The Growth Kinetics Of Spoilage Organisms And Shelf Life Prediction For Scophthalmus Maximus

The freshness changes and shelf life were were carried out on cultured Scophthalmus maximus stored aerobically at 0 (in ice), 3, 7 and 10℃by Sensory, chemical, and microbiological methods. And the correlation between the numbers of total aerobic counts, Psychrobacter, Pseudomonas spp., H2S-Producing bacteria (Shewanella putrefacien), total volatile base nitrogen (TVBN), trimethylamine (TMA-N) and sensory freshness were discussed in this paper. Both qualitative and quantitative tests were used for characterization of bacterial flora at initial cold storage, the end of high quality life and shelf-life, using the simple phenotype and the Sensititre identification of bacteria system. The bacteria flora changes in cold storage and dominate spoilage bacteria of Scophthalmus maximus were discussed. The growth changes of H2S-producing bacteria in chilled storage were used to build a specific spoilage organism growth model and shelf life prediction model, and to evaluate the veracity of shelf life prediction model.(1) The good quality lives of Scophthalmus maximus stored aerobically at 0, 3, 7 and 10℃were 433, 197, 93, 68 hours, respectively, and the shelf lives were 602, 362, 165, 116 hours, respectively. Under these four temperature conditions, at the good quality life and at the end of shelf life, the average counts of total aerobic bacteria were 5.46±0.34 and 6.99±0.39 lg cfu/g, Psychrobacter were 5.42±0.41 and 6.85±0.30 lg cfu/g, H2S-Producing bacteria were 4.91±0.20 lg cfu/g, and 6.61±0.20 lg cfu/g, Pseudomonas spp.were 5.30±0.25 and 6.26±0.71 lg cfu/g, respectively. At the same time, the average values of TVBN were 15.66±1.93 and 15.66±1.93 mg/100g, TMA-N were 2.73±0.12 and 10.71±0.81 mg/100g, respectively. There were no significant differences in the TVC, H2S-Producing bacteria, Psychrobacter, Pseudomonas spp., TVBN and TMA-N values at the four temperatures. The results showed that as freshness indictors, TVC, Psychrobacter, Pseudomonas spp., TVBN and TMA-N had good correlation with sensory value.(2) At initial cold period the bacteria flora of Scophthalmus maximus is complex, 114 strains of bacteria were isolated and 68.4% of them were gram negative bacteria,a small percent of gram positive bacteria were found (21.1%). The predominant bacterial floras were composed of Enterobacteria (14.9%), Pasteurella pneumotropica (13.2%), Vibrio mimicus (12.3%), Pseudomonas spp. (10.5%), Shewanella putrefacien (8.8%). The bacteria flora became gradually simple during the cold storage and the growth of Pseudomonas spp. and Shewanella putrefacien were prominent. Shewanella putrefacien were 42.2%, 39.0%, 57.1%, 56.3%, and Pseudomonas spp. reached 28.0%, 23.7%, 25.5%, 31.0% at the end of good quality at 0, 3, 7, 10℃respectively, and the average percentage of Shewanella putrefacien and Pseudomonas spp. were 50.2% and 27.2%. Shewanella putrefacien were53.9%, 50.0%, 57.4%, 47.6%, and Pseudomonas spp. reached 25.5%, 25.0%, 41.0%, 15.9% at the end of shelf life at 0, 3, 7, 10℃respectively, and the average percentage of Shewanella putrefacien and Pseudomonas spp. were 52.3% and 26.5%. Shewanella putrefacien was the most predominated spoilage bacteria of Scophthalmus maximus stored from 0 to 10℃, fllowed by Pseudomonas spp..(3) The growth kinetics model of Shewanella putrefaciens of Scophthalmus maximus was built by the growth kinetics of Shewanella putrefaciens and Belehradek equation was:Accroding to Shewanella putrefaciens growth modle, the remaining shelf life (SL) could be gotten through the generation time between the initial numbers bacteria (N₀) and the minimum numbers of spoilage bacteria (N_s). The SL model for Pseudosciaena crocea stored aerobically at 0-10℃is described as follows: The accuracy validation of built growth kinetic models and remaining shelf life prediction model was compared with experimental development of Shewanella grown on Scophthalmus maximus at temperature 5℃.Relative errors between predicted and observedμ_max ,λand SL were -14.36%, 5.61% and 6.74% respectively at 5℃, indicating microbial growth models built in our research were valuable for rapid and realistic prediction of the freshness quality and remaining shelf life of Scophthalmus maximus under aerobic storage in 0～10℃.