Effect of temperature on the saccharide composition obtained after alpha-amylolysis of starch

Enzymatic conversions of starch

This article surveys methods for the enzymatic conversion of starch, involving hydrolases and nonhydrolyzing enzymes, as well as the role of microorganisms producing such enzymes. The sources of the most common enzymes are listed. These starch conversions are also presented in relation to their applications in the food, pharmaceutical, pulp, textile, and other branches of industry. Some sections are devoted to the fermentation of starch to ethanol and other products, and to the production of cyclodextrins, along with the properties of these products. Light is also shed on the enzymes involved in the digestion of starch in human and animal organisms. Enzymatic processes acting on starch are useful in structural studies of the substrates and in understanding the characteristics of digesting enzymes. One section presents the application of enzymes to these problems. The information that is included covers the period from the early 19th century up to 2009.

Development of a certified reference material for genetically modified potato with altered starch composition

The presence of genetically modified organisms (GMOs) in food and feed products is subject to regulation in the European Union (EU) and elsewhere. As part of the EU authorization procedure for GMOs intended for food and feed use, reference materials must be produced for the quality control of measurements to quantify the GMOs. Certified reference materials (CRMs) are available for a range of herbicide- and insect-resistant genetically modified crops such as corn, soybean, and cotton. Here the development of the first CRM for a GMO that differs from its non-GMO counterpart in a major compositional constituent, that is, starch, is described. It is shown that the modification of the starch composition of potato (Solanum tuberosum L.) tubers, together with other characteristics of the delivered materials, have important consequences for the certification strategy. Moreover, the processing and characterization of the EH92-527-1 potato material required both new and modified procedures, different from those used routinely for CRMs produced from genetically modified seeds.

Hydrolysis of soluble starch using Bacillus licheniformis α-amylase immobilized on superporous CELBEADS

In the present work, indigenously prepared rigid superporous (pore size of approximately 3 microm) cross-linked cellulose matrix (CELBEADS) has been used as a support for the immobilization of Bacillus licheniformis alpha-amylase (BLA). Optimum pH and temperature, and Michaelis-Menten constants were determined for both free and immobilized BLA. Immobilized BLA was observed to produce a different saccharide profile than free BLA at any value of dextrose equivalent. It was observed that pH, temperature, and initial starch concentration has a significant effect on the saccharide profile of starch hydrolysate produced using immobilized BLA in the batch mode, whereas the ratio of concentration of enzyme units to initial starch concentration has no influence on the same. Hence immobilized BLA can be used as an additional tool for production of maltodextrins with different saccharide profiles. Immobilized BLA has better thermostability than free BLA. Immobilized BLA was found to retain full activity even after eight batches of hydrolysis, each of 8h duration at 55 degrees C and 90 mg/mL initial starch concentration. A semiempirical model has been used for the prediction of saccharide composition of starch hydrolysate with respect to time.

Temperature Impacts the Multiple Attack Action of Amylases

The action pattern of several amylases was studied at 35, 50, and 70 degrees C using potato amylose, a soluble (Red Starch) and insoluble (cross-linked amylose) chromophoric substrate. With potato amylose as substrate, Bacillus stearothermophilus alpha-amylase (BStA) and porcine pancreatic alpha-amylase displayed a high degree of multiple attack (DMA, i.e., the number of bonds broken during the lifetime of an enzyme-substrate complex minus one), the fungal alpha-amylase from Aspergillus oryzae a low DMA, and the alpha-amylases from B. licheniformis, Thermoactinomyces vulgaris, B. amyloliquifaciens, and B. subtilis an intermediate DMA. These data are discussed in relation to structural properties of the enzymes. The level of multiple attack (LMA), based on the relation between the drop in iodine binding of amylose and the increase in total reducing value, proved to be a good alternative for DMA measurements. The LMA of the endo-amylases increased with temperature to a degree depending on the amylase. In contrast, BStA showed a decreased LMA when temperature was raised. Furthermore, different enzymes had different activities on Red Starch and cross-linked amylose. Hence, next to the temperature, the action pattern of alpha-amylases is influenced by structural parameters of the starch substrate.

An alpha-(1,4)-amylase is essential for alpha-(1,3)-glucan production and virulence in Histoplasma capsulatum

Histoplasma capsulatum is a dimorphic fungus that causes respiratory and systemic disease and is capable of surviving and replicating within macrophages. The virulence of Histoplasma has been linked to cell wall alpha-(1,3)-glucan; however, the role of this polysaccharide during infection, its organization within the cell wall, and its synthesis and regulation remain poorly understood. To identify genes involved in the biosynthesis of alpha-(1,3)-glucan, we employed a forward genetics strategy to isolate physically marked mutants with reduced alpha-(1,3)-glucan. Insertional mutants were generated in a virulent strain of H. capsulatum by optimization of Agrobacterium tumefaciens-mediated transformation. Approximately 90% of these mutants possessed single insertions with no chromosomal rearrangements or deletions in the host genome. To confirm the role and specificity of identified candidate genes, we phenocopied the disrupted locus by either RNA interference or targeted gene deletion. Our findings indicate alpha-(1,3)-glucan production requires the function of the AMY1 gene product, a novel protein with homology to the alpha-amylase family of glycosyl hydrolases, and UGP1, a UTP-glucose-1-phosphate uridylyltransferase which synthesizes UDP-glucose monomers. Loss of AMY1 function attenuated the ability of Histoplasma to kill macrophages and to colonize murine lungs.

Effect of temperature on subsite map of Bacillus licheniformis alpha-amylase

To elucidate how temperature effects subsite mapping of a thermostable alpha-amylase from Bacillus licheniformis (BLA), a comparative study was performed by using 2-chloro-4-nitrophenyl (CNP) beta-maltooligosides with degree of polymerisation (DP) 4-10 as model substrates. Action patterns, cleavage frequencies and subsite binding energies were determined at 50 degrees C, 80 degrees C and 100 degrees C. Subsite map at 80 degrees C indicates more favourable bindings compared to the hydrolysis at 50 degrees C. Hydrolysis at 100 degrees C resulted in a clear shift in the product pattern and suggests significant differences in the active site architecture. Two preferred cleavage modes were seen for all substrates in which subsite (+2) and (+3) were dominant, but CNP-G1 was never formed. In the preferred binding mode of shorter oligomers, CNP-G2 serves as the leaving group (79%, 50%, 59% and 62% from CNP-G4, CNP-G5, CNP-G6 and CNP-G7, respectively), while CNP-G3 is the dominant hydrolysis product from CNP-G8, CNP-G9, and CNP-Gl0 (62%, 68% and 64%, respectively). The high binding energy value (-17.5 kJ/mol) found at subsite (+2) is consistent with the significant formation of CNP-G2. Subsite mapping at 80 degrees C and 100 degrees C confirms that there are no further binding sites despite the presence of longer products.

A kinetic model to explain the maximum in α-amylase activity measurements in the presence of small carbohydrates

The effect of the presence of several small carbohydrates on the measurement of the alpha-amylase activity was determined over a broad concentration range. At low carbohydrate concentrations, a distinct maximum in the alpha-amylase activity versus concentration curves was observed in several cases. At higher concentrations, all carbohydrates show a decreasing alpha-amylase activity at increasing carbohydrate concentrations. A general kinetic model has been developed that can be used to describe and explain these phenomena. This model is based on the formation of a carbohydrate-enzyme complex that remains active. It is assumed that this complex is formed when a carbohydrate binds to alpha-amylase without blocking the catalytic site and its surrounding subsites. Furthermore, the kinetic model incorporates substrate inhibition and substrate competition. Depending on the carbohydrate type and concentration, the measured alpha-amylase activity can be 75% lower than the actual alpha-amylase activity. The model that has been developed can be used to correct for these effects in order to obtain the actual amount of active enzyme.

Enzymatic hydrolysis of chestnut purée: process optimization using mixtures of alpha-amylase and glucoamylase

The enzymatic hydrolysis of starch present in chestnut purée was performed through a one-step treatment with a mixture of a commercial thermostable alpha-amylase (Termamyl 120 L, type S) and glucoamylase (AMG 300 L) at 70 degrees C. The effect of the enzyme concentration and the ratio of both amylases in the reaction mixture was studied by means of a factorial second-order rotatable design, which allowed conditions to be set leading to the total conversion of starch to glucose after 15 min of incubation (60 total enzymatic units g(-1) of chestnut; ratio of alpha-amylase/glucoamylase enzymatic units, 0.35:0.65). At lower enzyme concentration, the delay in the addition of the glucoamylase with regard to the addition of the alpha-amylase allowed a slightly higher hydrolysis percentage to be reached when compared to the simultaneous addition of both amylases at the same low enzyme concentration. The kinetics of liberation of glucose supports the existence of a synergistic effect between these two enzymes only in the first moments of the reaction. Finally, a sequential one-step hydrolysis was assayed, and more concentrated glucose syrups were thus obtained.