Comparative study of starch hydrolysis by free or immobilized alpha-amylase produced by B. subtilis in aqueous two-phase systems

Zoi Konsoula, Maria Liakopoulou-Kyriakides

Research output: Contribution to journalMeeting Abstractpeer-review


The partitioning of extracellular alpha-amylase produced by B. subtilis, a bacterium isolated from fresh sheep’s milk, in aqueous two-phase systems has been investigated with the purpose of designing a phase system for the bioconversion of starch. Various combinations of polyethyleneglycol (PEG 10 000) and calcium chloride, ammonium sulfate or dextran (505 000) were employed for amylase partitioning. It was found that the system with 12.5% (w/v) PEG and 10% (w/v) calcium chloride was most effective in terms of alpha-amylase purification. This purification showed a protein reduction of 50% of the original protein content of the culture filtrate, while the specific activity was increased fourfold. Various starches were hydrolyzed using this crude alpha-amylase in PEG-Dextran and PEG-substrate aqueous two-phase systems. Batch hydrolysis experiments with two-phase systems resulted in higher production of reducing sugars and exhibited higher reaction rates in comparison to the single-phase processing. This crude amylase preparation was also immobilized in sodium alginate gel capsules, which were used for starch bioconversion. The concentration of sodium alginate was restricted to 2–3% (w/v) because it was found that further increase of the concentration reduces the enzyme leakage as well as the hydrolysis rate. Microencapsulation of the biocatalyst presents advantages in terms of biocompatability and cost since it reduces enzyme loss and offers the potential of recycling the biocatalyst. The effect of temperature on starch hydrolysis was also investigated, in the range from 50 to 70 °C, and it was found that in all cases higher reaction rates were achieved upon raise of the temperature. According to our experiments the crude amylase preparation not only hydrolyses sufficiently various starchy substrates at elevated temperatures (up to 70°C) but it can also be immobilized in sodium alginate gel capsules and be used repeatedly for starch bioconversion.
Original languageEnglish
Article numberP3.2-36
Pages (from-to)78-78
Number of pages1
JournalEuropean Journal of Biochemistry
Issue numbers1
Publication statusPublished - 2004


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