Ultrasonic monitoring of softening in solid foods during in-vitro gastric digestion

This study aims to evaluate the feasibility of using non-destructive ultrasound to monitor textural softening in potato and cheese during in vitro gastric digestion. Textural measurements were taken after different digestion times (5, 10, 15, 20, 25, 30, 60, 90, and 120 min) at 37 °C, while in vitro digestion was non-destructively monitored using ultrasound in through-transmission mode. The textural softening resulted in a substantially greater variation in hardness, ranging from 0.418 to 1.241 N for potato and from 0.200 to 0.534 N for cheese. Meanwhile, the ultrasonic velocity increased during gastric digestion from 745 ± 106.6 m/s to 1342.9 ± 131.5 m/s in potato and from 1377.4 ± 3.8 m/s to 1502.8 ± 4.6 m/s in cheese. Both the softening and velocity increase were attributable to the compositional variation occurring within the food structure due to gastric fluid diffusion into the food matrix. The Weibull model kinetic parameter “k” indicated that potato exhibited a higher softening rate than cheese, due to a faster gastric fluid migration. This was also evidenced by the effective diffusivity of gastric fluid (Deff) obtained by modeling the evolution of the ultrasonic velocity during digestion (Deff, potatõ2.5 Deff, cheese). A noticeable relationship was found between the softening of both food matrices and the change in the ultrasonic wave velocity. Additionally, it should be highlighted that the measurement of the ultrasonic velocity by ultrasound presented a lower degree of variability than instrumental texture assessment. Therefore, ultrasound proves to be an accurate technique for the on-line monitoring of textural changes in foods during in vitro digestion. This non-destructive approach provides a powerful instrumental tool in the design of new products with enhanced nutritional properties by better monitoring how in vitro digestion affects their mechanical properties. •Gastric fluid migration was faster in potato than cheese.•Ultrasonic velocity and softening increased due to gastric fluid migration.•A relationship between velocity and hardness changes was found.•Ultrasonic testing showed lower variability than instrumental texture.•Ultrasonic monitoring of gastric digestion was proven to be a tool for food design.