35-3

M. P. RICHARDS, Food Science, University of Massachusetts, UMASS Marine Station, P.O. Box 7128 Lanesville Station, Gloucester, MA 01930 and H. O. Hultin.

JUSTIFICATION: Determining the mechanism and means to inhibit hemoglobin-induced lipid oxidation could lead to shelf-life extension of muscle foods.

OBJECTIVES: The objective of this work was to examine factors that modulate the ability of hemoglobin to promote lipid oxidation.

METHODS: Oxygenation of hemoglobin at various pH values was measured spectrophotometrically. Hemoglobin was added to washed cod muscle or linoleic acid emulsions which acted as lipid substrates. The level of preformed lipid hydroperoxides was decreased using sodium borohydride. Lipid oxidation was measured by determining conjugated dienes, lipid hydroperoxides, TBARS, and sensory analysis. The range of pH values investigated was 6.0 to 7.6.

RESULTS: The role of hemoglobin-mediated lipid oxidation was studied by adding trout hemolysate to washed cod muscle. The rate of rancid odor and TBARS development during storage increased greatly as the pH was reduced. Two factors could account for this observation. Formation of methemoglobin due to autoxidation of the heme pigment was found to occur more rapidly at reduced pH. Also, the level of deoxyhemoglobin was found to increase sharply with pH reduction. This suggested a role for deoxyhemoglobin as a catalyst. Structural changes that occur with deoxygenation of hemoglobin are presented to possibly explain a catalytic effect of deoxyhemoglobin. Peroxidation of linoleic acid by oxy/deoxyhemoglobin and methemoglobin was investigated at two levels of preformed lipid hydroperoxides. At a reduced level of preformed lipid hydroperoxides, oxy/deoxyhemoglobin stimulated peroxidation of linoleic acid, whereas methemoglobin did not. This suggested that reduced hemoglobins exclusively cause the formation of lipid hydroperoxides in the early stages of lipid oxidation.

SIGNIFICANCE: Deoxyhemoglobin has received little attention as a catalyst of lipid oxidation. Further investigations into the role of deoxyhemoglobin as a catalyst may improve our understanding of quality deterioration in muscle foods.