From K-snack to copolymer: conversion of silkworm pupa oil into poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) by engineered Cupriavidus necator H16

Silkworm pupae are continuously generated as a major byproduct of the silk industry and have long been consumed as inexpensive, high-energy snacks in Korea. However, consumer acceptance has become increasingly variable due to their distinctive appearance and odor. Gas chromatography–mass spectrometry (GC–MS) analysis revealed that silkworm pupa oil (SPO) consists of approximately 54% oleic acid, 29% linoleic acid, 17% palmitic acid, and minor amounts of cyclopropane fatty acids. Based on this composition, this study evaluated the feasibility of producing poly(3-hydroxybutyrate- co -3-hydroxyhexanoate) [P(3HB- co -3HHx)] using engineered Cupriavidus necator H16 with SPO as a sustainable substrate. Compared with other carbon sources, SPO supported comparable growth and polyhydroxyalkanoate (PHA) content, which was 2.64-fold higher than fructose and 1.42-fold higher than bean oil in flask cultures, demonstrating its potential as an efficient substrate. Supplementation with 1.0% fructose as an auxiliary carbon source further increased dry cell weight (DCW) and total PHA accumulation by up to 20%. To improve emulsification, various emulsifiers were screened, and Tween 20 enhanced DCW and PHA yield by 1.4-fold and 1.55-fold, respectively. The resulting film exhibited a tensile strength of 6.0 ± 0.6 MPa and an elongation at break of 53.4 ± 4.6%, and showed approximately 90% degradation after 7 days by Microbulbifer sp. SOL66. Overall, this study demonstrates that SPO is a promising and sustainable carbon source for PHA production, highlighting the valorization of silk industry byproducts into high-value biopolymeric materials.