993		0.388	0.796	0.992	0.961	0.541	0.732	0.732
PH	Pearson Correlation	−0.483**	0.103	1	0.218	0.427**	0.566**	−0.180	0.249*	0.132
	Sig. (2-tailed)	0.000	0.388		0.063	0.000	0.000	0.128	0.042	0.266
Redness	Pearson Correlation	−0.479**	0.031	0.218	1	0.388**	0.165	−0.087	0.151	0.040
	Sig. (2-tailed)	0.000	0.796	0.063		0.001	0.163	0.466	0.223	0.735
Sensory Color	Pearson Correlation	−0.905**	−0 .001	0.427**	0.388**	1	0.300**	−0.342**	0.164	0.225
	Sig. (2-tailed)	0.000	0.992	0.000	0.001		0.010	0.003	0.186	0.055
Sensory Odor	Pearson Correlation	−0.377**	0.006	0.566**	0.165	0.300**	1	−0.232*	00.189	0.192
	Sig. (2-tailed)	.001	0.961	0.000	0.163	0.010		0.048	.125	0.104
Texture (hardness)	Pearson Correlation	0.434**	0.073	−.0180	−0.087	−0.342**	−0.232*	1	−0.263*	−0.807**
	Sig. (2-tailed)	0.000	0.541	0.128	0.466	0.003	0.048		0.032	0.000
TVB-N	Pearson Correlation	−0.196	0.043	0.249*	0.151	0.164	0.189	−0.263*	1	0.176
	Sig. (2-tailed)	0.111	0.732	0.042	0.223	0.186	0.125	0.032		0.154
Sensory Texture (hardness)	Pearson Correlation	−.307**	−0.041	0.132	0.040	0.225	0.192	−0.807**	0.176	1
	Sig. (2-tailed)	0.008	0.732	0.266	0.735	0.055	0.104	0.000	0.154

**Correlation is significant at the 0.01 level (2-tailed).

*Correlation is significant at the 0.05 level (2-tailed).