Plant-based meat can be expected to serve as a popular food in daily life. However, it is often required for the textural properties and sufficient characteristic flavor in 3D-printed plant-based meat. Fortunately, ultrasonic vibration can induce the secondary structure unfolding of plant proteins after cavitation, thereby exposing more reactive groups and disulfide bond cross-linking. While laser irradiation can be utilized to realize photothermal conversion for the precise and rapid heating, and finally instantaneously activate the Maillard reaction for the protein cross-linking and solidification. The combined action of ultrasound and laser can simultaneously enhance the gel strength and Maillard reaction rate of 3D-printed plant-based meat. This study aims to investigate the effects of ultrasound-laser dual-energy-field assistance on the texture and Maillard reaction-derived flavor compounds using ultrasonic-laser dual-energy-field-assisted 3D printing (UL-3DP). Two printing inks were prepared: a basic formulation without glucose (F0) and an optimal formulation with 2.5% glucose (F1). Five groups were compared in the experiments: U-3DP (ultrasonic-assisted 3D printing), L-3DP (laser-assisted 3D printing), 3DP-L (pure extrusion with interlayer laser-assisted 3D printing), U-3DP-L (ultrasonic extrusion with interlayer laser-assisted 3D printing), and UL-3DP (ultrasonic-laser dual-energy-field-assisted 3D printing), with 3DP (3D printing without energy-field assistance) as the control group. Rheological tests of the inks were conducted to assess the effects of the different energy-field assistance modes on textural properties, microstructure, volatile flavor compounds, and sensory properties of printed samples. The rheological results showed that the addition of glucose enhanced the shear recovery and self-supporting performance of the 3D printing ink. The shear recovery rate of the optimal formulation ink (F1) increased from 69.56% to 73.36%, compared with the basic formulation ink (F0). Textural analysis revealed that the UL-3DP sample increased the springiness, hardness, and chewiness by 14.79%, 22.5%, and 43.84%, respectively, compared with the 3DP control. Microstructural observations indicated that the UL-3DP sample shared a three-dimensional gel network structure with high uniformity and density, compared with the 3DP sample with a loose and irregular pore structure. Volatile flavor compounds were also measured at the same time. It was found that the UL-3DP sample further accelerated the Maillard reaction rate in the glucose. The total peak area of volatile compounds increased by 193.08%, compared with the 3DP control, indicating the high meaty aroma compounds. The sensory evaluation results demonstrated that the UL-3DP group achieved overall sensory scores closest to those of beef tenderloin, effectively bridging the gaps in meaty aroma, taste, and juiciness, compared with animal meat. In conclusion, ultrasound and laser energy fields were introduced into the plant-based meat during 3D printing. The UL-3DP samples synergistically improved textural properties and flavor quality after gel network construction during the Maillard reaction. The findings can provide a strong reference and technical basis for plant-based meat using 3D printing.

Meat demand is ever-increasing the globally, as the constant expansion of animal husbandry leads to massive resource consumption and serious environmental pollution. Plant protein meat (PPM), as the meat analogue, is gradually replacing animal meat to alleviate resource consumption and environmental pollution. The current processing technology of SSPM mainly includes extrusion, spinning, shearing, and 3D printing. As an emerging production technology in the food industry, 3D printing has been successfully applied to the PPM production with personalized nutritional content, shape, texture and taste. The current research focuses mainly on the optimization of ink materials and hydrocolloid components for the PPM using 3D printing. It is lacking in the relationship between process parameters and the quality of PPM, in order to obtain the optimal process parameters. There is still a great quality gap between 3D-printed PPM and animal meat. In this study, the process parameters were optimized for the PPM using 3D printing. A single-factor test was carried out to explore the effects of process parameters, including the print speed, nozzle height and extrusion rate on the hardness, springiness and chewiness of PPM. The multiple regression fitting models of hardness, springiness and chewiness were established by Box-Behnken Design (BBD) response surface test design. As such, an optimal combination was obtained for the hardness, springiness and chewiness using multi-objective fireworks. The results showed that hardness, springiness, and chewiness were achieved in similar chicken quality with the increase in print speed. The quality parameters of PPM deviated from the chicken parameters with the low quality, when the print speed was too high. Furthermore, the PPM shared higher quality characteristics at the print speed of 40-80 mm/s. The hardness, springiness and chewiness tended to be stable with the increase in nozzle height. The 3D printing quality gradually approached the chicken quality. The PPM presented the higher quality characteristics, when the nozzle height was 1.0-1.4 mm. The hardness, springiness and chewiness also tended to be stable with the increase of extrusion rate. Once the extrusion rate was too high, the 3D printing quality of PPM deviated from the chicken quality. The higher quality characteristics of PPM were achieved at the extrusion rate of 57.6-86.4 mm³/s. Design-Expert 13 software was combined to evaluate the single factor and response surface test. The results showed that the nozzle height posed the most significant effect on the hardness of PPM. The extrusion rate had the most significant effect on the springiness of PPM, while the print speed had the most significant effect on the chewiness of PPM. The BBD analysis was used to fit the multiple regression model with the variance analysis, according to the range of optimized process parameters. The optimal 3D printing process parameters were obtained using multi-objective fireworks. Therefore, when the print speed was 49.06 mm/s, the nozzle height was 1.21 mm, and the extrusion rate was 80.75 mm³/s, the hardness of PPM was 43.14 N, the springiness was 2.78 mm, and the chewiness was 75.92 mJ, indicating the highest similarity with the chicken quality. The errors of the hardness, springiness and chewiness were 2.21 %, 5.48 % and 2.52 %, respectively, compared with the confirmatory test. The quality of PPM was improved using the optimal 3D printing process parameters. The finding can provide a strong reference for the high-quality PPM production.

Since animal meat has been a major source of protein, conventional livestock farming is ever-increasing, as the global population grows. But the livestock farming has caused serious resource and environmental issues in recent years, such as greenhouse gas emissions, land occupation, water consumption, and loss of biodiversity. Alternatively, plant protein meat (PPM) can be expected to serve as the animal meat analogue, in order to alleviate the shortage of animal meat, resource consumption, and environmental pollution. The primary processing techniques for PPM currently include extrusion, spinning, shearing, and 3D printing. Specifically, the emerging 3D printing has been successfully applied to PPM production in the food industry, thus enabling customization of nutritional content, shape, texture, and flavor. Previous studies of 3D-printed PPM have focused primarily on material formulations, process parameters, or nozzle structures in conventional 3D printing. Among them, ultrasonic vibration has been used to print highly viscous fluid materials in protein extraction, gelation, and food processing. Better performance has also been achieved to mitigate the clogging caused by small nozzle diameters or high material viscosity. However, it is still lacking in the application of ultrasonic vibration for the high quality of 3D-printed PPM. In this study, ultrasonic vibration was introduced to improve the quality of 3D-printed PPM. A systematic analysis was made to explore the mechanism of ultrasonic vibration on plant proteins. Rheological property tests and numerical simulations of 3D printing nozzles were then carried out to investigate the effect of ultrasonic vibration on the gelation of plant proteins. A novel ultrasonic vibration-assisted 3D printing system was developed for PPM using single-nozzle 3D printing. A series of experiments were conducted to clarify the influence of ultrasonic vibration on the quality of 3D-printed PPM. The numerical simulation results demonstrated there was a cyclic variation in the fluid velocity inside the printing nozzle, with the trend of increasing, decreasing, and then increasing for the uniform mixing of protein molecules. Additionally, the shear rate within the nozzle exhibited repetitive fluctuations with decreasing and then increasing, where relatively high shear rates were observed on both the surface and cross-sections of the fluid. A high-shear environment was provided for the stepwise depolymerization of protein molecules during printing. The internal fluid pressure within the nozzle also showed a cyclic variation in the decreasing and then increasing. The lowest pressure value was still higher than that in the absence of ultrasonic vibration. This fluctuation of pressure greatly contributed to the necessary conditions for the depolymerization of protein molecules. Thus, the ultrasonic vibration supplied the higher shear and pressure to the plant proteins during 3D printing. The gelation process was promoted to ultimately improve the molding quality of 3D-printed PPM products. Experimental results revealed that the printed products exhibited decreased hardness, comparable elasticity, and chewiness after ultrasonic vibration, compared with conventional 3D printing. In terms of the stability of hardness, elasticity, and chewiness, the fluctuations in these quality parameters were lower than those in the samples printed without ultrasonic vibration. Specifically, the stability of hardness, elasticity, and chewiness increased by 27.75%, 83.14%, and 59.30%, respectively, indicating a more consistent quality for the samples printed with ultrasonic vibration. The ultrasonic vibration was incorporated into the 3D printing of PPM for the stability of quality attributes. The finding can also provide valuable insights into producing high-quality plant-based protein meat using 3D printing.