Study On The Catalytic Infrared Radiation Disinfection Technology Of Rewetting-dried Shiitake Mushroom

As one of the most prevalent modes of consumption for shiitake mushrooms,dried shiitake mushrooms are appreciated among consumers for its superior umami flavor and richness in nutrients.However,due to its hygroscopic,dried shiitake mushrooms can easily absorb water from their environment under improper storage conditions,resulting in the total number of moulds exceeds the permissible limit prescribed by the national food safety standards.At present,fumigation,high temperature steam and ⁶⁰Co radiation are the most common disinfection techniques employed for shiitake mushrooms with excessive moulds content.However,these conventional processes have many limitations,including low disinfection efficiency,high energy consumption,poor quality,and food safety hazards.Catalytic infrared radiation（CIR）represents an emerging food disinfection technology,mainly relies on natural gas as the heat source with the advantages such as high efficiency,energy-efficient and environmentally friendly,and its application in food disinfection has attracted the attention of domestic and foreign food safety researchers.Therefore,the present work aims to develop a new disinfection technology of rewetting-dried shiitake mushrooms with CIR to ensure the edible safety of rewetting-dried shiitake mushrooms.The main research contents and conclusions are as follows:（1）Isolation and identification test of the dominant mould that causing the mildew of dried shiitake mushrooms.In order to conduct the targeted research on disinfection technology,the dominant mould that caused the mildew of dried shiitake mushrooms was isolated and purified by aerobic plate culture.Then the morphological and microscopic characteristics of the dominant mould were observed.Finally,the dominant mould was identified by ITS r DNA and 18S r DNA molecular sequence analysis and phylogenetic tree construction.Results showed that the main moulds of dried shiitake mushrooms were identified as Aspergillus flavus,Aspergillus niger,Aspergillus chevalieri,Aspergillus versicolor,Penicillium oxalicum,Penicillium sclerotiorum and Trichoderma longibrachiatum.Among them,the detection rate of Aspergillus niger was the highest（33.3%）,and it was inferred that Aspergillus niger was the dominant mould causing mildew of dried shiitake mushrooms.（2）Study on the catalytic infrared disinfection technology of rewetting-dried shiitake mushrooms.The effectiveness of simple CIR and CIR coupled with holding treatment on disinfection of rewetting-dried shiitake mushrooms contaminated with Aspergillus niger（A.niger）was investigated by the batch catalytic infrared radiation device（BCIR）;the drying effect of simple CIR and CIR coupled with holding treatment was analyzed based on the changes in moisture content of the mushrooms;the hardness,rehydration ratio,tissue structure,retention rate of crude protein,polysaccharides and total phenolics of mushrooms were used as evaluation indicators to evaluate the effect of simple CIR and CIR coupled with holding treatment on the quality of mushrooms,in order to establish the high-efficiency and high-quality CIR disinfection technology employed for rewetting-dried shiitake mushrooms.Results showed that both simple CIR and CIR coupled with holding treatment could meet the requirement of irradiation disinfection in industry,while achieving simultaneous drying.According to the three-dimensional disinfection curve of IMCs-CIR heating time-holding time at 60℃,70℃and 80℃,respectively,it was possible to predict the CIR heating time and holding time needed for shiitake mushrooms with IMCs of16.0%～21.4%at each temperature to meet the disinfection requirement.Under the same disinfection requirement,CIR coupled with holding treatment exhibited a significantly smaller influence on the quality of shiitake mushrooms,as compared with mushrooms processed with only CIR heating.Considering the disinfection time and product quality,CIR heating for 52～78 s to 70℃,followed by holding at 70℃for75～30 min was recommended as the most suitable disinfection process condition.Under this process condition,compared with those disinfected only by CIR,mushrooms disinfected by CIR coupled with holding treatment displayed smaller color change,better tissue structure,higher the rehydration ratio（5.20～5.57）,lower hardness（651.10～680.41 g）,and the crude protein retention rate increased by9.07%～14.88%,the retention rate of polysaccharides increased by 12.84%～30.73%,and the retention rate of total phenols increased by 11.89%～22.98%.（3）Study on the inactivation kinetics of A.niger spores on the rewetting-dried shiitake mushrooms.Linear,Weibull,Logistic and Log-Linear+Tail models were used to investigate the inactivation kinetics of A.niger spores on rewetting-dried shiitake mushrooms with CIR coupled with holding treatment.Results showed that the Weibull model（R²>0.98）could best fit the non-linear inactivation curve of A.niger spores during the CIR stage,and the Log-Linear plus tail model（R²>0.97）fitted well the linear plus trailing inactivation regularity of A.niger spores during the holding phase at different disinfection temperatures（60℃,70℃and 80℃）.（4）Study on the inactivation mechanism of A.niger spores.By investigating the effect of CIR on the cell structure of A.niger spores,the reason of the inactivation of A.niger spores by CIR was preliminarily explored at the cellular level.The study of the inactivation mechanism of CIR on A.niger spores showed that CIR could destroy the overall morphology and cell structure of spores,causing the spores to shrink and sag violently,leading to shrinkage of the spore cytoplasm,leakage of cell contents,degradation of liposomes and organelles,DNA denaturation,which would result in the loss of the normal membrane function and may cause the death of spores.（5）Study on the scale-up of CIR disinfection technology of rewetting-dried mushrooms.Based on the small-scale results of BCIR static disinfection of rewetting-dried shiitake mushrooms,the drum catalytic infrared radiation device（DCIR）was used to carry out continuous disinfection and amplification experiments to verify the feasibility of the small-scale parameters.Results showed that the use of DCIR coupled with holding treatment could not only achieve the disinfection effect of small-scale batch catalytic infrared static disinfection,but also shorten the holding time required to achieve the disinfection requirement,and remove more moisture of mushrooms.When the disinfection temperature was 60℃,70℃and 80℃,respectively,rewetting-dried shiitake mushrooms with IMCs of 16.0%～21.4%were subjected to DCIR coupled with holding treatment for 88.7～41.2 min,the total number of moulds was less than 2 lg CFU/g,achieving the requirement of irradiation disinfection in industry,while 2.2%～6.0%of moisture was removed,achieving simultaneous drying.Considering the disinfection time and product quality,it was recommended that mushrooms treated with DCIR for 10.8～15.2 min to 70℃（the feed rate of DCIR was 50～38 kg/h）,followed by holding at 70°C for 60～30 min as the most suitable disinfecting process condition.Under this process condition,the product displayed smaller color change and better rehydration ratio.