These derivatives are more stable
at pH 5 than at pH 7, so we can not exclude that these derivatives
have been degraded over time, thus reducing the final concentration
and inducing an increase in the total amount extracted. Evolution
of derivatives during thermal degradation seems to be a key
point for folate degradation by oxidation, which is why the next
step of this study would be to determine the evolution of vitamers
during oxidation in presence of different oxygen conditions