Hui-Juan Chen, Ying Shi, Jun Liu, Lixia Mu, Yu-Xiao Zou and Sen-Tai Liao
Silkworms are drawing international scientific attention owing to their significant hypoglycemic activity, attributed to 1-deoxynojirimycin (DNJ), which they obtain from eating mulberry leaves. DNJ content in silkworms varies significantly during its life cycle as a holometabolic insect. The effect of metamorphosis and molting on DNJ accumulation remains unclear, however. More knowledge is needed about DNJ dynamics during the silkworm life cycle given their potential use as a functional food with hypoglycemic effect. This paper aims to elucidate the DNJ dynamics of silkworms over their life cycle. We propose the best physiological stage for silkworm harvesting in consideration of DNJ production. The effect of metamorphosis and molting on DNJ accumulation is also discussed. Samples from key physiological stages of silkworms were collected and the DNJ content analyzed by reverse-phase high-performance liquid chromatography (RP-HPLC). We observed fluctuations in DNJ levels depending on the physiological stage of the silkworm. A higher level of DNJ was found in the molted larvae than the molting ones. The highest DNJ level was detected in the molted larvae of instar III (5.46 mg/g) in terms of bodyweight, while a silkworm from Day 3 of instar V possesses the highest level of DNJ (1512.46 μg per silkworm). These results imply that natural physiological changes in the silkworm, including molt and metamorphosis, affect DNJ accumulation significantly. The period from Day 3 to Day 4 of the 5th instar is considered the best time for silkworm harvesting given both DNJ concentration and silkworm biomass.
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