Inhibitory effect of d-Tryptophan on the spoilage potential of Shewanella baltica and Pseudomonas fluorescens and its potential application in salmon fillet preservation

In this study, we found the inhibitory effect of d -Tryptophan ( d -Trp) on the bacterial growth and spoilage potential of P. fluorescens and S. baltica . The effectiveness of d -Trp in bacterial growth inhibition was highly dependent on environmental NaCl concentrations. The growth/no growth models were developed to clarify the relationship between salt and d -Trp concentrations for optimal growth-inhibitory effect. It showed that higher levels of NaCl (>3.5%) with d -Trp (>15 mM) are required for growth inhibition. The d -Trp treatment combined with NaCl also retarded the psychrotrophic growth and reduced the respiratory active bacteria at low temperature, indicating that the inhibitory effect of d -Trp might be associated with the tolerance to osmotic and cold stress. Furthermore, the treatment d -Trp combined NaCl (artificial seawater) on salmon fillets was investigated. During refrigerated storage, the d -Trp treated salmon fillet either inoculated with S. baltica or P. fluorescen maintained remained a relatively low level of total volatile basic nitrogen (TVBN) (below 30 mg N/100 g during 8-days storage) and delayed increase of low total viable bacteria counts (TVC) with a longer lag phase of 2 days.