Study On The Rule Of Evaporative Loss And Control Technology For Pig Carcass During Chilling

Chilled meat is the main form and future trend of meat consumption in China,and the output value proportion of the chilled meat in meat industry has risen to over one third.Carcass chilling is the most important stage of the chilled meat processing.Causing by the difference of vapor pressures between its surface and the air,the water in carcass surface evaporates during chilling.However,under the hydrothermal coupling,the internal water diffuses and immigrates to the surface,leading to a decrease of internal water of carcass and the evaporative loss.For pig carcasses,the evaporative loss in 24 h after slaughter could achieve to 3.5%,which causes serious economic losses to the company.Researchers have found that the increase of the relative humidity of the cooling environment and the surface spraying of the pork could effectively decrease the evaporative loss.However,the mechanism is not clear and the technical processing and equipment have to be improved.This study investigated the change in water mobility of pork during chilling by using the relaxation time and images of the low-field nuclear magnetic resonance and compared effects of environmental humidifier condition and spray-chilling condition on evaporative loss.On the basis of the selection of the spray chilling treatment and the optimal parameter,a new automatic spray chilling equipment was developed.Furthermore,the nozzle flow consistency and the spray uniformity were tested and the operation effect verification was carried out.It provides a theoretical basis and equipment references to upgrade technology of China's chilling meat processing industry.The study mainly includes the six following parts:1.Investigation of the change in water mobility of pork during chillingThis study was designed to explore the change in water mobility in skin-on and skin-off pork during blast chilling and spray-chilling by using the relaxation time and images of the low-field nuclear magnetic resonance.The results indicated that the water vapor pressure on the meat surface was greater than that of the cold air in the environment.The water on the surface was lost in the environment by evaporation,leading to a water potential difference between the interior and the surface.Under the action of water potential difference,the inner water is gradually migrated to the surface.The evaporative loss was mainly derived from free water at the initial stage of blast chilling,while it was immobilized water that contributed to the evaporative loss at the late stage.Similar to the blast chilling,the potential water of meat surface was increased by the evaporation of free water in the spray-chilling treatment.However,the potential water could be decreased by spraying water over meat,which could replace the immobilized water during the removal of heat from pork,resulting in a reduction of evaporative loss.2.Effects of environmental humidifier condition and spray-chilling condition on evaporative loss of pork during chillingIn order to compare the different evaporative reduction effects of environmental humidifier condition and spray-chilling condition of pork,ultrasonic atomization humidification and gas-liquid mixing atomization spray in cold storage environment was simulated in an artificial climate chamber at 0-4?.And it is necessary to investigate the chilling rate and the evaporative loss under different chilling conditions.The cooling process under the spray-chilling condition and the environmental humidifier condition could both significantly decrease the evaporative loss of pork.Therefore,the result reflects that reducing evaporative loss effect for spray-chilling is better than that for environmental humidifier.On the basis of the quality of the pork,the final average of evaporative loss of samples under spray-chilling condition for 24 h was 1.07%,which was 0.37%lower than that under environmental humidifier condition and 1.84%lower than the control.Moreover,spray-chilling and environmental humidifier cooling treatment could increase the cooling velocity of pork,which can reach a stable internal temperature of the carcass in advance.The spray-chilling treatment and environmental humidifier treatment could reduce effectively the evaporative loss peak time.Relationship of the evaporative loss peak time for three groups was spray-chilling<environmental humidifier<control group.The spray-chilling treatment could decrease the water dissipation,leading to a lower evaporative loss(P<0.05).3.Investigation of the selection of the spray chilling treatment and the optimal parameterIn the condition of carcass spraying with a fixed frequency,a reddish color of pig suface was appered in insufficient spraying,while a white color serious water marks were appered in sufficient spraying.In order to achieve a better surface color and the 24h evaporative loss,the pig carcass surface was sprayed under high frequency spray chilling at the early stage and low frequency spray chilling at the later stage by a multi-factor orthogonal test.The results showed that,the order of importance of the spray parameters which affected the water loss rated from high to low was total time of spray chilling with high frequency,interval time of high frequency spray period,interval time of low frequency spray period,single spray time,and total time of spray chilling with low frequency.Total time of spray chilling with high frequency had extremely significant effect on the evaporative loss(P<0.05).Moreover,it also had significant effect on L*value and a value(P<0.05),while other parameters had no significant effect on them.In order to decrease the evaporative loss and keep the surface color of the pig carcass,high frequency spray chilling at the early stage and low frequency spray chilling at the later stage was used.The total time of spray chilling with high frequency was 2 h,the single spray time was 10 s,the interval time of high frequency spray period was 5-9 min,the interval time of low frequency spray period was 30-50 min,and the total time of spray chilling with low frequency was 4 h or even shorter.4.The main parts selection and design of the spray chilling equipmentIn order to design a spray-chilling equipment on the basis of the surface color and the minimizing evaporative loss of pig carcass,this study designed a gas-liquid mixing atomization spray equipment combined with the water film coverage requirements of carcass surface and the spray characteristics of different conditions,according to environmental parameters(temperature,humidity and wind speed)and changes of different parts of the pig carcass based on the determination of the cold storage factor.The equipment was mainly composed of a frame,an atomizing spray-chilling equipment and a swing drive system.The atomizing spray-chilling equipment was composed of high pressure water supply system,high pressure gas supply system,high pressure water-gas mixing spray system(the spray nozzle).The equipment could form many uniform droplets with small diameter,spraying at a certain speed on the surface of the pig carcass.According to the mechanical transmission mechanism,the swing drive system could rotate the bar of the spray nozzle at a certain angle,leading to a uniform water film of the pre-cooled pig carcass and without water marks.The test proved that the spray equipment had the same flow rate and uniform spray,and the spray nozzle was rotated by the swing drive system,droplets could evenly cover the pig surface as expected.5.Selection of control system hardware and software design of the spray chilling equipmentIn order to improve the automation level of the spray operation during chilling of pig carcass,the control system of gas-liquid atomizing and spraying was designed according to the optimal parameters and functions requirements of the spray-chilling equipment,on the basis of control system PLC,expansion module,touch screen,relay and other key components.The automatic opening-closing of each spray pipeline,the interlock of spray operation between pipelines,the sequential operation of waterways and air routes,and the automatic start-stop of air compressor were realized in trapezoidal diagram control program which was written by the process of atomized and spray humidifying;the gas-liquid atomized and spray humidifying control system uses PLC as a processor,the touch screen for the man-machine interface,the embedded main window,parameter setting window and user login window can be used for monitoring the deice running state,modifying the spray operation parameters and management control of device.By using this control system,the device could be automatically controlled,reducing labor intensity of manual operation and avoiding misoperation were realized at the same time.6.Verification of effectiveness and benefit analysis of humidification and evaporative loss of the spray chilling equipmentThis study used the developed automatic spray chilling equipment with the optimal spray parameters.In compared with the manual spray and the conventional air-cooled operation,the results showed that the evaporative loss of the system was 1.02%± 0.02%by 24h.Compared with 1.72%±0.05%of manual spray and 2.07%± 0.09%of the control,it was reduced about 0.7%and 1.05%,achieving purpose of decreasing evaporative loss.The L*index which reflects the brightness of pig carcass surface and the a value which reflects the color under spray-chilling condition were 78.58 ±1.17 and-1.13 ± 0.11,which significantly better thant the control and the manual group.From the view of reducing loss and saving manpower cost in terms of economic benefits,if the factory slaughter 1 million pigs per year,the automatic spray chilling equipment could save 9.64 million yuan and 13.05 million yuan respectively compared with the manual spray and non-spray control groups.The system designing is scientific and the automation is in a higher degree,which can achieve the ideal effect in loss reduction and consumption reduction and can also improve the sensual quality of carcass surface,Moreover,the benefits of saving expenditure and increasing income are considerable,which leading to a better production-application prospect.