Drying method

Fig. 1 Effect of microwave drying on _E values of bread crumbs. ^∗ Means bars containing different letters are significantly different

(p≤0.05)
	25
		a	a	a
		a	a
	20
	b*
∆E	15
∆E
	10
	5
	0
	conventional	30% halogen only	50% halogen only	70% halogen only

Drying method

Fig. 2 Effect of infrared drying on _E values of bread crumbs. ^∗ Means bars containing different letters are significantly different (p≤0.05)

Beaudry et al. [6] might have occurred and this might have influenced browning reactions in a way that gave different _E values. In addition, different results might be a conse-quence of using different drying conditions. Bread crumbs dried at 30 and 50% microwave powers and crumbs dried at 50 and 70% microwave powers were observed to have significantly same _E values (Fig. 1). This is in agree-ment partially with the previous studies of Maskan [11] and Demirekler et al. [19]. Demirekler [20] reported that microwave power was not effective on total color change since distinct differences between different powers were not seen. Partial agreement might be due to the grinding

process after drying as grinding provides mixing of inner and outer layers of the dried samples and hence might have caused the similarities in _E values. It was also observed that as the power of microwave increased, _E value of the crumbs decreased. This is similar to the studies of Sumnu et al. [4] who reported lighter color in increased microwave powers. In addition, Krokida and Maroulis [10] also re-ported microwave drying and microwave-vacuum drying prevented color damages during drying.

As can be seen from Fig. 2, _E values of infrared dried samples were found to be significantly higher than that of conventionally dried samples meaning that sam-ples dried by infrared heating were darker in color. As the infrared heating provided the achievement of browning, hence caused darkness in the color of dried samples [18]. Observed results are in agreement with the previous results reported by Tan et al. [21] and Baysal et al. [5]. Variation of halogen lamp power did not affect the total color change of crumbs significantly (Fig. 2).

According to Fig. 3, bread crumbs dried at 50% mi-crowave and 70% halogen lamp power had significantly dif-ferent total color change values from conventionally dried crumbs with higher _E value. This shows that samples dried at the stated power combination were darker than con-ventionally dried ones. This is probably due to the brown-ing effect of infrared heating coming into play leading to darkness in color as the highest halogen power was used. Halogen lamp heating is known to provide low penetration depth and concentrate radiation at the surface resulting in higher surface temperatures and therefore browning [19]. On the other hand, drying at 70% microwave and 30% halogen lamp power caused significant difference in _E value with respect to conventional oven drying with lower _E value (Fig. 3). This might be due to the fact that low-est halogen power was used resulting in less browning and hence darkness. In addition to this, short drying time might have had contribution to less browning. Remaining power combinations provided _E values similar to convention-ally dried samples (Fig. 3), which is in agreement with the previous studies in which halogen lamp-microwave combi-nation oven provided color similar to conventionally baked breads at high halogen lamp powers [18, 19].

Fig. 3 Effect of infrared-assisted microwave drying on _E values of bread crumbs. ^∗ Means bars containing different letters are significantly different (p≤0.05)