Construction Of Growth Predictive Model Of Listeria Monocytogenes In Low-temperature Prepared Foods And Application Of Photodynamic Bacterial Inactivation

Food safety is a major issue related to people’s health,national economy and people’s livelihood,as well as one of the main factors affecting the development of food industry in China.Nowadays,there are many factors that can affect food safety.Among them,foodborne diseases caused by pathogenic microorganisms are still one of the most prominent public health problems in the world.Low-temperature prepared foods,also known as RET-foods,can be eaten directly without or after simple heating.Therefore,it is prone to food poisoning caused by pathogen contamination.Listeria monocytogenes（L.M.）is an important zoonotic food-borne pathogen in Listeria,which widely exists in nature and easily causes listeriosis.L.M.has strong environmental tolerance and can grow and reproduce at low temperature（such as 4℃refrigerator）and survive for a long time,posing a serious threat to the quality and safety of low-temperature prepared RET food.Therefore,in this study,refrigerated chicken salad and apple juice were used as the research objects to establish the growth prediction model of L.M.in low-temperature prepared foods at different initial contamination concentration under different storage temperatures for exploring the effect of storage temperature and initial concentration on the L.M.growth.Subsequently,the photodynamic inactivation（PDI）technology was developed using berberine hydrochloride（BBR）as a photosensitizer and its bacteriostatic effect and mechanism on the L.M.was further studied.On this basis,the photosensitizer BBR was added into the sodium alginate-chitosan matrix to prepare the BBR/sodium alginate/chitosan composite packaging film,and the preservation effect of this film on salmon was investigated.This study provides a theoretical basis for L.M.growth prediction in the process of storage and transportation of low-temperature prepared food,and also provides a new idea and method for the development of novel composite packaging materials with PDI effect and the preservation of salmon at low temperature.This main research results were as follows.1.Construction of L.M.growth prediction model in refrigerated chicken salad and apple juiceThe effect of different storage temperatures and initial concentrations on the L.M.growth in low-temperature prepared foods were studied.The growth prediction models of L.M.in refrigerated chicken salad and apple juice were constructed.Gompertz and Weibull models of L.M.with different initial contaminations at different storage temperatures were fitted by Matlab software,and the corresponding prediction model parameters were calculated,including maximum growth rate(μ_max),hysteresis period（λ）and inactivation scale parameter（b）.The results showed that in refrigerated chicken salad,L.M.with three initial contaminated concentrations showed slow growth at different storage temperatures,and with the increase of temperature from 2℃to 16℃,the hysteresis growth period of L.M.was shortened,and the maximum growth rateμ_maxincreased from 0.3006 h^-1 to 1.7673 h^-1;in refrigerated apple juice,L.M.with three different contaminated concentrations was inactivated at different storage temperatures.With the increase of storage temperature from 2℃to 16℃,the inactivation rate decreased from 0.433 h^-1 to 0.31 h^-1,and the inactivation scale parameter b decreased from 0.063 to 0.009.These results indicate that the harm of pathogenic microorganisms to food quality can be reduced and the quality safety can be improved by controlling the storage temperature and the initial contaminated concentration of L.M.This study provides a theoretical reference and scientific basis for the growth prediction of pathogenic bacteria in low-temperature prepared food.2.Inactivation and biofilm removal of L.M.by BBR-mediated PDI technologyA natural photosensitizer BBR with aggregation-induced luminescence properties was obtained and used to construct photodynamic inactivation technology.The effect of this method on L.M.inactivation and biofilm removal was evaluated.The results showed that BBR had a significant inhibitory effect on L.M combined with light irradiation,and this inhibitory effect is more obvious with the increase of BBR concentration.When the BBR concentration was increased above 50μM,the sterilization efficiency was as high as 99.9%.This study also found that 100μM BBR combined with light for 30 min could remove more than 60%of the biofilm.Further mechanism studies showed that BBR-mediated PDI technology mainly inhibited the specific gene expression of L.M.and damaged its DNA,thereby reducing its adhesive growth and escape ability,and achieving the L.M.inactivation.3.Inhibition effect of BBR/sodium alginate/chitosan composite packaging film on L.M.and its preservation roleThe photosensitizer BBR was added into the sodium alginate and chitosan matrix to prepare the BBR/sodium alginate/chitosan composite antibacterial packaging film by the hot melt casting method.The inhibitory effect of this composite packaging film on the growth of L.M.in salmon was investigated.In addition,the preservation effect of the composite film on salmon was investigated by analyzing the physicochemical indexes such as volatile base nitrogen（TVB-N）,free fatty acid（FFA）,pH value,protein content and texture.The results exhibited that the BBR/sodium alginate/chitosan composite antibacterial packaging film combined with LED light treatment significantly inhibited the L.M.growth,decreased the TVB-N and free fatty acid generation,delayed protein degradation and lipid oxidation,maintained the normal pH value,delayed the softening of meat quality,effectively maintained the good sensory quality of salmon.The above results indicate that the storage method of BBR/sodium alginate/chitosan composite packaging film combined with light treatment has an important role in preventing the deterioration of salmon caused by microorganisms and prolongating the storage and preservation time of salmon.