Low-intensity ultrasound as a tool for assessing the mechanical properties of pea protein-based high-moisture meat analogues produced by nitrogen gas-assisted extrusion

Nitrogen gas-assisted extrusion cooking is a novel processing technique that can potentially improve the physical properties of extruded foods. However, this technique remains underexplored for the production of high-moisture meat analogues (HMMAs). In this study, a blend of pea protein concentrate and isolate was extruded with direct injection of nitrogen gas into the extruder barrel at different pressures (0, 225, 450 kPa) to explore the potential of this technique in manufacturing HMMAs. X-ray microtomography analyses revealed a significant number of bubbles in the HMMAs produced at 450 kPa, whereas no bubbles were observed for the lower gas injection pressure of 225 kPa or the control (0 kPa). The presence of bubbles in the HMMAs produced at 450 kPa was confirmed by air-coupled low-intensity ultrasonic measurements that showed a large decrease in the ultrasonic velocity (from 1674.24 ± 5.58 m/s to 129.90 ± 2.13 m/s) and an increase in attenuation coefficient from 0.01 ± 0.00 mm -1 to 1.50 ± 0.01 mm -1 . The longitudinal modulus determined from the ultrasonic data showed that HMMAs produced at 0 and 225 kPa were firmer compared to those at 450 kPa, aligning with the softer textures for the latter, as confirmed by cutting force analysis. Nitrogen gas-assisted high-moisture extrusion opens up new possibilities to enhance the microstructural properties of HMMAs suitable for a wide range of consumers. This study demonstrated that low-intensity ultrasound waves are sensitive to the presence of bubbles in HMMAs, offering a rapid, non-destructive tool for quality control in food production.