Application of electrical bio-impedance for the evaluation of strawberry ripeness

Figures & data

Figure 1. Schematic diagram of the device used for measuring strawberry ripeness by electrical bio-impedance.

Figure 2. Nyquist plot of the impedance spectrum (Re [Z] versus Im [Z]), left; single-dispersion Cole model, right.

Table 1. Lightness (L*), firmness (Fx), resistance (R_∞), and homogeneity degree (CPE-P) of the strawberries¹.

Ripeness degree	Lightness (L*; %)	Firmness (Fx; Newtons)	Resistance (R∞; ohms)	CPE-P
2	65^a ± 5	8^x ± 2	240^i ± 30	0.80^a ± 0.01
4	54^b ± 4	6^y ± 2	220^ii ± 20	0.80^a ± 0.01
6	37^c ± 3	3^z ± 1	170^iii ± 20	0.70^b ± 0.01

¹Values represent the mean ± SD of 50 fruits at each stage of ripeness (the two sizes combined).

^{(a,b,c), (x,y,z)}, and ^(i,ii,iii) indicate statistically significant differences.

Table 2. Classification matrix of the discriminant analysis of the previously established and predicted ripeness stages (2, 4, and 6; from least to most ripe) according to the bio-impedance variables (CPE-P, R_0, and R_∞).

		Predicted categories
		2	4	6
Ripeness stages	2	65.0%	35.0%	0.0%
	4	32.5%	67.5%	0.0%
	6	0.0%	0.0%	100.0%

Figure 3. Dispersion diagram of the discriminant analysis of the three ripeness stages (2, 4, and 6; from least to most ripe) according to CPE-P and R_∞ (ohms) values.