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Research Project: CONTROL OF HUMAN PATHOGENS ASSOCIATED WITH ACIDIFIED PRODUCE FOODS

Location: Food Science Research

Title: Effects of acetic acid and arginine on pH elevation and growth of Bacillus licheniformis in an acidified cucumber juice medium

Author
item YANG, ZHENQUAN - YANGZHOU UNIVERSITY
item MENG, XIA - YANGZHOU UNIVERSITY
item Breidt, Frederick
item Dean, Lisa
item ARRITT, FLETCHER - NORTH CAROLINA STATE UNIVERSITY

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2014
Publication Date: 4/1/2015
Publication URL: http://handle.nal.usda.gov/10113/60632
Citation: Yang, Z., Meng, X., Breidt, F., Dean, L.L., Arritt, F.M. 2015. Effects of acetic acid and arginine on pH elevation and growth of Bacillus licheniformis in an acidified cucumber juice medium. Journal of Food Protection. 78(4):728-737.

Interpretive Summary: Spore-forming bacilli bacteria have been known to cause spoilage in tomato products, including causing a rise in pH. This pH increase can result in the growth of disease causing bacteria if the pH goes above 4.6. Because pickled vegetables and tomato products have similar pH values (below 4.6), there has been concern that pH rise by bacilli could also occur in pickled vegetables, but there has not been evidence to show whether this may or may not happen. To address this knowledge gap, we investigated the mechanism(s) of pH rise by bacilli in vegetable brines, and the conditions that would or would not allow pH rise to occur. Our data show that pH rise can be due to the breakdown of particular amino acids in vegetable brines. However, under conditions of most pickled vegetable products containing vinegar, bacilli cannot grow and raise pH. This research will support science based regulation of pickled vegetables, and help commercial producers of pickled vegetables know what conditions assure safety.

Technical Abstract: Bacillus licheniformis has been shown to cause pH elevation in tomato products having an initial pH below 4.6 and metabiotic effects that can lead to the growth of pathogenic bacteria. Because of this, the organism poses a potential risk to acidified vegetable products; however, little is known about the growth and metabolism of this organism in these products. To clarify the mechanisms of pH change and growth of B. licheniformis in vegetable broth under acidic conditions, a cucumber juice medium representative of a noninhibitory vegetable broth was used to monitor changes in pH, cell growth, and catabolism of sugars and amino acids. For initial pH values between pH 4.1 to 6.0, pH changes resulted from both fermentation of sugar (lowering pH) and ammonia production (raising pH). An initial pH elevation occurred, with starting pH values of pH 4.1 to 4.9 under both aerobic and anaerobic conditions, and was apparently mediated by the arginine deiminase reaction of B. licheniformis. This initial pH elevation was prevented if 5 mM or greater acetic acid was present in the brine at the same pH. In laboratory media, under favorable conditions for growth, data indicated that growth of the organism was inhibited at pH 4.6 with protonated acetic acid concentrations of 10 to 20 mM, corresponding to 25 to 50 mM total acetic acid; however, growth inhibition required greater than 300 mM citric acid (10-fold excess of the amount in processed tomato products) products under similar conditions. The data indicate that growth and pH increase by B. licheniformis may be inhibited by the acetic acid present in most commercial acidified vegetable products but not by the citric acid in many tomato products.