Improving the quality of vegetarian sausage prepared with textured fibril soy protein using oil pre-emulsification

Plant protein-based meat analogues are becoming popular, such as textured fibril soy protein, and gluten, because of the healthy cholesterol-free, meat-like texture, and low cost. However, vegetarian sausages that are prepared with a plant source of protein usually taste dry and inelastic, compared with meat sausages, due mainly to the low emulsifying and gelling functionality. Recently, several studies have also reported that the incorporation of pre-emulsified vegetable oil into emulsion-type sausages can markedly promote the Water- and Fat-Binding (WFB) capacities of sausages, as well as the textural and sensory properties. Since chemical modification was focused mainly on the functionalities of proteins, few reports were to optimize the processing parameters of vegetarian sausages for better quality. Therefore, this work aimed to investigate the effects of pre-emulsified oil on the stability, texture, and microstructure of vegetarian sausage prepared with Textured Fibril Soy Protein (TFSP). Rapeseed oil and soy protein isolate were used to prepare the pre-emulsified oil with a high-speed mixer. A Box-Behnken model using Response Surface Method (RSM) was used to optimize the formulation of pre-emulsified oil, thereby maximizing the gel strength of TFSP-vegetarian-sausage. The optimal combination of parameters was achieved as follows: rapeseed oil content: 445 g/L, SPI concentration: 105 g/L, and the shear rate of high-speed mixer: 9.0×103 r/min. The gel strength, hardness, and chewiness of TFSP-sausage increased by approximately 100%, 10%, and 26%, respectively, compared with the traditional. An RSM quadratic model was selected to conduct the analysis of variance for the regression equation. It was found that the importance of influential factors was ranked in order of rapeseed oil content > SPI concentration > shear rate. The sensory evaluation showed that the TFSP-sausage prepared with pre-emulsified oil tasted tenderer, juicier, and more delicious, compared with the control group, indicating the improved textural and sensory attributes after the addition of pre-emulsified oil. A confocal laser scanning microscope was used to characterize the microstructure and the loss of cooking, water, and fat. It was found that the emulsion stability of TFSP-sausage was remarkably improved in the addition of pre-emulsified oil, where the emulsified oil droplets were homogeneously dispersed in the gel matrix of TFSP sausage. In conventional, the rapeseed oil was directly mixed and homogenized with other raw and subsidiary materials, while the emulsion droplets were unstable in the resultant sausage pastes, due to the bridge flocculation and coalescence. It was the reason that the comprehensive droplet coalescence and ‘oiling off’ often occurred in the control TFSP-sausage after cooking. As a result, the ‘filler effect’ of emulsified oil droplets was introduced to strengthen the WFB capacities of TFSP-sausage, particularly on the textural and sensory attributes. The finding demonstrated that the application of pre-emulsified vegetable oil can effectively improve the emulsion stability, with prominent effects and economic benefits in the textural and sensory attributes during the preparation of TFSP-sausage.