As an alternative chitosan source, edible insects have been proposed as an unconventional but viable option. Taking fly pupae as an example, this work performed chitosan extraction through a traditional chemical method with some modifications, and investigated its physicochemical properties and antimicrobial activity. The results showed that adding 0.5% sodium sulfite (Na₂SO₃, w/w, Na₂SO₃/fly pupae) synergized with sodium hydroxide (NaOH) for deproteinization was more effective than lye alone. Acid leaching was applied for desalination, and the optimal concentration of hydrochloric acid (HCl) was determined as 2 mol/L by ash content. For decoloration, the optimal decolorization oxidant was sodium hypochlorite (NaClO) with a concentration of 1.0%. For the deacetylation of chitin to chitosan, both the yield and degree of deacetylation (DD) using segmented treatment with alkali-NaOH were higher than those of traditional one-time deacetylation. The established physicochemical properties corresponded with the typical characteristics of chitosan. The determination of antimicrobial activity of chitosan by the turbidimetric method showed that chitosan exhibited notable activity in the order of Staphylococcus aureus > Escherichia coli > Saccharomyces cerevisiae, and this effect decreased with the increase in viscosity-average molecular weight (Mη). These results proved the viability of our improved method for the preparation of chitosan, a valuable antimicrobial agent, using an alternative natural source.

A static magnetic field (SMF)-assisted liquid-state fermentation strategy using Lacticaseibacillus paracasei (L. paracasei) is proposed to improve the comprehensive utilization value of Ginkgo biloba leaves. Taking total flavonoid extraction yield as the objective, Box-Behnken response surface methodology was adopted to optimize the fermentation process. Meanwhile, the nutritional components and hypoglycemic activity of Ginkgo biloba leaves in vitro before and after fermentation were compared and analyzed. The optimal fermentation conditions were determined as follows: 3-fold-diluted De Man, Rogosa, and Sharpe (MRS) medium, an SMF intensity of 4.2 mT, an SMF duration of 2.9 h, and an inoculum size of 6.5%. Under these conditions, the total flavonoid extraction yield reached (3.41 ± 0.11)%, which was 3.33 times that of unfermented raw material. Analysis of the nutritional components revealed that after SMF-assisted fermentation, crude protein and crude fat contents increased by 59.58% and 13.72%, while ash and crude fiber contents decreased by 24.84% and 35.66%, respectively. SMF application also significantly affected the crude fiber content (p < 0.05). Meanwhile, the contents of phytic acid, tannins, phenolic acids, and ginkgolic acids in the SMF-assisted group declined by 29.56%, 43.10%, 23.42%, and 50.37%, respectively, and the SMF further promoted the degradation of anti-nutritional factors. Hypoglycemic activity analysis indicated that fermentation markedly enhanced the inhibitory effect of Ginkgo biloba leaf-derived flavonoids against α-glucosidase and α-amylase, and that SMF stimulation may also contribute to strengthening this inhibitory activity. This study demonstrates that SMF-coupled probiotic fermentation is an effective and environmentally friendly approach for processing Ginkgo biloba leaves, providing experimental support for high-value utilization of plant-based resources through physical-field-assisted microbial fermentation.