Table 2. Free organic acid contents of onion juice (OJ), black onion juice (BJ), onion vinegar (OV), and black onion vinegar (BV)

Free organic acids	Contents (g/L)
	Not fermented		Fermented
	OJ1)	BJ	OV	BV
Oxalic acid	-2)	0.01±0.003)	0.02±0.00	0.10±0.00
Citric acid	0.40±0.02	0.25±0.02	0.50±0.03	0.32±0.04
Malic acid	9.76±0.18	6.13±0.43	33.60±1.36	9.73±0.30
Succinic acid	-	-		-	-
Lactic acid	-	-	-	-
Acetic acid	0.88±0.05	1.15±0.1	37.60±1.47	45.90±1.64
Total	11.04±0.13	7.53±0.35	71.70±2.85	56.10±1.72
Acidity (%)	1.50	1.57	4.45	5.12

OJ, onion juice; BJ, black onion juice; OV, onion vinegar; BV, black onion vinegar.
Not detected.
Values are mean±SD (n=3).