Ultrasound-induced yield increase of yuba (protein-lipid film from soybean milk) and changes in structural, physicochemical, and digestive properties during film-peeling process

Yuba, as a traditional soybean food, is protein-lipid film from soybean milk. This study proposed a novel ultrasound-assisted yuba preparation strategy and investigated the structural, physicochemical, and digestive properties of yuba during the film-peeling process. The process parameters of yuba preparation were optimized using response surface method and Box-Behnken design. The results showed that total yield of 5 yuba films was 39.8 ± 0.3% under the optimum conditions (315 W ultrasound power, 8 min ultrasound time, and 1:9 solid-to-liquid ratio) with an increase rate of 12.6%, compared with that of the control group. With the increasing yuba film-peeling times, protein and lipid contents in yuba decreased, whereas carbohydrate content displayed an increasing trend. The analyses of mechanical properties, protein secondary structure, X-ray diffraction, disulfide bond, and microstructure showed that the protein network structure of yuba films became looser with film-peeling progression. Furthermore, in vitro simulated digestion experiments indicated that yuba obtained in the early film-peeling stage (the first four films) exhibited better protein degradation performance and higher degree of lipid hydrolysis. This study provides technical references for the process innovations of yuba and theoretical basis for systematically evaluating yuba quality and better utilizing its nutritional value.