Effects Of Drying Methods On The Quality Of Moso Bamboo Shoots

Bamboo shoots are prone to dehydration,aging and corruption after being picked.These will reduce the edible quality of bamboo shoots.Bamboo shoots generally grow in remote mountainous areas and are inconvenient to transport.The above reasons restrict the development of bamboo shoot industrialization.Drying can not only enhance the shelf life of fruits and vegetables but also drying products are small in volume,easy to package,low in cost and convenient for transportation.Therefore,In this paper,the winter moso bamboo shoots were used as experimental materials to investigate the changes of the common nutrients of bamboo shoots stored at 22～25 ℃ and 4 ℃.The technological condition for microwave drying bamboo shoots to safe moisture content(≤15%)were explored.In order to obtain the best drying way,the quality of dehydrated shoots obtained with using vacuum freeze drying(VFD),hot air drying(HAD)and microwave drying(MD)were compared by some indexes.The main results are as follows:(1)The weight loss rate,soluble protein content soluble sugar content and crude fiber content were adopted as evaluation indicators.And compared with storaged at room temperature(22～25 ℃),the change of quality of bamboo shoots during storage at 4 °C was carried out.The results show that the content of some nutrients decreases during storage of bamboo shoots,such as soluble protein and soluble sugar.However,the crude fiber content and weight loss rate increase.Compared with storage at room temperature(22 ～ 25 ℃),low temperature(4 ℃)effectively prevented the bamboo shoots from losing water,delayed the degradation of soluble protein and soluble sugar,and inhibited the their lignification process.However,the storage period was Shorter,which was not more than 7 days.The content of these4 indicators were relatively stable before 4 ℃ refrigerated for 3 days.(2)The moisture content and appearance of dried bamboo shoots were taken as the experimental index,and the microwave power and continuous microwave heating time were taken as factors to optimize the microwave drying process.The results showed the determined microwave drying process is that at a microwave power of 200 W,bamboo shoots were firstly heated continuously for 22 min,intermittently 1 min.Then bamboo shoots were continuously dried for 1 min and intermittently for 1 min for 5 times,Finally,dried continuously for 0.5 min,intermittently for 1 min,this operation is performed 3 times.Bamboo shoots were dried under this process condition,and the final wet base moisture content is 13.45%.(3)In order to evaluate the effect of drying methods on the quality of bamboo shoots,the differences in texture,rehydration,color,microstructure,nutrient content,DPPH free agent removal and cholesterol absorption capacity of fresh bamboo shoots and their dried products were studied.The results showed that the rehydration ratio(6.04%)and the adsorption capacity of cholesterol for vacuum freeze drying bamboo shoots were greater than that of hot air drying and microwave drying samples,and the color difference(2.52),hardness(163.33g)and brittleness(1.74mm)were significantly lower than that of hot air drying and microwave drying samples.Total phenol content,soluble protein content,soluble sugar content and free amino acid content in vacuum freeze drying bamboo shoots are slightly different from hot air drying samples.The scavenging ability of 3 kinds of dry products on DPPH free radicals increases with the increase of the extract concentration.microwave drying seriously damages the structure of bamboo shoots.It has a hard shell on its surface,which causes more nutrient loss,especially the soluble protein content,which is 92.97% lower than that of fresh bamboo shoots.(4)In order to compare the impact of vacuum freeze drying,hot air drying and microwave drying on the volatile flavour compounds of bamboo shoots,the volatile components were analyzed by headspace solid-phase microextraction and gas chromatography-massspectrometry technology.The results showed that a total of 52 volatile flavour compounds were identified.A total of 30,31,12 and 33 volatile flavour compounds detected in fresh bamboo shoot and 3 dried products respectively.Compared with fresh shoots,the relative content of volatile flavor components in vacuum freeze drying dried products was decreased by 50.86%,and the other two drying methods were increased by 43.20% and 28.98%,respectively.The main volatile components(aldehyde compounds)were not changed after drying.In summary,comprehensively considering the above indicators,vacuum freeze drying is a more suitable method for processing bamboo shoots,and hot air drying can achieve a relative balance between the quality of dried bamboo shoots and the economic cost.