Introduction: Since heat and antimicrobials cannot be applied to the foods consumed raw such as beef tartare and Sashimi, food safety for the foods has been issued. κ-carrageenans are linear polysaccharides sulfated galactan, and it has hydroxyl group in structures which could be useful in forming hydrogel.
Purpose: The objective of this study was to develop an antimicrobial hydrogel patch composed of κ-carrageenan to inhibit L. monocytogenes in foods consumed raw.
Methods: κ-carrageenan-based hydrogel was prepared by dissolving 1, 2, and 3% of κ-carrageenan powder in 25 ml distilled water, mixed with co-polymers (1% w/w; sodium alginate, xanthan gum, and collagen), and mixed with crosslinkers CaCl2 and KCl. The mixture was heated at 98oC and stirred until a homogeneous solution was obtained. The κ-carrageenan-based solution was poured into plastic plate and dried at 15oC for 20 min. The obtained κ-carrageenan gels were cut into 1.0 × 1.0 cm, and polymer properties (strength, elasticity, swelling and antimicrobial loading capacity) were determined. The hydrogel patches were placed in 1 ml of 0.1-3.0% natural antimicrobials (grapefruit seed extract, citrus peel extract, and ε-polylysine) from 30 min to 4 h, and the hydrogel patches were used for a diffusion assay on tryptic soy agar plus yeast extract (TSAYE).
Results: Addition of KCl (0.2%) or CaCl2 (0.2%) into κ-carrageenan increased the hydrogel strength, and the elasticity of the hydrogel gel was increased by adding collagen (1%) into κ-carrageenan. Among tested natural antimicrobials, 3% ε-polylysine was the most appropriate to inhibit L. monocytogenes growth. Thus, the antimicrobial hydrogel composed of 1% κ-carrageenan, 0.2% KCl, 1% collagen, and 3% ε-polylysine were prepared. The hydrogel patches formed clear zones (0.8 mm) of L. monocytogenes on TSAYE agar.
Significance: These results indicate that the developed hydrogel patch should be useful in controlling L. monocytogenes in food consumed raw.