Inhibition of Shigella sonnei and Shigella flexneri in Hummus Using Citric Acid and Garlic Extract

Hummus (chickpea dip) is a ready-to-eat product that may pose a significant risk to human if pathogens are present. Several organisms including Shigella spp. have been isolated from hummus. However, studies on the survival and inhibition of Shigella spp. in food are scarce. This study investigated the growth pattern of Sh. sonnei and Sh. flexneri in hummus at different temperatures (4, 10, and 24 degrees C). Additionally, the inhibitory activity of different concentrations of citric acid (CA) (0.5%, 1.0%, and 2.0%) and garlic extract (GE) (1.0%, 2.0%, and 3.0%) against Sh. sonnei and Sh. flexneri inoculated into hummus and stored at 4 and 10 degrees C was investigated. Both Shigella spp. survived well at 4 degrees C, while both grew to > 7.0 log(10) after 4 d at 10 degrees C or 1 d at 24 degrees C. At 4 degrees C, CA at 0.5% and 1.0% resulted in a slight reduction in the count (approximately 1.0 log(10)); a complete elimination of Sh. sonnei was attained by using 2.0% CA. However, approximately 3.0 log(10) reduction in Sh. sonnei was obtained at 10 degrees C. For Sh. flexneri, CA at 0.5% and 1.0% resulted in a bacteriostatic inhibition. GE at 1.0% and 2.0% resulted in approximately 1.0 to 2.0 log(10) reduction in Sh. sonnei count at 4 degrees C, while at 3.0% GE, approximately 4.0 and 3.0 log(10) reductions were obtained at 4 and 10 degrees C, respectively. In comparison, the 2.0% and 3.0% GE resulted in a bacteriostatic effect against Sh. flexneri at 4 and 10 degrees C.