Air Drying Behaviour of Fresh and Osmotically Dehydrated Onion Slices (Allium cepa) and Tomato Fruits (Lycopersicon esculentum)

Figures & data

Figure 1 Drying curves of onion slices from different osmotic pre-treatments.

Figure 2 Drying curves of tomato from different osmotic pre-treatments.

Table 1 Equilibrium moisture contents (g H₂0.g⁻¹ DM) of dried, fresh, and osmosed onion slices and tomato.

	Osmotic solution
	NaCl solution	Sucrose solution	Mixed solution
Osmotic pre-treatment		Onion slices
Untreated		0.34 ± 0.16
5 min	0.42 ± 0.04	0.42 ± 0.12	0.35 ± 0.05
10 min	0.29 ± 0.05	0.27 ± 0.04	0.39 ± 0.04
15 min	0.18 ± 0.05	0.20 ± 0.06	0.31 ± 0.05
30 min	0.11 ± 0.04	0.15 ± 0.04	0.25 ± 0.07
60 min	0.12 ± 0.07	0.15 ± 0.07	0.29 ± 0.08
120 min	0.18 ± 0.05	0.23 ± 0.08	0.24 ± 0.03
		Tomato
Untreated		0.01 ± 0.00
5 h	0.02 ± 0.00	0.02 ± 0.00	0.02 ± 0.00
10 h	0.04 ± 0.01	0.02 ± 0.01	0.02 ± 0.00
20 h	0.12 ± 0.02	0.13 ± 0.02	0.10 ± 0.03
40 h	0.08 ± 0.01	0.09 ± 0.02	0.04 ± 0.00
60 h	0.03 ± 0.01	0.26 ± 0.01	0.01 ± 0.00
80 h	0.03 ± 0.01	0.20 ± 0.01	0.01 ± 0.00

Figure 3 Drying rate curves for onion slices from different osmotic pre-treatments.

Figure 4 Drying rate curves for tomato from different osmotic pre-treatements.

Table 2 Drying constants k₁ and k₂, during the air drying of onion slices as a function of osmotic pre-treatment time and solution.

	Osmotic solution
	NaCl solution		Sucrose solution		Mixed solution
Osmotic pre-treatment	k1 (h^−1)	k2 (h^−1)	k1 (h^−1)	k2 (h^−1)	k1 (h^−1)	k2 (h^−1)
Untreated	0.25		0.25		0.25
5 min	0.52	0.27	0.44	0.08	0.36	0.20
10 min	0.44	0.17	0.40	0.10	0.30	0.16
15 min	0.51	0.11	0.49	0.09	0.33	0.25
30 min	0.43	0.15	0.41	0.08	0.48	0.26
60 min	0.39	0.12	0.33	0.11	0.37	0.20
120 min	0.33	0.17	0.42	0.10	0.36	0.20
Mean	0.44	0.16	0.42	0.09	0.37	0.21

Table 3 Drying constants k₁ and k₂, during the air drying of tomato fruits as a function of osmotic pre-treatment time and solution.

	Osmotic solution
	NaCl solution		Sucrose solution		Mixed solution
Osmotic pre treatment	k1 (h^−1)	k2 (h^−1)	k1 (h^−1)	k2 (h^−1)	k1 (h^−1)	k2 (h^−1)
Untreated	0.15	0.03	0.15	0.03	0.15	0.03
5 h	0.24	0.05	0.16	0.04	0.10	0.04
10 h	0.32	0.09	0.14	0.03	0.07	0.01
20 h	0.10	0.06	0.10	0.04	0.06	0.01
40 h	0.14	0.05	0.20	0.04	0.09	0.02
60 h	0.08	0.05	0.44	0.06	0.13	0.01
80 h	0.04		0.43	0.06	0.24

Figure 5 Changes in apparent moisture diffusivity in onion slices as a function of residual moisture content during the drying process.