## 3 Results and Discussion
### GC-MS Assay of Specimens before and after Fermentation
#### 3.4.3 Volatile Flavor Substances of the Four Groups of Fermented Specimens

Table 4: _Cont._Furthermore, the contents of the main off-flavor substances in the four groups of fermented specimens were reduced to a certain extent. In contrast to unfermented CP (20.91%) and CPY (15.27%), the contents of hexanal in fermented CP and CPY were reduced to 7.29% and 4.58%, respectively, whereas those in fermented CPB and CPBY were not detectable. In a previous study, hexanal in legume milk could be converted into capric acid through acid dehydrogenase during lactic acid bacterial fermentation [43; 44; 45]. Consequently, the content of hexanal was reduced or even no longer found in fermented specimens. The above results indicated that the content of hexanal in fermented specimens with enzymolysis was metabolized during fermentation via lactic acid bacteria. Previous studies reported that part of the bound hexanal could be converted into free hexanal after legume milk was enzymatically hydrolyzed, thereby increasing the metabolism of hexanal by lactic acid bacterial proliferation [19; 46]. Compared with unfermented CP (16.21%), CPB (14.60%), CPY (11.27%), and CPBY (11.56%), the relative contents of hexanol in fermented specimens decreased to 12.82% (CP), 5.67% (CPB), 9.30% (CPY), and 9.23% (CPBY), respectively. The presence of 1-octene-3-ol, which has a mushroom odor, in fermented specimens has  
Figure 7: Comparison of volatile odor substances in four groups of fermented specimens. CP-12 h, fermented chickpea milk; CPB-12 h, fermented chickpea milk with papain treatment; CPY-12 h, fermented chickpea milk with papain treatment plus yarn addition. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & **CP-12 h** & **CPB-12 h** & **CPY-12 h** & **CPBY-12 h** & **Sum** & **Shared** \\ \hline \multicolumn{2}{c}{**Type**} & & & & & \\ \hline Hydrocarbon & 2 & 1 & 2 & 13 & 15 & 0 \\ Alcohol & 6 & 4 & 3 & 5 & 9 & 2 \\ Aldehyde & 7 & 5 & 6 & 4 & 7 & 4 \\ Ketone & 2 & 5 & 4 & 4 & 7 & 2 \\ Ester & 2 & 4 & 2 & 3 & 6 & 1 \\ Acid & 3 & 2 & 3 & 4 & 5 & 2 \\ Phenol & 0 & 2 & 2 & 2 & 2 & 0 \\ Other & 2 & 3 & 3 & 2 & 3 & 2 \\ Total & 24 & 26 & 25 & 37 & 54 & 13 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Types of volatile odor substances in four groups of fermented specimens. chiefly been linked to 10-hydroperoxide (the precursor substance), which is the degradation product of linoleic acid via the photo-oxidation pathway [19], and also considered to be the main source of the beamy odor [46]. Compared with the unfermented specimens, the content of 1-octene-3-ol in fermented CP, CPB, CPY, and CPBY specimens was reduced to 3.42%, 2.93%, 3.17%, and 2.45%, respectively. The heterocyclic compound 2-amyl furan is also a beamy component [47]. Compared with unfermented specimens, the contents of this substance in fermented CP, CPB, CPY, and CPBY specimens were reduced to 7.98%, 5.18%, 6.96%, and 4.35%, respectively. The lower content of beamy flavor in the fermented specimens obtained in this research compared with unfermented samples might indicate that carbonyl compounds were converted by lactic acid bacterial metabolism into further well-known odor substances, such as ketones, esters, or organic acids ([PERSON]. 2001), and volatile flavors of chickpea millks were improved. Moreover, as shown in Table 5, the types and contents of ketones, esters, and organic acids in the four groups of fermented specimens were increased. At the same time, the contents of alcohols and aldehydes were reduced. For example, 2, 3-glutarone and 2, 3-butanedione were not detected in the four groups of unfermented specimens. However, the relative contents of 2,3-glutarone and 2,3-butanedione were 4.88% and 5.36% in CP, 5.81% and 5.66% in CPB, 5.19% and 5.58% in CPY, and 5.39% and 5.71% in CPBY, respectively. These two compounds were similar in flavor and had a creamy and nutty aroma, contributing to the flavor of the cream in milk [48]. In previous literature, these two yogurt-like aroma substances were detected in fermented soymilk [12], resulting in characteristic dairy odors.