Color and Microstructure Properties of Tomatoes Dried by Microwave, Convective, and Microwave-Convective Methods

Figures & data

TABLE 1 The effects of drying treatments on the drying parameters of tomato samples

Drying method	Drying time (min)	Average drying rate (g water/g dry matter/min)	Energy consumption (kWh)	Percent improvement in drying time (compared with 50°C)
Convective drying
50°C	1370 a	0.01 f	3.44 a	—
75°C	780 c	0.02 e	3.00 b	43.07
Microwave drying
90W	1060 b	0.02 e	2.61 c	22.63
160W	360 e	0.04 d	1.83 e	73.72
350W	120 h	0.09 a	1.07 g	91.24
500W	80 h	0.13 b	0.94 g	94.16
Microwave-convective drying
90W-50°C	580 d	0.02 e	2.19 d	57.66
90W-75°C	360 e	0.04 d	1.94 e	73.72
160W-50°C	280 f	0.04 d	1.42 e	79.56
160W-75°C	200 g	0.06 c	1.36 f	85.40

Different letters of the alphabet in the same column differ significantly (P ≤ 0.01).

FIGURE 1 Drying curves of tomato samples at (A) different convective temperatures, (B) microwave power levels, and (C) microwave-convective combinations.

FIGURE 2 The effects of different drying methods (

Fresh,, 

50°C,, 

75°C,, 

90W,, 

160W,, 

350W,, 

500W,, 

90W-50°C,, 

90W-75°C,, 

160W-50°C, and, 

160W-75°C) on color values (L* (A), a* (B), b* (C), C (D), and α (E)) of tomatoes. Bars with different letters are significantly different (P ≤ 0.01).

FIGURE 3 Scanning electron micrographs of fresh and dried tomato samples: convective drying at (A) 50°C and (B) 75°C; (C) microwave drying at 90W, (D) 160W, (E) 350W, and (F) 500W; and microwave-convective drying at (G) 90W-50°C, (H) 90W-75°C, (I) 160W-50°C, and (J) 160W-75°C.