Regional and Varietal Variation of 1-Deoxynojirimycin (DNJ) Content in the Mulberry Leaves

This study was carried out to find out whether there exists any content variation in 1-deoxynojirimycin (DNJ) among regional and varietal mulberry leaves. HPLC analysis was performed for 22 samples collected from several localities in Korea and Tsushima Islands Japan. The highest content was observed in the Cheongilppong sample collected at Youngchun City, Kyungsangbuk Province (1,882.7 $\mu\textrm{g}$/g DW), whereas lowest content was observed in the Cheongilppong sample collected at Jiniu City, Kyungsangnam Province (395.65 $\mu\textrm{g}$/g DW). In the comparison of regional samples of Kaeryangppong variety, DNJ content was highest in the order of Woniu City (1,460.1) > Boungun (999.85) > Hweongsung-gun (939.12) > Cheongju City (688.78). In case of Cheongilppong, DNJ content was highest in the order of Youngchun City (1.882.8) > Sanchung-gun (1,125.3) > Sunchon City (649.17) > Byunsan-myon (441.54) > Jinju City (395.65). Average content of regional samples was higher in Kaeryangppong (1,021.7 $\mu\textrm{g}$/g DW) than that of Cheongilppong (898.87 $\mu\textrm{g}$/g DW). Average DNJ content of the wild mulberry loaves collected from Cheju Island and Tsushima Island (1,012.9$\mu\textrm{g}$/g DW) was high enough to reach to that of the regional Kaeryangppong samples. In the comparison among varietal samples collected in Suwon, the highest DNJ content was observed in YK209 (768.16 $\mu\textrm{g}$/g DW), amongst overall low DNJ content of the varietal samples. Considering a few pieces of information from our data, DNJ content appears not to be influenced solely by annual temperature of the planted areas.