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The antibacterial mechanism of chitosan-grafted caffeic acid (CS-g-CA) against Pseudomonas fluorescens (P. fluorescens) was studied. The results indicated that the MIC of CS-g-CA to P. fluorescens was 1.25 mg/mL, and CS-g-CA in MIC could effectively inhibit the growth of bacteria. CS-g-CA can greatly destroy the cell membrane of P. fluorescens, enhancing its permeability and leading to the leakage of macromolecular proteins. The results of reactive oxygen species (ROS) and lipid peroxidation activities demonstrated that CS-g-CA could destroy the respiratory and metabolic system. According to scanning electron microscope (SEM), CS-g-CA can destroy the somatic cells of bacteria, resulting in the leakage of their contents and death by lysis. In addition, thallus movement was inhibited by CS-g-CA. Electrophoresis results showed that the DNA of P. fluorescens with CS-g-CA treatment was destroyed, which further led to the death of microorganisms. Eventually, the normal growth and reproduction of bacteria were also hindered. These findings suggested that CS-g-CA is a promising antimicrobial agent to control P. fluorescens in aquatic products.

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This project aimed to evaluate the effects of chitosan (CS) on the quality and protein characteristics of large yellow croaker (Pseudosciaena crocea) during ice storage. Samples were treated with different solutions (10.0 g/L chitosan solution [CS1], 20.0 g/L chitosan solution [CS2], 1% acetic acid [AA], and deionized water [CK]) for 15 min and then stored at 4°C. Microbiological (total viable counts [TVCs] and psychrophilic bacteria counts [PBCs]), physicochemical (total volatile basic nitrogen [TVB‐N], thiobarbituric acid [TBA], and texture profile analysis [TPA]) analyses were used to analyze the quality of large yellow croaker. The changes of protein characteristic were analyzed by total sulfhydryl (‐SH) content, Ca2+‐ATPase activity, and Fourier transforms infrared spectroscopy. The results showed that chitosan could effectively inhibit the microbial growth, and the hardness value was consistent with the reduction of protein characteristic indicators (‐SH content and Ca2+‐ATPase activity). For protein structure analysis, the amide I band and amide II band of CK group changed significantly, which indicated that α‐helix might be transformed into β‐fold or random coil. Therefore, 20.0 g/L chitosan treatment had better effect, and it could extend the shelf‐life for another 6 days, which had also protective effects on the secondary structure of protein and maintained its structure stability. Practical applications Packaging of meat products has become increasingly popular in the industry to maintain product characteristics for longer periods of storage. There is an increasing interest in food additives nowadays. This study investigated the effects of chitosan (CS) on the quality and protein characteristics of large yellow croaker (Pseudosciaena crocea) during ice storage. In conclusion, chitosan treatment had better effect, and it could extend the shelf‐life for another 6 days. Chitosan draws attention as a preservative substance in food industry because of its antioxidant and antimicrobial properties. It also has good film‐forming and antimicrobial properties, which has wide range of applications as coatings/packaging materials to protect aquatic products. Chitosan coated on the surface of fish, which could be a barrier to oxygen, inhibited microbial growth, protein degradation, and lipid oxidation, thus extending the shelf‐life, reducing spoilage and economic losses. Freshness and shelf‐life assume crucial importance to industry and consumers, as they determine the product acceptability and its commercial value consequently. These findings provide a theoretical basis for large yellow croaker during ice storage and can be well utilized by researchers as well as manufacturers for the storage of fish and fish products.

The effects of allicin (All) and antioxidant of bamboo leave (AOB) on the quality of bullfrog (Lithobates catesbeiana) during refrigerated storage were investigated. The results demonstrated that the treatment of All and AOB could reduce the decline of moisture loss and maintain the water-holding capacity (WHC). In addition, combination treatment inhibited the increase of total viable counts (TVC), exhibited good antibacterial activity, delayed the decrease of amino acid content and retarded the sensory deterioration. The reduction of thiobarbituric acid (TBA) and total volatile basic nitrogen (TVB-N) indicated that allicin combined with antioxidant of bamboo leave (AA) could restrain the degradation of protein and lipid oxidation. As a consequence, AA treatment prolonged the shelf-life of bullfrogs for another 6 days. Allicin combined with antioxidant of bamboo leave treatment could be an effective approach to extend the shelf-life and delay the biochemical reaction of refrigerated bullfrog.