Colour changes in chilling, freezing and storage of meat 77 unwrapped or poorly wrapped meat. The problem is accentuated in areas exposed to low humidity air at high velocities, and by poor temperature ontrol. Since most meat is now wrapped and temperature control much improved this is less of a problem than it once was commercially Provided problems of freezer burn can be eliminated, the major appearance prob- m that affects frozen meat arises from oxidation of oxymyoglobin to metmyoglobin. Both temperature and illumination level affect the rate of discolouration luring frozen storage, but light is by far the more serious factor. Townsend and Bratzler (1958)found that frozen beef steaks stored under fluorescent light(60 dekalux) discoloured in 2-3 days at -18C. Lane and Bratzler (1962)found that metmyoglobin formation in frozen extracts of meat was similar to the pattern seen in frozen steaks and was increased by exposure to fluorescent illumination. Tuma(1971)showed that the acceptable storage fe of M. longissimus dorsi beef steaks was 3-4 weeks at -26C under fluo- rescent illumination(110 dekalux)although colour changes could be seen within 7 days. M. psoas major steaks were unacceptable under these con ons within 7 days. Lentz(1971) reported the progress of discolouration in the light (160-220 dekalux) and in the dark for frozen beef stored at a range of tem peratures in terms of the Munsell colour notation. The prefreezing colour f most samples in the study was 7. 5R 4/8. Based on the notation, this means that the hue was 7.5 Red, which is an intermediate step between Red and Yellow-Red. The lightness was 4 on a scale where 10 is white and o is black and the chroma or saturation was 8 on a scale which ranges from 0(neutral or grey)to about 12 (intense or strong ). During frozen storage the chroma decreased and the hue became more yellow, producing a brown appear ance.A chroma of 6 at a hue of 7. 5-10R is no longer an attractive meat colour but is greyish red to reddish brown. The time from freezing to reach a chroma of 6 is shown in Table 4.3 where the effect of temperature and Table 4.3 Effect of storage temperature and light on th colour stability of frozen beef Time after freezing to reach Munsell Chroma 6(days) light 160-220 dekalux Souse: macopmou gmlmegzteif at te nreerg was 8 to iounwrapped or poorly wrapped meat. The problem is accentuated in areas exposed to low humidity air at high velocities, and by poor temperature control. Since most meat is now wrapped and temperature control much improved this is less of a problem than it once was commercially. Provided problems of freezer burn can be eliminated, the major appearance prob￾lem that affects frozen meat arises from oxidation of oxymyoglobin to metmyoglobin. Both temperature and illumination level affect the rate of discolouration during frozen storage, but light is by far the more serious factor. Townsend and Bratzler (1958) found that frozen beef steaks stored under fluorescent light (60 dekalux) discoloured in 2–3 days at -18 °C. Lane and Bratzler (1962) found that metmyoglobin formation in frozen extracts of meat was similar to the pattern seen in frozen steaks and was increased by exposure to fluorescent illumination.Tuma (1971) showed that the acceptable storage life of M. longissimus dorsi beef steaks was 3–4 weeks at -26°C under fluo￾rescent illumination (110 dekalux) although colour changes could be seen within 7 days. M. psoas major steaks were unacceptable under these con￾ditions within 7 days. Lentz (1971) reported the progress of discolouration in the light (160–220 dekalux) and in the dark for frozen beef stored at a range of tem￾peratures in terms of the Munsell colour notation. The prefreezing colour of most samples in the study was 7.5R 4/8. Based on the notation, this means that the hue was 7.5 Red, which is an intermediate step between Red and Yellow-Red. The lightness was 4 on a scale where 10 is white and 0 is black, and the chroma or saturation was 8 on a scale which ranges from 0 (neutral or grey) to about 12 (intense or strong). During frozen storage the chroma decreased and the hue became more yellow, producing a brown appear￾ance. A chroma of 6 at a hue of 7.5–10R is no longer an attractive meat colour but is greyish red to reddish brown. The time from freezing to reach a chroma of 6 is shown in Table 4.3 where the effect of temperature and Colour changes in chilling, freezing and storage of meat 77 Table 4.3 Effect of storage temperature and light on the colour stability of frozen beef Temperature (°C) Time after freezing to reach Munsell Chroma 6 (days) No light 160–220 dekalux -7 31 -18 60–90 3 -29 60 7 -40 90 7 Munsell Chroma immediately after freezing was 8 to 10. Source: MacDougall, 1974 after Lentz, 1971