Comparative study of the effects of three food proteins on the cooking quality of pork sausages
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Low-fat pork sausages were prepared with soy protein isolate (SPI), egg albumin (EA) and whey protein isolates (WPI) as binders at 1%, 2% and 3% w/w. The quality of cooked sausages was evaluated against control through cook loss, expressible moisture, cutting force, hardness, adhesiveness, cohesiveness, color and torsion test. Significantly (p < 0.05) lower cook loss and expressible moisture were observed with the addition of protein. Cutting force, hardness and cohesiveness were also increased with increase in added protein. L* and b* color values increased, while a* decreased with higher levels of all proteins, indicating a slightly lighter and less-red color. Sausage with added protein was juicier than control and overall acceptability was greatest for sausage with 2% SPI whereas least cook loss at 3% SPI among the treatments. Dispersions of 15% SPI, WPI and egg albumin were microfluidized and gel strength, particle size, storage and loss moduli, and torsional strength were measured at 0%, 1%, 2% and 3% NaCl. With increase in NaCl concentration up to 2% particle size and gel strength increased significantly (p<0.05) followed by a decrease at 3% NaCl. The gel point time and temperature shear stain and slope ratio decreased whereas shear stress increased with increasing NaCl concentration and microfluidization. A decrease in particle size and strain hardening and increase in gel strength was observed due to microfluidization. Confocal laser scanning microscopy showed more uniform distribution of the protein aggregates after microfluidization. Microfluidized dispersions of SPI, WPI and EA were added as binders at 1%, 2%a and 3% levels to 80% lean pork trimming to formulate pork sausages. At the same level of protein microfluidization resulted in significantly (p < 0.05) lower cook loss and expressible moisture. No significant difference was observed in cutting force hardness, cohesiveness, adhesiveness, shear stress, shear strain, fracture modulus and color due to microfluidization. Microfluidization resulted in significant changes in the structure and gelation of all the protein dispersions in isolation, as well as in sausage emulsions, and can be used as a useful tool for manipulating the functionality of the proteins for different food processing conditions.