Effect of different concentrations of carbon dioxide and low concentration of carbon monoxide on the shelf-life of fresh pork sausages packaged in modified atmosphere

This paper reports the effects of different concentrations of carbon dioxide and the presence of low levels of carbon monoxide on quality attributes throughout storage of fresh pork sausages. Four pork forelegs (initial pH 5.5–5.7) were used to prepare a total of 120 fresh sausages, which were packaged in different atmospheres containing (%O2/%CO2/%N2): 0/20/80; 0/60/40; 40/20/40; 40/60/0; 80/20/0; and 0.3% CO/30% CO2/rest argon. The packs were stored for 20 days at 2 ± 1 °C in the dark. Three packs for each atmosphere were opened every 4 days for subsequent analysis of pH, colour CIE L*, a*, b*, TBARS formation, microbial psychotrophic aerobes and sensory discolouration and off-odour. Results showed that increasing concentrations of carbon dioxide promoted oxidation of both myoglobin and lipids, most probably due to its effect of lowering pH. Therefore, preservation of colour and odour of fresh pork sausages packaged in modified atmosphere was better achieved using atmospheres containing low CO2 concentrations (20%) rather than high (60%). However, their shelf-life depended also on the concentration of O2; 20% CO2 with high O2 (80%) enhanced the red colour, but shortened shelf-life, while 20% CO2 in the absence of O2 extended freshness to 16 days. The atmosphere containing 0.3% CO, together with 30% CO2, maintained the red colour for 20 days, but failed to keep fresh odour longer than 16 days.