Preservation Effect Of Phloretin On Refrigerated Salmon

Due to high content levels of water and protein, aquatic products are easy to spoilage, and microorganisms are responsible for the spoilage. The traditional preservation methods which can have some effect on the sensory quality and safety can not meet consumer demand. Natural preservative with its advantages of safety, high efficiency, broad spectrum, has attracted widespread attention.Phloretin which is the characteristic phenolics of apple polyphenols has strong antibacterial activity and high safety, thus having a very broad application prospects. In this study, we evaluated its antibacterial spectrum initially and measured the minimum inhibitory concentration (MIC) value against 6 strains of common foodborne pathogens. And its security was investigated by the acute toxicity experiment on mice. Using the High-throughput sequencing, the effect of phloretin on refrigerated salmon bacteria community was analyzed and the dominant bacteria of the microflora were determined. We then tested the use of phloretin as a natural preservative for salmon during storage.The main results of this study are as following:(1) Phloretin has wonderful antibacterial activity. The MIC values against Listeria monocytogenes, Staphylococcus aureus, Bacillus subtilis, Pseudomonas fluorescens, Escherichia coli, Salmonella typhimurium were 25?30?15?400?300 and 350 ?g/mL, respectively. The result of the acute toxicity test showed that the lethal dosage 50 (LD50) of phloretin was greater than 8.4 g/kgbw, so it belongs to the actual non-toxic according to the classification standard of acute toxic dose. Thus, the security of phloretin could be determined for the actual non-toxic.(2) The addition of phloretin could greatly reduce the total number of bacteria on the refrigerated salmon and changed the community structure, diversity, the number of OTU and the relative abundance of the dominant spoilage bacteria. After 4 days of storage, the salmon samples treated with 4 mg/mL of phloretin could reduce the total number of bacteria by 2 logarithmic, suppress the diversity and increase the OTU number. Meanwhile, the dominant spoilage bacteria of the treated sample were Pseudomonas, Photobacterium, Shewanella, Chryseobacterium and Acinetobacter, distributing as 64.82%,22.83%,4.8%,3.38% and 2.97%, respectively. According to the 16S rDNA sequences and the phylogenetic tree analysis of the top 50 representative sequences of the most abundant sequences in OTU clustering results, these representative sequences were divided into six categories, namely Pseudomonas, Photobacterium, Shewanella, Acinetobacter, Flavobacterium and Chryseobacterium.(3) Phloretin had a good protective effect on the sensory qualities of the refrigerated salmon, such as colour, smell and taste, and could delay the formation of lipid oxidation and biogenic amines, the growth of Enterobacteriaceae and Pseudomonas effectively. Compared with the control group, in day 4, the salmon samples treated with 4 mg/mL of phloretin could decrease the lipid oxidation value by 3.23 times, the formulation of biogenic amines could be reduced by 18.84 times, the total number of Enterobacteriaceae and Pseudomonas could be suppressed by 0.8 and 1.6 logarithmic, respectively, thus the samples maintained a high quality.In the study, phloretin was used as a novel biological preservative in the preservation of refrigerated salmon slices to provide a new idea for extending the application scope of phloretin, and also give a new method for the preservation of aquatic products.