Non-microbiological factors affecting quality and safety 229 H3C H3C Pr C= cH Pr -NO Fig. 9. 2. Nitrosylmyoglobin. Myoglobin with the nitrite ligand haemoproteins form nitrosylmyochrome and nitrosylhaemochrome complexes in which the iron is stabilised by the linking of nitric oxide to the porphyrin ring (Fig. 9.2); however, the pink coloration of the meat may be undesirable; causes of pinking in uncured cooked meat is further considered later in this chapter. The effectiveness of pyrophosphate, tripolyphosphate and hexametaphosphate, which chelate metal ions, particularly prooxidative ferrous ions, was demon strated by Tims and Watts(1958)in pork. It has since been verified for ground beef (Sato and Hegarty 1971), for restructured beef steaks(Mann et al. 1989) and for battered and breaded chicken(Brotsky 1976). Phosphates in combination with ascorbic acid may exert a synergistic effect, such that cooked ground pork was protected against lipid oxidation for up to 35 days at 4 C( Shahidi et al. 1986) An alternative approach is to protect the meat from oxidation. This can be achieved by creating an oxygen barrier, using a sauce or a gravy that can be in place at the time of cooking and during subsequent storage. This principle has been demonstrated by comparing the shelf-life of frozen meat to that of the same meats cooked without gravy coverings(Dalhoff and Jul 1965). Cooked pork covered with gravy could be stored at -18C for more than 100 weeks, whereas pork stored without gravy was unacceptable after 22 weeks Modified-atmosphere packaging to reduce Wof has been applied to precooked turkey and pork and pork products. Although those stored in nitrogen and carbon dioxide atmospheres were less oxidized than those in air, packaging was the most effective(Nolan et al. 1989 and Juncher et al ( 1998). Shaw(1997)reviewed the potential benefits of the use of MAP for cook chill ready meals. Protection against oxidation at the time of cooking is also beneficial. Cooking and subsequent storage of chicken breasts in a nitrogenhaemoproteins form nitrosylmyochrome and nitrosylhaemochrome complexes in which the iron is stabilised by the linking of nitric oxide to the porphyrin ring (Fig. 9.2); however, the pink coloration of the meat may be undesirable; causes of pinking in uncured cooked meat is further considered later in this chapter. The effectiveness of pyrophosphate, tripolyphosphate and hexametaphosphate, which chelate metal ions, particularly prooxidative ferrous ions, was demon￾strated by Tims and Watts (1958) in pork. It has since been verified for ground beef (Sato and Hegarty 1971), for restructured beef steaks (Mann et al. 1989), and for battered and breaded chicken (Brotsky 1976). Phosphates in combination with ascorbic acid may exert a synergistic effect, such that cooked ground pork was protected against lipid oxidation for up to 35 days at 4ºC (Shahidi et al. 1986). An alternative approach is to protect the meat from oxidation. This can be achieved by creating an oxygen barrier, using a sauce or a gravy that can be in place at the time of cooking and during subsequent storage. This principle has been demonstrated by comparing the shelf-life of frozen meat to that of the same meats cooked without gravy coverings (Dalhoff and Jul 1965). Cooked pork covered with gravy could be stored at
18ºC for more than 100 weeks, whereas pork stored without gravy was unacceptable after 22 weeks. Modified-atmosphere packaging to reduce WOF has been applied to precooked turkey and pork and pork products. Although those stored in nitrogen and carbon dioxide atmospheres were less ‘oxidized’ than those in air, vacuum packaging was the most effective (Nolan et al. 1989 and Juncher et al (1998). Shaw (1997) reviewed the potential benefits of the use of MAP for cook￾chill ready meals. Protection against oxidation at the time of cooking is also beneficial. Cooking and subsequent storage of chicken breasts in a nitrogen Fig. 9.2. Nitrosylmyoglobin. Myoglobin with the nitrite ligand. Non-microbiological factors affecting quality and safety 229