Effect of packaging materials, environmental factors and rRNA transcriptional activity of surface microflora on red-smear cheese defect development

Two Swiss cheese varieties were investigated to elucidate how microbial growth and rRNA transcriptional activity leads to a defective cheese surface when red-smear cheese portions are wrapped in plastic films. Four alternative films with different water and gas permeabilities were used for packaging experiments. A defective smear was associated with anaerobic conditions, increased water activity and decreased pH over a period of 8 weeks at 8 °C. Decreases of log 0.7–1.6 total bacteria, log 0.6–1.2 Corynebacterium casei and log 0.6–1.6 Bacillus spp. 16S rRNA copy numbers measured by RT-qPCR were obtained for both varieties under packaging conditions, suggesting a decrease in transcriptional activity. One alternative film, porous to O2, CO2 and water vapour, created a less humid smear and higher pH during storage. Cheese smear development mainly depended upon the permeability of the packaging film, and was associated with a decrease in rRNA transcriptional activity of cheese smear microorganisms.