Myoglobin Content and Color of Raw Pork Loin Roasts as Affected by Freezing at Two Rates

Longissimus dorsi and psoas major muscles from fresh and frozen paired pork loin roasts were evaluated for myoglobin content and color reflectance. One of each paired roast was analyzed fresh and the other analyzed after freezing and thawing. Myoglobin in the thaw drip from frozen roasts was measured, also. Two freezing rates were tested: fast freezing in an air blast freezer at -27° to -29°C and slow freezing in a home freezer at -18°C. Roasts were stored for 28 days before thawing.

Myoglobin in the longissimus dorsi was significantly (P < 0.001) lower than in psoas major muscle. Less myoglobin (P < 0.05) was found in fresh than frozen thawed roasts; but there was no difference (P > 0.05) in myoglobin content associated with freezing rate. Apparently, myoglobin extraction from frozen muscles was more efficient than from fresh muscles. No difference was detected in the total myoglobin in the thaw drip of blast and home frozen roasts.

Significant (P < 0.001) differences between muscles were detected for lightness index and purity. No significant (P > 0.05) differences were found between dominant wavelength, purity, or lightness index and freezing treatment. For fresh muscles, purity and lightness index were related to myoglobin content.