Abstract
A Lactobacillus sp. was screened from various cereal sourdoughs and was designated as Lactobacillus plantarum YXY418 based on the 16S rRNA gene analysis. A putative Lactobacillus plantarum maltogenic amylase, LpMA, was discovered based on computer-aided analysis. Then, its encoding gene (lpma) was expressed in E. coli BL21(DE3). The expressed recombinant LpMA (reLpMA) was efficiently purified to 12.2-fold using the one-step nickel-nitrilotriacetic acid (Ni–NTA) affinity chromatography. The final recovery yield and specific activity of the purified reLpMA were 61% and 36.4 U/mg towards soluble starch, respectively. The purified reLpMA exhibited optimal amylolytic activity towards soluble starch at 45 °C and pH 6.0, with a good pH stability ranging from pH 5.0 to 8.0. Besides, the reLpMA also hydrolyzed soluble starch, β-CD and pullulan to maltose with specific activity of 96.4 SU/mL, 78.2 CU/mL and 2.0 PU/mL, respectively. The reLpMA hydrolytic activity was increased in the presence of metal ions especially Ca2+ and Zn2+, which could be applied to different processing processes. Baking test indicated after 7-day storage, the reLpMA at a dosage of 2000 U/300 g could significantly reduce hardness and chewiness by 29.5% and 26.4%, respectively, compared with the control. Adding reLpMA improved bread quality, increased bread volume and decreased hardness during storage, thus extending its shelf life.
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