Study On Characteristics Of Brochothrix Thermosphacta In Pork Protein Decomposing And Protease Secretion In Liquid Culture

On account of being hard to achieve complete sterilization,chilled pork,an important consumption pattern of pork,is perishable.Furthermore,the Microbial phase analysis of chilled pork shows,under aerobic conditions,Brochothrix thermosphacta is one of main initial microorganisms in chilled pork.Whereas,the study of Brochothrix thermosphacta,which demonstrated to be the dominant microorganism leading to corruption of pork under aerobic conditions,so far,has concentrated on the proliferation of variation in different chilled pork products.However,the research about its corruption mechanisms is still rarely reported.The main nutrient of chilled pork is protein.Thus,the corruption mechanisms may closely relate to the degradation of proteins.In this paper,by studying the effects of temperature and the concentration of NaCl on the concentration of protein,the sterilization effect of four sterilizations and the accompanying nutrient change in the water-soluble protein extract of pork,a water-soluble pork protein sterile research system was constructed.The results concluded that the effect of temperature and the concentration of NaCl on the concentration of protein was non-significant,moreover,compared to microwave and ultrasonic wave,the microfiltration achieved the better sterilization effect without destroying nutrients,can ensure the water-soluble protein extract of pork sterile in three days when stored in 150 mL conical flask on an orbital shaker?200r/min?at 30?,at least.Accordingly,the microfiltration was proved to be the preferable sterilization method to construct the water-soluble pork protein sterile research system.Afterwards,the number of Brochothrix thermosphacta and the protein content were monitored to study the decomposition of Brochothrix thermosphacta on the water-soluble proteins in different culture medium.It was found that the content of the water-soluble protein in two kinds of water-soluble protein extract of pork,which merely added 1g/L MgSO₄?1g/L K2HPO4 and 15g/L glycerol and added urea as additional nitrogen,both decreased,at some level,with the lengthening of storage time.While,the descending degree of both were far less than the descending degree of the protein content in the culture medium added NH₄NO₃ or?NH₄?₂SO₄ as additional nitrogen.Hence,the above results illustrated that being cultured in the water-soluble protein extract of pork added MgSO₄,K2HPO4,glycerol,?NH₄?₂SO₄ or?NH₄?₂SO₄,the Brochothrix thermosphacta proliferated,and showed the decomposition on protein.Nevertheless,the Brochothrix thermosphacta cultured in liquid medium added 20g/L?NH₄?₂SO₄ grew better than being cultured with additional 12g/LNH₄NO₃.In addition,the content of protein in the former culture decreased much more significant.The above results demonstrated,under certain conditions,the Brochothrix thermosphacta showed significant decomposition on water-soluble proteins of pork,which suggested the decomposition may repose mainly on the its extracellular proteases secreting.The follow-up measurement of the activity of protease in incompletely sterilized water-soluble protein extract of pork demonstrated that the measurement with Folin method will be more precise by extending the reaction time.Then the activity of extracellular proteases secreted by Brochothrix thermosphacta,cultured in sterile water-soluble protein extract of pork respectively added MgSO₄,K2HPO4 and glycerol,or MgSO₄,K2HPO4,glycerol and?NH₄?₂SO₄ or MgSO₄,K2HPO4,glycerol and NH₄NO₃,was measured.The result showed that the content of protease was so low that cannot be detected by the Folin method.Afterwards,the extracellular protease,secreted by Brochothrix thermosphacta in sterile water-soluble protein extract of pork with additional MgSO₄,K2HPO4,glycerol and?NH₄?₂SO₄ was concentrated.It was found that the activity of protease in crude extracts was still low.In this paper,by detecting the changing of the protein content and the molecular weight,causing by Brochothrix thermosphacta under the water-soluble pork protein sterile research system,the degradation process on protein was studied systematically.Accordingly,it was demonstrated that the Brochothrix thermosphacta have a certain decomposition on protein in pork.