The Effect of Combined Clove and Cinnamon extracts on Growth and Survival of Escherichia fergusonii and Salmonella typhimurium in milk pre and post fermentation
Author(s): Betty A. Ogwaro, Elizabeth A. O’Gara, Dave J. Hill and Hazel Gibson
The antimicrobial activities of extracts of clove buds (CL) and cinnamon bark (CE) were investigated individually and in combination in fermenting and fermented full cream milk against Escherichia fergusonii and Salmonella typhimurium. Clove and cinnamon were extracted for their essential oils (EOs) and eugenol and cinnamaldehyde were the major components representing 60-80% of the total oils. Preheated milk was inoculated with 1% (v/v) of a mixed culture of Lactobacillus delbrueckii subspecies bulgaricus (NCIMB 11778) and Streptococcus thermophilus (NCIMB 10387) and incubated at 25 or 37oC for 24 h. E. fergusonii or S. typhimurium (3 x 105 CFU/mL) were introduced into the milk pre - or post-fermentation. CL and CE were added at the same time as the pathogens based on their Minimum Inhibitory Concentrations of 0.25% for both pathogens as follows: CL and CE at 0.25% each alone; 0.0625% CL/0.1875% CE; 0.125% CL/ 0.125% CE; and 0.1875% CL/0.0625% CE. When added at the start of fermentation at 25oC, the CL and CE combinations inhibited the growth of E. fergusonii, and S. typhimurium, whereas at 37oC and associated with more rapid and higher acidification, the CL and CE combinations showed a marked antimicrobial activity against both pathogens. In post fermentation inoculated milk, survival of E. fergusonii and S. typhimurium was reduced by all CL and/ or CE treatments and were undetectable in samples containing 0.0625% CE with 0.1875% CL and 0.1875% CE with 0.0625% CL within 48 to 72 h of storage. The extent of the effect was most marked in the samples fermented at 37oC compared to 25oC and related to the pH after fermentation of 4.2 ±0.2 and 5.0 ±0.2 respectively. The use of these extracts both during fermentation and storage have the potential to enhance the microbiological safety of these products.