Cellulose casing impregnated with chitosan: Its antimicrobial activity and application in ready-to-eat sausage.

Outbreaks of Listeria monocytogenes associated with ready-to-eat (RTE) sausages have occurred worldwide for many years. Their causes have been mainly due to post-processing contamination. Consequently, the current study developed an antimicrobial sausage casing to protect RTE sausages from recontamination after heat treatment throughout storage. The cellulose casing was impregnated with chitosan, a natural antimicrobial substance. The proper conditions of the vacuum impregnation technique to produce the antimicrobial-impregnated casing were 2 % v/v of chitosan solution, vacuum pressure at 74.66 kPa for 120 s, and a relaxation time of 30 s. When examined in broth media, the antimicrobial-impregnated casing obtained from these conditions decreased L. monocytogenes Scott A by 1.50 log CFU/g (∼96.8 %) within 24 h. The quantitative amount of chitosan released from the impregnated cellulose casing was 0.1180 % w/v, as determined using the ninhydrin test. The penetration of chitosan into the cellulose casing was evaluated using Fourier transform infrared microspectroscopy to monitor the distribution and intensity of chitosan's amino group (-NH2), nitrogen-containing groups (N), and the saccharide structure. The contour mapping of the impregnated casing presented the highest distribution of the chitosan functional groups in all casing areas that was determined based on the specific functional groups of chitosan (NH, CH) at 1406-1353 cm-1, as well as other dominant changes, including the wavelength ranges 1183-1140 cm-1 (CO stretching), 3658-3027 cm-1 (OH, NH, CH), 2997-2828 cm-1 (NH stretching, CH stretching, CH3 symmetric stretching, CH ring) and 1139-1009 cm-1 (CO stretching), respectively. In addition, application of the impregnated casing for sausage emulsion was evaluated. Under vacuum-packed conditions, the antimicrobial-impregnated casing retarded L. monocytogenes Scott A growth in the inoculated Vienna sausage at 4 and 10 °C throughout the storage for 28 and 5 days, respectively. In un-inoculated sausage, the antimicrobial-impregnated casing extended the shelf-life of fresh sausage at 4 and 10 °C for 63 and 14 days, respectively. It was concluded that cellulose casing impregnated with chitosan was suitable for use as an antimicrobial-impregnated casing to protect post-processing contamination on the food surface, to maintain wholesomeness of the product, and to extend the shelf-life of RTE sausage.