Initial weight of sample
tion in the drying time with respect to the conventional oven drying was observed at 30, 50 and 70% halogen lamp powers, respectively (Table 1). This shows that by infrared
Three replications were done for determination of water binding capacity.
Statistical analysis
Analysis of variance (ANOVA) was performed to deter-mine the significant differences between the independent variables (p≤0.05). Variable means were compared by Duncan’s Multiple Range test. Three replications were used for all of the experimental conditions.
Results and discussion
Conventional drying time was reduced significantly by us-ing microwave, infrared and infrared-assisted microwave drying methods (Table 1). It was seen that the drying time decreased with increase in power (microwave and/or halo-gen lamp) in all of the drying treatments. It was observed that microwave drying reduced the processing time dras-tically due to the high drying rates. It was possible to re-duce the drying times by 96.5, 98 and 98.6% at 30, 50 and 70% microwave powers respectively compared to the conventional oven drying (Table 1). Shorter drying time in microwave oven can be explained by high internal pres-sure and concentration gradients created which increased the flow of liquid through the food to the boundary [13]. Similar results were reported by different studies in which microwave drying was found to reduce convection drying time [4, 8, 11, 14, 15]. Again as expected with increasing halogen lamp powers, food was exposed to more radiative
drying method it is possible to decrease drying time signif-icantly. Similarly, Nowak et al. [16] found that drying with application of infrared energy was much faster than con-vective drying. Since infrared-assisted microwave drying is the combination of both microwave and infrared drying, reduction in conventional drying resembled the trends of both drying methods.
The total color change (_E) values, which takes into ac-count changes in lightness, redness and yellowness, were compared. No significant difference between bread crumbs dried at 30% microwave power and conventionally dried crumbs were found (Fig. 1). Similar trend between low power microwave drying and conventional drying was also reported by Sumnu et al. [4] in L∗ and a∗ values which affect the total color change. It was further observed that samples dried at 50 and 70% microwave powers had significantly lower _E values than that of conventionally dried ones. This means that crumbs dried at 50 and 70% microwave powers were lighter in color when compared with conven-tionally dried crumbs (Fig. 1). This is in agreement with the previous studies of Feng and Tang [17] and Maskan [11] who reported lower _E values in microwave drying with respect conventional drying. Keskin et al. [18] also observed lower _E values in microwave baked breads and explained this by short times and low temperatures common to microwave processing which did not promote browning
reactions. However, Beaudry et al. [6] observed no sig-nificant difference between microwave and conventionally dried cranberries. Different results with respect to Beaudry et al. [6] are probably due to the type of the food material being dried, the dimensions and the weight of the samples. Different temperature profiles with respect to the study of
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25 |
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20 |
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a* |
ba |
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bc |
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15 |
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c |
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∆E |
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10 |
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5 |
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0 |
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conventional |
30% mw only |
50% mw only |
70% mw only |
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