Characterization of odor components of Pixian Douban (broad bean paste) by aroma extract dilute analysis and odor activity values

Figures & data

Table 1. Quantitative analysis of 21 odourants in PXDB

No.	aroma compound	quantifying ion (m/z)	standard curve			concentrations		quantitative methods^a
			slope	Intercept	R^2	(µg/kg)	RSD^b
1	2-Methyl-1-propanol	43(42,41)	-^c	-	-	140.02	-	IS
2	3-Methylbutanal	44 (43, 58)	127.1	−9.9	0.998	676.38	8%	IS, ES
3	2-Methylbutyraldehyde	57 (58, 41)	880.1	169.6	0.999	119.29	3%	IS, ES
4	3-Hydroxy-2-butanone	45(88, 43)	243.7	18.3	0.992	141.82	7%	IS, ES
5	3-Methyl-1-butanol	55 (42, 43)	188.5	−24.6	0.994	2167.13	6%	IS, ES
6	Furfural	96 (95, 39)	121.4	−1.3	0.992	4300.09	3%	IS, ES
7	Ethyl 2-methylbutyrate	57(102, 41)	107.1	11.3	0.991	2.08	8%	IS, ES
8	3-Methylbutanoic acid	60 (41, 43)	-	-	-	1007.46	-	IS
9	3-Methylthiopropionaldehyde	48 (104, 47)	166.0	6.1	0.998	66.41	2%	IS, ES
10	2,5-Dimethyl pyrazine	108 (42,40)	131.3	−1.9	0.996	2821.98	5%	IS, ES
11	5-Methyl furfural	110 (109, 53)	-	-	-	32.13	-	IS
12	Benzaldehyde	105 (106, 77)	102.4	−2.8	0.994	497.48	1%	IS, ES
13	2-Acetylpyrrole	94 (103, 66)	138.5	−6.2	0.992	601.10	4%	IS, ES
14	1-Nonanal	57 (98, 43)	170.9	−0.1	0.991	6.09	10%	IS
15	Phenylacetaldehyde	91 (92, 120)	46.4	8.8	0.994	377.36	2%	IS, ES
16	Tetramethylpyrazine	136 (54, 42)	120.5	5.0	0.998	1228.2	1%	IS, ES
17	2-phenylethanol	91 (92, 120)	49.1	−0.2	0.997	1047.73	2%	IS, ES
18	4-Ethylphenol	107 (122, 77)	124.2	14.6	0.995	286.97	2%	IS, ES
19	Ethyl phenylacetate	93 (164, 65)	-	-	-	253.84	-	IS
20	4-Ethyl-2-methoxyphenol	137 (152, 39)	71.8	−6.4	0.993	516.26	1%	IS, ES
21	Unknown^d	-	-	-	-	143.92	-	IS

^aQuantitation based on IS (internal standard method) and/or ES (external standard method). ^bRSD, relative standard deviation of the average concentration. ^c-: no corresponding values obtained due to the only use of IS. ^dUnknown: compound failed to identification.

Table 2. Odour activity values (OAVs) of the odour-active compounds identified in PXDB

NO.	Compounds	Odour description^a	Retention index		Thresholds	OAVs
			DB-5	DB-WAX	(µg/Kg)^b
1	2-Methyl-1-propanol	Slightly sour	597	926	7000^[Citation28]	0.02
2	3-Methylbutanal	Malty, almond	643	941	1.1^[Citation27]	614.89
3	2-Methylbutanal	Reagent-like, almond	650	1129	4.4^[Citation27]	27.11
4	3-Hydroxy-2-butanone	Sweet	717	1192	800^[Citation29]	0.18
5	3-Methyl-1-butanol	Fruit, slightly sour	811	1308	220^[Citation30]	9.85
6	Furfural	Nuts	831	1504	3000^[Citation20]	1.43
7	Ethyl-2-methylbutyrate	Floral	841	1578	1^[Citation31]	2.08
8	3-Methylbutanoic acid	Sour, musty	845	1662	1200^[Citation27]	0.84
9	3-(Methylthio)-propionaldehyde	Sauce, cooked potato	858	1451	1.4^[Citation27]	47.43
10	2,5-Dimethyl pyrazine	Cooked peanut	932	1203	2600^[Citation20]	1.09
11	5-Methyl furfural	Musty	957	1834	-^d	-
12	Benzaldehyde	Roasted nuts	982	1524	350^[Citation31]	1.42
13	2-Acetylpyrrole	Cooked potato	1035	1602	19^[Citation28]	31.64
14	1-Nonanal	Floral	1108	1393	8^c	0.76
15	Phenylacetaldehyde	Honey-like	1081	1644	4^[Citation27]	94.34
16	Tetramethylpyrazine	Soy sauce-like	1121	1829	1000 ^c	1.23
17	2-phenylethanol	Rose-like, floral	1135	1903	211 ^c	4.97
18	2-Ethylphenol	Raw pepper, green	1168	2086	40 ^c	7.17
19	2-phenylbutanoate	Floral	1229	2102	650 ^c	0.39
20	4-Ethyl-2-methoxyphenol	Sweet, warm, spicy, herb-like	1299	2369	50^[Citation32]	10.33
21	Unknown^e	Grass, green	1403	2891	-	-

^aOdour description: based on (I) the University of Florida Citrus Flavour database (http://www.crec.ifas.ufl.edu/rouseff/#) and (II) Flavour net (http://www.flavournet.org/flavournet.html). ^bThresholds were taken from the references about fermented sauce with same matrix, ^c thresholds on http://www.leffingwell.com/odourthre.htm. ^d-: failed to find the threshold. ^eUnknown, not identified due to trace amounts.

Table 3. Grouping of PXDB aroma description

No.	type	odour profile	odourant
1	Soy sauce-like	Soy sauce, cooked potato, malty	3-Methylthiopropanal, furfural, benzaldehyde, 2-acetylpyrrole, 2,5-dimethylpyrazine, 2,3,5,6-tetramethylpyrazine
2	Alcoholic	Floral, fruits	3-Methyl-1-butanol, 2-phenylethanol, ethyl 2-methylbutyrate
3	Sweet	Sweet, honey-like	Phenylacetaldehyde
4	Grass	Grassy, green, smoky, herb-like	2-Ethylphenol, 4-ethyl-2-methoxyphenol
5	Spicy	Spicy, pungent	4-Ethyl-2-methoxyphenol, 2-ethylphenol
6	Sour	Sour	3-Methylbutanoic acid
7	Musty	Musty	3-Methylbutanoic acid

Figure 1. Flavour dilution chromatogram indicating the key odourants in the gas chromatogram of the volatile fraction isolated from PXDB (FD factor 1, 2, 3 represent diluted by different split ratios, different sample weight, different extract time, respectively)

Figure 2. The sensory score of PXDB (solid line indicates authentic PXDB, and broken line indicates recombination samples)

Table 4. Omission Experiments from Complete Recombinate

NO.	Missing compound	n^a	Signicance^b
1	3-Methylthiopropanal	10	***
2	furfural	6	**
3	benzaldehyde	7	***
4	2-acetylpyrrole	8	***
5	2,5-dimethylpyrazine,	8	***
6	2,3,5,6-tetramethylpyrazine	7	***
7	3-Methyl-1-butanol,	4	*
8	furfuryl alcohol	3	*
9	ethyl 2-methylbutyrate	2	*
10	2-phenylethanol	7	***
11	4-ethyl-2-methoxyphenol	6	**
12	3-methyl butyraldehyde	6	**
13	3-Methylbutyric acid	4	*
14	phenylacetaldehyde	8	***
15	2-Phenylethanol	7	***

^aNumber of correct judgments from 10 assessors. ^b “*”, “**”, and “***” indicate significance at p < 0.05, 0.01, and 0.001, respectively.

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