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Oxidation of cod microsomal lipids in situ and in vitro as affected by processing parameters
Muscle foods are a major source of food protein in many parts of the world including the United States. Acid and/or alkali solubilization is a recent method developed to separate muscle proteins with good functional properties. The unsaturated lipids of the fish muscle are highly susceptible to oxidative degradation, especially in the presence of hemoglobin. The goal of this research work was to study structural and physicochemical changes of fish membranes that occur during the acid or alkali solubilization procedures. The effect on lipid oxidation and ways to stabilize the membrane lipids against oxidation were also studied. Washed and unwashed cod, as well as cod microsomes were used as model systems for the study. Peroxide value, TBARS and sensory were employed to follow lipid oxidation. Citric acid and calcium chloride were effective in protecting the muscle from lipid oxidation either when used in washing the muscle or when added directly to the minced muscle. The maximum effect was achieved when citric acid and calcium chloride were added in the first washing step. Solubilizing the muscle at pH 3 or 10.8 in the absence of hemoglobin protected the protein isolates from lipid oxidation. However, when the muscle and hemoglobin were together exposed to low pH, oxidation was promoted. Protein isolates prepared by citric acid/calcium chloride-treated washed cod solubilized at pH 3 in the presence of hemoglobin exhibited very good oxidative stability. Part of the protection that citric acid/calcium chloride offered against lipid oxidation was attributed to the ability of citric acid to break down unstable peroxides. Hydrochloric acid was also able to break down formed peroxides to a similar degree as citric acid. At pH 5.3 or lower, 99% of isolated cod membranes sediment at low centrifugation speeds. Isolated membranes that were exposed to pH 3.0 or 10.8 were less susceptible to hemoglobin-mediated lipid oxidation. Cod hemoglobin exposed for 20sec or 20min to pH 3 was rendered less pro-oxidative than the untreated cod hemoglobin. However, when microsomes and hemoglobin were together exposed to low pH, oxidation was promoted. Microsomes prepared in the presence of citric acid and calcium chloride were less susceptible to hemoglobin-mediated lipid oxidation compared to untreated microsomal suspensions. The soluble fraction of the cod muscle (press juice) was able to retard lipid oxidation of washed cod and protein isolate, even when washed cod was solubilized at low pH in the presence of hemoglobin. Press juice retained its anti-oxidative activity even after exposure to low pH. Press juice was able to prevent hemoglobin-mediated, NADH-dependent and Fe-ascorbate mediated lipid oxidation of isolated cod microsomes.
Vareltzis, Patroklos, "Oxidation of cod microsomal lipids in situ and in vitro as affected by processing parameters" (2006). Doctoral Dissertations Available from Proquest. AAI3215903.