This study investigated the physical properties of polymers and antimicrobial activities of organic acids on Listeria monocytogenes to develop hydrogels. κ-carrageenan (1, 2, and 3%), carboxymethylcellulose (CMC; 1, 3, and 5%), and agar (1.5 and 3%) were mixed with cross-linkers (Na+, K+, Ca2+, and Al3+) or each other by stirring or heating to form cross-linkage, and their physical properties (hardness, elasticity, and swelling) were measured. The hydrogels formulated with organic acid (1, 3, and 5%) were analyzed by spot assay against L. monocytogenes. κ-carrageenan formed hydrogels with high hardness without other cross-linkers, but they had low elasticity. The elasticity was improved by mixing with other cross-linkers such as K+ or other polymer, especially in 3% κ-carrageenan. CMC hydrogel was formed by adding cross-linkers Al3+, Na+, or Ca2+, especially in 5% CMC. Thus, stickiness and swelling for selected hydrogel formulations (two of κ-carrageenan hydrogels and three of CMC hydrogels) were measured. Among the selected hydrogels, most of them showed appropriate hardness, but only 3% κ-carrageenan-contained hydrogels maintained their shapes from swelling. Hence, 3% κ-carrageenan+0.2% KCl and 3% κ-carrageenan+1% alginate+0.2% KCl+0.2% CaCl2 were selected to be formulated with lactic acid, and showed antilisterial activity. These results indicate that 3% κ-carrageenan hydrogels formulated with lactic acid can be used to control L. monocytogenes on food surface.

Introduction
 Materials and Methods
  Preparation of hydrogels
  Measurement of hydrogel mechanical properties
  Spot assay of antimicrobials
  Statistical analysis
 Results and Discussion
 Acknowledgment
 Disclosure Statement
 References

• Sejeong Kim(Risk Analysis Research Center, Sookmyung Women’s University, Seoul, Korea, Department of Food and Nutrition, Sookmyung Women's University, Seoul, Korea)
• Hyemin Oh(Risk Analysis Research Center, Sookmyung Women’s University, Seoul, Korea, Department of Food and Nutrition, Sookmyung Women's University, Seoul, Korea)
• Heeyoung Lee(Risk Analysis Research Center, Sookmyung Women’s University, Seoul, Korea, Department of Food and Nutrition, Sookmyung Women's University, Seoul, Korea)
• Soomin Lee(Risk Analysis Research Center, Sookmyung Women’s University, Seoul, Korea, Department of Food and Nutrition, Sookmyung Women's University, Seoul, Korea)
• Jimyeong Ha(Risk Analysis Research Center, Sookmyung Women’s University, Seoul, Korea, Department of Food and Nutrition, Sookmyung Women's University, Seoul, Korea)
• Jeeyeon Lee(Risk Analysis Research Center, Sookmyung Women’s University, Seoul, Korea, Department of Food and Nutrition, Sookmyung Women's University, Seoul, Korea)
• Yukyung Choi(Risk Analysis Research Center, Sookmyung Women’s University, Seoul, Korea, Department of Food and Nutrition, Sookmyung Women's University, Seoul, Korea)
• Yohan Yoon(Risk Analysis Research Center, Sookmyung Women’s University, Seoul, Korea, Department of Food and Nutrition, Sookmyung Women's University, Seoul, Korea) Correspondence to