| Tianma(Gastrodia elata),also known as Chijian,Shencao,Helicao,and Limu,is a tuber of the orchid plant Gastrodia elata that is rich in active ingredients such as gastrodin,p-hydroxybenzyl alcohol,and balisin.It was used in medicine more than2,000 years ago and was included in the pilot list of medicinal foods in 2019,rich in nutrients,with sedative and calming effects on the liver and wind,and has a regulatory effect on the central nervous system.Widely distributed in Asia,especially in China is very popular,Tianma has appeared frequently on the table as food.However,the current research on Tianma is more focused on the medicinal aspects,such as hypertension,anticonvulsant and other clinical studies,and a small part of the research on the active ingredients of Tianma,such as the extraction of gastrodin and polysaccharides,the impact of Tianma processing on the medicinal effect,etc.,for the comprehensive quality evaluation of fresh Tianma is not enough,for Tianma after different treatments,its edible nutritional value and the impact of changes in bioactive components of the study is less There are few studies on the effects of different treatments on the nutritional value and bioactive components of Tianma,and there are few studies on the off-flavored substances in Tianma and the reduction of off-flavored substances.Therefore,in this study,the quality of seven batches of Chongqing fresh Tianma was firstly evaluated comprehensively,and then the Tianma was treated with hot air drying,vacuum freeze drying,steaming,boiling,and microbial fermentation to analyze which treatments could bring the maximum utility value to Tianma,and finally the changes of volatile compounds of Tianma before and after treatment were analyzed,in order to provide a scientific basis for Tianma processing,as well as to provide research on Tianma"flavor correction"."The main results are as follows.The main research results are as follows:(1)Seven batches of Chongqing local fresh Tianma were analyzed for differences in nutrients,active ingredients,heavy metal content and volatile substances,and combined with principal component analysis(PCA),orthogonal least squares-discriminant analysis(OPLS),and the analysis of the differences in the nutrients,active ingredients,heavy metal content and volatile substances.discriminant analysis(OPLS-DA)and cluster analysis(CA)were used to identify the patterns of seven batches of fresh Tianma.The experimental results showed that the similarity of the HPLC fingerprint profiles of the seven batches of Tianma was 0.970～0.997,with small differences among different batches of Tianma;the contents of leachate,polysaccharide and crude fiber in the G2 samples were generally higher than those of other samples;the total contents of gastrodin and p-hydroxybenzyl alcohol in the G2 samples were the highest,at 5.92 mg/g;16 amino acids were detected from all samples,of which9.77～18.66%of amino acids were essential amino acids,the total amino acid content was within the mass fraction of 7466.61～11870.54 mg/kg.67 volatile compounds were detected in 7 batches of Tianma,and 12 compounds with OAV>1 were identified through the analysis of aroma activity value(OAV),of which 7 batches of Tianma contained trans-2-nonenal and had a large OAV value,and G7 samples had the highest had the highest content of volatile compounds,which was conducive to the subsequent study of volatile compound changes.Seventy-seven different volatile compounds were detected in the seven batches of Tianma using GC-IMS,and the seven batches were classified into two categories according to the growth altitude by PCA,one for G1,G3and G4 Tianma,and the other for G2,G5,G6 and G7 Tianma.(2)Based on the experiments in the previous chapter,sample G7 was selected for the study.In this chapter,the effects of hot air drying and vacuum freeze-drying treatment of Tianma on nutrients,active ingredients,organic acids,free amino acids,antioxidant activity and flavor substances were investigated.The results showed that vacuum freeze-drying could retain the original nutrients of Tianma to the greatest extent.The composition of organic acids of Tianma changed,and their content was significantly lower compared with that before treatment(P<0.05).The total amino acid content and total essential amino acid content were higher in the vacuum freeze-dried group.The results of HS-SPME-GC-MS showed that aldehydes were more abundant in the hot-air-dried group,with 2.70 times the content of the freeze-dried group,and phenols and terpenoids were formed in large quantities in the freeze-dried group.The results of sensory analysis showed that hot-air drying and vacuum freeze-drying had no significant effect on attenuating the"horse urine odor"of Tianma.(3)In Chapter 2,we did not find an effective way to reduce the"horse urine odor"of Tianma,so this chapter continued the study in Chapter 2 by using steam,boiling and fermentation treatments.Firstly,Lactobacillus acidophilus(N2),Lactobacillus plantarum(XZ3)and Pediococcus pentosaceus(8-2,8-14)were used to ferment Tianma,and the dynamic changes of the active components of Tianma were analyzed during the fermentation process.The dynamic changes of the active components of Tianma during fermentation were analyzed to screen the most suitable strains of fermented Tianma.Then the effects of three different treatments on the nutrients,active ingredients,organic acids,free amino acids,antioxidant activity and flavor substances of Tianma were investigated.The results showed that the N2 group could reach the maximum of gastrodin and p-hydroxybenzyl alcohol content in the 3rd d of fermentation,which were1.33 mg/g and 1.71 mg/g,respectively,indicating that the N2 strain was suitable for Tianma fermentation,and the strains 8-14 and XZ3 were found to be favorable for the synthesis of balisin A.Fermentation treatments significantly increased crude polysaccharide and water-soluble protein contents by 41.91%and 2.59%,respectively(P<0.05).Steaming,boiling and fermentation treatments all significantly increased gastrodin content(P<0.05),with the greatest change in gastrodin content after fermentation,which was four times higher than that of untreated Tianma.Therefore,the fermentation of Tianma by N2 strain can improve the content of active ingredients of Tianma.Steaming,boiling and fermentation treatments significantly reduced the total organic acid and free amino acid contents of Tianma(P<0.05).The total phenolic and total flavonoid contents of Tianma were reduced after three different treatments,as well as the reducing ability,hydroxyl radical scavenging ability,DPPH radical scavenging ability,ABTS cation radical scavenging ability and Fe2~+chelating ability.After detection by HS-SPME-GC-MS,it was concluded that the content of aldehydes was1.86 times higher after steaming,the number and content of esters decreased in all three groups of samples,the content of alcohols,phenols and terpenoids increased significantly after steaming and boiling,the content of aldehydes decreased significantly after fermentation(P<0.05)while the content of acids and phenols increased significantly(P<0.05),and ethers were The ether substances were not detected in any of the three groups of Tianma.The results of sensory evaluation analysis showed that the odor of Tianma was improved after steaming,boiling and fermentation treatments,and fermentation treatment was the most effective way to attenuate the odor of Tianma.Using GC-IMS,82 volatile compounds were detected in five different groups of Tianma,the composition and content of volatile compounds were more similar between steamed and boiled Tianma,and the differences between freeze-dried and fermented Tianma were the greatest,the content of aldehydes and terpenoids in the freeze-dried group was significantly higher than that in the fermented group,while the content of acids,alcohols and phenolic compounds in the fermented group was significantly higher than that in the freeze-dried(P<0.05).In conclusion,G2 Tianma had the best overall quality among the seven batches of Tianma,N2 strain was the superior strain of fermented Tianma,vacuum freeze-drying could retain the nutrients and active ingredients of Tianma to the greatest extent,fermentation treatment could significantly improve the flavor of Tianma,making Tianma"horse urine odor"odor is effectively reduced. |
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