Non-microbiological factors affecting quality and safety 231 potential to initiate lipid oxidation by providing a source of initiating radicals German and Kinsella 1985). A complicating factor in the assessment of the significance of oxidation to the quality of fish is that many products distributed chilled have previously been frozen, particularly for example, herring, to sprea seasonal availability 9.3.2 Pink discoloration in meat products Discoloration in foods is a common problem which can take many forms and be ssociated with a wide range of chemical reactions: biochemical or enzymic browning is considered later in this chapter. Pink discoloration in cooked meats br is a long-standing and all too common problem affecting manufacturing, retailing food service and domestic sectors and is often interpreted as undercooking. The problem is particularly evident with sliced meats, reformed roast products, pasties and casseroles. Various causes of pinking have beer identified and these are indicated in Table 9. 1 on the basis of the pigment type thought to be involved. Maga(1994)has reviewed the causes and factors affecting pink discoloration in cooked white meats L Myoglobin is a monomeric globular haem-protein found in all vertebrates hich together with haemoglobin give rise to the red colour of meats. The amount of myoglobin varies from species to species, tissue to tissue and is affected by a wide range of environmental factors. As indicated in Table 9. 1 myoglobin can be present in several forms, some of which can impart a red or pink residual colour to the meat even after cooking. Recent work has indicated that over 80% of instances of pinking are due to nitrosomyoglobin arising from nitrate contami- nation and its subsequent bacterial reduction to nitrite( Brown et al. 1998) 9. 4 Characteristics of biochemical reactions Biochemical reactions are catalysed by specialized proteins called enzymes They are highly specific and efficient catalysts, lowering the activation threshold so that the rate of reaction of thermodynamically possible reactions is Table 9.1 Pigment types and causes giving rise to pink coloration in meat products Brown et al. 1998) Cause of pink discoloration Oxymyoglobin Low temperature cooking Nitrosomyoglobin Nitrite contamination directly or from reduced nitrate nitrogen oxides in ovens Carboxymyoglobin Carbon monoxide in ovens; gamma-irradiation Reduced denatured myoglobin High pH, slow cooking, high salt and availability of educing agentspotential to initiate lipid oxidation by providing a source of initiating radicals (German and Kinsella 1985). A complicating factor in the assessment of the significance of oxidation to the quality of fish is that many products distributed chilled have previously been frozen, particularly for example, herring, to spread seasonal availability. 9.3.2 Pink discoloration in meat products Discoloration in foods is a common problem which can take many forms and be associated with a wide range of chemical reactions: biochemical or enzymic browning is considered later in this chapter. Pink discoloration in cooked meats is a long-standing and all too common problem affecting manufacturing, retailing food service and domestic sectors and is often interpreted as undercooking. The problem is particularly evident with sliced meats, reformed roast products, pasties and casseroles. Various causes of pinking have been identified and these are indicated in Table 9.1 on the basis of the pigment type thought to be involved. Maga (1994) has reviewed the causes and factors affecting pink discoloration in cooked white meats. Myoglobin is a monomeric globular haem-protein found in all vertebrates which together with haemoglobin give rise to the red colour of meats. The amount of myoglobin varies from species to species, tissue to tissue and is affected by a wide range of environmental factors. As indicated in Table 9.1 myoglobin can be present in several forms, some of which can impart a red or pink residual colour to the meat even after cooking. Recent work has indicated that over 80% of instances of pinking are due to nitrosomyoglobin arising from nitrate contami￾nation and its subsequent bacterial reduction to nitrite (Brown et al. 1998). 9.4 Characteristics of biochemical reactions Biochemical reactions are catalysed by specialized proteins called enzymes. They are highly specific and efficient catalysts, lowering the activation threshold so that the rate of reaction of thermodynamically possible reactions is Table 9.1 Pigment types and causes giving rise to pink coloration in meat products (Brown et al. 1998) Pigment type Cause of pink discoloration Oxymyoglobin Low temperature cooking Nitrosomyoglobin Nitrite contamination directly or from reduced nitrate; nitrogen oxides in ovens Carboxymyoglobin Carbon monoxide in ovens; gamma-irradiation Reduced denatured myoglobin High pH, slow cooking, high salt and availability of reducing agents Non-microbiological factors affecting quality and safety 231