Abstract:

The effects of different drying methods on the contents of hypoglycemic components in mulberry leaves
(Morus alba L.) were explored to find the most appropriate drying method for in-depth development of mulberry leaves.
1-Deoxynojirimycin (DNJ) in mulberry leaves was quantified by high performance liquid chromatography (HPLC),
polysaccharide content was measured by phenol-sulfuric acid method, and the content of flavonoids was assayed by sodium
nitrite method. The results showed that freeze dried mulberry leaves presented the best quality but lower contents of DNJ
and flavonoids. Vacuum drying provided the lowest contents of DNJ and polysaccharide as well as the worst color in dried
mulberry leaves. Microwave drying had little effect on the hypoglycemic components and color of mulberry leaves; the
highest contents of DNJ and polysaccharide of (297.15 ± 6.35) mg/100 g and (11.71 ± 0.01)%, respectively, were obtained
by microwave drying at 140 W for 10 min. Hot air drying was time saving and only slightly affected the color of mulberry
leaves, leading to higher contents of DNJ, flavones and polysaccharide of (227.47 ± 5.79) mg/100 g, (49.51 ± 1.18) mg/g
and (11.29 ± 0.01)%, respectively, in dried mulberry leaves. Thus, hot air drying is more suitable for industrial processing
of mulberry leaves. At the same time, during the drying process no structural change was observed for the hypoglycemic
components and they were still effective against alpha glycosidase and alpha amylase suggesting that the hypoglycemic
activity was retained.

Key words: mulberry leaf, drying, 1-deoxynojirimycin, flavonoids, polysaccharide