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Effect of low pH and citric acid-calcium chloride on precipitation and oxidation stability of microsomal suspensions. Acid solubilization is a recent method developed to separate muscle proteins with good functional properties. Oxidation of the membrane poly-unsaturated lipids in the membranes is a major cause of quality deterioration. The objective of this research was to study how structural and chemical changes of microsomal membranes occurring at low pH affect their precipitation and oxidation stability. The effect of citric acid and calcium chloride, as well as the effect of low pH on cod hemoglobin (Hb) were also explored. Thiobarbituric acid-reactive substances were employed to follow lipid oxidation. Lowry method was used to determine membrane protein concentrations. Cod hemoglobin was used to promote lipid oxidation. At pH 5.3 or lower 99% of microsomal membranes precipitated. When microsomal suspensions (MS) were incubated for 24h, then 99% precipitation was observed for pH 5.5. Resuspension of MS after incubating them at pH 5 for 10 min or 24 h could not be achieved. Exposing membranes to low pH renders them less susceptible to hemoglobin mediated oxidation. The order of oxidative stability for MS was: pH 3 (best) > pH 3 and then 6.8 > pH 6.8. When Hb was exposed to pH 3 seemed to become less reactive than untreated Hb, causing slightly less oxidation in both treated and untreated MS. Citric acid and calcium chloride were effective in reducing lipid oxidation when added in the microsomal suspensions. Using citric acid and calcium chloride in preparing microsomal suspensions could also lead to good oxidative stability. Incubation of citric acid and calcium chloride at pH 4.65 seemed to be more efficient. The results suggest that exposure of microsomal membranes to low pH can render them less susceptible to lipid oxidation. The addition of citric acid and calcium chloride either at the end or at the beginning of membrane preparation can further improve their oxidative stability.