For “red colour” evaluation, high oxygen packaged samples performed better than the other groups at days 1 and 3. Significant differences were no longer observed after day 5 (P > 0.05). However, ostrich meat packaged with high O2 and 3:1 headspace ratio atmosphere was more acceptable during the entire storage time. These results fit only partially with the a* values ( Table 2a and Table 2b).
Fernandez-Lopez et al. (2008) stated that MAP + CO (30% CO2 + 69.8% argon + 0.2% CO) packaged ostrich meat showed the best scores (P < 0.05) throughout all the storage time (18 days). Some researchers indicated that, in packaged meat, the presence of oxygen is necessary to have a better perception of the characteristic red colour of fresh meat due to oxymyoglobin pigment ( Luño et al., 1998 and Renerre et al., 1992).
Although significant differences were not observed over the entire storage time (P > 0.05), the 1:1 headspace ratio and CO2 atmosphere packaged samples were more acceptable by the panellists. For this reason, “appearance” scores were not in accord with the colour scores.
“Off-odour” evaluation showed no differences (P > 0.05) between air and MAP packaged samples up to 5th day of storage. Those packaged with high O2 and 3:1 headspace ratio atmospheres received better scores during the entire storage. Fernandez-Lopez et al. (2008) determined that off-odour evaluation showed differences (P < 0.05) between air and MAP packs. They emphasised that the off-odours were mainly putrefactive and sour, and the air packed samples had the highest scores (P < 0.05) for off-odour. Vergara and Gallego (2001) reported that off-odour developed much more rapidly (from 7 days onwards) in low CO2 packaged lamb meat compared to other MAP packs and also, redness was significantly decreased (P < 0.05). John et al. (2005) stated that steaks packaged in 80% oxygen or CO retained desirable red colours for 14 and 21 days, respectively. Zakrys et al. (2007) emphasised that panellists expressed a preference for steaks stored in packs containing 50% oxygen, despite detecting oxidised flavours under these conditions.
4. Conclusion
Although ostrich meat is perceived as a red meat, the comparison between ostrich and beef may lead to very different bacterial counts because of differences between birds' and mammals' gastrointestinal tracts and the early processes of meat preparation. The relatively high pH of ostrich meat creates an ideal environment for rapid microbial spoilage. The quality and shelf-life of ostrich meat packaged by various gas compositions of modified atmosphere were somewhat improved; microbial growth in the meats was delayed due to high CO2 usage and shelf-life was increased by 5–7 days. The longer the exposure to high CO2 concentration, the more effective the inhibition of microbial growth.
Additionally, high O2 concentrations promote the formation of oxymyoglobin (OxyMb), but this may impact negatively on the oxidative stability of muscle lipids and lead to the development of undesirable flavours. The high CO2 contents prevented increased lipid oxidation and increased acceptable shelf-life by more than 5 days. Furthermore, the increase in O2 inside the package causes rapid loss of redness of ostrich meat and thus the desired red-colour is not obtained. The consumer may be adversely affected by this.