Detection And Repair Mechanism Of Injured Aeromonas Spp. From Thawing Pork

Frozen meat plays an important role in meat market of state regulation. It is notonly one of the main product forms in import and export of meat products in domesticand international trade, but also raw materials of all kinds of meat processingenterprises. The safety of thawing meat was significantly threatened by microorganism.After many treatments (e.g thawing), some microorganisms may be killed, some maysurvive (non-injured), the other may be sublethally injured. Microorganisms in meat cansuffer from some degrees of sub-lethal injury to become injured bacteria during freezingprocessing. However injured bacteria can resuscitate and become functionally normal ina favorable environment (e.g. thawing), and the repaired bacteria may restore itstolerance of selective substances and has re-oxygenic, pathogenic. Traditionalmicrobiological detection methods were high false-negative and only fit for detectingthe inactivation and remaining microbial, while the injured was hard to grow onselective medium, and they were often ignored as inactivation type. Therefore, it isnecessary to study the injured types and determine effective methods to detecte them.Moreover, determining the injury mechanism of microorganisms can provide atheoretical guide for better detecting microbial counts.This paper focuses on Aeromonas spp. on the thawing meat, because it is one ofthe specific spoilage bacteria. Predictive microbiology theory was used to buildinactivation model of injured Aeromonas spp. during thawing process. Besides, in orderto better understanding injury model and substrate for detection of sub-lethalAeromonas spp., researches about freezing injury and repair mechanisms were carriedout, and the injury was explained on both cell membrane and cytoplasm levels, Allthese results would contribute for the safety of meat industry.Content and results of this study are as follows:(1) Comparing solid with liquid repair method showed that medium (TSAYE) wassuit for repair research. The medium was added1.0%,1.5%,2.0%,2.5%and3.0%ofNaCl, respectively. Results showed that TSAYE+1.5%NaCl medium could be used forcounting injured Aeromonas spp. by analysis of SPSS17.0software. The number of injured Aeromonas spp. colonies was counted by difference between TSAYE andTSAYE+1.5%NaCl medium(2) This study indicated that repair time of injured Aeromonas spp. was about75min during meat thawing process at25℃, also this result was obtained on both TSAYEand TSAYE+1.5%NaCl medium. The Origin8.0software was used to fit theinactivation curve, and results showed that the inactivation curve could be fitted withPolynomial model (R2=0.9937) and Boltzmann model (R2=0.9884), respectively.Moreover, Polynomial model might be better fitting injury inactivation process by themodel evaluation.(3) To explore freezing injury mechanism preliminarily, experiments on measuring260nm and280nm absorbance variations of cell supernatant centrifugation andinhibition of nucleic acids, peptidoglycan and ATP were carried out. The resultsindicated permeability of cell membrane was damaged, thus leading it sensitive for1.5%NaCl. Moreover, DNA and peptidoglycan synthesis were not destroyed, but RNAand ATP synthesis were inhibited.This study contains detection of injuried Aeromonas spp. on thawing meat,establishing its inactivation model and exploring freezing injury mechanism. Resultsshowed that difference between TSAYE and TSAYE+1.5%NaCl medium is the numberof injured Aeromonas spp., suitable temperature and repair time are25oC and1h,respectively; Polynomial model could be used for fitting the inactivation model;membrane permeability, synthesis of RNA and ATP were damaged.These conclusionscan provide a guidance for meat safety, making consumer regain their confidence for thesafety of meat.