Abstract
In starch degrading industry, the first step to be performed is gelatinization of starch granules at elevated temperature. This process tends to form a viscose suspension, thus making mixing and pumping a huge challenge. Therefore, to lower the viscosity of starch paste thermostable enzymes are added for breaking down the polysaccharides into oligosaccharides by a process known as liquefaction. Therefore, the availability of these enzymes can be considered a prerequisite to start successful starch liquefaction and saccharification industry. The main objective of this study was, therefore, to produce efficient microbial amylolytic enzymes for starch hydrolysis. One bacterial isolate designated as BACC 2107 was isolated from locally collected samples. The enzyme has optimum activity at pH of 5.0 and 70°C. The addition of calcium in the reaction mixture was shown to stabilize the enzyme. The isolate BACC 2107 was able to grow under solid-state fermentation (SSF) using wheat bran as a solid substrate. Optimum enzyme production was recorded at 32°C, and at 120 h of incubation and at a moisture content of 75%. Addition of peptone to the SSF medium as an organic nitrogen supplement enhanced enzyme production. The enzyme was used to hydrolyze a 25% (w/v) of starch at 70°C and pH 5.0, and the resulting hydrolysate was analyzed on TLC plates. After 4 h hydrolysis, the TLC chromatogram showed the release of glucose, maltose, maltotriose, and other oligosaccharides, indicating that the enzyme is endo-acting alpha-amylase. The results of this study show that amylase from BACC 2107 has a good potential to be used in starch liquefaction and saccharification processes. The ability of the isolate to grow and produce the enzyme under SSF using cheap agro-industrial wastes could help to greatly reduce the production cost of the enzyme.
Highlights
Starch is a polysaccharide made of glucose molecules linked together with an alpha-D-(1-4) linkage and alpha-D(1-6) linkages at branching points [1]
The reaction mixture was made of 25% (w/v) raw starch mixed with 22.8 U concentrated crude enzyme from the bacterial isolate and 10.85 U of malt enzyme extracted using method which was incubated at 70 and 60°C for 4 h in the water bath but the malt enzyme was included in the reaction after 3 h of the incubation period
Alpha-amylase of BACC 2107 has a property of low pH activity and a thermo stability (70°C - 75°C) and thermal activity (60°C - 75°C) that can be enhanced with the addition of 5mM Ca2+
Summary
Starch is a polysaccharide made of glucose molecules linked together with an alpha-D-(1-4) linkage and alpha-D(1-6) linkages at branching points [1]. Starch is isolated from such agricultural crops as tubers (potato), cereals (e.g maize, sorghum, millet, and rice), and root (cassava, sweet potato, arrowroot) [3]. In Ethiopia agriculture is considered the backbone of the national economy. Among the common crops in Ethiopia that can serve as a commercial source of starch include enset [4], Ethiopian yam [5], godare [6], anchote [7], cassava [8], and kottee harree [9]. Starch can be hydrolyzed both enzymatically and chemically
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