Efficient hydrolysis of raw starch and ethanol fermentation: a novel raw starch-digesting glucoamylase from Penicillium oxalicum

Abstract

BackgroundStarch is a very abundant and renewable carbohydrate and is an important feedstock for industrial applications. The conventional starch liquefaction and saccharification processes are energy-intensive, complicated, and not environmentally friendly. Raw starch-digesting glucoamylases are capable of directly hydrolyzing raw starch to glucose at low temperatures, which significantly simplifies processing and reduces the cost of producing starch-based products.ResultsA novel raw starch-digesting glucoamylase PoGA15A with high enzymatic activity was purified from Penicillium oxalicum GXU20 and biochemically characterized. The PoGA15A enzyme had a molecular weight of 75.4 kDa, and was most active at pH 4.5 and 65 °C. The enzyme showed remarkably broad pH stability (pH 2.0–10.5) and substrate specificity, and was able to degrade various types of raw starches at 40 °C. Its adsorption ability for different raw starches was consistent with its degrading capacities for the corresponding substrate. The cDNA encoding the enzyme was cloned and heterologously expressed in Pichia pastoris. The recombinant enzyme could quickly and efficiently hydrolyze different concentrations of raw corn and cassava flours (50, 100, and 150 g/L) with the addition of α-amylase at 40 °C. Furthermore, when used in the simultaneous saccharification and fermentation of 150 g/L raw flours to ethanol with the addition of α-amylase, the ethanol yield reached 61.0 g/L with a high fermentation efficiency of 95.1 % after 48 h when raw corn flour was used as the substrate. An ethanol yield of 57.0 g/L and 93.5 % of fermentation efficiency were achieved with raw cassava flour after 36 h. In addition, the starch-binding domain deletion analysis revealed that SBD plays a very important role in raw starch hydrolysis by the enzyme PoGA15A.ConclusionsA novel raw starch-digesting glucoamylase from P. oxalicum, with high enzymatic activity, was biochemically, molecularly, and genetically identified. Its efficient hydrolysis of raw starches and its high efficiency during the direct conversion of raw corn and cassava flours via simultaneous saccharification and fermentation to ethanol suggests that the enzyme has a number of potential applications in industrial starch processing and starch-based ethanol production.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0636-5) contains supplementary material, which is available to authorized users.

Purification and biochemical characterization of extracellular glucoamylase from Paenibacillus amylolyticus strain

“…The raw‐starch digesting ability of P. amylolyticus NEO03 glucoamylase was found to be in accordance with amylases of B. amyloliquefaciens and A. niger AM07 . On the other hand Xu et al also demonstrated identical hydrolysis patterns on different raw‐starches. However, hydrolysis of rice bran by the glucoamylase under study was more significant than the commercial enzyme.…”

Identification of a Novel Transcription Factor TP05746 Involved in Regulating the Production of Plant-Biomass-Degrading Enzymes in Talaromyces pinophilus

“…RSDEs contain the specific starch-binding domain (SBD) that enables them to bind onto the surface of raw starch granules (Sorimachi et al, 1997;Machovic and Janecek, 2006;Xu et al, 2016). RSDE application can reduce the process cost since the liquefaction step would not be needed (Sun et al, 2010;Lee et al, 2012).…”

Consolidated Bioprocess for Bioethanol Production from Raw Flour of Brosimum alicastrum Seeds Using the Native Strain of Trametes hirsuta Bm-2

“…The liquefied starch is cooled, pH is adjusted to 4-4.5, temperatures to 60-65 • C, and a fungal glucoamylase is added to hydrolyze the oligosaccharides to glucose. The liquefaction and saccharification stages represent about 40%-50% of the total energy used during starch-based ethanol production [8][9][10].Owing to this technical complexity and the economic implications of this approach, other biological alternatives have been investigated, such as simultaneous saccharification and fermentation (SSF) and consolidated bioprocessing (CBP). The latter is a promising strategy for effective ethanol production, since it employs only one type of microorganism that is capable of both producing the enzymes to hydrolyze the biomass and converting sugars into ethanol [11,12].…”

“…The liquefied starch is cooled, pH is adjusted to 4-4.5, temperatures to 60-65 • C, and a fungal glucoamylase is added to hydrolyze the oligosaccharides to glucose. The liquefaction and saccharification stages represent about 40%-50% of the total energy used during starch-based ethanol production [8][9][10].…”