الفهرس 
Part IOnly 14 pages are availabe for public view
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Abstract
In the present study, GDL, acetic, citric and lactic acid were used to study their effects on the growth, inhibition or activation of pathogenic and lactic acid bacteria in terms of pH values, biomass concentrations, total viable counts and microbial growth rates. In addition, organic acids were used in the production of hard cheese, studying its physicochemical, microbiological, ripening indices and sensory properties. The study was handled in three parts as follow:
Firstly, the used organic acids inhibited the growth of Salmonella enteritidis, Staphylococcus aureus, Bacillus cereus, Escherichia coli and Pseudomonas aeruginosa. GDL had the higher inhibition effect among other organic acids, followed by lactic acid, citric, while acetic acid had the lower inhibition effect. The inhibition of GDL continued at pH 5.2, while Staphylococcus aureus and Salmonella enteritidis were totally inhibited by GDL at pH 5.2. The effect of other organic acids for total inhibition of pathogens was pronounced only till pH 4.8.
Secondly, organic acid promoted the growth of Lactobacillus acidophilus, Streptococcus thermophilus, Lactobacillus bulgaricus, Lactobacillus paracasei. Citric acid was more effective for enhancing the growth of lactic acid bacteria followed by lactic acid, GDL and the lower effect was observed with acetic acid. Citric acid promoted the growth of all lactic acid bacteria when compared with other organic acids.