科研之友
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摘要
A new amylolytic strain of Lactobacillus paracasei able to convert starch directly into L-(+)-lactic acid (LA) was isolated. The identification of the by 16S rDNA sequencing proved that this strain, B41, is the first amylolytic representative of Lactobacillus casei group. The amylase activity assay revealed that L. paracasei B41 produced extracellular amylolytic enzyme, reaching 62?U/mL in the cell-free supernatants. The optimal conditions for its action were pH 5.0 and temperature 45 degrees C. The gene amy1 (1779?bp) encoding the putative B41 amylopullulanase was cloned, sequenced, and analyzed. The deduced protein contained a leader peptide of 28 amino acids and a mature peptide of 564 amino acids. Compared to the amylases of closely related species, B41 enzyme had several amino acid substitutions. An inducible control at amy1 expression was demonstrated. The starch fermentation abilities of L. paracasei B41 were studied in batch processes performed with and without pH control. The highest amount of LA from starch was obtained during 48?h fermentation from 40?g/L substrate at pH maintained at 5.037.3?g/L. In addition, 93.3% starch conversion into LA and the highest reported productivity for 24?h were achieved 1.30?g/L/h.
- 出版日期2012-1
