Table 1. Concentration of PQQ in food samples determined by the enzymatic method.

Sample	PQQ contents (ng/g fresh weight or ng/mL) measured by the enzymatic method
Green Tea	< 0.1
Oolong tea	< 0.1
Beer	0.77 ± 0.17
Fermented soybeans	N.D.
Green pepper	0.47 ± 0.03
Parsley	< 0.1
Rape blossoms	< 0.1
Spinach	< 0.1
Tomato	N.D.
Vinegar A	< 0.1
Vinegar B	0.23 ± 0.02
Vinegar C	0.20 ± 0.00
Vinegar D	0.80 ± 0.04
Vinegar E	2.63 ± 0.15
Vinegar F	2.48 ± 0.10
Vinegar G	3.25 ± 0.22
Vinegar H	5.41 ± 0.42

Means ± SD (n = 3), N.D. = Not detected.

Detailed analytical procedures are described in Materials and methods section.