Abstract
Despite the existence of many different food preservation methods, foodborne pathogens are still the most common related problems to dairy products. Developing alternative natural methods to control such problems is necessary. This research was planned to assess the bacteriological quality of yoghurt samples commercially available in Kafr El-Sheikh city, Egypt. Also to study the impact of natural antibacterial agents on the inhibition of selected foodborne pathogens artificially inoculated in yoghurt samples. The obtained results revealed poor bacteriological quality of the examined samples, as total staphylococci and coliforms were detected in 80% and 90% yoghurt samples, with mean values of 2.4 x103 +/- 0.13x 103 CFU/g and 3.6x105 +/- 2.4x105 MPN/g, respectively. Staphylococcusaureus was noticed in 4% of examined samples, polymerase chain reaction (PCR) confirmed the presence of virulence gene (clumping factor A-clfA) in one isolate. Escherichiacoli was detected in 14% of yoghurt samples, then serologically identified as O146:H5 (2), O111:H2 (2), O125:H11 (1), O26:H10 (1), and O158:H7 (1). Artificially inoculated yoghurt with S. aureus (7.39 log10 CFU/g) and E. coli (8.3 log10 CFU/g), were used to investigate the ability of hen egg-white lysozyme either with LAB classic or with ABT-5 (L. acidophilus LA5+ S. thermophiles + Bifidobacterium Bb12) starter cultures to inhibit the growth of these pathogens. During refrigerated storage, all yoghurt batches showed a reduction in pH value. It was observed that both pathogens couldn't be detected in the yoghurt batch containing LAB classic starter + heated lysozyme. Furthermore, S. aureus was completely inhibited in that containing ABT-5 cultures alone, while E. coli decreased by 6.23log. Conversely, there was not complete inhibition in other batches containing (LAB classic starter, LAB classic starter+ native lysozyme, ABT-5 culture+ native lysozyme and ABT-5 culture+ heated lysozyme) as the reduction rate during all storage periods for S. aureus count was 1.66, 2.63, 4.47,and 4.19 log10 CFU/g, While for E. coli count was 3.3, 3.81, 5.53, and 4.89 log10 CFU/g, respectively. This study highlighted the importance of adding natural antibacterial agents like lysozyme with LAB culture to yoghurt as a bio-control strategy to overcome foodborne pathogens that cause a public health hazard.