# The Flavor Profiles of Highland Barley Fermented with Different Mushroom Mycelium
## 3 Results and Discussion
### Volatile Compound Analysis of Highland Barley  
Information on volatile metabolites in different types of fermented highland barley samples is shown in Table 1. A total of 58 volatile flavor compounds were detected in the six samples, including 16 aldehydes, 8 alcohols,7 ketones, 9 esters, 5 acids and 13 other compounds. As shown in Table 2, 18 volatile substances were detected in highland barley including 7 aldehydes, 1 alcohol, 3 esters, 2 ketones and 5 other substances. After fermentation, the amounts of substances detected in the products (SC-HB, TS-HB, SR-HB, ME-HB and CM-HB) were 24, 22, 23, 17, and 27, respectively. Among them, differences were produced in the type and amount of volatile components depending on the fermentation strain. The results also indicated that different types of mushroom mycelium could lead to varied levels of volatile-flavor-compound formation in the fermented highland barley [27]. Aldehydes are mainly produced by lipid oxidation, thermal degradation, microbiological reaction and Maillard reaction. Because of their lower threshold, they had a greater impact on the final flavor profiles of products. In addition, aldehydes have strong flavor effects that overlap with those of many other substances [28]. As shown in Figure 3, the dominant volatiles in the six samples were aldehydes. In the unfermented highland barley, the relative content of aldehydes was also high. Among them, decanal, hexanal and heptanal showed grassy smell, flowery and fruity flavors, respectively [29]. However, the content of decanal, hexanal and heptanal in the products after fermentation of the five mushroom mycelium species was significantly reduced, indicating that the original characteristics of the off-flavors produced were significantly reduced after fermentation. Compared with the original highland barley, eight new aldehydes were detected in the fermented samples. In addition, benzaldehyde and phenylacetaldehyde were detected in all samples, and their contents increased after fermentation. They were derived from the decarboxylation of phenylalanine catalyzed by aromatic l-amino acid decarboxylase. Benzaldehyde had a special cherry and almond aroma, while phenylacetaldehyde had the sweetness of rose and honey to give the highland barley a richer odor expression. After analyzing the changes in the types and contents of the aldehydes of the products before and after fermentation, it was found that the relative contents of decanal, hexanal and heptanal present in the original plateau barley decreased after fermentation, indicating a decrease in grassy, floral and fruity aromas. In contrast, phenylacetaldehyde, benzaldehyde and other newly produced aldehydes brought fruit and floral aromas. Among them, the relatively high contents of trans-2-Octen-1-al, gamma-nonanoiclactone, 2-Ethyl-2-hexenal, (E)-2-butyloct-2-enal and cyclohexanecarboxylate present in the CM-HB sample brought strong fatty and fruity aromas. Alcohols produced by fermentation and lipid oxidation had significant contributions to flavor [30]. As shown in Figure 3, the number and amount of alcohols increased after fermentation. In particular, 1-Octen-3-ol increased significantly after fermentation. 1-Octen-3-ol has a signature mushroom odor, earthy flavor and rose odor [31]. 2-Phenylethanol was detected in the samples of SC-HB, TS-HB, ME-HB and CM-HB, which provided aromas similar to honey and rose. Linalool and nerolidol were also detected in CM-HB, TS-HB and SR-HB samples, and CM-HB had the highest levels. The results indicated that fermentation brought a sweet smell to the product, which might be due to microbiological reactions and enzymatic activities [32]. Esters produced through esterification can give foods a sweet aroma and oily taste [33]. As shown in Figure 3, the number and amount of esters in highland barley after fermentation were different. After fermentation, ester levels in TS-HB and CM-HB increased, and the CM-HB samples were most rich in ester species.