Temporal And Spatial Distribution Of Surface Microorganisms During Cooling Of Pig Carcass

Carcass chilling is an important part of the process of chilled meat.The temperature and humidity of the cold storage will affect the microbial pollution and the shelf life of the product.However,it is less known about the associations between environmental temperature/humidity and microbial counts.This study aims to investigate the the spatial and temporal changes in wind speed,temperature,humidity,and microbial composition on the surface of pig carcass during chilling.1.Change in wind speed,temperature and humidity in the chiller and the establishment of a fluid simulation model for pig carcass chillingAt different time points(0,2,4,6,8,10,12,14 h postmortem),pig carcasses at 14 positions in a chiller were selected for measuring wind speed,temperature and humidity using a thermometer and humidity meter.The measurements were repeated for 5 batches.Fluid dynamic models were achieved by the Ansys 16.0 software,in which grids were used to simulate dynamical changes in the wind speed,temperature and humidity.The results showed that,at the early stage of chilling(0 to 8 h),due to door opening and the heat dissipation of the pig carcass itself,the wind speed in the chiller varied greatly,and the temperature and humidity were gradually increased(p<0.05).The total number of microbial colonies on the surface of carcasses increased to different extents at the early and middle stages of chilling(P<0.05),but decreased at the late stage of chilling(8 to 14 h).At that stage,the door was closed,and the chiller had been full of carcasses.The temperature and humidity decreased rapidly,resulting in a significant decrease in the total number of microbial colonies(P<0.05).2.Changes and correlation analysis of total microbial colonies on the carcass surface during chillingBefore pig carcasses entered,500 L of air samples were collected at each sampling point using an airborne plankton sampler and a PC A plate,and then cultured in a 37?incubator for(48±2)h.When sampling places were occupied by carcasses,bacteria sampling were performed by wiping back side,foreleg,abdominal cavity,and thoracic cavity of carcasses with an area of 100 cm2.Bacteria were cultured at 37 ? for 48 h±2 h.The results showed that the total number of colonies on the windward side of the pig carcass was higher than that of the leeward side.The microorganisms in the foreleg and the thoracic cavity were higher.Correlation analysis showed that the total number of colonies were significantly correlated with temperature,humidity,chilling time,and sampling locations(P<0.01)and with wind speed(P<0.05).3.Composition of microorganisms in pig carcasses during chillingAt different chilling conditions,the bacterial samples were obtained by wiping the forelegs and thoracic cavity of the pig carcass with a size of 100cm2.The wiper after wiping was stored at-80? for future use.Microorganisms in the air were captured by the airborne plankton sampler and PCA plate.Each plate captured 500L of airborne microorganisms and cultured at 37? for 48±2h.Each plate was eluted with 1-2 ml of sterile water and stored at-80 ? until use.The obtained air microorganisms and swabs containing microorganisms on the surface of swine carcass were sequenced,and flora analysis was performed.The results showed that during the chilling process,the species and quantity of microorganisms in different parts were different.Proteobacteria was dominant.The types of microorganisms on the forelegs and thoratic cavity were partially same as those in the air.Air may be one of the main sources of bacteria on the pig carcasses.As chilling time increased,bacteria in the air and on the carcass surface were maintained diferent,but the difference in microbial composition among the three groups decreased.Proteobacteria,predominant in the air and the carcass surface,was likely to come from human skin.Firmicutes and Bacteroidetes were abundant in the intestines of humans or mammals.Actinobacteria was widely distributed in soil and water.Thus,the workers on the processing line may be one of the main sources of microorganisms on the carcass surface during chilling.In addition,the cooling water and incomplete cleaning also affected the population structure of microorganisms on the surface of pig carcasses.