| Traditional ready-to-eat?RTE?abalone products,normally with high salinity and low moisture content,due to their salty taste,tough mouthfeel as well as poor sensory quality,would no longer meet the needs for healthy diet in modern life.Meanwhile,autoclaving could easily result in juice exudation and mealiness of RTE abalone products,which had negative influence on mouthfeel and nutritive value of RTE abalone.Therefore,the food safety control and quality maintenance technology for keeping RTE abalone products of high moisture content and low salinity with good palatability were studied in this paper.Firstly,the effects of storing temperature on quality characteristics of fresh abalone were studied.Then change law of microbial community in RTE abalone during processing were studied by using T-RFLP technology,which helped reveal those processing stages vulnerable to contamination and the residues of specific spoilage bacteria.The volatile components of abalone were analyzed through GC-MS in order to verify the specific spoilage bacteria and to find out the causes of those smell.And the processing technology of RTE abalone product was further optimized by response surface methodology.Finally,the biological inhibition technology combined with hurdle factors setting was applied to extend the shelf-life of RTE abalone products.Major contents and results were as followed.1.Effects of storing temperature on the quality characteristics of fresh abaloneThe fresh abalone were frozen under-20 ? and-80 ?,and the changes of both biochemical characteristics,physical characteristics and sensory index,as well as the microbial community change law of abalone were studied.Results showed that moisture content,salt-soluble protein,ATPase activity and sensory indexes of abalone stored under-80 ? after thawing and water cooking were higher than that under-20 ?.Meanwhile,TBA value,pH value,TVB-N value,total colony count of abalone stored under-80? were all lower than that under-20 ?.Hardness,coherency and chewiness of abalone storing under-80 ? were better than that under-20 ?.The color of abalone stored under-80 ? was much closer to the fresh ones.To sum up,the storing temperature of-80 ? helped delaying quality decline of abalone,slowing down protein degradation and degeneration,inhibiting bacterial growth,improving quality and commodity value of frozen abalone.Thus,to guarantee quality of RTE abalone products,fresh abalones for further processing should be stored under-80?.2.Study on change law of microbial community of ready-to-eat abalone during processingThe change law of microbial community and the main residues of spoilage bacteria in abalone products from different processing stages were analyzed by using T-RFLP technology.Results showed that thawed and salted at room temperature easily encouraged the growth of spoilage bacteria-Operations like washing with running water,low-temperature salting and high-temperature baking could help eliminate microbial contamination.Most of the thermo-labile bacteria were killed through high-temperature baking,while those few thermotolerant ones which mostly were Bacillus subtilis,Clostridium sp.,Bacillus spherical and so on still remained.Then the growth of aerobic bacteria were inhibited by vacuum packing which on the other hand provided suitable environment for the growth of anaerobic bacteria such as Clostridium sp.and Enterococcus saccharolyticus.Analysis showed that main bacteria found in spoilage abalone were Clostridium sp.,Bacillus sp.,etc.Clostridium sp.accounted for the largest proportion particularly.It is considered that Clostridium sp.was the dominant spoilage organism,and Bacillus was also one of the most important residual bacteria in vacuum packing abalone.Therefore in order to eliminate Clostridium and Bacillus,it is necessary to take antibacterial measures in later procedures to prevent vacuum packing abalone from spoilage.3.Study on the variation of volatile components of RTE abalone and the growth characteristic of Spoilage bacteriaAccording to the analysis of GC-MS,abalones with different treatments had significantly different volatile components,which mainly were alcohols,aldehydes,ketones,hydrocarbons,acids,esters,aromatic substances and sulphur,nitrogen-containing compounds,etc.The major volatile components of thawed abalone were benzaldehyde and 1-octen-3-ol.Baking abalone in high-temperature remarkably helped enhance the barbecue flavor,of which alcoholic substances,nitrogen compounds,sulfur compounds and esters compounds were typical flavor components.The spoilage abalone with black spots on the surface and juice exudation in the package would give off a bad smell and spread a strong rancid flavor.The main volatile components of spoilage abalone were indole,phenol and butanoic acid.Abalone infected by Clostridium sporogenes looked much alike the spoilage ones,which also had a strong odour and stink smell.It is said that Clostridium sp.was one of the most important biological contamination cause of vacuum packing abalone product.Abalone infected by Bacillus subtilis didn't appear exactly the same as the spoilage ones,but would still partially turn rancidity and had juice exudation.The enzymes secreted by Bacillus subtilis may become a crucial factor of abalone's deterioration.Clostridium sporogenes has low salt-resistance and low acid-resistance,while Bacillus subtilis has strong salt-resistance and strong acid-resistance.The growth of these two species of bacteria could be inhibited under the conditions of strong-acid?pH<4?,high-salt?NaCl>10%?.But high-salt and strong-acid process will seriously affect the sensory and eating quality of RTE abalone product.It is necessary to look for a more efficient and safer sterilization method.4.Optimization of RTE abalone processing technology with response surface methodologyBased on the earlier research,the RTE abalone processing was further optimized and processing steps that were vulnerable to contamination should be avoided as soon as possible.The response surface optimized experiments were made by choosing the key factors affecting the safety and quality of RTE abalone such NaCl addition?X1?,salting time?X2?,heat-pump drying time?X3?and baking time?X4?as independent variable and such sensory evaluation?Y?as dependent variable.The dynamic model of RTE abalone processing was gained:Y =-21.38+1.59X1+0.08X2+0.13X3+2.26X4-XiX2-X1X3+0.03X1X4+X2X3-X2X4-X3X4-0.39X12—X22-X32-0.09X42.The optimal processing technology of RTE abalone product was as followed:added with 0.80%NaCl,salted for 130 min under 4?,dried with heat-pump drier for 125 min under?40±3?? temperature,and baked for ? min under the condition of up temperature 150? and down temperature 180?.After such processing,the actual sensory evaluation of RTE abalone product was up to 4.90.Taste quality was up to the optimal state.5.Study on the application of bio-inhibitor agents on RTE abalone product during storageFirstly,the response surface optimized experiments were made by choosing the factors such s-PL?X1?,Nisin?X2?,lysozyme?X3?as independent variable and such inhibitory rates of Clostridium sporogenes?R1?and Bacillus subtilis?R2?as dependent variable.The dynamic models of the inhibitoty rates of Clostridium sporogenes?R1?and Bacillus subtilis?R2?were set up as followed:R1 = 124.20-401.24A-670.90B+56.70C-1470.59AB-2873.45AC-5959.75BC+2225.62A2+7958.20B2+15554.86C2;R2=195.43-1469.78A-953.10B-1604.30C-2027.86AB+5872.68AC+7797.99BC+5877.71A2+7721.36B2+7009.48C2.The optimized parameters of dynamic models was the combinition of ?-PL 0.20 g/L,Nisin 0.05 g/L,lysozyme 0.05 g/L.Under such optimum condition,the actual inhibiting rate of Clostridium sporogenes and Bacillus subtilis was up to 99.34%and 99.28%respectively.Then,the application of compound bio-inhibitor agents on RTE abalone product during storage was studied.And the quality changes of RTE abalone product during period of storage under 4? and 25 ? were analyzed.Results showed that the shelf-life of RTE abalone product without and with bio-inhibitor agents were respectively 3 days and 6 days under of 25 ?.Meanwhile,the shelf-life of abalone without and with bio-inhibitor agents were up to 30 d and 90 d under 4?,which meant that bio-inhibitor agents can effectively maintain quality of RTE abalone product and prevent it from spoilage under 4?. |
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