# Screening of Sourdough Starter Strains and Improvements in the Quality of Whole Wheat Steamed Bread
## 2 Results and Discussion
### Determination of Volatile Compounds of Whole Wheat Steamed Bread
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Category**} & \multirow{2}{*}{**Compound Name**} & **DY-WB** & **SY-WB** & **CS-WB** \\ \cline{3-5}  & & **Content (\%)** & **Content (\%)** & **Content (\%)** \\ \hline \multirow{3}{*}{Hydrocarbon} & Dodecane & / & / & 1.53 \\  & Tetradecane & / & 0.46 & 0.49 \\  & Cuparene & / & / & 0.20 \\  & Ethanol & 2.32 & 3.94 & 4.69 \\ \multirow{3}{*}{Alcohols} & 2-methylpropanol & / & 0.50 & 0.35 \\  & 3-methyl-1-butanol & 3.44 & 3.60 & 1.58 \\  & 1-Pentanol & 6.65 & 7.67 & 5.97 \\  & Phenylethanol & 43.69 & 18.11 & 10.51 \\  & Ethyl Hexanoate & / & 0.25 & / \\  & Ethyl caprylate & / & 4.86 & 5.97 \\  & Phenethyl formate & / & 1.22 & / \\  & Ethyl nonanoate & / & 0.50 & 0.74 \\  & Ethyl caprate & 2.76 & 3.48 & 5.38 \\  & Ethyl 5-methylnonanoate & 1.57 & 4.19 & 4.05 \\  & (Z)-Ethyl cinnamate & / & 1.68 & 1.78 \\ \multirow{3}{*}{Esters} & Sulfurous acid, butyl dodecyl ester & / & / & 0.35 \\  & Sulfurous acid, pentadecyl pentyl ester & / & / & 0.30 \\  & Sulfurous acid, octadecyl pentyl ester & / & 0.38 & / \\  & Methyl myristate & / & 3.23 & / \\  & Diisobutyl phthalate & 0.52 & 4.02 & 0.94 \\  & Methyl 14-methylpentadecanoate & 7.32 & 6.29 & 5.08 \\  & Octyl P-methoxycinnamate & 1.79 & 1.93 & 1.92 \\  & Acetic acid & 8.29 & 11.65 & 21.37 \\  & Propionic acid & 7.54 & 5.83 & 7.01 \\ Acid & Octanoic acid & 0.22 & 0.42 & 1.28 \\  & Isovaleric acid & 0.37 & 1.97 & 2.52 \\  & Hexanoic acid & 1.34 & 1.22 & 1.58 \\  & Hexanal & 0.15 & 0.42 & 0.54 \\  & 3-hydroxy-Butanal & / & / & 0.30 \\  & Heptanal & 0.075 & 0.21 & 0.64 \\ Aldehydes & Octanal & / & 1.42 & 1.43 \\  & Phenylacetaldehyde & / & 0.084 & 0.35 \\  & Nonanal & / & 0.46 & 0.39 \\  & Butyraldehyde & / & / & 0.59 \\ Ketones & Acetoin & / & / & 0.64 \\  & 2-Nonadecanone & 2.39 & 2.35 & / \\ Other & 2-Pentylfuran & 0.37 & 1.22 & 1.23 \\  & Indole & 9.19 & 6.45 & 8.29 \\ \hline \hline \end{tabular} Note: DX-WB—whole wheat steamed bread fermented by commercial dry yeast; SY-WB—whole wheat steamed bread fermented by _Saccharomyces cerevisiae_; CS-WB—whole wheat steamed bread fermented by compound starter. Content: The content of the volatile compounds is expressed as relative MS peak areas (MS peak area of each compound/total MS peak area \(\times\) 100).  
\end{table} 
Table 6: Composition of flavor substance in different whole wheat steamed breads. total MS peak area in CS-WB. Esters, aldehydes, and alkanes increased in whole wheat steamed bread added with LAB and acetic acid bacteria. The increasing content of esters may be caused by the esterification reaction of alcohols and acids during the steaming process [33; 34]. aldehydes are the main products of Maillard reactions, and their content was higher than that of DY-WB and SC-WB. Seven types of substances, including hexanal, heptanal, and nonanal chemicals, were detected in CS-WB. Hexanal is commonly found in steamed bread, and heptanal and nonanal are produced through fermentation and lipid oxidation. The smell of hexanal is soapy, fruity, rose, citrus, and orange [26; 35]. Phenymacetaldehyde can be used as a fragrance and has a strong rose fragrance. However, the threshold of hydrocarbons is relatively high, so their contribution to the flavor of bread is small. In addition, the content of 2-Pentyfuran of CS-WB was increased from 0.37 to 1.23% when compared to that of DY-WB, and 2-Pentyfuran has the aroma of mushrooms, lavelander, and hay [30; 33]. The whole wheat steamed bread had higher volatile compounds when fermented by _Saccharomyces cerevisiae_, _Lactobacillus johnsonii_, and _Acetobacter pasteurii_, which produced some unique volatile compounds, such as acetoin, 3-hydroxy-butanal, butyraldehyde, cuparene, etc. The production of these volatile compounds may be caused by the synergistic effect of _Saccharomyces cerevisiae_, _Lactobacillus johnsonii_, and _Acetobacter pasteurii_, leading to reactions among the metabolites to generate a series of secondary metabolites [2; 33].