Effect of processing methods on mineral bioaccessibility in common beans

Mineral bioaccessibility is a concern in legume based foods and can be enhanced using different techniques. This study aimed to evaluate the effects of processing conditions on the in vitro mineral bioaccessibility of small black common beans cultivated in Mozambique. The samples were collected from the 'Instituto de Investigação Agrária de Moçambique' (IIAM), Maputo, Mozambique. Soaking (in water and sodium bicarbonate), germination (for 24 and 48 h at 25 °C), and cooking (ordinary and pressure) were applied. The oven-dried and finely ground samples of processed beans were in vitro digested and analyzed for mineral bioaccessibility. The in vitro gastrointestinal simulation assay was conducted, and the dialyzable portion of the samples was used to determine the bioaccessibility of iron, zinc, and copper. Overall, mineral bioaccessibility was not was not significantly impacted by the processing methods of the beans with the exception of pressure cooking, which notably increased iron bioaccessibility. Each processing method improved enhanced the in vitro bioaccessibility of iron, zinc, and copper when compared to the control sample. Iron bioaccessibility ranged from 2.22% to 7.79% with pressure cooking showing the highest improvement. It is worth nothing that the in vitro bioaccessibility of iron is relatively lower compared to that of zinc. Germination for 24 and 48 h resulted in zinc bioaccessibility of 7.58% and 10.08%, respectively, while zinc bioaccessibility of 6.52% for ordinary cooking and 8.41% for pressure cooking was achieved. The in vitro copper bioaccessibility obtained for soaking in water and sodium bicarbonate was found to be 6.04% and 6.78% respectively, which are almost similar. Similarly, germination for 24 and 48 h showed copper bioaccessibility of 7.01% and 7.63% respectively, whereas the copper bioaccessibility of 5.79% for ordinary cooking and 8.50% for pressure cooking was observed in this study. This shows that it is expected that the solubility of pressure-cooked beans in the intestine and the release of minerals from their matrix are high. The results illustrate that pressure cooking of presoaked beans had the highest value for all minerals' bioaccessibility except for zinc, suggesting that the processing techniques could help improve minerals' bioaccessibility.