| The faba bean is one of the oldest crops that ranks sixth in production among the different legumes grown in the world. Faba beans are a good source of energy, proteins, vitamins, minerals and dietary fiber. They are relatively inexpensive compared to meat foods and as they have a high carbohydrate content. Therefore, faba beans are beneficial for human nutrition perspectives because they are good source of energy, protein and dietary fiber. In China, plant foods provide at least50%of the dietary energy and nutrients, and faba bean is one of the most important legumes. Faba beans are a good source of dietary minerals, such as phosphorus, potassium, calcium, sulphur and iron. However, the utilization of the minerals are limited by the presence of phytic acid. Phytic acid (myoinositol1,2,3,4,5,6hexakidishydrogen phosphate) is common in faba beans and is the principal storage form of phosphorus in many dry beans. A nutritional concern about the presence of phytic acid in dry beans arises from the fact that phytic acid decreases the bioavailability of essential minerals and may possibly interfere in the utilization of proteins due to phytate-protein and phytate-mineral-protein complexes. This paper studied the effects of different processings on phytic acid contents in fractions of faba bean, and found that phytic acid and dietary fibre were main factors which inhabited the Ca, Fe, Zn bioavailability of the bean.1、Germination was an effective approach reducing phytic acid in cotyledon and phytic acid was removed by50%in cotyledon of the bean in the eighted day during germination. The cotyledon had the highest contents of Ca, Fe, Zn followed by radicle, embryonic axe, plumula. During faba bean germination, some mechanisms can lead to changing of iron chemical forms. By this mechanism the content of soluble iron and ferric iron increased obviously. So germination is a good way to improve the iron bioactivity in faba bean.The amount of the soluble iron and ferrous iron in faba bean which have higher bioavailability for human increased during germination.2、Whole seeds, dehulled seeds and hulls underwent different patterns of losses of dry matter, minerals and phytic acid, when soaked with demineralized water, acidic buffer and phytase solutions after preheating.Whole seeds contained8.36mg g-1phytic acid which was removed best from seeds (51%of initial) by soaking in acidic buffer, but in flour by phytase application to below detection levels. Dry matter losses due to soaking ranged from0.8～32.8%with highest losses observed after soaking in acidic buffer. Whole seeds contains higher levels of calcium, iron and zinc than dehulled seeds. However, losses due to soaking were similar as in dehulled seeds, for calcium (20～61%), iron (33～61%), and zinc (8～51%).Dehulled faba bean contained8.16mg g-1phytic acid which could be reduced by all treatments. But phytase soaking treatment was the most effective in dehulled seeds flour. Dry matter losses due to soaking ranged from2.4～18.6%with the highest losses observed after soaking in acidic buffer. Whereas relatively high losses of calcium (12～63%) and iron (10～43%) were recorded, zinc losses were lower (1～36%).Hulls contained9.25mg g-1phytic acid which was removed best (-85%) by phytase treatment, followed by soaking in acidic buffer (-43%). Dry matter losses from hulls due to soaking were highest (6.4～28.7%) of all faba bean products. Hulls contains the highest levels of calcium (327mg g-1), iron (44.6mg g-1) and zinc (52.4mg g-1), and phytase treatment resulted in dissolution of46～60%calcium and zinc in the soaking medium.In conclusion, phytase application is an effective method to rapidly remove phytic acid while preserving relatively more dry matter and minerals than other soaking approaches in faba bean fractions.3、Soaking and germination decreased phytic acid content in faba bean. The most effective approach, which was germination120h. Soaking and germination can improve iron, calcium and zinc bioavailability. The result showed that the presence of components such as dietary fiber leading to the formation of insoluble iron complexes. It remains to be investigated to what extent this would affect in vitro iron, calcium and zinc-solubility and bioavailability.4、Phytate degradation that occurred during incubation increased calcium, iron and zinc in vitro bioavailability of faba bean flour. Calcium, iron and zinc in vitro bioavailability were86.5%,78.2%and58.8%in faba bean flour.30%,28.1%and34.4%in dehull faba bean flour;40.1%,33.1%and43.7%in hull. The addition of exogenous phytase did not lead to additional improvement in calcium, iron and zinc in vitro bioavailability as compared to that obtained after action of endogenous phytases. A reduction of calcium, iron and zinc in vitro bioavailability was even observed in some cases, indicating that phytase addition may affect mineral bioavailability by changing molecule interactions in the food matrix. Furthermore, phytate are not the only components that reduce calcium, iron and zinc bioavailability in faba bean. A large proportion of calcium, iron and zinc located in the core of the faba bean are chelated to phytate, but calcium, iron and zinc located in the hulls appear to be more closely linked to fibers and/or to tannins.5、The calcium and iron in faba bean flour was mainly chelated by complexes involving both fibers and phytates, so that calcium and iron were solubilized by simultaneous action of cellulase and phytases. However, in the hull of faba bean that contain high fiber and tannin contents, the majority of calcium and iron appeared to be chelated by tannins (iron-tannins). Thus, phytates, fibers, and tannins alike, decrease the bioavailability of calcium and iron in faba bean flour. In dehulled faba bean flour, calcium and iron can be chelated by phytic acid and cellulose, but in hull flour calcium and iron can be chelated by phytic acid and tannin.Concerning the zinc of faba bean flour, it was mainly linked to phytates and the greater the degree of phytate degradation before in vitro digestion, the greater the quantity of zinc released. Furthermore, fibers and probably also tannins or some proteins could be involved in the formation of complexes with zinc in the hull of faba bean. Some lower inositol phosphate resulting from phytate hydrolysis appears to contribute to a considerable extent to low zinc bioavailability in faba bean flour. |
PDF Full Text Request