Abstract: The purpose of this study was to explore the changes in the protein and fatty acid composition in silkworm pupa and the in vitro antioxidant activity of silkworm pupa oil during storage and after reeling in order to provide theoretical support for deep processing of the silk reeling by-products. The pupae were divided into four groups according to their morphology during storage. The proximate composition, protein composition, and fatty acid composition were determined by the Chinese national standard methods, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and gas chromatography-mass spectrometry (GC-MS), respectively, and the in vitro antioxidant effect was evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and 2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation scavenging assays. The results showed the chemical constituents were significantly different among storage times (P < 0.05). The molecular masses of proteins in silkworm pupa were mainly distributed near 30 and 70 kDa, and the protein expression levels were decreased with prolonged storage. Totally 16 fatty acids were found in silkworm pupa oil, the major ones being palmitic acid, stearic acid, oleic acid, linoleic acid and α-linolenic acid, all of which changed significantly with storage time (P < 0.05). The half maximal inhibitory concentration (IC50) values for scavenging of DPPH and ABTS cation radicals were in the range of 20.93–52.00 and 33.32–156.81 mg/mL, respectively. The change in the antioxidant effect of silkworm pupa oil was correlated with the change in the total phenol content (15.95–77.50 mg/kg). After silk reeling, the protein and fatty acid composition were changed significantly, and the antioxidant effects were decreased. Taken together, storage time and silk reeling both influenced the protein and fatty acid compositions in silkworm pupa and the total phenol content in silkworm pupa oil, and they also had a great impact on the antioxidant properties of the oil. Accordingly, at various stages of storage, silkworm pupa samples can be collected from processing according to the bioactivity and expression level of target components.

Key words: silkworm pupa; storage period; silkworm protein; silkworm pupa oil; fatty acids; antioxidant activity