Residual levels of folates are lower for spinach (20% at pH 7 and
10–30% at pH 5) than for green beans (40–70% at pH 7 and 40–60%
at pH 5). This indicates that more folates are extracted from spinach
than from green beans. Spinach and green beans represent two
different tissues, consisting of a leaf and pod respectively. Spinach
leaves are composed of two layers, each with only a few cell layers.
In contrast, green beans are composed of pods and seeds parenchyma,
which are two different histological structures. The existence
of these different compartments and the possibility that
folates are retained in these compartments by bondage to macromolecules
would result in a lower residual ratio and a slower rate
of diffusion. In beans, the existence of a compartmentalization of
folates in the parenchyma and in the seeds is clearly established.
This was verified here: folate concentration in the parenchyma
was 0.252 mg/kg while it was three times higher in the seeds with
a concentration of 0.709 mg/kg.