Combined effects of organic acids and salt depending on type of acids and pathogens in laboratory media and acidified pickle

Aim In this study, the effectiveness of combining each of seven types of acids with 3% salt as a treatment against pathogens was investigated in laboratory media and acidified food. Methods and Results When 0·5% malic, 0·5% tartaric, 0·5% citric or 0·25% phosphoric acid was combined with 3% salt, there was a higher reduction in Gram‐negative bacteria (Escherichia coli O157:H7 and Salmonella Typhimurium) compared to when using acid alone. However, when 0·5% acetic, 0·5% propionic or 0·25% lactic acid was combined with 3% salt, the salt provided protection against the acid treatment. However, the antagonistic effects of acetic, propionic and lactic acid seen with Gram‐negative bacteria were not observed in Listeria monocytogenes. Antagonistic effects were similarly observed when E. coli O157:H7 was treated with acetic acid and salt in food. Conclusions These results show that the addition of salt increases the resistance of Gram‐negative bacteria to acid treatments when using acetic, propionic and lactic acid. Significance and Impact of the Study This study shows that antagonistic effects were observed when Gram‐negative bacteria were treated with organic acids of simple structure. It may provide useful information for understanding the acid resistance mechanism of Gram‐negative bacteria and developing methods for preserving acidified food.