Microbial α-amylases: a biotechnological perspective

Starch constitutes a major component of foods and also a raw material for use in the production of industrial products. The constituent macromolecules of starch are packaged in a highly ordered and compact manner, resulting in inert, insoluble granules. Food processing destroys starch structure, thereby releasing the component molecules, which are subsequently made available for hydrolysis or serve a functional role in the food system. The application of starch as a raw material usually requires the prior disruption of the inert granule structure, which involves additional processing steps. The hydrolysis of native granules has ramifications at all levels of the food processing chain, from postharvest losses to nutritional consequences of the ingested food. Technologists have not been able to take advantage of, or control, this process because the body of the information that is available on starch granule structure and the behaviour of hydrolysing enzymes is still incomplete. In this review, I have highlighted some of the more recent advances in this field, with the view to opening up the way for more efficient native starch hydrolysis.

Towards an understanding of starch granule structure and hydrolysis

A novel raw starch digesting thermostable α-amylase from Bacillus sp. I-3 and its use in the direct hydrolysis of raw potato starch

Improved molecular disassembly and depolymerization of grain starch to glucose are key to reducing energy use in the bioconversion of glucose to chemicals, ingredients, and fuels. In fuel ethanol production, these biorefining steps use 10-20% of the energy content of the fuel ethanol. The need to minimize energy use and to raise the net yield of energy can be met by replacing high-temperature, liquid-phase, enzymatic digestion with low temperature, solid-phase, enzymatic digestion. Also called cold hydrolysis, the approach is a step toward a "green" method for the production of fuel ethanol. There has been substantial prior and increased recent interest in this approach that is presented in this first review of the subject. We include incentives, developmental research, fundamental factors of raw starch digestion, and novel approaches in enzymology and processing. The discussion draws on resources found in enzymology, engineering, plant physiology, cereal chemistry, and kinetics.

Native or raw starch digestion: a key step in energy efficient biorefining of grain.

Production of a thermostable α-amylase from Bacillus sp. PS-7 by solid state fermentation and its synergistic use in the hydrolysis of malt starch for alcohol production

A newly isolated bacterium, identified as Bacillus subtilis 65, was found to produce raw-starch-digesting α-amylase The electrophoretically homogeneous preparation of enzyme (molecular weight, 68,000) digested and solubilized raw corn starch to glucose and maltose with small amounts of maltooligosaccharides ranging from maltotriose to maltoheptaose This enzyme was different from other amylases and could digest raw potato starch almost as fast as it could corn starch, but it showed no adsorbability onto any kind of raw starch at any pH The mixed preparation with Endomycopsis glucoamylase synergistically digested raw potato starch to glucose at 30°C The raw-potato-starch-digesting α-amylase showed strong digestibility to small substrates, which hydrolyzed maltotriose to maltose and glucose, and hydrolyzed p-nitrophenyl maltoside to p-nitrophenol and maltose, which is different from the capability of bacterial liquefying α-amylase

Production and Characteristics of Raw-Potato-Starch-Digesting α-Amylase from Bacillus subtilis 65

α-Cyclodextrin specifically inhibited raw starch digestion by Bacillus subtilis 65 α-amylase. The raw starch digestibility and α-cyclodextrin-Sepharose 6B adsorbability of this α-amylase were simultaneously lost when the specific domain corresponding to the affinity site essential for raw starch digestion was deleted by proteolysis. Occurrence of the affinity site on raw-starch-digesting enzymes was proven also with bacterial amylase.

Takehiro Inoue

Papers

Production and Characteristics of Raw-Potato-Starch-Digesting α-Amylase from Bacillus subtilis 65

Occurrence of an affinity site apart from the active site on the raw-starch-digesting but non-raw-starch-adsorbable Bacillus subtilis 65 α-amylase