Morphological Changes Of Pleurotus Eryngii During Drying Based On Three-dimensional Vision Technology

Drying is a crucial method for extending the shelf life of Pleurotus eryngii.However,the drying process leads to significant three-dimensional morphological changes such as shrinkage,hardening,and curling,which negatively impact its appearance quality and commercial value.This study employed three-dimensional vision technology to investigate the morphological changes of P.eryngii during the drying process.The research was conducted in three stages: Firstly,the study assessed the effects of different drying methods(hot air drying,infrared drying,and microwave drying)on the three-dimensional morphological changes(shrinkage,surface roughness and average curvature)of P.eryngii.It also examined color,total polysaccharide content,antioxidant activity and other physicochemical properties under different drying methods.Secondly,the study evaluated the effects of different temperatures and humidity levels on the three-dimensional morphological changes,moisture distribution,and physicochemical properties of P.eryngii under hot air drying.Finally,P.eryngii was categorized into different freshness levels to investigate the effects of each level on the drying kinetics,physicochemical properties,and nanostructure of cell wall polysaccharides,which were aimed at revealing the relevant mechanism of freshness levels on the appearance and quality changes of P.eryngii.The main results of the study are as follows:(1)The effects of three drying methods,namely hot air drying,infrared drying and microwave drying,on the drying characteristics,three-dimensional morphology and physicochemical properties of the P.eryngii were investigated,and the results showed that the drying method and drying conditions had a significant effect on the drying time,with microwave drying having a significant advantage in reducing the drying time to only 12 min.The best appearance was obtained by hot air drying at55 °C and 65 °C.In addition,hot air drying and infrared drying at lower drying temperatures resulted in better colour,total polyphenol content and antioxidant activity,while microwave drying significantly impaired the colour and nutritional quality of the mushrooms.The microstructure of the dried samples was observed and it was found that the drying method and drying conditions had a significant effect on the microstructure of the P.eryngii.At lower drying temperatures,significantly dispersed mycelium was observed in the hot air dried and infrared dried samples,while higher drying temperatures resulted in cross-linking and aggregation of mycelium.(2)Under hot air drying conditions,both drying temperature and relative humidity have a significant effect on drying time.Increasing the drying temperature and decreasing the relative humidity significantly increased the drying rate and shortened the drying time.Increasing the drying temperature from 55 °C to 85 °C increased the final shrinkage of the slices from 37.91% to 66.40%,while increasing the relative humidity from 10% to 40% increased the shrinkage from 30.63% to68.16%.Similarly,the surface roughness of the P.eryngii increased with the increase in drying temperature and relative humidity.Hyperspectral imaging was used to visualise the surface moisture distribution during the drying process of the P.eryngii and revealed variability in the moisture distribution on the surface of the material at different drying temperatures and relative humidities.The P.eryngii slices obtained under low temperature and low humidity drying conditions had better colour quality,brighter surface,optimal total polysaccharides,total polyphenols and antioxidant activity,and had a loose and porous structure,showing good rehydration.(3)The freshness degree of P.eryngii was graded(Ⅰ,Ⅱ,Ⅲ,Ⅳ,Ⅴ,Ⅵ).The weight and hardness gradually decreased with the decrease of freshness,and the surface color difference gradually increased.With the decrease of fresh grade,the total extraction rate of cell wall polysaccharide gradually decreased,and the extraction rates of cold water extraction(PC),hot water extraction(PH)and hot alkali extraction(PA)also gradually decreased.According to the observation of the nanomicrostructure of cell wall polysaccharides by AFM,more linear branches and long chain structures in PC and PH were gradually degraded to short linear chains and globular structures,and the number of branches and the size of aggregates were gradually reduced with the decrease of freshness.The alkali extraction has a certain effect on the destruction of polysaccharide chain structure,PA does not have crosslinked three-strand helix structure,with the freshness decreases,irregular short linear chains and small aggregates gradually become spherical aggregates.With the decrease of the freshness degree of P.eryngii,the color difference ΔE,total polysaccharide content,total polyphenol content and DPPH free radical scavenging activity of P.eryngii after drying decreased gradually,and the shrinkage rate and deformation increased gradually.Through correlation analysis,the total polysaccharide content,total polyphenol content,color difference ΔE and shrinkage rate of dried samples were significantly correlated with the freshness grade of P.eryngii.The total polysaccharide content and total polyphenol content were significantly positively correlated with the freshness grade,while the color difference ΔE and shrinkage rate were significantly negatively correlated with the freshness grade.The freshness of P.eryngii not only affects the drying time and water migration rate,but also has significant effects on the nutritional quality,color and deformation after drying.