Development of 3D-printed artificial muscles for meat analogs: structural and functional changes modulated by ultrasound-assisted glycosylation of rice protein with d-xylose.

3D food printing enables the fabrication of meat analogs with controlled structures and textures that are difficult to achieve using conventional processing. Therefore, suitable food-inks are essential for 3D-printed meat analogs to ensure precise extrusion, shape retention, and enhanced texture and color development during cooking. Given the inherently low solubility and limited functional properties of rice protein isolate (RPI), chemical and physical modification strategies are required to improve its applicability as a food-ink. In this study, ultrasound-assisted glycosylation was applied to improve the structural and functional properties of protein-based inks for 3D-printed meat analogs. RPI was glycosylated with D-xylose (Xyl) using a horn-type ultrasonic processor operating at 24 kHz and a nominal output power of 500 W under varying ultrasonic treatment times (UT; 0, 5, 30, and 50 min) to produce RPI-Xyl conjugates. Ultrasonic treatment promoted glycosylation and Maillard reaction between RPI and Xyl. Protein-based inks were formulated by adjusting the ratios of soy protein isolate (SPI), RPI, and RPI-Xyl conjugates. Printing parameters were optimized using response surface methodology based on the rheological properties of each ink, after which 3D-printed muscle-like plant protein structures were fabricated as artificial muscles. The structural and functional properties of the artificial muscles varied depending on UT. The Maillard reaction of RPI-Xyl conjugate contributed to meat-like color development in artificial muscles after heat treatment. Ultrasonic treatment altered the secondary and tertiary structures of proteins in glycosylated artificial muscles. Among the treatment conditions, UT30 enhanced protein solubility and disulfide bond formation in the cooked artificial muscles. The textural properties of the 3D-printed artificial muscles were further compared to those of beef steak. Notably, artificial muscles subjected to UT30 exhibited superior water retention, hardness, elasticity, and tensile strength compared to beef steak. In contrast, excessive ultrasonic treatment (UT50) induced partial protein denaturation and aggregation, thereby weakening the functional properties of the artificial muscles. Collectively, these findings demonstrate that ultrasound-assisted glycosylation is a effective strategy for improving the structural and functional performance of 3D-printed artificial muscles, providing approach for developing more realistic and high-quality meat analogs.