Edible coatings for enhancing microbial safety and extending shelf life of hard-boiled eggs.

Hard-boiled eggs were coated with chitosan-lysozyme (CL), whey protein isolate (WPI), or Bake sheen (BS), inoculated with Listeria monocytogenes or Salmonella enterica Ser. Enteritidis at 10(4) CFU/g, and stored for 4 wk at 10 degrees C. Microbial populations were enumerated weekly. Two nonchallenge studies were also conducted with hard-boiled eggs: coated shell-on eggs packaged in plastic containers or peeled eggs coated and vacuum-packaged. Total plate counts (TPC), coliforms, yeasts, molds, weight loss, pH, and color of eggs were determined during the 10-wk storage at 10 degrees C. Uncoated eggs served as controls. All the coatings were not effective in inhibiting the growth of L. monocytogenes, but CL coating controlled the growth of S. Enteritidis. At the end of 4-wk storage, the numbers of S. enteritidis on CL-coated eggs were about 4-log(10) CFU/g less than that of the controls. Coatings reduced (P < 0.05) the populations of coliforms and TPC, and completely inhibited mold growth during the 10-wk storage. Coatings also reduced (P < 0.05) the weight loss of eggs, 4.1% to 4.8% on coated eggs compared with 7.5% in uncoated ones at the end of 10-wk storage. The pH of CL-coated eggs remained stable throughout the storage period, while the control eggs increased from 7.6 to 8.6. Color changes in CL- and WPI-coated eggshells were less (P < 0.05) than those of BS-coated and the control. The CL coating effectively suppressed the numbers of TPC, coliforms, yeasts, and molds on peeled eggs during the 6-wk storage (P < 0.05). The results suggest that CL coating on hard-boiled eggs can control the growth of S. Enteritidis and reduce undesirable changes in the interior quality of eggs.