Assessment of the anti-microbial activity of dried garlic powders produced by different methods of drying

Summary

The anti-microbial activity of a range of garlic products including dried garlic powder produced by different methods, commercial garlic products, and garlic oil was determined against a range of selected bacteria. The bacteria were food borne pathogens, spoilage agents, and health-beneficial agents, namely Staphylococcus aureus, Escherichia coli, Salmonella typhimurium, Bacillus cereus, and a mixed lactic culture consisting of Lactobacillus delbrueckii subsp. bulgaricus + Streptococcus termophilus. The dried powders were produced using air-drying at both 60 and 80 ºC, vacuum-drying at 50 and 60 ºC, and freeze-drying at –20 ºC. Before testing, the moisture content of the dried garlic powders was raised to that of fresh garlic. Garlic oil was used without any addition of water. In general, the results showed that the mixed lactic culture was the most sensitive to the growth inhibitory activity of the garlic preparations, followed by S. aureus. In contrast, S. typhimurium and B. cereus demonstrated the greatest resistance to garlic. On the whole, fresh garlic produced the greatest inhibition followed by freeze-dried powder. The results showed that both drying temperature and time had major effects on inhibition of microbial growth. Higher heating temperature caused faster loss of anti-microbial activity. The decrease in growth-inhibition zones for moist-heated fresh garlic followed zero-order kinetics.