Abstract
As consumers have showed a concern for the reduction of chemical preservatives in food, the interest for natural compounds with antimicrobial properties has been investigated. In this study the acid potency and the antimicrobial effect of cinnamon and clove and their water extracts were tested in water and milk. Additionally, survival of S. aureus in yogurt inoculated with cinnamon and clove (0.3% conc.) during three days of storage was monitored. Clove and cinnamon showed strong acid potency in water as 2.5% concentration from both herbs dropped the PH of water to 5.4 and 6, respectively. However, the same concentration of both herbs had a slight effect on PH of milk as they lowered it to 6.5. Interestingly, 10% concentration of clove and cinnamon in water made zones of inhibition of 18 mm and 15mm, respectively. But, at the same concentration in milk only clove made zone of inhibition of 14mm. No zone of inhibition was observed at concentration equal to or below 5% of clove and cinnamon in milk. On the other hand, the mean counts of S. aureus in yogurt were similar in control samples and samples treated with cinnamon and clove. The P value during three days of storage was above 0.05, indicating non-significant differences between the treated and control samples. In conclusion, the buffering capacity of milk and dairy products neutralize the acidity of cinnamon and clove and make them ineffective on S. aureus. Therefore, cinnamon and clove may improve the sensory quality of milk and dairy products but not provide any degree of safety against S. aureus in these products.

Key words: Cinnamon, clove, S. aureus, antimicrobial effect