Influence of Salting on Drying Kinetics and Water Diffusivity of Tomato Halves

Figures & data

Figure 1 Whole tomatoes (left) and flesh view (right) of the tested variety. (Colour figure available online.)

Table 1 Single-layer drying models

Model	Model expression	Reference
Newton	MR = exp(−k t)	[9]
Page	MR = exp(−k t^n )	[9]
Henderson and Pabis	MR = a exp(−k t)	[10]
Logarithmic	MR = a exp(−k t) + c	[11]
Two term	MR = a exp(−ko t) + b exp(−k 1 t)	[12]
Wang and Singh	MR = 1 + a t + b t ^2	[13]
Mod. Henderson and Pabis	MR = a exp(−k t) + b exp(−g t) + c exp(−h t)	[14]

Figure 2 Drying rate of the tomato halves.

Figure 3 Evaluation of D_eff with the method of slopes: (a) non-salted and (b) salted.

Figure 4 Forced convection drying oven (BINDER GmbH, Tuttlingen, Germany). In A and B, points were suspended to temperature and relative humidity sensors.

Figure 5 Volume variation of whole tomatoes with mass (points = experimental values, solid line = estimated values from Eq. 6).

Table 2 Measured characteristics of whole tomatoes

	Peel colour
				Internal	Brix	Acidity	Mdb	Dry	Density
Lot	L*	a*	b*	appearance	(%)	(%)		matter (g)	(kg m^−3)
1st	41 ± 2	32 ± 4	20 ± 3	M−3 to M−4	5.3 ± 0.9	0.9 ± 0.1	10 ± 2	2.1 ± 0.4	1,007 ± 19
2nd	40 ± 2	26 ± 4	19 ± 4	M−3 to M−4	4.0 ± 0.8	1.1 ± 0.3	17 ± 1	1.8 ± 0.2	1,046 ± 12
Notes: The M−3 stage = Seeds pushed aside when tomato sliced; all locules have gel; internal colour is still green; M−4 stage = Appearance of red colour in gel and pericarp tissue.[29]

Figure 6 Volume variation during drying of tomato halves with the respective moisture content.

Table 3 Parameters of Eq. (6) for the different drying cases

	Drying temperature (°C)	a	b
Non-salted tomatoes	45	0.988	0.521	0.985
	55	1.008	1.613	0.988
	65	0.877	1.289	0.992
Salted tomatoes	45	0.744	0.987	0.991
	55	0.996	1.389	0.993
	65	1.026	3.572	0.991

Table 4 Regression analysis coefficients of the Logarithmic drying model

Relaxation
Case	a	k (h ^−1)	c	time (h)		SEE	χ^2
Non-salted tomatoes
45°C	1.064	0.020	−0.049	49.07	0.999	0.009	0.006
55°C	1.072	0.030	−0.061	32.99	0.999	0.008	0.005
65°C	1.202	0.039	−0.189	25.31	0.999	0.005	0.001
Salted tomatoes
45°C	1.045	0.029	−0.012	34.99	0.998	0.013	0.013
55°C	1.047	0.035	−0.031	28.69	0.999	0.006	0.003
65°C	1.099	0.048	−0.091	20.72	0.999	0.008	0.003

Table 5 Single-layer drying models that have been used for tomato drying

Tomato geometry	Chosen drying model	Statistical parameters	References
Halves (Santorini), re  = 0.015 ± 0.001 m	Logarithmic[11]	R ^2 = 0.998, RMSE = 0.013 (salted)	Present study
		R ^2 = 0.998, RMSE = 0.013 (non-salted)
Halves, de  = 0.050 ± 0.002 m	Page[34]	R ^2 = 0.994–0.998, χ^2 = 0.0001–0.0008	[2]
Slices (organic), 1 kg	Logarithmic[11]	R ^2 = 0.996–0.997, RMSE = 0.017–0.021 (untreated)	[6]
		R ^2 = 0.994–0.997, RMSE = 0.0002–0.0003 (blanched)
Halves, de  = 0.058 m	Middili et al.[35]	R ^2 = 0.999, RMSE = 0.008	[4]
Halves (cv Milen), 250 g	Logarithmic[11]	R ^2 = 0.999	[3]
Slices (cv Olympian Gold), thickness = 4, 6, 8 mm	Page[34]	R ^2 = 0.983–0.987, RMSE = 0.025–0.027 (solar cabinet dryer)	[8]
		R ^2 = 0.946–0.983, RMSE = 0.001–0.004 (open sun drying)
Halves (organic, cv Milen)	Approximation of diffusion[11]	R ^2 = 0.969, RMSE = 0.01, χ^2 = 3.14 10^−3	[7]

Figure 7 Drying curves of tomato halves (points = experimental values, solid lines = theoretical values).

Figure 8 Experimental and predicted k values from Eqs. (8a) and (8d).

Table 6 Estimated D_{ef f} values for tomato drying

Tomato geometry	Modelgeometry		Estimated Deff (m^2 s^−1)	Activation energy Ea (kJ mol^−1)	References
Halves (Santorini),	Slab	With shrinkage	45°C, (1.3 ± 0.5)^.10^−10 (salted); (1.1 ± 0.3)^.10^−10 (non-salted)	46.8 (non-salted)	Present study
re  = 0.016 ± 0.001 m			55°C, (1.9 ± 0.6)^.10^−10 (salted); (1.9 ± 0.4)^.10^−10 (non-salted)	56.3 (salted)
			65°C, (4.0 ± 1.2)^.10^−10 (salted); (3.2 ± 0.8)^.10^−10 (non-salted)
		Without shrinkage	45°C, (3.3 ± 0.9)^.10^−10 (salted); (2.9 ± 1.1)^.10^−10 (non-salted)	40.3 (non-salted)
			55°C, (4.4 ± 1.8)^.10^−10 (salted); (4.2 ± 1.6)^.10^−10 (non-salted)	45.9 (salted)
			65°C, (7.5 ± 3.7)^.10^−10 (salted); (7.4 ± 3.9)^.10^−10 (non-salted)
Halves, re = 0.016 m	Slab	110°C, 40.1^.10^−10			[1]
		80°C, 22.6^.10^−10
Halves, de  = 0.050 ± 0.002 m	Slab	55°C, 5.65 10^−10 pretreated,	3.91 10^−10 untreated	17.40 (pretreated)	[2]
		60°C, 6.11 10^−10 pretreated,	4.91 10^−10 untreated	32.94 (untreated)
		65°C, 6.56 10^−10 pretreated,	5.78 10^−10 untreated
		70°C, 7.53 10^−10 pretreated,	6.65 10^−10 untreated
Slices (organic), 1 kg	Slab	50°C, 1.68 10^−06 untreated,	1.80 10^−06 blanched	21.10 (untreated)	[6]
		60°C, 1.91 10^−06 untreated,	2.18 10^−06 blanched	22.41 (blanched)
		70°C, 2.73 10^−06 untreated,	2.84 10^−06 balanched
Halves, de  = 0.0582 m	Slab	44.9–64.3°C, 92.2 10^−10–216 10^−10		37.72	[4]
Halves (Milen), 250 g	Slab	50°C, 25.6 10^−10 untreated,	42.9 10^−10 blanched	23.73 (untreated)	[3]
		60°C, 34.8 10^−10 untreated,	51.1 10^−10 blanched	17.55 (blanched)
		70°C, 42.8 10^−10 untreated,	62.8 10^−10 blanched
Halves(organic, Milen)	Slab	13.1 10^−10 (solar tunnel), 10.7 10^−10 (open sun)			[7]
Slices (Olympian Gold), thickness = 4, 6, 8 mm	Slab	4.25–7.67 10^−07 (solar cabinet drying), 30.9–92.8 10^−10 (open sun drying)			[8]
Slices (Roma), 15 mm thickness	Slab	45–75°C, 37.2 10^−10–122.7 10^−10			[5]

Figure 9 Experimental (points) and predicted (dotted line: salted; continuous line: non-salted) D_eff values for tomato halves with and without the shrinkage effect.

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