Salt and moisture content determination of fish by bioelectrical impedance and a needle-type multi-electrode array

Figures & data

Figure 1. Needle-type multi electrode array (12 gold-plated needles arranged in 2 rows of 6 electrically connected needles).

Table 1. Physicochemical analysis of the epaxial muscle of the rainbow trout samples (N = 52) after wet salting up to 6 hours.

Duration of salting		Parameter
		ΔM* (g)	L*	a*	b*	Moisture (g/100 g)	NaCl (g/100 g)	WPS**
2h	N	20	20	20	20	20	20	20
	Min./Max.	−7.22/−2.73	64.74/79.41	1.92/3.80	17.74/22.29	72.2/73.20	5.5/5.8	7.00/7.40
	Average ± st. deviation	−4.52 ± 1.03	72.13 ± 3.63	2.88 ± 0.45	20.53 ± 1.36	72.7 ± 0.30	5.68 ± 0.10	7.20 ± 0.10
4h	N	19	20	20	20	20	20	20
	Min./Max.	−7.60/−3.33	61.04/74.50	0.85/1.10	7.79/19.57	70.70/72.20	6.30/6.90	8.10/8.80
	Average ± st. deviation	−6.09 ± 1.08	67.56 ± 3.88	0.16 ± 0.49	14.01 ± 3.15	71.4 ± 0.40	6.70 ± 0.20	8.50 ± 0.20
6h	N	12	12	12	12	12	12	12
	Min./Max.	−10.38/-6.46	55.42/63.56	0.06/1.13	11.09/13.67	69.0/69.90	8.70/9.00	11.10/11.40
	Average ± st. deviation	−7.93 ± 1.10	60.70 ± 2.37	0.63 ± 0.34	12.13 ± 0.97	69.50 ± 0.30	8.80 ± 0.10	11.20 ± 0.10
Statistical significance (p<0.05)		+	+	+	+	+	+	+

*differences in the average weight values.

**WPS - water phase salt.

Table 2. Principal component analysis (PCA) of the impedance module (|Z|) and phase (φ) spectra measured at 150 frequencies (5 kHz–100 MHz) on trout samples subjected to wet salting up to 6 hours at 25% (w/w) brine (F1, F2, F3, and F4 are the symbols of the PCs used for the regression models, as the number of the predictors per 60 observations should maximally be four).

Extracted PCs	% variance extracted by the PC	Original variables extracted in the PC (“loading of the PC”)
Phase PC1 (F1)	41.32	φ (180 kHz–10 MHz)
Phase PC2 (F2)	33.27	φ (5 kHz–114 kHz)
Phase PC3	13.01	φ (11–100 MHz)
Phase PC4	8.89	φ (140–178 kHz)
Imp PC1 (F3)	85.20	|Z|(5 kHz–10 MHz)
Imp PC2 (F4)	14.26	|Z|(11–100 MHz)

Table 3. Linear/multiple regression analysis for prediction of WPS (water phase salt) of the rainbow trout samples based upon their electrical properties.

Model	Predictor(s)	Model summary				ANOVA	Coefficients
		R	R^2	AdR^2*	SEE**		Model	Unstandardized B /st. error (bootstrapped)	Standardized Beta	Sig.	Zero-order correlations	Part correlations
A1***	F1, F2, F3 and F4 calculated by the PCA (Table 2)	0.937	0.870	0.867	1.205	F(4.55) =90.436 P < 0.001	constant	7.523/0.164		.000
							F1	−.209/0.180	.159	.193	.060	−.065
							F2	.217/0.334	.185	.244	−.403	.058
							F3	−3.015/0.286	.185	.000	−.898	−.796
							F4	.739/0.112	.158	.000	.232	.230
A2***	F3 and F4 calculated by the PCA	0.928	0.861	0.856	1.217	F(2.57) = 175.816 P < 0.001	constant	7.523/0.158		.000
							F3	−2.878/0.178	−.899	.000	−.899	−.899
							F4	−.736/0.117	−.230	.000	−.230	−.230
A3***	F3 calculated by the PCA	0.899	0.808	0.804	1.418	F(1.58)= 243.503 P < 0.001	constant	7.523/0.181		.000
							F3	−2.878/0.196	−.899	.000	−.899	−.899
B****	Selected frequency range of |Z|and φ	.921	.848	.842	1.272	F(2.57) =158.464 P < 0.001	constant	8.800/0.532		.000
							φ(10–30M)	−.462/0.088	−.216	.000	−.479	−.205
							|Z|(5–10k)	−.093/0.008	−.829	.000	−.897	−.786
C1*****	|Z|at 50 kHz	.942	.888	.864	1.341	F(1.58)= 278.586 P < 0.001	constant	10.948/0.274		.000
							Z at 50 kHz	−.106/0.000	−.910	.000	−.910	−.910
C2*****	|Z|at 10 MHz; φ at 30 MHz	.939	.882	.878	1.119	F(2.57) =213.074 P < 0.001	constant	8.957/0.423		.000
							φ-30MHz	−.322/0.006	−.251	.000	−.595	−.226
							|Z|−10MHz	−.117/−0.001	−.804	.000	−.911	−.726

*AdR² – adjusted R².

**SEE- standard error of estimate;

***Models A: predictors used are obtained by the PCA analysis.

****Model B: predictors used are average values of the selected frequency ranges.

*****Models C: predictor is the impedance module (and phase) measured at one or two frequencies.

Table 4. Linear/multiple regression analysis for prediction of moisture and salt of the rainbow trout samples based upon their electrical properties.

		Model summary					Coefficients
Model*	Predictor(s)	R	R^2	AdR^2**	SEE***	ANOVA	Model	Unstandardized B /st .error (bootstrapped)	Standardized Beta	Sig.	Zero-order correlations	Part correlations
C1 moisture	|Z|at 50 kHz	.920	.847	.844	1.040	F(1.58)=259.048 P < 0.001	constant	69.698/0.204		.000
							|Z|at 50 kHz	.079/0.005	.904	.000	.904	.904
C2 moisture	|Z|at 10 MHz; φ at 30 MHz	.934	.873	.869	0.874	F(2.57) =195.913 P < 0.001	constant	71.235/0.320		.000
							φ-30MHz	.249/0.035	.257	.000	.598	.232
							|Z|-10MHz	.087/0.007	.795	.000	.905	.718
C1 salt	|Z|at 50 kHz	.925	.856	.853	1.054	F(1.58) = 275.437 P < 0.001	constant	8.561/0.208		.000
							|Z|at 50 kHz	−.083/0.005	−.909	.000	−.909	−.909
C2 salt	|Z|at 10 MHz; φ at 30 MHz	.938	.881	.877	.881	F(2.57) = 210.458 P < 0.001	constant	6.997/0.331		.000
							φ-30MHz	−.253/0.035	−.252	.000	−.596	−.227
							|Z|-10MHz	−.092/0.008	−.803	.000	−.911	−.725

*Models C: predictor is the impedance module (and phase) measured at one or two frequencies.

**AdR² – adjusted R^2.

***SEE- standard error of estimate.