Study On The Effect And Mechanism Of Sulfur-fumigation On The Edible Quality Of Gastrodia Elata

Gastrodia elata Bl.the rhizome of the Orchid family plant genus Gastrodia,containing active substances such as gastrodin,Gastrodia elata polysaccharides,p-hydroxybenzyl alcohol,and balioside.Fresh Gastrodia elata needs to be dried immediately after harvesting to prevent mold and rot.Currently,the commonly used drying methods in production are sun-drying（SD）,hot air drying（HAD）,and vacuum freeze drying（VFD）.However,Gastrodia elata treated with SD and HAD is prone to decay.Through long-term production practices,the Chinese people have discovered that steaming and sulfur fumigation（Sf）followed by HAD treatment is an effective method to prevent Gastrodia elata from molding.This method has the advantages of simple operation,significant anti-corrosion and whitening effects.Currently,in order to improve the appearance quality and achieve the purpose of preservation,most Gastrodia elata producing areas still use the processing method of steaming,sulfur fumigation,and hot air drying.However,it has not been reported whether sulfur fumigation will affect the taste and flavor of Gastrodia elata.In order to provide data support for the scientific drying processing of Gastrodia elata and improving its edible quality,this study used VFD and SD as controls and used electronic nose,electronic tongue,UPLC-MS,GC-TOF-MS,and other technologies to compare the physical properties,cooking properties,nutritional components,taste,and aroma of Gastrodia elata after HAD and Sf treatments.The study also verified the regulation method of improving the taste of Gastrodia elata through sulfur fumigation.The main results of this study are as follows:（1）Compared with VFD,which can preserve the original flavor of food the best,and SD,which is the most prone to decay,the whiteness of Gastrodia elata treated with HAD is the lowest,and that of VFD-treatment is the highest.Steaming is beneficial for preserving the whiteness of SD and HAD treated Gastrodia elata,but not for VFD.Among the three drying methods,the appearance of VFD-treated Gastrodia elata is the most intact.HAD-treated Gastrodia elata maintains good chewiness,with lower hardness than SD-treated Gastrodia elata but higher than VFD-treated Gastrodia elata.The total content of gastrodin and p-hydroxybenzyl alcohol in the three drying treatments is VFD>HAD>SD,while the content of Gastrodia elata polysaccharides is VFD>HAD>SD.Steaming is also beneficial for increasing the content of active ingredients in Gastrodia elata.In addition,the water-soluble protein,free amino acid,and fat content of Gastrodia elata treated with HAD are lower than those treated with VFD.The three drying methods did not show significant differences in Caco-2 cell viability,but the starch digestion rate of Gastrodia elata treated with HAD was the lowest.（2）The different odor compounds produced by the three drying treatments of Gastrodia elata without steaming mainly consist of alkanes,fatty acids,and alcohols.However,the different odor compounds produced by the three drying treatments of steamed Gastrodia elata mainly consist of aldehydes and short-chain volatile fatty acids.Among them,HAD-treated Gastrodia elata has more aldehydes and phenolic compounds than VFD-treated Gastrodia elata,making the aroma richer.In Gastrodia elata without steaming,SD-treated Gastrodia elata has the highest bitterness value,while the sour,sweet,umami flavors are lower than VFD-treated Gastrodia elata.The bitterness value of HAD-treated Gastrodia elata is the lowest,and the sour,sweet,umami flavors are significantly higher than VFD-treated Gastrodia elata,indicating that HAD-treatment is beneficial for improving the taste of Gastrodia elata.In steamed Gastrodia elata,VFD has the highest bitterness value,but the sour,sweet,umami flavors are higher than SD-treated Gastrodia elata.After HAD-treatment,the bitterness is lower than VFD,and the response value of sour,sweet,umami flavors is higher,indicating that HAD is beneficial for improving the taste response of Gastrodia elata.（3）The residual SO₂ content in Gastrodia elata treated with Sf（1/20）after steaming is 355 mg/kg,which meets the limit requirements of the"Chinese Pharmacopoeia",and the p H is significantly reduced.Compared with HAD-treatment,Sf-treatment can significantly improve the color and cooking properties of Gastrodia elata,reduce the content of nutritional and medicinal components,but has no significant effect on the drying efficiency and chewiness of dried Gastrodia elata.Compared with HAD treatment,Sf treatment resulted in a decrease in the content of sourness compounds（heptanoic acid,azelaic acid）,sweetness compounds（alpha-dimorphecolic acid,13-L-hydroperoxylinoleic acid,2-hydroxy-6-pentadecyl benzoic acid）,astringent compound（4-hydroxycinnamic acid）,and oily compound（beta-cryptoxanthin）in Gastrodia elata.The content of bitter-tasting compounds（L-Valine and 4-Guanidinobutanal）increased.Aldehyde compounds in Sf Gastrodia elata increased compared to HAD-treatment,producing aldehyde compounds with fruity and bitter flavors（benzaldehyde,hexanal,and phenylacetaldehyde）.The odor became worse and caused stronger odor uniformity.In addition,Sf-treatment inhibited the viability of Caco-2 cells and increased the digestibility of starch.（4）Sf-treatment after steaming utilized the bleaching properties of SO₂ to increase the whiteness and paste clarity of Gastrodia elata starch,and promoted the breaking ofα-1,6 glycosidic bonds,thereby increasing the content of amylose starch and rapidly digestible starch（RSD）.The increase in amylose starch content also caused a decrease in starch solubility and limited the excessive increase in swelling power caused by steaming,thereby enhancing the cooking qualities of gel texture,hardness,chewiness,adhesiveness,and so on.In addition,Sf-treatment after steaming also increased the release of starch chains from starch granules and increased the viscosity of starch gel.This means that the taste and quality of Gastrodia elata starch were improved after Sf-treated.In summary,HAD treatment after steaming can improve the taste and flavor of Gastrodia elata,while Sf treatment can improve the appearance quality and chewiness,but reduces the rich flavor of Gastrodia elata and produces inferior odor.Therefore,it is recommended to abandon the Sf-treated before drying in production to ensure the flavor of Gastrodia elata.