Fibrous soy protein meat analog from low moisture twin-screw extrusion
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Mixtures of soy protein isolate (SPI), defatted soy flour, and wheat flour were extruded at 34% (w.b.) moisture using a twin-screw extruder. A 3x3x3 factorial experiment with two replications was conducted. Properties of soy protein meat analog products were compared to chicken breast. Prepared by deep-fat frying method, the texture properties of meat analog, including moisture, Warner-Bratzler (W-B) shear force and tensile strength, were either similar to the chicken breast or slightly inferior. The effects of soy protein isolate (SPI) content, barrel temperature and screw speed on extruder responses (die pressure, toque, and product temperature) and the physical properties of meat analog were investigated. All operation parameters significantly affected responses process parameters and the physical texture properties of meat analog including specific volume, porosity, water holding capacity, Warner-Bratzler shear force, Kramer shear force, fiber microstructure, and fiber development angle. The fiber formation mechanism of soy protein meat analog during the extrusion process was investigated. The unfolding of biopolymer chains was critical for the fiber formation during extrusion, instead of the denaturation of native protein. The fiber formation by extrusion was a reversible process. To achieve extrusion stability and a similar degree of fiber formation one could extrude either a feed mixture with a higher SPI content at a lower temperature or a feed mixture with a lower SPI content at a higher temperature.
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