Effect of display case cooling technologies on shelf-life of beef and chicken

Abstract

Shelf-life is defined as the time a food product retains its desired sensory, chemical, and physical characteristics while also remaining safe for consumption. Bacteria associated with meat spoilage produce off-odors and flavors, tissue discoloration, gas, and slime. The objectives of this study were, 1) to determine the effect of refrigerated-display-case type on the shelf-life and microbial load of the natural flora found on beef steak and chicken breasts and, 2) to evaluate the effect of gravity coil conductive cooling vs. complete conductive cooling on the growth of Escherichia coli K12 artificially inoculated onto beef steak under abusive conditions. In Study 1, beef steak and chicken breasts were placed for 8 or 5 days, respectively, in a conduction cooling gravity assist service case, gravity coil service case with partial conduction coil base deck, gravity coil service case with serpentine assist, or blower coil service case with an additional fogging system. Mesophilic bacteria, Pseudomonas spp. and psychrotrophic bacterial counts on meat surfaces, and meat color, internal meat temperature, case temperature and case relative humidity were determined daily. In Study 2, two of the four types of display case ̶ the complete conductive cooling and gravity-coil conduction cooling systems ̶ were chosen to evaluate microbial growth on beef steak due to novel conductive cooling technologies. Temperature and weight loss, aerobic plate counts and viable E. coli colony-forming-units on the beef steaks were determined daily. In study 1, the warmest display ambient air temperature was found in the gravity coil service case with partial conduction coil base deck (PCC). The coldest tissue temperatures were observed for steaks and chicken breasts placed in the conduction cooling gravity assist service display case. The lowest RH also tended to occur in the PCC case. Overall, the type of retail display case had no effect on the growth of mesophilic and psychrotrophic bacteria or Pseudomonas on both steaks and chicken breasts. In study 2, the initial numbers of viable E. coli K12 on inoculated steaks were low and remained low through 7 days storage, regardless of display case. The novel conduction cooling gravity assist service display case used in this study has the greatest potential for extending shelf-life due to lower overall tissue temperatures and reduced water loss from meat products held in this case during high traffic and abusive retail conditions.