Fermentation Quality Characteristics and Flavor Formation Changes During the Process of Pickled Wax Gourd in Eastern Zhejiang

Figures & data

FIGURE 1 Changes in reducing sugar content and pH value during wax gourd fermentation.

TABLE 1 Changes of total amounts of lactic acid bacteria, total bacteria and yeast (log CFU/mL) during fermentation of wax gourd

	Fermentation time (d)
	0	5	10	15	20
The total amounts of lactic acid bacteria	3, 68	5, 69	6, 24	6, 97	7, 15
The total amounts of bacteria	3, 30	6, 18	6, 45	7, 23	7, 79
The total amounts of yeasts	3, 54	7, 43	8, 14	8, 11	7, 90

TABLE 2 Changes of organic acids content (g/L) in pickled wax gourd during fermentation

Name	Fermentation time (d)
	0	5	10	15	20
Ascorbic acid	–	–	–	–	0.002 ± 0.002^a
Oxalic acid	0.312 ± 0.027^a	0.294 ± 0.042^a	0.316 ± 0.015^a	0.331 ± 0.013^b	0.352 ± 0.039^c
Tartaric acid	0.026 ± 0.008^a	0.037 ± 0.011^b	0.029 ± 0.016^a	0.035 ± 0.004^b	0.043 ± 0.018^c
Citric acid	0.036 ± 0.010^a	0.082 ± 0.008^c	0.069 ± 0.013^b	0.077 ± 0.013^b	0.073 ± 0.009^b
Malic acid	0.023 ± 0.006^b	0.076 ± 0.002^d	0.043 ± 0.007^c	0.021 ± 0.001^b	0.005 ± 0.002^a
Lactic acid	0.037 ± 0.003^a	0.132 ± 0.019^b	0.302 ± 0.062^c	0.311 ± 0.048^c	0.346 ± 0.022^d
Acetic acid	–	0.055 ± 0.011^a	0.089 ± 0.016^b	0.104 ± 0.017^c	0.133 ± 0.008^d
Succinic acid	–	0.029 ± 0.004^a	0.065 ± 0.005^d	0.036 ± 0.002^b	0.041 ± 0.009^c

^a-d Different lowercases indicate significant differences (P < 0.05) among different fermentation time.

TABLE 3 The content of volatile compounds (percentage of peak area) of pickled wax gourd during fermentation

No.	Compounds	Fermentation time (d)
		0	5	10	15	20
	Alcohols
1	1,2,3-Propanetriol	0.16	-	-	-	-
2	1-Pentanol	5.60	-	-	-	-
3	1-Hexanol	2.21	-	0.26	-	0.50
4	1-Nonanol	0.13	-	-	-	-
5	Ethanol	-	10.38	11.44	16.79	23.69
6	2-Methyl-1-propanol	-	0.74	1.48	0.70	2.16
7	1-Butanol	-	0.26	4.18	2.64	0.90
8	2,3-Butanediol	-	21.85	21.98	13.89	5.49
9	2-Propanol	-	-	0.66	0.42	0.12
10	2-Methyl-1-butanol	-	-	2.84	2.16	6.94
11	3-Methyl-1-butanol	-	1.32	5.20	4.46	7.74
12	2-Ethanolamine nitrate	-	-	-	-	0.24
Subtotal		8.10	34.55	48.04	41.24	47.58
	Acids
1	Acetic acid	-	5.81	29.23	30.54	27.97
2	Butanoic acid	-	-	2.38	4.75	1.54
3	3-Methyl-butanoic acid	-	-	0.57	0.60	1.16
4	2-Methyl-butanoic acid	-	-	0.65	0.55	1.74
5	Propiolic acid	-	-	-	-	3.30
6	Propanedioic acid	-	-	-	-	0.29
Subtotal		0	5.81	32.83	36.44	36.00
	Aldehydes
1	Hexanal	62.16	3.26	1.61	0.88	0.41
2	Acetaldehyde	-	3.10	1.72	1.16	0.83
3	2-Methyl-butanal	0.31	-	-	-	-
4	Butanal	0.40	-	-	-	-
5	Pentanal	9.64	-	-	-	-
6	(E)-2-pentenal	0.47	-	-	-	0.19
7	2-Ethyl-3-methyl-butanal	2.20	-	-	-	-
8	(E)-2-hexenal	0.35	-	-	-	-
9	(Z)-2-heptenal	2.27	-	-	0.48	0.76
10	Nonanal	2.27	-	-	-	-
11	2-Butenal	0.66	-	-	-	0.34
Subtotal		80.03	6.36	3.33	2.52	2.53
	Ketones
1	1-Penten-one	1.23	-	-	0.34	0.28
2	2,3-Pentanedione	0.29	-	-	-	0.13
3	2-Methyl-3-pentanone	1.84	-	-	-	-
4	3-Penten-2-one	0.42	-	-	-	-
5	2,3-Octanedione	0.13	-	-	-	-
6	1-Octen-3-one	0.55	0.15	0.11	0.26	0.22
7	4-Methyl-2-pentanone	0.20	-	-	-	-
8	3-Hepten-2-one	0.36	-	-	-	-
9	2-Propanone	-	5.65	2.97	1.42	2.03
10	2,3-Butanedione	-	1.94	-	-	-
11	3-Hydroxy-2-butanone	-	39.70	3.89	1.78	0.56
12	2-Butanone	-	-	-	0.40	-
Subtotal		5.02	47.44	6.97	4.20	3.22
	Esters
1	Ethyl acetate	0.10	1.23	5.57	7.03	5.17
2	Methyl acetate	-	0.11	-	0.69	0.35
3	Methyl propionate	-	-	-	0.17	0.12
4	Amyl formate	-	-	-	-	0.30
Subtotal		0.10	1.34	5.57	7.89	5.94
	Siloxane
1	Hexamethyl-cyclotrisiloxane	-	0.62	-	0.78	-
2	Octamethyl-cyclotetrasiloxane	1.07	0.67	0.50	1.49	0.37
3	Decamethyl-tetrasiloxane	-	-	-	0.45	-
4	Decamethyl-cyclopentasiloxane	2.68	2.31	1.74	2.79	1.24
5	Dodecamethyl-pentasiloxane	-	-	-	0.11	-
6	Dodecamethyl-cyclohexasiloxane	0.91	0.73	0.64	0.88	0.55
Subtotal		4.66	4.33	2.88	6.5	2.16
	Others
1	Methyl-oxirane,	1.00	-	-	-	-
2	Dimethyl-sulfide	-	0.17	0.26	0.88	0.67
3	Dimethyl disulfide	-	-	0.12	-	0.51
4	1-Bromo-2-methyl-butane	0.39	-	-	-	-
5	1,3,5,7-Cyclooctatetraene	-	-	-	0.33	-
6	Fluoro-ethyne	-	-	-	-	0.64
7	1,2-Dimethyl-hydrazine	-	-	-	-	0.13
8	Acethydrazide	-	-	-	-	0.20
9	Diheptyl-disulfide	-	-	-	-	0.24
Subtotal		1.39	0.17	0.38	1.21	2.57

- indicate not detected

FIGURE 2 PCA analysis of the volatile components in wax gourd during fermentation.