Discrimination of three commercial tuna species through species-specific peptides: From high-resolution mass spectrometry discovery to MRM validation.

The risk of tuna adulteration is high driven by economic benefits. The authenticity of tuna is required to protect both consumers and tuna stocks. Given this, the study is designed to identify species-specific peptides for distinguishing three commercial tropical tuna species. The peptides derived from trypsin digestion were separated and detected using ultrahigh-performance liquid chromatography-quadrupole-time of flight mass spectrometry (UPLC-Q-TOF/MS) in data-dependent acquisition (DDA) mode. Venn analysis showed that there were differences in peptide composition among the three tested tuna species. The biological specificity screening through the National Center for Biotechnology Information's Basic Local Alignment Search Tool (NCBI BLAST) revealed that 93 peptides could serve as potential species-specific peptides. Finally, the detection specificity of species-specific peptides of raw meats and processed products was carried out by multiple reaction monitoring (MRM) mode based on a Q-Trap mass spectrometer. The results showed that three, one and two peptides of Katsuwonus pelamis, Thunnus obesus and Thunnus albacores, respectively could serve as species-specific peptides.

The luxS deletion reduces the spoilage ability of Shewanella putrefaciens: An analysis focusing on quorum sensing and activated methyl cycle.

The luxS mutant strains of Shewanella putrefaciens (SHP) were constructed to investigate the regulations of gene luxS in spoilage ability. The potential regulations of AI-2 quorum sensing (QS) system and activated methyl cycle (AMC) were studied by analyzing the supplementation roles of key circulating substances mediated via luxS, including S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), methionine (Met), homocysteine (Hcy) and 4,5-dihydroxy-2,3-pentanedione (DPD). Growth experiments revealed that the luxS deletion led to certain growth limitations of SHP, which were associated with culture medium and exogenous additives. Meanwhile, the decreased biofilm formation and diminished hydrogen sulfide (H2S) production capacity of SHP were observed after luxS deletion. The relatively lower total volatile base nitrogen (TVB-N) contents and higher sensory scores of fish homogenate with luxS mutant strain inoculation also indicated the weaker spoilage-inducing effects after luxS deletion. However, these deficiencies could be offset with the exogenous supply of circulating substances mentioned above. Our findings suggested that the luxS deletion would reduce the spoilage ability of SHP, which was potentially attributed to the disorder of AMC and AI-2 QS system.

[Effect of ultra high pressure treatment on Vibrio parahaemolyticus].

OBJECTIVE: We explored the mechanism of the microbial inactivation by high hydrostatic pressure. METHODS: We investigated the effect of ultra high pressure treatment on inactivation of Vibrio Parahaemolyticus cells, and the damages inflicted on the microstructure and the membrane proteins of the Vibrio Parahaemolyticus cells. RESULTS: The result indicated that after pressure treatment at 100 MPa, 200 MPa and 20 degrees C for 10 min, the viable cell was reduced to 60% and 15.3% respectively, viable cell counts were not detected following pressure treatment at 300 MPa and 20 degrees C for 10 min. High pressure treatment at 300 MPa also caused changes in the microstructure of the cell, such as the cell wall of Vibrio Parahaemolyticus was shrunk, breached and cytoplasm leaked out, the layer structure of cytoplasm disappeared, and a large electron transmission area appeared in the cell after compression, the membrane disappeared, the nucleoids condensed and the proteins aggregated after compression. At the same time, the membrane proteins of cells were damaged, and the cell membrane permeability increased, resulting in leakage of the cell. CONCLUSION: This study showed that the damaged cell membrane was the major reason of the mechanism of microbial inactivation by high hydrostatic pressure.