Effects of pre-emulsification of oil treated by high pressure homogenization on the texture properties of textured fibril soy protein vegetarian sausages

Plant-based meat products have been the popular food at present, in order to prevent processed meat from cardiovascular disease and cancer today. The pre-emulsification technique can often be used to prepare an oil-in-water emulsion, before introducing the fat/oil into a meat product. Compared with the direct oil addition, the ability to bind water and oil can allow for the better dispersion of oil into the meat batter. Recently, several studies have also reported that the particle size of the pre-emulsified oil can influence the textural properties and gel formation of the sausage. However, few studies have reported the effects of droplet size and emulsifier in the pre-emulsion on the rheological and textural properties of vegetarian sausage. Therefore, the aim of this work was to apply the pre-emulsification for the processing of vegetarian sausages with Textured Fibril Soy Protein (TFSP). An investigation was made to clarify the effects of oils pre-emulsified on the rheological properties, texture, and microstructure of TFSP vegetarian sausages using different protein emulsifiers and homogenization conditions. The results show that the apparent viscosity of both Soybean Protein Isolate (SPI) and Sodium Caseinate (SC) emulsions increased gradually, as the pressure homogenization increased from 0 to 30 MPa. The particle size d3,2 of SPI emulsions ranged from 24.80 to 0.39 μm, and the particle size d3,2 of SC emulsions ranged from 12.37 to 0.12 μm. The temperature and frequency sweep of the TFSP vegetarian meat batter demonstrated all the vegetarian meat batters formed an emulsion gel with viscoelasticity after cooking. The higher the homogenization pressure of the pre-emulsion was, the higher the storage modulus (G′) of the vegetarian meat batter was. In the Warner-Bratzler (WB) shear test and texture properties (Texture Profile Analysis, TPA), it was found that the breaking force and TPA (Hardness, Springiness, Cohesiveness, Chewiness) of TFSP vegetarian sausages increased with the decrease of the particle size d3,2 of the pre-emulsion. The microstructures of different emulsions and TFSP vegetarian sausages were characterized by Confocal Laser Scanning Microscopy (CLSM). It was found that the coalescence of emulsion droplets occurred in the TFSP vegetarian sausages after cooking, when the SC emulsions were prepared at the pressure of 0-20 MPa. However, the TFSP vegetarian sausages prepared by the SPI emulsions showed a strong ability to resist the coalescence of emulsion droplets after cooking. Therefore, the shear force and textural properties of TFSP vegetarian sausage can be effectively improved, when the pressure was more than 20 MPa during the pre-emulsification of plant oils using the SPI. The finding can provide a strong reference for the development and application of the oil pre-emulsification process in vegetarian products.