| Summary: | The pH of beef muscle affected water-holding capacity (WHC) and tenderness. When the pH was brought to 4.0 and below by immersion in citric acid or lactic acid or brought to ∼7.0 after base immersion, WHC and tenderness of beef muscle increased. When the pH was brought back to the isoelectric point of the major myofibrillar proteins after either acid or alkaline treatment (e.g. from ∼3.7 or 7.0 to ∼5.5), most of the weight gained from prior acidic or basic treatment was lost. The Warner-Bratzler shear force values (WBSF) returned at least to the level of the WBSF of the controls after the readjustment of pH to 5.5. This reversibility strongly suggests that tenderization is not caused primarily by proteolysis. It is proposed that myofibrillar structures could swell and disrupt at acid/neutral pH due to electrostatic repulsion. When the pH was brought back near the isoelectric point, the myofibrillar structure might collapse and/or aggregate. Less water could be held with the aggregated proteins than in the initial myofibrillar structure of raw beef. Lactic acid and citric acid produced essentially the same shear force if WBSF values after marination were compared at a similar pH value. CaCl 2 showed a synergistic effect and negative effect, respectively, on the tenderization induced by citric acid and lactic acid. The solubility of beef myofibrillar proteins increased steeply from pH 4.27 to 4.03, where a significant decrease in WBSF was often observed. The solubility of beef muscle protein was below 20% between pH 6.9 and 7.6. The relation of protein solubilization to tenderization observed at acid pH was not seen in the tenderization induced by base treatment. Elastic gels from washed chicken breast muscle with a moisture content of 88% were formed at an acid pH (∼3.7 and lower) and low ionic strength. A decrease of pH from 4.1 to 3.7 or below increased gel elasticity and decreased water loss under pressure. In the presence of NaCl, gels made at pH ∼3.7 had decreased elasticity and increased water loss under pressure compared to those prepared without salt.
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