3.5. Classification of soy sauces
All deproteinized samples were diluted 1000-fold with deionized
water before the measurements. Fig. 5a plots the relationship
of DF475 to F475
300 for 8 different pure fermented soy sauces from
trustful makers, 2 soy sauces with nitrogen content labels and 3
cheap soy sauces of unknown quality. DF475 is positively related
to the content of tryptophan and tyrosine (to a lesser extent),
and F475
300 reflects the content of total amino acids. For the pure fermented
soy sauces, the absolute values of DF475 and F475
300 varied but
highly related to each other in a linear manner (R2 = 0.9678), which
may be due to the different fermentation or blending (or dilution)
extent for commercialization. The regression coefficient for DF445
and F445
300 of pure fermented soy sauces was lower (R2 = 0.8145)
since DF445 is prone to be affected by tyrosine. Blended soy sauces
were adulterated with savory amino acids such as glutamate, so
the data points (the 2 solid triangles in Fig. 5a) deviated from the
regression line and appeared in the upper-left of the plots. The
cheap ‘‘chemical’’ soy sauces were low in both total amino acids
and tryptophan contents since the additives of these seasonings
are caramel colorants but not savory amino acids (the 3 solid
squares in the lower left of Fig. 5a). The analysis showed that pure
fermented soy sauces contained certain proportion of tryptophan
against total amino acids (DF475/F475
300 0.11–0.12), the ratio of
adulterated soy sauces were about 0.09 and chemical soy sauces