Study On Stage-Microwave Vacuum Freeze-Drying Characteristics And Quality Analysis Of Letinous Edodes

Letinous edodes(Lentinus edodes(Berk.)sing)belonging to Tricholomataceae of Marasmiaceae is popular for its unique aroma,delicious taste and rich nutrition.Fresh letinous edodes is relatively hard to preserve,therefore,they are generally stored and saled after drying.This paper discussed the feasibility and advantages of three-stage microwave vacuum freeze drying(MVFD)the whole mushrooms.The parameters of MVFD power were optimized through drying time,rehydration properties,texture and nutritional composition,etc.The water migration rules of mushroom at each stage of MVFD were studied by low field NMR.Objective to evaluate the microstructure,aroma components,free amino acid content,sensory quality and rehydration rate of MVFD letinous edodes by the comparison with freeze drying(FD)and hot air drying(HD)ones.The results will provide technical guidance and theoretical support for MVFD processing of high quality whole mushrooms.In the first stage the water loss of letinous edodes was less than 5% using microwave power 10-20 W,drying time 0.5 h.In the second stage of accelerated sublimation drying,the effects of microwave power 40 W,50W,60 W,70W and 80 W on the drying efficiencies of mushrooms were investigated by single factor method.The results showed that the drying time was gradually decreased with the increase of microwave power,which were 7 h,5.5 h,5 h,4.5 h and 4 h needed for dried letinous edodes products(moisture content <13%).However when the power was over 70 W,the local coking and structure of drying products was easily to collapse phenomenon.When the microwave power was 50 W,the rehydration rate of mushroom products was 63.41%,the crude polysaccharide content was 5.98 g/100 g DW,the color difference ?E of the fresh sample was 5.93,and the sensory quality score was the highest.In the third stage of MVFD,about 30% of water in letinous edodes was removed.The effects of microwave power 20 W,30W,40 W and 50 W on the drying efficiencies and the moisture migration of mushrooms were investigated.The results showed that the quality of dried letinous edodes products were the best when the microwave power was 30 W.The Low field nuclear magnetic resonance studies showed that the free water was completely removed in the dried samples,and only a few binding water and bound water are left,which was not easily used by microorganisms and was more conducive to the preservation of letinous edodes samples.The effects of three-stage MVFD on the drying characteristics,nutrient composition,sensory quality and micro-structure of Lentinula edodes were analyzed by comparing with FD and HD.The results showed that the dehydration time of MVFD,FD and HD was 14 h,5 h and 8 h respectively,when the water content of letinous edodes was less than 13%.The cross section of FD mushroom had porous honeycomb network structure,uniform microporous distribution,good sensory evaluation and less nutrient loss.The shrinkage rate of diameter and thickness were12.38% and 25.30%,and the rehydrating rate was about 90.16%.The micro-structure of MVFD products was similar to FD samples.Moreover its pore size was slightly larger and more uniform,so the rehydrating rate was 91.40%.The sensory evaluation scores and nutrientional retention rates beween MVFD and FD products were no significant differences.HD mushroom had stacked cross-section structure and serious cell wall collapse.The thickness shrinkage rate and rehydrating rate reached 57.28%and 66.97%.It had the worst sensory evaluation and nutrients loss among the three treatments.The total free amino acids contents in MVFD,FD and HD products were34.41mg/g,36.15 mg/g,and 25.41 mg/g,respectively.There were obvious significant differences in the volatile components of the three drying methods.The main volatile substances in FD letinous edodes were alcohols and hydrocarbons,such as 1-octene-3alcohol,acetaldehyde,and 1,3-dimethyl-benzene,etc.The main volatile compounds in MVFD mushrooms were 1-octene-3 alcohol,benzaldehyde,undecane,and dodecane.There were more sulphur-containing compounds in HD products,which were mainly composed of dimethyl disulfide,dimethyl trisulfide,lenthionine and so on.After an overall analysis,MVFD letinous edodes is superior in quality and energy consumption,so that it is a kind of drying method worth promotion and application.