Enrichment of maize and triticale bran with recombinant Aspergillus tubingensis ferulic acid esterase
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Ferulic acid is a natural antioxidant found in various plants and serves as a precursor for various fine chemicals, including the flavouring agent vanillin. However, expensive extraction methods have limited the commercial application of ferulic acid, in particular for the enrichment of food substrates. A recombinant Aspergillus tubingensis ferulic acid esterase Type A (FAEA) was expressed in Aspergillus niger D15#26 and purified with anion-exchange chromatography (3487 U/mg, K m = 0.43 mM, K cat = 0.48/min on methyl ferulate). The 36-kDa AtFAEA protein showed maximum ferulic acid esterase activity at 50 °C and pH 6, suggesting potential application in industrial processes. A crude AtFAEA preparation extracted 26.56 and 8.86 mg/g ferulic acid from maize bran and triticale bran, respectively, and also significantly increased the levels of p-coumaric and caffeic acid from triticale bran. The cost-effective production of AtFAEA could therefore allow for the enrichment of brans generally used as food and fodder, or for the production of fine chemicals (such as ferulic and p-coumaric acid) from plant substrates. The potential for larger-scale production of AtFAEA was demonstrated with the A. niger D15[AtfaeA] strain yielding a higher enzyme activity (185.14 vs. 83.48 U/ml) and volumetric productivity (3.86 vs. 1.74 U/ml/h) in fed-batch than batch fermentation.
KeywordsFerulic acid esterase Aspergillus niger Aspergillus tubingensis Triticale Maize
This work is based on the research supported in part by the National Research Foundation of South Africa (Grant 76597 to MVB and Grant 86423 to WHvZ). Prof Peter Punt, TNO Microbiology and Systems Biology, Netherlands, kindly provided the Aspergillus niger D15#26 host strain.
ENZ was the principal researcher responsible for experimental planning, execution, data collection and analyses, as well as drafting the manuscript. PJvZ assisted with the fermentation protocol; KGD with bran treatments and chemical analyses; SHR and KR with enzyme characterisation. WHvZ provided intellectual input together with MVB who prepared the final manuscript with all authors participating in the final editing.
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