Abstract: To evaluate the effect of oregano essential oil against Pseudomonas fluorescens and quality of salmon during cold storage, the minimal inhibit concentration of oregano essential oil against P. fluorescens was determined in vitro, as well as the growth curve, membrane fluidity, microstructure, electric conductivity and AKPase activity. After inoculation of P. fluorescens on salmon fillets and soaking treatment of oregano essential oil, the quality indicators including sensory quality, bacterial counts, total volatile basic nitrogen (TVB-N), biogenic amines and T2 parameters of Nuclear Magnetic Resonance were studied. The results showed that the MIC of oregano essential oil against P. fluorescens was 0.0625% (v/v). The fluorescence intensity of membrane of P. fluorescens treated by oregano essential oil was higher than control, indicating that oregano essential oil could inhibit the recovery of membrane fluidity during cold adaption. The corruption of cell membrane was also observed by scanning electron microscope and proved by the increase of conductivity. The oregano essential oil at 0.0625% also displayed the effectiveness on inhibiting the spoilage of salmon inoculated by P. fluorescens, as the bacterial counts and TVB-N value could be reduced by about 1 log CFU/g and 7 mg N/100g, respectively at the end of storage. The contents of putrescine and cadaverine was also inhibited by about 50%. The changes of LF-NMR parameters showed that less trapped water transferred to free water by the treatment of oregano essential oil, so that it displayed effectiveness on inhibiting the growth of P. fluorescens and its caused deterioration of salmon fillets.

Key words: oregano essential oil, Pseudomonas fluorescens, cold storage, salmon, preservation