# The Flavor Profiles of Highland Barley Fermented with Different Mushroom Mycelium
## 3 Results and Discussion
### Volatile Compound Analysis of Highland Barley
The other volatile compounds in the highland barley samples were mainly hydrocarbons and 2-pentylfuran. The high content of 2-pentylfuran contributed a green, bean and fruits smell to highland barley. After fermentation, the original hydrocarbons and furans were greatly decreased or disappeared. Some phenolic compounds were detected in the fermented samples. These phenolic compounds are mainly produced by decarboxylation of phenolic carboxylic acids and thermal degradation of cellulose, lignin or hemicellulose [37]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Compounds**} & \multicolumn{6}{c}{**Sample Categories**} \\ \cline{2-7}  & **HB** & **SC-HB** & **TS-HB** & **SR-HB** & **ME-HB** & **CM-HB** \\ \hline Aldehydes & 7 & 9 & 9 & 8 & 7 & 11 \\ Alcohols & 1 & 4 & 5 & 3 & 2 & 5 \\ Esters & 3 & 3 & 4 & 2 & 3 & 5 \\ Ketones & 2 & 1 & 1 & 4 & 0 & 2 \\ Acids & 0 & 1 & 1 & 1 & 4 & 3 \\ Others & 5 & 6 & 2 & 5 & 1 & 1 \\ Total & 18 & 24 & 22 & 23 & 17 & 27 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of the classification of volatile components in raw and fermented highland barley samples. Figure 3: Changes in the total amount and types of volatile compounds in original and fermented highland barley samples: HB (original highland barley), CM-HB (fermented highland barley with _C. milliaris_), SR-HB (fermented highland barley with _S. rugoso-annulata_), ME-HB (fermented highland barley with _M. esculenta_), SC-HB (fermented highland barley with _S. commune_), TS-HB (fermented highland barley with _T. sanguinea_). In summary, fermentation with mushroom mycelium could increase the richness of volatile compounds and improve the aroma of highland barley. The original grassy taste and astringency of highland barley disappeared after fermentation due to decreases in decanal, hexanal and heptanal. The increase in phenylacetaldehyde, benzaldehyde and 1-octen-3-ol brought floral, sweet and mushroom aromas to the fermented highland barley. In particular, the higher content of the newly produced substance furan-3-carboxaldehyde detected in the SC-HB sample can provide a burnt odor. Producing 3-(methylthio)propionaldehyde brought an irritating sour odor. These newly produced volatile flavor substances were partly metabolites of the raw material in the highland barley when it was fermented with the mushroom mycelium and partly from the raw material. A recent study carried out analysis of volatile compounds of four mushrooms (_Agaricus bisporus_ ssp. _bisporus_, _Agaricus bisporus_ ssp. _brunnescens_, _Lentinuula edodes_ and _Grifola fondose_) using GCMS. The 3-octanone, 1-hexanol and 1-octen-3-ol contained in the measured samples were found to be the secondary metabolites present in most of the mushrooms. These compounds were detected in samples from different mushrooms after mycelial fermentation [38]. Some researchers also found that 3-(methylthio)propionaldehyde was the most predominant aromatic active compound in Boletus edulis [39]. This compound was detected in SC-HB samples and had a significant impact on the overall flavor of the product. In a study on the use of edible fermentation to improve food flavor, researchers used four edible bacteria to ferment soybeans to remove off-flavors. It was found that substances such as hexanal, which brings off-flavors to soybeans, were consumed and utilized in the growth of mycelium [15]. Moreover, substances that present floral aromas such as phenylethanolamine, nonanal and linalool were detected in the fermented products, which is consistent with the results of this study.