Study On The Intensive Pulsed Light Combined With Controlled Humidity Drying Of Shiitake Mushroom Based On Shrinkage,Browning And Storage Characteristics

Shiitake mushrooms are not only rich in nutrition and delicious,but also a traditional bulk export agricultural product in China.However,due to the high water content of fresh shiitake mushrooms,the post-harvest metabolism is fast,and the shelf life is only 2?3 days,which is not conducive to its market circulation and transportation.Therefore,dried shiitake mushrooms have become the main circulation method of shiitake mushrooms in the market.Moreover,dried shiitake mushrooms have a unique fragrance and are very popular among consumers.However,the market has extremely high requirements on the shape of dried shiitake mushrooms,and the current drying method is still mainly hot air drying,and the obtained dried products have extremely severe shrinkage,which cannot meet the needs of the market and consumers.Therefore,it is necessary to find a drying method that can reduce the shrinkage of shiitake mushrooms.Shiitake mushroom has a high content of phenolase and phenolic substances,and it is very easy to brown during processing.Inhibiting browning is the key to improving the quality of its products.The traditional method of blanching(hot water blanching)not only causes waste of water resources and loss of nutrients,but also softens its texture and affects subsequent processing.Therefore,a pretreatment method that can inactivate polyphenol oxidase(PPO)without destroying nutrients is needed to reduce the degree of browning during drying and storage.This research compares the effects of thermal and non-thermal processing on the quality of shiitake mushrooms,screens out the controlled humidity drying with low shrinkage during the drying process,and explores the effect of intensive pulsed light(IPL)pretreatment on the content,mechanism of PPO and the quality of shitake mushroom during storage.In order to explore the“pretreatment+drying+storage”processing method that can improve the quality of dry products without affecting the quality during storage.The main contents and results of the study are as follows:(1)Two processing methods of non-thermal processing(vacuum freeze drying)and thermal processing(hot air convection drying,infrared hot air convection drying,vacuum pulse drying and controlled humidity drying)were applied to the drying of shiitake mushrooms,and the changes of drying rate,physical properties(shrinkage,hardness,rehydration,surface color,etc.)and chemical properties(electronic nose,antioxidant,etc.)under different processing methods of shiitake mushrooms were discussed.The results showed that the processing methods had significant effects on the drying rate,physical and chemical properties of shiitake mushroom.Thermal processing is more conducive to the formation of aroma components of shiitake mushrooms than non-thermal processing.In thermal processing,the drying efficiency of infrared hot air and vacuum pulse drying is increased by 37.5%.Infrared hot air drying is significantly better than other thermal processing methods in terms of the chemical properties of dried shiitake mushrooms,but the controlled humidity drying shrinkage rate is significantly lower than other heat treatment methods(10.21?28.91)%,but its browning degree is only better than hot air drying.Therefore,it is necessary to increase pretreatment methods to reduce the browning degree and improve the quality.(2)The effect of IPL as a pretreatment method on the activity of PPO in shiitake mushroom was studied.By changing the pulse intensity and fluence,the content of PPO in dried shiitake mushroom was reduced,and the browning of dried shiitake mushroom was reduced.The mechanism of action of IPL on PPO shows that IPL can reduce or even inactivate the activity of PPO by affecting the natural structure of PPO,that is,by reducing the content of?-helix and?-turn,increasing the content of?-fold and irregular coil in the secondary structure of PPO,the endogenous fluorescence intensity decreases,and the optimal emission wavelength red shifts.It was found that when the pulse intensity and fluence were 0.48 J/cm²/pulse,and 12.0 J/cm²,respectively,the PPO activity,browning index(AI)and browning degree(BD)were reduced by 42.83%,43.02%and 47.54%,respectively.It also improves its polysaccharide,reducing sugar content and antioxidant capacity,promotes the conversion of ergosterol to VD₂,and reduces the accumulation of 5-HMF without affecting its flavor components.In summary,intensive pulsed light can be used as a new pretreatment method that can reduce browning in the drying process of shiitake mushrooms.(3)The stability of IPL as a pretreatment method in storage of shiitake mushrooms was studied.At the end of storage,the treatment with intensity of 0.48J/cm²/pulse and fluence of 12.0 J/cm² reduced the total number of colonies of fresh shiitake mushrooms by 41.90%,the browning degree by 19.18%and the browning degree of dried shiitake mushrooms by 31.78%.The quality(reducing sugar,total phenol,polysaccharide,hardness and antioxidant activity)of both fresh and dried shiitake mushrooms were improved.The results showed that IPL could be used as pretreatment before storage to extend the shelf life of fresh shiitake mushrooms,and could also be used as pretreatment before drying to extend the shelf life of dried shiitake mushrooms by affecting enzyme activity and browning degree.The above research results show that controlled humidity drying can effectively reduce the shrinkage during the processing of shiitake mushrooms.Intensive pulsed light pretreatment can affect the natural structure and reduce the activity of polyphenol oxidase,and make up for the poor quality and short storage period of shiitake mushroom caused by browning during controlled humidity drying and storage.Thus,a green and quality guaranteed“pretreatment+drying+storage”process suitable for shiitake mushroom processing was explored.