Evaluation of Antioxidant and Antibacterial Properties of Licorice Root Extract in Liquid Chocolate

Licorice is one of the most important medicinal plants that has been considered by the pharmaceutical, food and even tobacco industries due to its important medicinal and nutritional compounds in its roots and rhizomes. The aim of this study was to evaluate the antioxidant and antibacterial properties of licorice root extract in liquid chocolate. After extracting the extract, antioxidant activity was evaluated by free radical scavenging activity tests. The antimicrobial effect of the extract on the growth of Staphylococcus aureus and Escherichia coli was investigated by well diffusion method and the Minimum Inhibitory Concentration (MIC) and the Minimum Bactericidal Concentration were determined. To control the growth of microorganisms, licorice extract was used in concentrations of 0.5% and 1% in liquid chocolate formulation. Samples containing the extract along with the control sample were exposed to 30 ℃ temperature and microbial growths were examined at 1, 15 and 30 days after treatments. Sensory evaluation of the samples was also performed. The results showed that licorice extract has high antioxidant properties. Minimum Inhibitory Concentration and the Minimum Bactericidal Concentration were observed on Staphylococcus aureus 19.53 μg/ml, 39.6 μg/ml and on Escherichia coli 156.25 μg/ml and 312.50 μg/ml, respectively. The results of microbial test showed that the use of licorice extract increases the shelf life of liquid chocolate for 30 days. Adding licorice extract up to 1% in liquid chocolate formulation increases overall acceptance in sensory evaluation. In general, the use of 1% licorice extract in liquid chocolate formulation can increase its shelf life and improve its sensory properties.