The bioavailability of folic acid in pectin - coated fortified rice in humans using stable isotope techniques

摘要

Rice is an important dietary grain but may be difficult to fortify with water-soluble vitamins due to the losses incurred during processing and preparation. Edible coatings can offer reasonable protection against folate processing losses in fortified rice, in particular pectin (Shrestha, 2003). However, pectin, an indigestible fibre, may entrap or bind added folate, decreasing its absorption efficiency. Healthy volunteers (n=26, 18-39 yrs) received oral 400μg [13C5]PteGlu doses in three separate test meals in randomized cross-over trials as follows: 1) aqueous 2) 200g white rice and 3) 200g of pectin-coated rice premix. A plasma AUC0-8 was conducted (0, 1, 2, 5 and 8 hrs postprandial). Subjects followed a low folate basal diet (112±12 μg/day) - verified using L.casei microbiological assay - during the AUC and for 24 hours prior. Optimisation of the pectin-coated rice premix gave folic acid coating and cooking losses of 33.5% and 15.5% respectively. The mean test dose error per 400μg folic acid was ± 26 μg. Single- or tri- enzyme extraction of fortified rice extracts did not significantly increase the mean assayable folate content compared to the mean folic acid content.The levels of plasma [13C5]5-methyl-THF, [13C5]PteGlu and 5-methyl-THF were quantified using a validated HPLC-tandem MS method. The calibration curves indicated good response linearity in the 0-100 ng/mL range (R20.9978). Inter- and intra-assay variation of 5-methyl-THF (100 ng/mL) was 6.9% (n=6) and 5.2% (n=4) respectively. The mean recovery of 5, 20 and 50 ng/mL 5-methyl-THF in spiked plasma extracts was 98.6 ± 8.7%, 89.3 ± 2.8% and 92.6 ± 3.7% (n=3) respectively. Standard Reference Material-1846, infant formula (129±28 μg/100g) was measured at 110 ± 15 μg folic acid/100g. The relative bioavailability of the folic acid in meals 2 and 3 was measured by comparing their [13C5]5-methyl-THF AUC’s relative to meal 1. The relative bioavailabilities (Mean % ± CI) of meals 2 and 3 were 86.5 ± 4.6 % and 68.7 ± 5.4 % respectively. It appears the pectin coat moderately reduces short-term folic acid bioavailability. These studies define the basis for calculating the amount of folic acid to be added to rice so that an adequate amount can be absorbed after coating and cooking losses. Pectin coatings may be a useful means of increasing the folate status of populations that rely heavily on rice as a staple.