Diffusivity constants calculated for folates from spinach and
green beans, both at pH 7 and pH 5, were close to 10–12 and 10–
10 m2/s respectively, and similar to the constants calculated for
sugars and acids for both vegetables and at both pHs. The pH
had no effect on folate, sugar and acid diffusion. At pH 5 and pH
7, the global negative electric charge of malic or citric acids, has
the same polarity as that of cell walls. We can assume the existence
of electrostatic repulsion between the cell walls and sugars and
acids resulted in a limitation of diffusion. For green beans, a difference
between the diffusivity constant of citric acid and malic acid
of about a factor of ten was observed, although they are of similar
size and charge in the conditions used. This difference could be due
to the nature of the salts which neutralize citric acid, which have a
greater ability to complex divalent cations. At pH 5 and pH 7, the
overall electrical charge of folates is also negative