Table 6
Influence of different drying methods on the quality of dried mulberry products
Drying method
|
Preser. of antho-cyanins/
(mg/g)
|
ΔE Rehydration factor
|
Total phenols / (mg/g)
|
Hardness (N) Brittleness
|
Drying time (min)
|
Infrared drying
|
18.56
|
3.66
1.58
|
30.33
|
8170,21
16,3
|
120
|
Microwave dryer
(500 W)
|
3.772
|
3,9
0,84
|
22.17
|
14081,28
15,4
|
3
|
Drying in the shade
|
11.55
|
3,78
1,11
|
27.66
|
1833,22
3,2
|
2280
|
In this case, the moisture content of the product in all three drying methods was around 7% in the dry state. The optimum conditions for infrared drying were 70 °C and an infrared radiation power of 230 W and an air speed of 0.2 m/s. From the experimental results shown in Table 6, it can be seen that the product dried using infrared radiation from the three mulberry fruit samples had the best nutritional qualities. The product dried by a combination of convection and IR radiation had the best overall quality with the highest total phenolic content (30.33 mg/g), high anthocyanins content (18.56 mg/g), lowest colour difference (3.66), highest crispness (16.3) and shortest drying time (120 min); whereas the microwave dried product had the worst overall quality of all three. In the combined convection-infrared drying process, infrared radiation has a certain penetrating ability, which allows to heat the material uniformly in a short time and increase the effective moisture diffusion coefficient in the material, while infrared radiation has a certain ability to sterilise and destroy enzymes, which allows the material to better preserve polyphenols, so combined convection-infrared drying not only reduces drying time but also makes the dried product better quality [10].
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