Isoelectric point, meat

Fermentation lowers the pH toward the isoelectric point of the meat proteins (Bacus, 1986), which assists in the removal of water from fermented sausages. Carbohydrates are added to provide food for the bacteria, and thus, accelerate fermentation. Acton et al. (1977) have discussed utilization of various carbohydrates and their role in the fermentation process. 

The isoelectric point of a protein is defined as that pH at which the net charge is zero (Wismer-Pedersen, 1971). Since protein-protein ionic interactions are promoted at this point, it would be expected that the protein matrix would shrink and WHC would be at a minimum (Kapsalis, 1975). It follows that increasing the pH away from isoelectric point would also result in a higher WHC, since protein-water interactions are favored (Hamm, 1960). Bouton et al. (1971) were able to increase the ultimate pH and WHC of meat by preslaughter injection of epinephrine and showed that tenderness increased directly with pH values. Further work by Bouton et al. (1972) and Bouton and Harris (1972) showed that as pH increased from normal values of 5.5 to 7.0, tenderness of the tissue increased and became independent of the contracture state. 

Traditionally, extrusion texturization of soy protein has been used to create meat analogues. Addition of sodium hydroxide during extrusion does not aid in texturization, with worse product quality at high pH (Dahl and Villota, 1991). Precipitation within the extruder at the soy isoelectric point may be necessary for adequate texturization. Huang and colleagues (1995) at Iowa Sate University devised a process in which soy protein isolate could be extruded into textile fibers. Brittleness was offset by addition of glycerol during extrusion and by various chemical treatments post-extrusion. A similar process could be developed to produce superior meat-like fibers. 

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