Effect of ultrasonic-microwave treatment on the structure and gel properties of soybean meal

Low-temperature defatted soybean meal (LDSM) is rich in nutrients, but its poor solubility restricts its application in the food industry. In this study, the LDSM solution was adjusted to alkaline (AT-SM), and then the AT-SM was treated with ultrasound (U-AT-SM), microwave (M-AT-SM), ultrasound-microwave (UM-AT-SM) and water bath (WB-AT-SM). All treatments significantly improved protein solubility compared to untreated samples (29.17%). UM-AT-SM had the highest protein solubility, increasing by 121.22%. This is related to the particle size, zeta potential and structure of the sample. Glucono-δ-lactone (GDL) was added to LDSM to induce the formation of a gel (SM-Gg) from LDSM. The properties of the gel prepared with UM-AT-SM (UM-SM-Gg) were greatly improved. UM-SM-Gg had the densest and most homogeneous gel network structure with the highest hardness (295.54 g) and water holding capacity (66.84%), and the highest apparent viscosity, storage modulus and loss modulus. This may be attributed to the high solubility of proteins, which enhances cross-linking during GDL-induced gelation. Therefore, ultrasound-microwave treatment is an effective method to improve the gel properties of LDSM, which provides a new idea for the processing of low-fat food.