This study attempted to develop chitosan-based nanoparticles with increased stability and antibacterial activity. The chitosan/protamine hybrid nanoparticles were formed based on an ionic gelation method by mixing chitosan with protamine and subsequently cross-linking the mixtures with sodium tripolyphosphate (TPP). The effects of protamine on the chemical structures, physical properties, and antibacterial activities of the hybrid nanoparticles were investigated. The antibacterial experiments demonstrated that the addition of protamine (125 µg/mL) in the hybrid nanoparticles (500 µg/mL chitosan and 166.67 µg/mL TPP) improved the antimicrobial specificity with the minimum inhibitory concentration (MIC) value of 31.25 µg/mL towards Escherichia coli (E. coli), while the MIC value was higher than 250 µg/mL towards Bacillus cereus. The chitosan/protamine hybrid nanoparticles induced the formation of biofilm-like structure in B. cereus and non-motile-like structure in E. coli. The detection of bacterial cell ruptures showed that the inclusion of protamine in the hybrid nanoparticles caused different membrane permeability compared to chitosan nanoparticles and chitosan alone. The chitosan/protamine nanoparticles also exhibited lower binding affinity towards B. cereus than E. coli. The results suggested that the hybridization of chitosan with protamine improved the antibacterial activity of chitosan nanoparticles towards pathogenic E. coli, but the inhibitory effect against probiotic B. cereus was significantly reduced.

Ophiopogon japonicus polysaccharides (OJPs) have great anti-inflammation and immunomodulatory abilities. However, the low bioavailability of OJPs reduces its applicability in the biomedical and pharmaceutical fields. Chitosan (CS) has excellent mucoadhesive properties and absorption-enhancing ability in oral administration. Casein hydrolysate (CL) has good interfacial diffusivity and emulsifying ability, and can interact with polysaccharides to form complexes combining the individual properties of both. Therefore, chitosan and casein hydrolysate are good candidates for developing nanoformulations for oral delivery. In this study, bioactive polysaccharides (OJPs), CS and CL, were combined to prepare CS/OJPs/CL co-assembled biodegradable nanoparticles. The interactions between polysaccharides (CS and OJPs) and peptide (CL) resulted in the formation of nanoparticles with an average particle size of 198 nm and high OJPs loading efficiency. The colloidal properties of the nanoparticles were pH-dependent, which were changed significantly in simulated digestive fluid at different pH values. OJPs released from the CS/OJPs/CL nanoparticles were greatly affected by pH and enzymatic degradation (trypsin and lysozyme). The nanoparticles were easily internalized by macrophages, thereby enhancing the OJPs’ inhibitory ability against Ni²⁺-induced cytotoxicity and LPS-induced nitric oxide production. This study demonstrates that prepared polysaccharide/protein co-assembled nanoparticles can be potential nanocarriers for the oral delivery of bioactive polysaccharides with anti-inflammatory functions.

Fusarium Wilt Tropical Race 4 (TR4) is spreading rapidly all over the world and threatens banana production, especially the Cavendish variety, which is the main commercial cultivar in Asia. This work aims to use beneficial microbes and fertilizers to control TR4. Both Bacillus mycoides NP02 (BM) and Bacillus amyloliquefaciens BaPD1 (BA) antagonized TR4 growth in plate tests. In addition, basal nutrients (BN) in combination with BM and BA were used to treat 1-month-old banana seedlings infected by Fusarium Wilt; plant growth and nutrients of leaves were investigated after 6-month cultivation in the field. The seedling survival rates for uninfected and infected controls without the microbes were 89.4 ± 14.8% and 50 ± 10.7%, respectively. In contrast, the corresponding rates for 2BM, 5BM, 1BA, F1 (5BM + 4BN + 1BA) and G1 (1BM + 4BN + 1BA) in the infected plants were 80 ± 9.4%, 83 ± 4.3%, 85 ± 14.2%, 96.7 ± 1.9% and 96.7 ± 3.3%, respectively. The 2BM treatment promoted the growth of both uninfected and infected banana plants and the 5BA treatment significantly reduced the severity index by 1.45-fold. Plants infected with TR4 showed significantly reduced contents of nitrogen and potassium, but the contents of iron, copper and zinc were higher than those of healthy plants. Additionally, 1BM treatment stimulated the accumulation of nitrogen and zinc ions in the leaves of uninfected plants. Both the 1BA and 2BN treatments increased the iron (Fe) and nickel (Ni) metal ion levels of TR4 infected plants. The F2 (5BM + 2BN + 1BA) treatment significantly maintained the growth of banana plants under TR4 stress with increased contents of nickel and zinc in banana leaves, suggesting that these ions may play a key role in stimulating the growth of banana plants under the threat of TR4. This work shows the potential of applying BM, BN and BA in the control of Fusarium wilt in field conditions.

Visual freshness monitoring is challenging in intelligent seafood packaging. This study developed low-acyl gellan gum (LGG)-based intelligent films incorporating anthocyanin (BRE), carboxymethyl chitosan (CMCh), and black rice starch (BRS) and evaluated their effects on film structure, physical–mechanical properties, and shrimp freshness-monitoring performance. Films prepared via solution casting were evaluated using structural, mechanical, and barrier analyses, alongside shrimp spoilage trials at 25 °C. Structural analyses revealed an integrated polysaccharide network. CMCh reinforced the matrix and increased tensile strength, whereas partially retained BRS granules introduced microstructural heterogeneity, reducing strength and increasing water vapor permeability, highlighting a trade-off between mechanical performance and moisture transport. Consequently, BRS-containing films reduced BRE release, improved pigment retention, and resulted in less intense color changes associated with total volatile basic nitrogen (TVB-N) accumulation during shrimp spoilage. Overall, these results suggest that CMCh and BRS composition-dependently modulate the structure, water vapor transport, pigment retention, and colorimetric response of LGG-based films for visual monitoring of shrimp freshness under accelerated spoilage conditions.