## 3 Results and Discussion
### Effect of BZ25 Addition on the VOCs of Natto
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Number** & **Name** & **Aroma Description** & **RI** & **ID** &
\begin{tabular}{c} **Threshold** \\ **Value (ug/L)** * \\ \end{tabular} & \multicolumn{4}{c}{**OAV**} \\ \hline  & \multicolumn{2}{c}{Anlines} & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} \\ A1 & \(NN\)-dimethyl-Methylamine & Fish & 2081.3 & MS, RI, Sdd & 8–23  & — & — & 7-20 & — \\ \hline  & Esters & & & & & & & & \\ B1 & Hexanoic acid ethyl ester & Fruit, pineapple, banana aroma & 1233.3 & MS, RI & 55.3  & \(<\)1 & \(<\)1 & 10 & 98 \\ B2 & Octanoic acid ethyl ester & & Cream, milk & 1436 & MS, RI & 13  & 1 & 28 & 4 & 20 \\ B3 & Benzoic acid ethyl ester & & Cammie, flower, celery fruit & 1676.6 & MS, RI & 0.6  & 193 & 29 & — & 16 \\ B4 & 2-Methyl-propanoic acid ethyl ester & & Fruily & 969 & MS, RI & 85  & 49 & — & 3 & 3 \\ B11 & Benzacetic acid methyl ester & & Jasmine flower, sweet, fruit & 1767.6 & MS, RI & 0.1  & — & 1347 & 1171 & — \\ \hline  & \multicolumn{2}{c}{Pyzrazenes} & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} \\ C1 & Trimethyl-pyrazine & Nutty, coca-like, roasted & 1407.7 & MS, RI & 50–96  & 40-77 & 36-90 & 62–119 & 171–328 \\ C2 & 2,5-Dimethyl-pyrazine & Cocoa, roasted nut, roast beef & 1325.7 & MS, RI & 1700  & 1 & 1 & 5 & 14 \\ C3 & 2-Ethyl-3-5-dimethyl-pyrazine & Roasted potato & 1465 & MS, RI & 7.5  & 2 & 74 & 182 & 10 \\ C4 & 2-Ethyl-5-methyl-pyrazine & Nutty & 1394.4 & MS, RI & 16  & — & 8 & 10 & 7 \\ \hline  & Ketones & & & & & & & & \\ D2 & 5-Methyl-2-hexanone & — & 1141.8 & MS, RI & 62–89  & 1 & 2-3 & 17-24 & 11–16 \\ D3 & 2,3-Headacanone & Buttet, cramed, fruit & 2079.1 & MS, RI & 7.3  & 12 & 4 & 33 & 72 \\ D4 & 2,3-Butanedione & Sweet, cream & 984.7 & MS, RI & 5  & — & 33 & — & 644 \\ D5 & 2-Nonanone & Sweet, coconut & 1342.7 & MS, RI & 32  & 4 & 42 & 46 & 46 \\ D6 & 2-EtGenome & Mild mechanical fragrance & 1181.3 & MS, RI & 1  & 2376 & 982 & — \\ D8 & 3-Octanone & Herb, butter & 1251.9 & MS, RI & 1  & 602 & 24 & 172 & — \\ D9 & 2,3-Pentanedione & Carmed, nuts & 1061.6 & MS, RI & 30  & 6 & 11 & 7 & — \\ D10 & Acotine & irritating flavors & 819.8 & MS, RI & 1100  & 25 & 16 & 7 & — \\ D19 & 6-Methyl-5-hepten-2-one & Pepper, mushroom & 1338.9 & MS, RI & 68  & 16 & — & — & — \\ \hline  & Acids & & & & & & & \\ E1 & Acetic acid & & & & & & & \\ E2 & 2-Ethyl-butanago acid & Fruit milchigs & 1380.5 & MS, RI & 93–460  & — & 6–29 & 1–7 \\ \hline  & \multicolumn{2}{c}{Aldehydes} & & & & & & \\ F1 & Decanal & Sweet flowery, wax & 1502 & MS, RI & 0.1  & 5510 & 379.9 & — & 6675 \\ F2 & Nonanal & Flower, citrus, fat, wax fragrant & 1396.1 & MS, RI & 3.1  & 151 & 124 & 40 & 278 \\ F3 & 3-Methyl-butanol & Malt unpleasant smell & 919.7 & MS, RI & 31.6  & 505 & — & 16 & — \\ \hline \hline \end{tabular}
\end{table} 
Table 1: OAV of flavor compounds identified in steamed soybean (SS), soybean fermented by BZ25 (SFB), natto made by GUTU90 (NMB), and natto fermented by two-strain (NMBB). \begin{table}