Underlying mechanisms of sodium alginate with different viscosities on the texture characteristics and protein digestibility of soybean curd

Aging leads to decline in chewing and digestive capabilities, increasing the risk of nutritional deficiencies. Elderly generally have insufficient intake of dietary fiber and protein. Soybean curd is an ideal protein source, while lack of dietary fiber might limit its nutritional effect. Therefore, this study aims to develop a sodium alginate (SA) soybean curd product with low (L-SA), medium (M-SA), and high (H-SA) viscosities which is easy to chew and digest. The impact of SA on soybean curd yield, water holding capacity (WHC), gel strength, texture, microstructure, bolus properties and simulated in vitro digestion were investigated. The results indicate the addition of SA shows more hydrogen bonds and enhance the WHC of protein-SA network structure, thereby improving the yield, hardness, chewiness, and gel strength. L-SA exhibited a more homogeneous and continuous microstructure. Sensory evaluation and bolus properties indicated the addition of SA influenced volunteers’ preference. L-SA was easier to chew and more acceptable. Furthermore, SA decreased the digestibility of soybean curd proteins, particularly at H-SA due to forming stronger gels in gastric conditions. These findings provide valuable insights into the development of novel high-fiber soybean curd and clarify the impact of different viscosities on physicochemical properties and protein digestibility. • WHC and texture properties improved with increasing viscosity of SA. • The addition of SA promoted β-sheet formation and tended to expand the masticated particle size. • L-SA soybean curd was preferred by volunteers. • SA exhibited the reduction in protein digestibility through electrostatic complexation.