OBJECTIVETo investigate the effect of lemon peel extracts (LPE) on the activity of lactate dehydrogenase and sucrase of Streptococcus mutans (Sm).

METHODSAfter serial dilution with trypticase soy broth (TSB) medium containing 2% glucose, LPE was used as the experimental group, and TSB without LPE as the control group. Sm was added to each group, which was then cultured for 6, 18, 24 and 48 hours in the anaerobic tank. The activity of lactate dehydrogenase(LDH) was measured with the method of oxidation of reduction coenzymeIand the pH value of the culture solution was also detected. The activity of the sucrose was determined with the method of coloration of 3,5-dinitrosalicylic acid.

RESULTSThe activity of LDH, sucrase and the changes of solution pH were decreased with the increase of the concentration of LPE (P < 0.01). The activity of LDH were declined from (0.8025 ± 0.0913) × 10(3) U/L to (0.2099 ± 0.0283) × 10(3) U/L; the activity of sucrase were declined from (-0.0107 ± 0.0003) × 10(3) U/L to (-0.0078 ± 0.0002) × 10(3) U/L; the ΔpH were declined from (2.8067 ± 0.0404) to (2.5033 ± 0.0416) (24 h results). The differences were significant between experimental groups and the control group (P < 0.01), and there were also significant differences among experimental groups with different LPE concentration (P < 0.01). The inhibitory effect of acid generation and lactate dehydrogenas' activity of Sm were positively correlated (P < 0.01).

CONCLUSIONSLPE can inhibit the activity of lactate dehydrogenase, sucrase and the acid production capacity of the Sm in a dose dependent manner. The inhibitory effects in logarithmic phase is stronger than that in other phases of growth cycle.