Low phytate lupin flour based biomass obtained by fermentation with a mutant of Aspergillus niger
Introduction
Phytic acid (myo-inositol 1,2,3,4,5,6 hexakis dihydrogen phosphate) (PA) is the main storage form of phosphorus in many cereal and legume seeds. Due to its strong chelating property PA is regarded as an anti-nutritive factor because it forms insoluble complexes with nutritionally important minerals such as calcium, zinc, magnesium and iron, decreasing their bioavailability [1], [2]. One alternative to increase the bioavailability of minerals in phytate containing seeds is its removal from the food product.
Many processes have been reported to remove PA from seeds [3], [4], but the better results are obtained by the use of enzymatic hydrolysis. Phytase (myo-inositol hexaphosphate hydrolase) hydrolyses PA to myo-inositol and inorganic phosphate. It is produced during seed germination [3], [5], [6] or by microorganisms [3], [7], [8]. In solid state fermentation (SSF), Aspergillus has been reported to produce this enzyme [1], [7], [8], [9], [10].
In SSF, studies on characterization of the factors affecting the growth of microorganism are relatively scarce in comparison with submerged fermentation [11]. The amount of solids involved in SSF is very high and the medium is heterogeneous making it difficult to obtain accurate parameters such as cell biomass level, nutrient concentration and determination of metabolites [12].
The influence of the fermentation medium composition on enzyme production in solid state or submerged fermentations has already been described [12]. However, reports about the production of phytase and degradation of PA in SSF are scarce. The present article reports some factors that influence the SSF process to produce biomass, phytase and to degrade PA from lupin seed.
Section snippets
Selection of microorganisms
Ten morphological mutants Aspergillus niger strains [13] from Embrapa Food Technology (Brazil) stock collection were screened for growth potential with phytic acid as source of phosphate in the growth medium. Screening was performed using plates with a modified selection medium [14]. The medium contained (g/l): galactose, 15.0; phytic acid, 5.0 or KH2PO4, 2.0; (NH4)2SO4, 3.0; MgSO4·7H2O, 0.5; KCl, 0.5; CaCl2, 0.1; MnSO4·H2O, 7.9; agar, 25.0; pH 4.5. Point inoculations were adopted and plates
Results and discussion
The ability of A. niger strains to grow on solid culture medium with and without PA was tested and results are presented in Table 1. Strains showing a colony diameter of 1.0 cm, after the 4th day of fermentation, were selected for phytase production. Based on this criterion strains 9D40, 11D40, 9D80, 11D80 and 11T25A5 showed the best growth performance. However, strain 11T25A5 showed growth only in the presence of PA indicating that its growth is induced by PA as a source of phosphate and
Acknowledgements
The authors would like to acknowledge Conselho Nacional de Desenvolvimento Cientı́fico e Tecnológico e Fundação de Amparo á Pesquisa RJ, Brazil, for financial support. Author LCT is recipient of research fellowship from CNPQ.
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