Effect of metal ions on the enzymatic activity of Lactobacillus reuteri ATCC 55730 grown in a sweet potato base medium

Lactobacillus reuteri ATCC 55730 is a probiotic strain used in commercial products providing several health benefits. Metal ions play an important role in the functionality of probiotic bacteria. Sweet potato is abundant agricultural community in North Carolina. The objective of this study was to determine the effect of metal ions on the enzymatic activity of L. reuteri ATCC 55730 grown in a sweet potato base medium (SPM). SPM was previously developed in our laboratory to serve the growth of Lactobacillus sp. The growth and enzymatic activity of L. reuteri ATCC 55730 grown in SPM was compared to that in the standard lactobacilli MRS. Enzymatic activity including α–glucosidase, β-glucosidase, acid phosphatase, and phytase were determined spectrophotometrically using a corresponding substrate after16 h of incubation at 37ºC. L. reuteri ATCC 55730 grown in SPM showed a 103.5, 74.5, and 43.6 % increase in β-glucosidase, acid phosphatase, and phytase respectively compared to MRS. Final bacterial populations reached 8.59±0.21 and 8.55±0.31 log CFU/mL in SPM and MRS respectively. The addition of metal ions to SPM caused an additional increase in the tested enzymes. The increase in β-glucosidase due to the addition of Mn²⁺, Na⁺, Mg²⁺ and Ca²⁺ ranged between 167 and 208 %. Phytase was increased by 69 and 62 % in the presence of Mn²⁺ and Ca²⁺ respectively. These findings indicated that the addition of selected metal ions to the growth media of L. reuteri ATCC 55730 could produce an enhanced level of enzymes.