Although many culture methods have been developed for Eastern oysters (Crassostrea virginica), scientific examination of the effects of culture methods upon the quality of the Eastern oysters is scarce. The aim of this study was to evaluate the quality of oysters cultured by two different bio‐fouling control methods through characterizing the volatile organic compounds (VOCs) of the oysters. VOCs were extracted from oysters by headspace solid‐phase microextraction, coupled with GC/MS analysis. A total of 32 VOCs were detected in the oysters, among which nine compounds were related to the fresh aroma of oysters, while 7 compounds indicated the spoilage of oysters. By comparing the differences of VOCs between two different culture methods before and after a 25‐day cold storage, selected volatile compounds showed clear differences between oysters from the two culture methods. Moreover, the principle component analysis of the VOCs was capable to distinguish oysters from different culture methods and evaluate the freshness of oysters. It could be concluded that the bio‐fouling control treatment could improve the quality of oyster by extending the shelf life, while at the same time ensure the product's nutritional value of high contents of polysaccharide unsaturated fatty acids.

In this study, chitosan (CS) was grafted onto the surface of polylactic acid (PLA) film by covalent immobilization to prepare four kinds of CS-grafted PLA (CS-g-PLA) films with different molecular weights. The properties of the films were characterized, and their antibacterial effect and mechanism of action against Staphylococcus aureus (S. aureus) were explored. After being treated with CS-g-PLA films, the cell morphology was destroyed, the permeability of the cell membrane changed, and malate dehydrogenase (MDH) activity decreased. Furthermore, the large yellow croaker fillets were packaged by the films mentioned above and stored at 4 °C, the physicochemical changes and microbial counts were measured. The results showed that the CS-g-PLA films could effectively delay the decay of fish fillets for 1–4 days. Overall, this study demonstrated that grafted films showed great application potential in aquatic product packaging and preservation.

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Immobilization is a common strategy used to protect microbial cells to improve the performance of bioprocesses. However, the interaction mechanism between the cells and the immobilization material is generally poorly understood. In this study, we employed natural polysaccharide-based materials as immobilization carriers for clostridial fermentation in an attempt to enhance the production of butanol (a valuable biofuel/biochemical but highly toxic to the host cells) and meanwhile elucidate the interaction mechanisms related to immobilization. The utilization of chitosan powder as the immobilization carrier enhanced butanol productivity by 97% in the fermentation with Clostridium saccharoperbutylacetonicum N1-4 and improved butanol titer by 21% in the fermentation with Clostridium beijerinckii NCIMB 8052. Additionally, analogue derivatives using microcrystalline cellulose (MCC) and cotton cationized on the surface with 3-chloro-2-hydroxypropyltrymethylammonium (CHPTA) and 2-chloro-N,N-diethylaminoethyl chloride (DEAEC) were prepared and used as immobilization carriers for similar fermentation conditions. The CHPTA derivatives showed slightly increased production of butanol and total solvent with C. saccharoperbutylacetonicum. Overall, our results indicated that the interaction between the cell and the carrier material occurs through a double mechanism involving adsorption immobilization and induced aggregation. This work provides insights concerning the effects of the chemical properties of the carrier material (such as the cation density and surface area) on fermentation performance, enabling a better understanding of the interaction between bacterial cells and the cationic materials. The derivatization strategies employed in this study can be applied to most cellulosic materials to modulate the properties and enhance the interaction between the cell and the carrier material for immobilization, thus improving the bioprocess performance.

This research was aimed to quantify the effects of acetic acid, malic acid, and citric acid (0, 0.5, 1.0, and 2.0 g/100 g H2O) on the stress–strain responses of fish gelatin (FG) gels (2, 4, and 6.67 g/100 g H2O) under uniaxial compression up to 68% of deformation. The first‐order Ogden model fitted quite well for the compression responses of FG gels (R2 = 0.9909–0.9997). Protons from the acids played a key role on weakening the FG gel structures (gel rigidity, μ, decreased 11%–27%), as the μ values and pH values of FG gels were linearly correlated (R2 = 0.8240–0.9748), regardless of the acid type. The addition of an acid also resulted in a significant increase (p < .002) in the strain hardening capacity (α) of gels with 2 g FG/100 g H2O. Both μ and α values of FG gels with higher gelatin concentrations were less affected by an acid partly due to their stronger buffering effects. The μ and α values of FG gels as affected by acids could not be fully explained based upon the pH changes, implying that the effects of acetate, malate, and citrate ions on the gel structure could not be ignored.