| Lentinula edodes(Berk.)Pegler is rich in nutrients,unique in aroma,and has edible and medicinal value,and is very popular among consumers.Shiitake mushrooms have vigorous physiological metabolism,and are easy to soften and deteriorate after harvest,produce peculiar smell,and lose their edible value.Drying is the main technique for storing and preserving the nutrition quality of L.edodes after harvest.During the drying process of L.edodes,a strong aroma is formed,the flavor quality and commodity value are improved,aroma has become one of the core quality indicators to evaluating dried L.edodes products.In recent years,there has been an increase in the research on the drying technology of mushrooms and the aroma components of dried products,but there is still a lack of research on the aroma formation mechanism during the drying process,which restricts the improvement and promotion of the aroma quality during the drying process of mushrooms.In order to analyze the causes of the aroma components of L.edodes in the process of processing and drying,this study firstly compared and screened drying technologies,and discussed the effects of different drying technologies on the enrichment of the characteristic aroma components and quality of L.edodes during the drying process of L.edodes fruit bodies,and determined the drying technology which is conducive to the enrichment of aroma components of L.edodes;based on the drying technology obtained by screening,the relationship between the synthesis precursor substances of aroma components,the characteristic aroma components and the flavor synthase during the drying process of L.edodes was studied,and analyzed the response mechanism of the synthesis of characteristic aroma components to non-biological regulatory factors(temperature,moisture);based on the analysis results of the above mechanism,the process of flavor synthesis(enzymatic reaction,non-enzymatic reaction)involved in the drying process was strengthened,and the drying regulation process for the enrichment of the aroma components of L.edodes was obtain;Transcriptomic and metabonomic analysis on the L.edodes samples prepared under the optimized drying process conditions was carried out to verify the synthesis process of characteristic aroma components and the enhancement effect.The specific research results are as follows:1.Research on the synthesis reaction of flavor components and analysis of the quality of L.edodes during the drying process.By comparing the effects of hot air drying(HAD)and vacuum freeze drying(VFD)on the enrichment effect of flavor components in the drying process of shiitake mushroom fruit bodies,it was found that a total of 79 compounds were detected in the HAD samples,69 compounds were detected in the VFD dried samples,and the content of aroma components in the HAD dried samples was significantly higher than that in the VFD dried mushroom samples(P<0.05);Principal component analysis(PCA)found that the types of aroma components in the dried samples of VFD were more abundant,but the sample drying time was long and the equipment energy cost was higher.The HAD dried sample had a strong fragrance,the equipment was low operating cost and easy to operate;the activity of the synthase involved in the reaction in the aroma component biosynthesis pathway was studied,the results found that during the drying process of VFD,the activity of the synthetase was in a stable state of enzyme activity.It is inferred that the synthetase restricts the enrichment of the synthetic aroma components based on the enzymatic reaction pathway,resulting in a lower content of aroma components in the dried VFD samples.The quality of HAD and VFD dried L.edodes samples was compared,and the results showed that HAD dried L.edodes samples had higher chewiness and hardness,and the morphology of dried L.edodes was significantly different from that of fresh ones,and the rehydration ability was lower than that of VFD dried L.edodes.Based on the above research results,it was determined that HAD would be used as the drying technology for the fruit body of L.edodes,and the synthesis mechanism of characteristic aroma components in the drying process would be further studied;at the same time,the aroma component content,synthetase changes and quality changes during the drying process of VFD and HAD would be compared.Preliminary predictions were made of the synthetic pathways and chemical reactions involved in the synthesis of flavor components during the HAD process.2.Analysis of the synthesis mechanism of characteristic aroma components based on enzymatic reactions.The enzymatic reaction based on the biosynthetic pathway of characteristic aroma components under different HAD temperature points was studied,and the results showed that the enzymatic reaction time can reach 4?5 h at medium temperature hot air drying temperature(40?,50?),as the drying temperature increases(60?,70?),the enzymatic reaction time was shortened to 1.5?2 h.In the enzymatic reaction stage,the activity of the enzyme presents a trend of increasing first and then decreasing.Lipoxygenase(LOX)was activated by heat in the early stage(0.5h)of the enzymatic reaction at 50°C,and ?-glutamyl transpeptidase(?-glutamyl transpeptidase(?-GGT)has the highest activity at the mid-stage(2 h)of the enzymatic reaction at 60°C.The enzyme activity results showed that C-S lyase was a more temperature-sensitive synthetic enzyme than LOX and ?-GGT enzymes,and its activity was significantly higher than that of the other two enzymes,and the high enzyme activity was conducive to the synthesis of sulfur-containing characteristic aroma compounds;the characteristic aroma components in the enzymatic reaction stage were mainly sulfide,Eight-carbon alcohols and heterocyclic sulfur compounds,and heterocyclic macromolecular flavor precursors N-acetyl-S-farnesyl-L-cysteine,cysteine,hexanoylglycine and 3-Sulfo-L-alanine were detected;through correlation analysis,it was found that the enzymatic reaction mainly promoted the formation of heterocyclic compounds,and as the drying temperature increases,the correlation between flavor synthase and characteristic aroma components increased,but with the further extension of the drying process the correlation between flavor synthase and characteristic aroma components was weakened,and the correlation between synthetase activity and its enzyme gene expression was weaker.3.Analysis of the synthesis mechanism of characteristic aroma components based on non-enzymatic reactions.Soluble monosaccharides in flavor precursors were a consumption process,showing a trend of first decline and then increase,and accelerated consumption with increasing temperature.Among which glucose and fructose were most affected by drying;the total content of free amino acids showed a downward trend in low-temperature drying,while its content in high-temperature drying was increased,it was speculated that high temperature promoted the degradation of proteins and peptides;a total of 76 characteristic aroma components were detected at this stage,and the number of aroma components decreased with the increase of temperature,and the characteristic aroma components formed were more stable.4.Optimization of drying process based on enhancement of characteristic aroma synthesis.The drying process for the synthesis of two aroma-promoting components,G-HAD and P-HAD,was designed,and the determination of characteristic aroma components and enzyme activity verified that G-HAD was the best drying process.At the same time,through metabolism and transcriptomics analysis of the metabolic pathways in the G-HAD enzymatic reaction phase of mushrooms,mainly the metabolism of unsaturated fatty acids and amino acids(glycerolipid metabolism,alanine,aspartic acid and glutamic acid metabolism,tryptophan metabolism,etc.). |
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