Extending Shelf Life Of Lentinus Edodes By Vacuum Pre-cooling And Modified Atmosphere Packaging

Basic composition analysis and the basic physiological and biochemical conditions after postharvest were conducted on shiitake mushrooms.At the same time,the effect of vacuum pre-cooling technology on the postharvest physiology and biochemistry of shiitake mushrooms,as well as the effect of the combination of vacuum pre-cooling technology with two different packaging methods on the storage quality of shiitake mushrooms,were also studied.Specifically,this thesis studied the effect of five preservation methods on the quality of mushrooms;that is,mushrooms was stored（1）at room temperature after harvesting;（2）at low temperature（4℃）after storage;（3）at low temperature（4℃）after vacuum processing;（4）with the ordinary packaging method after harvested and vacuum pre-cooling technology;（5）with the modified atmosphere packaging method after vacuum pre-cooling treated.This study provides more research basis and reference for the storage and preservation of mushrooms.The main findings are summarized as follows:After picked,the mushrooms were transported to the laboratory within 2 hours.They were stored in fresh-keeping cabinets at room temperature and 4℃respectively.Then,the basic components of Lentinus edodes were determined by the national standard method.The moisture content of freshly picked mushrooms was 88.12%;the protein content was 12.77%;the crude fat content was 4.58%;the crude fiber content was 8.92%;the total sugar content in the mushrooms was 36.69%;the ash content was 11.21%.Followingly,the physiological and biochemical conditions of mushrooms were studied.The following tissue aging and physiological indicators were tested every 24 hours:moisture,weight loss rate,elasticity,umbrella opening rate,MDA content,PPO activity,reducing sugar content,total phenol content,soluble solids,ascorbic acid content,and respiratory strength.The results showed that the moisture content of mushrooms decreased,the elasticity,the reducing sugar content,the ascorbic acid content,and the respiration strength of the mushrooms gradually decreased with the increase of storage time;the weight loss rate,malondialdehyde content,polyphenol oxidase vitality is constantly increasing;the number of mushrooms opened during storage is increasing.Three key variables in vacuum pre-cooling technology（the optimal conditions for the amount of water were added,pre-cooling temperature and final pre-cooling pressure）were studied through single-factor experiments and orthogonal test.And the optimal vacuum pre-cooling conditions for the mushrooms were obtained:the moisture content was 3%,the pre-cooling temperature was 3℃,and the final pre-cooling pressure was 500Pa.The shiitake mushrooms treated under this pre-cooling condition can extend the shelf life by about 8 days compared to that stored at low temperature.The measured tissue aging and physiological index values were 6.39%higher than the untreated mushrooms group.The elasticity was 0.296,the total phenol content was 2.564 mg·g-1FW higher;the reducing sugar content was 0.16g/100g higher;the soluble solid content 5.2%higher;0.95mg/100g higher ascorbic acid;10.45CO₂mg/kg·h lower respiratory intensity;6.86 lower polyphenol oxidase activity;11%lower weight loss rate;1.375nmol/g lower malonaldehyde content;lower umbrella opening rate 27%;The above data were measured on the 12th day after the mushrooms were harvested,which was based on the last day when the mushrooms survive.The optimum proportions of O₂,CO₂ and N₂ in the controlled atmosphere packaging were studied based on the orthogonal test.The optimum proportion and storage temperature of the three gases were obtained:3%O₂,11%CO₂,86%N₂ and 5℃.After vacuum precooling,the effects of general packaging and air-conditioned packaging on the storage of Lentinus edodes were studied.After the vacuum precooling treatment,the mushroom can be packaged immediately to achieve the best fresh-keeping state.At this time,it can well inhibit the increase of polyphenol oxidase activity and malondialdehyde content of mushroom,control the decrease of total phenol content,ascorbic acid content,reducing sugar content,soluble solid content,water content and elasticity,and can well reduce the rise of respiratory rate during storage.It can effectively control the browning of Lentinus edodes and ensure the quality of Lentinus edodes.According to the standard of the last day of storage,the moisture content of the packaged Lentinus edodes was 5.47%higher than that of the ones stored directly at 4℃after vacuum precooling,and the elasticity was 0.181%,The content of total phenol was4.6583 mg·g-1FW,the content of reducing sugar was 0.29g/100g and the content of ascorbic acid was 0.75mg/100g;4%higher content of soluble solids;15.08CO₂mg/kg·h lower respiratory intensity;12%lower activity of polyphenol oxidase;12%lower weight loss rate;1.827nmol/g lower content of malondialdehyde;47%lower opening rate of umbrellas;It can be seen that the modified atmosphere packaging effect was significant（p<0.05）.After harvested,the mushroom were processed by vacuum pre-cooling technology followed by modified atmosphere packaging.Compared with the stored mushrooms at room temperature,the shelf life can be extended to about 20 days.