Colour changes in chilling, freezing and storage of meat 79 frozen at 15cmh-in liquid nitrogen spray and those which were blast frozen at 4cmh-(Pap, 1972). In both cases, they were frozen to the same final temperature of -30C. However, the bloomed meat before freezing was redder than the same material after thawing In thawed meat, the rate of pigment oxidation is increased(Cutting, 1970)and therefore the colour will be less stable than when fresh. On pro- longed frozen storage, a dark brown layer of metmyoglobin may form -2 mm beneath the surface so that on thawing the surface colour will idly deteriorate. Meat which has lost its attractiveness during frozen storage because of oxidation of oxymyoglobin on the surface will remain brown after thawing Unwrapped meat thawed in high humidity air, water or in steam under acuum appears very white and milky after thawing. However, if then stored in a chill room for 10-24 h it will be almost indistinguishable from fresh meat. Unwrapped meat thawed in air at high temperatures and low humidities will take on a dark, dry, tired appearance. It will not recover its appearance during chilled storage and will often require extensive trimming before sale 4.2.8 Retail display 4. 2.81 Chilled During refrigerated display, oxymyoglobin oxidises to brownish green metmyoglobin(MacDougall, 1993). Twenty per cent dilution of surface oxymyoglobin with metmyoglobin causes the product to be rejected at retail because of its faded colour(Hood and Riordan, 1973 The colour stability of fresh meat is infuenced to a very marked degree by the temperature of display Landrock and Wallace(1955) showed that heat held at 2C in packaging films whose oxygen permeability is greater than 5000mlm- atm" day will remain attractive for 4 days. In practice, com- mercial display cabinets are not controlled to maintain their contents at near reezing temperatures; meat temperatures during display at times may exceed 10.C(Malton, 1971, 1972). Heiss and Eichner(1969)showed that the rate of discolouration is roughly doubled for a 5C rise in temperature, while Buck and Peters(1970)demonstrated that the rate of colour deterioration is dependent upon the temperature of the meat, which in turn is depende upon location within the showcase. Similarly, Mac Dougall and Malton(1972) also found that the rate of colour change is influenced by position in the showcase and temperature differences of the order of5C have a large effect on the rate of colour change. For example, a change in redness, which takes 72-168hato°C, will occur in2448hat5° The discolouration rate is also different for different muscles. MacDougall and Malton(1972) found, for example, that the fillet dis- coloured faster than the loin. Similar observations were made byfrozen at 15 cm h-1 in liquid nitrogen spray and those which were blast frozen at 4 cmh-1 (Pap, 1972). In both cases, they were frozen to the same final temperature of -30 °C. However, the bloomed meat before freezing was redder than the same material after thawing. In thawed meat, the rate of pigment oxidation is increased (Cutting, 1970) and therefore the colour will be less stable than when fresh. On pro￾longed frozen storage, a dark brown layer of metmyoglobin may form 1–2 mm beneath the surface so that on thawing the surface colour will rapidly deteriorate. Meat which has lost its attractiveness during frozen storage because of oxidation of oxymyoglobin on the surface will remain brown after thawing. Unwrapped meat thawed in high humidity air, water or in steam under vacuum appears very white and milky after thawing. However, if then stored in a chill room for 10–24 h it will be almost indistinguishable from fresh meat. Unwrapped meat thawed in air at high temperatures and low humidities will take on a dark, dry, tired appearance. It will not recover its appearance during chilled storage and will often require extensive trimming before sale. 4.2.8 Retail display 4.2.8.1 Chilled During refrigerated display, oxymyoglobin oxidises to brownish green metmyoglobin (MacDougall, 1993). Twenty per cent dilution of surface oxymyoglobin with metmyoglobin causes the product to be rejected at retail because of its faded colour (Hood and Riordan, 1973). The colour stability of fresh meat is influenced to a very marked degree by the temperature of display. Landrock and Wallace (1955) showed that meat held at 2 °C in packaging films whose oxygen permeability is greater than 5000 ml m-2 atm-1day-1 will remain attractive for 4 days.In practice,com￾mercial display cabinets are not controlled to maintain their contents at near freezing temperatures; meat temperatures during display at times may exceed 10 °C (Malton, 1971, 1972). Heiss and Eichner (1969) showed that the rate of discolouration is roughly doubled for a 5°C rise in temperature, while Buck and Peters (1970) demonstrated that the rate of colour deterioration is dependent upon the temperature of the meat, which in turn is dependent upon location within the showcase.Similarly,MacDougall and Malton (1972) also found that the rate of colour change is influenced by position in the showcase and temperature differences of the order of 5 °C have a large effect on the rate of colour change. For example, a change in redness, which takes 72–168 h at 0 °C, will occur in 24–48 h at 5°C. The discolouration rate is also different for different muscles. MacDougall and Malton (1972) found, for example, that the fillet dis￾coloured faster than the loin. Similar observations were made by Colour changes in chilling, freezing and storage of meat 79