In recent years, plant-based yogurts have received considerable attention, with sales particularly increasing among younger consumers [1]. Soybean, a globally available and cost-effective food ingredient, is rich in high-quality protein, dietary fiber, and functional ingredients like soybean isoflavones [2]. Therefore, soybean holds significant potential as a raw material for developing plant-based yogurts [1]. However, soy yogurts, similar to many other plant-based yogurts, face issues of phase separation serious and lack the attractive mouthfeel that is similar to traditional dairy yogurts [[3], [4], [5], [6]]. The acidification of plant-based protein leads to the formation of a non-continuous weak gel, resulting in phase separation [7]. In addition, the mouthfeel of yogurts is a crucial sensory attribute that influences consumers' choices and consumption preferences, serving as an essential quality indicator for evaluating yogurts [8]. Notably, consumers' preferences for mouthfeel are consistent across both plant-based and dairy yogurts, favoring attributes such as softness, slipperiness, thickness, and creaminess [8,9]. Sonne, Busch-Stockfisch, Weiss and Hinrichs [10] found that the creaminess exists strongly correlated with attributes such as slipperiness, thickness, and graininess. Therefore, these factors merit attention in the development of soy yogurt products.

The mouthfeel and phase separation degree of yogurts are predominantly influenced by the protein network structure within the gel matrix [11]. Polysaccharides could interact with proteins in yogurt to form a binary mixed gel, regulating the structure of yogurt gels, and improving the stability and mouthfeel of yogurts [11,12]. When the pH of the system falls below the isoelectric point of protein, the protein with cation can polymerize with anionic polysaccharides, leading to the formation of a stable, three-dimensional gel network [13]. For instance, Kong, Xiao, Du, Wang, Yu, Chen, Liu, Cheng and Gan [3] found that soy yogurts with linear anionic polysaccharide low acyl gellan gum (LAG) has higher water holding capacity (WHC), viscosity and gel strength than soy yogurts without addition. Similarly, with the increase of anionic polysaccharide Mesona blumes polysaccharide (MBP) concentration, acid-induced soy protein isolate gels showed a smoother structure, higher apparent viscosity, and increased gel strength [14].

Carboxymethyl cellulose (CMC) is a carboxylated derivative of cellulose, belonging to the anionic linear polymer. CMC has several noteworthy properties, such as colorless, odorless, calorie-free, physiologically inert and stability in acidic conditions. It is commonly used as stabilizer and thickener [15,16]. Several studies have indicated that CMC can stabilize and disperse casein micelles, enhancing the stability and viscosity of dairy yogurts and as the molecular weight and degree of substitution increased, enhanced stability was observed [[17], [18], [19]]. However, to our knowledge, a report on the effect of CMC on the mouthfeel and stability of soy yogurts has not been found. Therefore, it is necessary to investigate the concentration and degree of substitution of CMC for the stability and mouthfeel of soy yogurts.

In this work, we aimed to investigate the effect of the degree of substitution and concentration of CMC on the stability and mouthfeel of soy yogurts. WHC, particle size and microstructure were explored, to determine the stability properties of soy yogurts. In addition, the rheology, tribology and sensory evaluation of mouthfeel were discussed. Furthermore, a correlation between sensory evaluation of mouthfeel and physical properties was established to determine the physical basis of the effect of CMC on the mouthfeel of soy yogurts.