Study On The Emission Characteristics Of Ripening Gas And Ventilation Strategies Of Apple Cold Storage

Apple is a typical climacteric fruit,the respiration intensity will suddenly rise to form a respiratory peak,and then decline until the apple ages and spoils,and eventually lose its nutritional value become inedible during the postharvest cold storage.The emergence of respiratory peak is the result of a sharp increase in the ethylene concentration of the ripening gas in the environment,and is also a sign of apple turning from maturity to aging.Therefore,to improve the storage quality of apple,it is necessary to reduce the postharvest respiration intensity,slow down the respiration,and delay the period of respiratory peak.Environmental factors affecting the postharvest respiration of apple include storage environment temperature,relative humidity,O2,CO2,and ethylene concentrations.In this study,based on the mechanism of apple preservation and the research status of factors affecting apple respiration,a combination of experiment and numerical simulation was used to study the variation of gas component concentration caused by respiration in apple cold storage,and then a method of ventilation was proposed.In this study,a numerical model of gas components diffusion in apple cold storage was first established to simulate the temporal and spatial variation of O₂,CO₂,and ethylene during storage.In addition,gas chromatographic analysis was used to study the variation of apple respiration intensity,ethylene release rate and ethylene concentration in storage environment,and the experimental value of ethylene concentration was compared with the simulated value to verify the reliability of the numerical model.Finally,according to the time of ethylene peak,the ventilation mode was determined to reduce the concentration of ethylene in the environment.The effect of turn-on and turn-off of the air cooler on the ethylene concentration elimination effect and temperature stability was studied.The main work and research results are as follows:（1）Taking the 12 L apple cold store container as the research object,a numerical model of gas components diffusion of apple cold storage was established to study the temporal and spatial changes of each component concentrations during storage.Studies have shown that with the increase of storage time,O2 concentration decreased continuously,while CO2 concentration increased continuously,after 32 days of storage,O2 concentration in the storage environment was equal to CO2 concentration,both of which were 10.55%.O2 and CO2 concentrations changed rapidly at the initial stage,and then the change rate tended to be flat.Moreover,the ethylene concentration increased continuously with the increase of storage period,and the growth rate gradually increased,after 70 days of storage,ethylene concentration was 2162μL/L.In addition,O2 concentration showed a spatial distribution characteristic of diffusion from the apple zone to the gas zone and from the inside of the apple to the skin of the apple layer by layer.The spatial distribution characteristic of CO2 and ethylene was opposite to the variation trend of O2.（2）The indoor gas quality detector and gas chromatograph were used to measure the CO2 release and ethylene release rates of apples per unit mass during storage.The change of apple respiration intensity and ethylene release rate with storage time were theoretically calculated and obtained.It was concluded that the peak of apple respiration appeared at 80 d with a peak value of 4.10 mg/（kg?h）,and the peak of ethylene appeared at 70 d with a peak value of 14.0μL/（kg?h）.The peak of ethylene appeared earlier than the peak of respiration,indicating that the apple respiration transition was caused by the sharp increase of ethylene content,so it was necessary to regulate the environment before the ethylene peak.（3）Based on the period of the ethylene peak,the environment in the cold store was studied and the ventilation strategy was optimized.An actual cold store ventilation model was established to study the effect of the start and stop of the air cooler on the ethylene gas emission effect and temperature stability.It was concluded that in the ventilation process,the air cooler should be turned on for shorter ventilation time and better temperature stability.This research may be helpful to thoroughly understand the phenomenon of O2,CO2 and ethylene emission and accumulation,and provide some theoretical guidance for determining practical ventilation measure of apple cold storage.