Degradation, amylase processing

In this chapter we describe the use of pea seeds to express the bacterial enzyme a-amylase. Bacterial exoenzymes like the heat stable a-amylase from Bacillus licheni-formis are important for starch hydrolysis in the food industry. The enzymatic properties of a-amylase are well understood [13,14], it is one of the most thermostable enzymes in nature and it is the most commonly used enzyme in biotechnological processes. Although fermentation in bacteria allows highly efficient enzyme production, plant-based synthesis allows in situ enzymatic activity to degrade endogenous reserve starch, as shown in experiments with non-crop plants performed under greenhouse conditions [12,15]. Finally, the quantitative and sensitive detection of a-amylase activ-... 

Starch Liquefaction. Starch in its natural state is only degraded slowly by CC-amylases. To make the starch susceptible to enzymatic breakdown, it is necessary to gelatinize and liquefy a slurry with a 30—40% dry matter content. Gelatinization temperature depends on the type of starch (67) com is the most common source of industrial starches followed by wheat, tapioca, and potatoes. Liquefaction is achieved by adding a heat-stable a-amylase to the starch slurry. The equipment used for liquefaction may be stirred tank reactors, continuous stirred tank reactors (CSTR), or a jet cooker. Most starch processing plants liquefy the starch with a single enzyme dose in a process using a jet cooker (Fig. 9). 

Inactivation or removal of plasma enzymes may be accomplished by several processes denaturation of the enzyme due to dilution in plasma or separation from its natural substrate or coenzyme presence of enzyme inhibitors (e.g., falsely decreased activity of amylase in acute pancreatitis with hyperlipemia) removal by the reticuloendothelial system digestion by circulating proteinases uptake by tissues and subsequent degradation by tissue proteinases and clearance by the kidneys of enzymes of low molecular mass (amylase and lysozyme). 

Under equilibrium conditions 39% is present as a-maltose, having the free glycosidic hydroxyl group in the a-configuration. Since degradation of starch by a-amylase primarily yields maltose, assay of maltose is of relevance in the control of brewery and distillery processes. 

Formation of disulfide bonds from cysteine residues is an oxidation reaction. A cysteine residue in a-amylase is oxidized at pH 8.O.818 Methionine and histidine residues are also susceptible to oxidation. Oxidation of methionine residues has been observed during storage of parathyroid hormone819 and relaxin.820 Degradation of freeze-dried ribonuclease A was ascribed to oxidation because molecular oxygen was involved in the degradation process.821... 

Sarikaya, E., Higasa, T., Adachi, M., and Mikama, B. 2000. Comparison of degradation abilities of a and P-amylases on raw starch granules. Process Biochem. 35, 711-715. 

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