Abstract:

The main form of folate, as a polyglutamate derivative of folate, in citrus is 5-methyltetrahydrofolate (5-MTHF).
The content of 5-MTHF is difficult to measure due to its instability and the complex matrix in citrus. Pre-treatment of
samples is very important for determining 5-MTHF in citrus accurately. In this work, the effect of different pre-treatment
methods on the extraction efficiency of 5-MTHF was explored using high performance liquid chromatography-fluorescence
detection (RP-HPLC-FLD). The results showed that the best hydrolysis conditions for citrus samples were found as follows:
homogenization of samples (3 g of pulp, exocarp plus mesocarp, endocarp or 2 g of seeds) and dilution to 20 mL with
phosphate buffer and adjustment of pH to 6.8, heating in a boiling water bath for 15 min (single hydrolysis), dilution of
supernatant to 25 mL after cooling down and centrifugation, addition of 0.5 mL of rat serum to 3 mL of the diluted sample,
and incubation at 37 ℃ for 20 h with an adjusted pH of 6.8 while shaking.

Key words: pre-treatment, citrus, 5-methyltetrahydrofolate (5-MTHF), detetermination