Reference Number: 12
Phytases are enzymes capable of sequentially dephosphorylating phytic acid to products of lower chelating capacity and higher solubility, abolishing its inhibitory effect on intestinal mineral absorption. Genetic construc- tions were made for expressing two phytases from bifidobacteria in Lactobacillus casei under the control of a nisin-inducible promoter. L. casei was able of producing, exporting and anchoring to the cell wall the phytase of Bifidobacterium pseudocatenulatum. The phytase from Bifidobacterium longum spp. infantis was also produced, although at low levels. L. casei expressing any of these phytases completely degraded phytic acid (2 mM) to lower myo-inositol phosphates when grown in MRS medium. Owing to the general absence of phytase activity in lactobacilli and to the high phytate content of whole grains, the constructed L. casei strains were applied as starter in a bread making process using whole-grain flour. L. casei developed in sourdoughs by fermenting the existing carbohydrates giving place to an acidification. In this food model system the contribution of L. casei strains ex- pressing phytases to phytate hydrolysis was low, and the phytate degradation was mainly produced by activation of the cereal endogenous phytase as a consequence of the drop in pH. This work shows the capacity of lactobacilli to be modified in order to produce enzymes with relevance in food technology processes. The ability of these strains in reducing the phytate content in fermented food products must be evaluated in further models.
SIGNIFICANCE OF THIS STUDY
During sourdough fermentation LAB produce a number of metabolites which have been shown to have a positive effect on the texture and staling of bread, e.g. organic acids, exopolysaccharides (EPS) and/or enzymes and this results in an enhancement of the nutritional and sensory quality of bread. The sourdough increases the bioavailability of minerals. Whole grain cereals contain significant amounts of phytic acid or its salts (phytates). which functions in the storage of phosphorus, calcium, magnesium and other minerals present bin whole grains for growth and it is a well-known inhibitor of mineral, proteins and trace element absorption when whole grains are ingested. Although some researchers have reported positive effects of phytate as antioxidant, this paper focusses on the mechanism of how minerals from wholegrains can be absorbed and utilised by us to its full potential. Sourdough results in phytate hydrolysis thereby decreasing the negative effects on mineral absorption and ensuring minerals from whole grains are more readily absorbed when ingested thereby positively affect human health.