Quality Changes Of Low-temperature Sausage During Room Temperature Storage

Compared with high-temperature meat products,low-temperature sausage,as a typical low-temperature meat product,has been favored by consumers due to it can maintain the edible quality and nutritional flavor to the greatest extent.China is a large country in the processing and consumption of meat products.As representative product of low-temperature meat products,low-temperature sausage has an increasing market share every year.At present,the production and distribution of low-temperature sausage are generally in a backward state of “seasonal processing and open sales”.Some heat-resistant microorganisms will survive at low sterilization temperature.Thus,low-temperature sausage is prone to spoilage with the action of microorganisms during the room temperature storage and shelf,such as slime,smells,acid production,which seriously affects the storage and circulation.It is a big challenge for the development of low-temperature sausage industry.Based on this,analyzing the quality change of low-temperature sausage during room temperature storage can provide theoretical and practical basis for the problems in storage and circulation,which is of great significance to guide production.At the present study,the low-temperature sausage was produced with basic formula,and was stored at20 ℃ for 12 days.This paper discusses the quality change of different storage period from the perspectives of quality change,microbial community structure and metabolites,excavates and analyzes the internal relationship between storage time and quality change,in order to establish the storage quality evaluation and quality control standard of low-temperature sausage.The main results are as follows:The quality of low-temperature sausage has changed significantly with storage time.The results showed that the number of microorganisms increased gradually with the extension of storage time.The total bacterial counts(PCA 36 ℃)and lactic acid bacteria(LAB)showed an obvious increased trend,and were basically in an order of magnitude.Followed by Staphylococci,Enterobacteriaceae,Pseudomonas,Brochothrix thermosphacta and yeast.TVB-N shows an increased trend,and L*,a* and b* values show a decreased trend in varying degrees.The results of electronic nose and electronic tongue can be used to judge the shelf life.Based on PCA,the changes of taste and smell of low-temperature sausage can be divided into three stages:0 ～ 2 d,4 ～ 6 d and 8 ～ 12 d,which provides a time node for the follow-up research.Compared with the odor attributes,the appearance attributes are reliable indexes to predict the microbial corruption of lowtemperature sausage during storage.Based on the sensory properties and microbial counts,the shelf life of low-temperature sausage during room temperature storage is 6 d.The spoilage characteristics are as follows:the negative odor include sour and rotten egg,white and darken color,loose texture and loss of elasticity,slime production,acidification is the most typical quality changes.The changes of lipid oxidation and lipolysis with the storage time during low-temperature sausage storage were determined,and quantified the effect on protein oxidation by the mixed effect model.With the extension of storage time,protein carbonyl continued to increased,peroxide value(PVs)and thiobarbituric acid(TBARS)also showed an increasing trend,the contents of free fatty acids and neutral lipids increased,while lipase activity decreased in varying degrees.Both PVs and TBARS could explain a large part of the variation in protein carbonyls.Free fatty acids were significant predictors of variation in protein oxidation when they were included in a model also including storage periods.The protein carbonyls were also influenced by lipase activity.Taken together,protein oxidation,lipid oxidation,and lipolysis in lowtemperature sausage during storage were interdependence and interaction,and mutually promoted each other.The bacterial community structure was detected by 16 S r DNA amplicon sequencing technology,combined with OTU cluster,species annotation,richness analysis,α and β Diversity analysis.The results showed that the amount of sequencing data was saturated and the sample size was sufficient.The sequencing results could reflect the bacterial diversity composition of low-temperature sausage during storage.With the extension of storage time,the bacterial community diversity and richness showed a decreased trend.After 4d,the relative abundance of Firmicutes increased to 85.50% at the phylum level,and there was no significant fluctuation at 4 ～ 12 d(P > 0.05).At the genus level,Bacillus was accounts for more than 75% of the bacterial composition,and there was no significant fluctuation at 4 ～ 12 d(P > 0.05).Therefore,it is suggested that Bacillus is the dominant spoilage bacterium of low-temperature sausage during room temperature storage.Controlling the growth,or pollution of thermostable Bacillus and improving the quality and safety of lowtemperature sausage and other related low-temperature meat products will be the focus and direction of research in the future.The evaluation of metabolites in low-temperature sausage during room temperature storage were analyzed using untargeted UHPLC–MS/MS metabolomics.The results show that the metabolomics platform remains stable and the quality of metabolomics data is reliable.During the 12 days storage,2979 metabolites were identified,1770 from positive ion mode and 1209 from negative ion mode,respectively.Among them,845 metabolites can be annotated by HMDB.Compared with samples from 0 d,significant differences were observed except on 2 d.With the extension of storage time,the number of differential metabolites between groups gradually increased.Taking VIP > 2 and P < 0.05 as the screening criteria,245 metabolites with significant differences were screened,among which organic acids and their derivatives,lipids and lipid-like molecules,organoheterocyclic compounds were the most.The differential metabolites that have a significant impact on the quality of low-temperature sausage mainly involve 7 metabolic pathways,including purine,pyrimidine,tyrosine,and tryptophan,as well as nicotinate and nicotinamide,in addition to biosynthesis of amino acids,and β-oxidation.Protein catabolism and β-oxidation was the main metabolic pathway that followed by quality deterioration.