Folates in bread: retention during bread-making and in vitro bioaccessibility

Background Bread is an important folate source in several countries. However, bread-making was reported to cause losses of endogenous bread folates (~40%) as well as added synthetic folic acid (~30%). Furthermore, the bread matrix is suggested to inhibit absorption of folates. Purpose To (1) estimate retention of both, endogenous folates and synthetic fortificants, during bread-making, (2) assess in vitro folate bioaccessibility from breads and a breakfast meal and (3) assess in vitro folate uptake. Methods Retention of folate forms was assessed by preparing fortified (folic acid and [6S]-5-CH₃-H₄folate) wholemeal breads and collect samples from dough, proofed dough and the bread. In vitro folate bioaccessibility was assessed using the TNO gastrointestinal model TIM. In vitro folate uptake was assessed using a novel Caco-2 cell/stable isotope model. Folate content in samples was measured using LCMS. Results Bread-making resulted in losses of 41% for endogenous folates and up to 25 and 65% for folic acid and [6S]-5-CH₃-H₄folate fortificant, respectively. 75% of endogenous bread folates and 94% of breakfast folates were bioaccessible as assessed by TIM. From [6S]-5-CH₃-H₄folate-fortified bread, relative folate uptake into Caco-2 cells was 71 ± 11% (P < 0.05) when compared with a standard solution. Conclusion Retention of folic acid fortificant during bread-making was substantially higher compared to retention of [6S]-5-CH₃-H₄folate fortificant. Data from the TIM and Caco-2 cell trials suggest an inhibiting effect of the tested bread matrices on in vitro bioaccessibility of folates, whereas folate bioaccessibility from a breakfast meal is almost complete.