RESULTS AND DISCUSSIONS
Principle of the Method
Under this method we prepared solutions of
Fehling I and II, taking certain quantities of CuSO4 and
potassium-sodium tartarate.
The complex Cu2+ salt of potassium-sodium
tartarate with deep blue color is obtained as a result of
the mixing of the two solutions
(2)
-
OOC
OOC
H
C
C
H
4-
O
O
Cu
O
O
H
C
C
H
COO-
COO-
CHO
4
+ CHOH
-
CH2OH
COOH
CHOH + Cu2O +2
4
HO
HO
H
C
C
H
COO-
COO-
CH2OH
The resulting residue of Cu2O equivalent to the
oxidized sugar is filtered. The surplus Cu2+ in the fil-
trate that has not reacted with the sugar is titrated
complexometrically by EDTA in acetic acid media (pH
5 5.1), against the indicator of PAR, according to the
reaction:
Cu2+ + H2Y2- →Cu Y2- + 2 H+
(3)
The quantity of Cu in the residue of Cu2O is cal-
culated and with it the quantity of the reducing sugars
in starch hydrolysate, is calculated using the Bertrand
tables [1] (as invert sugar or glucose).