Abstract: The present study aimed to investigate the effects of different cooking methods (microwaving, steaming, boiling, and deep-frying) on the contents of 1-deoxynojirimycin (DNJ) and phenolic compounds in leaves of mulberry (Morus alba L.). The total phenolic contents were determined by the Folin-Ciocalteu method. The contents of DNJ and phenol monomers were measured by high performance liquid chromatography (HPLC). The results showed that all the cooking methods except steaming for 5 min, increasing the total phenolic content, significantly reduced the levels of DNJ and phenolics. The highest contents of DNJ and phenolics were detected in steamed mulberry leaves, while the lowest contents of DNJ and phenolics were obtained by deep-frying and microwaving at 70 W for 3 min, respectively. All the cooking methods had significant effects on the composition of phenolics. Steaming for 3 min and microwaving at 700 W for 3 min increased the contents of isoquercitrin and astragalin. Notably, certain amounts of kaempferol-acetyl-glucoside (KAG), quercetin and kaempferol were found in the deep-fried mulberry leaves, but not in the other samples. In conclusion, steaming can be considered as a suitable cooking method for mulberry leaves to ensure the maximum retention of bioactive components.

Key words: mulberry leaves, cooking methods, DNJ, phenolics