Development of antimicrobial edible coatings to reduce microbial contamination of broiler carcasses.

摘要

Broiler carcasses are a significant source of pathogenic microorganisms which can cause food-borne illnesses if not properly cooked. The extent of broiler flock contamination varies, but normally increases by contact of birds with equipment, and by scalding, defeathering and chilling. The currently used on-line approved chemical antimicrobials vary in their activity and do not effectively inactivate contaminating microorganisms, presumably as a result of microbial cell entrapment inside the carcass skin. In this work, antimicrobial coatings were designed to be sprayed or coated on broiler carcasses during processing. The resistance of physical and mechanical properties of high amylose pea starch (PS) and rice starch (RS) films to high relative humidity (RH) and plasticizer addition was investigated in the first part of the thesis. PS films which contained higher amylose showed more desirable properties than the RS films which contained low amylose at the same RH. The addition of glycerol to the films helped to form a more continuous structure. Increasing the RH from 51 to 90% reduced tensile strength and increased the elongation of both films with PS films being more resistant to deformation. Both films were excellent oxygen barriers at low RH (&le 34%) but had relatively low water vapor permeability compared to other edible films in the literature.Current Canadian standards require that carcasses be free of any additive before leaving the processing plant. This is why the third objective of the study was to formulate coatings containing antimicrobials that would interact with broiler skin but disappear during processing. PS coating containing TSP and alginate coating containing ASC were designed with polymer concentrations that were able to absorb into the chicken skin and gradually dissolve once their pHs equilibrated with skin pH. The interactions of the coatings with the skin were determined by measuring coating drop contact angle with the skin (surface energy difference between the coating and the skin) and coating absorption rate into the skin at different polymer concentrations. Compared to alginate, the PS coating had higher skin contact and faster absorptiveness.The kinetics of coating dissolution from the skin were studied in the fourth part of thesis. Gels made of pea starch and alginate-containing antimicrobials were prepared and placed in a solution of 0.8% saline that mimicked broiler skin osmotic strength. The rheological properties (dissolution rate) of these gels and antimicrobial concentrations in the solution were measured over 8h. The alginate coating had rapid initial (15 min) dissolution and antimicrobial release rates followed by even faster changes in solubility and release. The PS coating was more stable than the alginate coating in solution. Experimental data for mechanical changes and antimicrobial release fit with established models (R2 > 0.95). These results indicated that PS coating containing TSP had better interaction with skin and slowly dissolved after application. This coating would increase the contact time with the target microorganisms but disappear from the carcass before chilling was completed in actual processing, which means it is possible that it may have commercial value.The inhibitory activity of the most commonly used commercial antimicrobials was examined against E coli O157:H7, Salmonella and Campylobacter spp. in the second part of the thesis. The commercial antimicrobials used were trisodium phosphate (TSP), Sanova (acidified sodium chlorite, ASC), Safe2O, Inspexx 100 and Cecure. Factors such as antimicrobial concentration, contact time, sequential use of two antimicrobials and the most appropriate stage of processing for use of the antimicrobials were studied. Results showed that TSP (10%) and acidified sodium chlorite (0.12%) were the most effective for reducing viability of the pathogens and this was related to their effect on surface pH of the skin. Increasing the antimicrobial concentration and contact time up to 20 min enhanced the antimicrobial effectiveness. Sequential use of antimicrobials also increased activity especially for compounds used before cetylpyridinium chloride (CPC), with TSP being the most effective. Antimicrobials were also more effective on warm (before chilling) than on cold (after chilling) carcasses, indicating the use of antimicrobials in early stages of processing would be more efficient. When TSP (10%) and ASC (0.12%) were stabilized by incorporation into coatings made of pea starch (3%) or calcium alginate (1.0%), respectively, their antimicrobial activity significantly (p 0.05) increased. Salmonella inoculated on the skin were reduced about 1.5 log cfu/g and 1.0 log cfu/g by the stabilized and unstabilized antimicrobials, respectively, after storage at 4°C for 24h.