Spatial And Temporal Distribution Characteristics Of Ethylene In Fruit And Vegetable Refrigeration Process And Optimal Control

Fruit and vegetable losses have always occupied a relatively large proportion of the cold chain losses,fruits and vegetables after harvest has also been physiological activities,consumption of their own nutrients,refrigeration as an important means of delaying postharvest physiological activities,for the storage of fresh fruits and vegetables have an important role.During the refrigeration process,ethylene gas is an important factor affecting the storage quality of fruits and vegetables.In this paper,we take apple as an example,based on cold storage refrigeration,in order to study the spatial and temporal distribution pattern of ethylene gas,improve the quality of cold storage and delay the arrival of ripening.A combination of experimental measurements as well as CFD simulations was used to study the spatial and temporal distribution pattern of ethylene gas during apple refrigeration and to find out the peak of ethylene gas release.And the experimental study was done on the effect of ethylene gas on the quality of different fruits and vegetables mixed loading during the retail period(15℃),aiming to reveal the effect of ethylene gas on their quality in mixed loading of fruits and vegetables.The main findings were as follows:The concentration of ethylene gas in the apple zone increased with the increase of refrigeration time during the process of apple refrigeration.Two peaks occurred,the first one was at 7 d with a peak of 5.1 μg/(kg?h),due to the fact that the apple fruits were just picked and were still in the growth stage.The rate of ethylene release decreased with growth.The second peak occurred at 32 d with a peak of 14.0 μg/(kg?h).In contrast,the respiration rate showed two respiration peaks,the first at 5 d with a peak of 2.6 mg/(kg?h).The second respiration peak occurred at 35 d with a peak of 4.2 mg/(kg?h).Moreover,the concentration of ethylene gas in the environment was increasing.Inside the apple,ethylene gas gradually diffused from the inside of the apple to the surface of the apple,which indicated that ethylene gas was produced by the apple.The accumulation of ethylene gas also occurs in the refrigerated environment,and the accumulation of ethylene gas occurs in places with low airflow velocity and poor ventilation.The pattern of ethylene gas release during apple refrigeration shows an increasing trend with the increase of refrigeration time,when the apples are in the ripening stage.After reaching the peak,complete ripening,apple fruit senescence,ethylene release rate decreases.By comparing the peak ethylene gas release with the peak respiration rate,the accompanying appears in the fruits during the respiratory leap,so the ethylene detection can represent the intrinsic quality of apples to some extent.Ethylene detection also reduces the complexity of apple flavor quality assessment.This study provides a novel and simple idea for nondestructive apple quality testing.By examining the effect of mixed fruit loading on their postharvest physiological response and quality,the highest ethylene concentration,capable of reaching 300 ppm,was found in the chamber containing apples alone,capable of releasing larger concentrations in a short period of time.In the mixed chamber containing apples,ethylene concentrations were higher than in kiwifruit alone as well as in banana.Mixed storage of apples with bananas and kiwis resulted in higher respiration rates and ethylene production rates in bananas and kiwis,and the productivity of ethylene for bananas used for storage with apples increased from 0.02mg/(kg?h)to 0.9 mg/(kg?h).The excessive accumulation of ethylene in the chambers containing only apples resulted in an increase in ethylene production rate from 28 mg/(kg?h)to 51 mg/(kg?h)for apples and an initial tissue strength of 26.09 ± 5.3 N was measured for kiwifruit,which decreased to 10-20 N when kiwifruit was stored alone and with bananas.the lowest decrease in tissue strength was found.Combining the mass loss before and after storage,the maximum percentage mass loss was observed in the mixture of apples and bananas,accelerating their mass loss.The need for proper separation(based on ethylene sensitivity)of fresh produce during transport,storage and retail display is emphasized.Long-term storage or transport of such mixed loads would be highly detrimental.This helps to minimize the exposure of ethylene-sensitive products to commodities with high ethylene emissions.