Monitoring in vitro gastric bolus digestion with ultrasound

Monitoring food degradation during gastric digestion is essential to understand how food properties impact nutrient absorption. Imaging techniques like ultrasound can be used to validate in vitro results in vivo. The aim was to assess the use of ultrasound (US) for monitoring changes in food bolus properties during in vitro gastric digestion with a newly designed model system. Artificial bread boli (n = 9) treated with amylase, pepsin or no enzyme underwent 90 minutes of static digestion (INFOGEST), during which US images were recorded. Bolus area and the number of pixels and Haralick image texture features were calculated. Average grey values were calculated at increasing distance from the bolus edge. The echogenic bolus area on ultrasound images increased over 90 min. From 10-60 min, amylase-treated boli were larger than pepsin-treated (ratios 2.00-2.40) and no enzyme boli (ratios 1.89-2.23). Regarding image texture, these boli had higher homogeneity and lower contrast than pepsin-treated boli. From 30 min onward, the bolus area of amylase-treated boli had 1.19-1.30 times higher homogeneity, and 2.5-4% lower entropy. From 10 min, the slope of the mean grey value curves for amylase-treated boli remained lower than for the other treatments. In the amylase-treated boli, an increase in homogeneity (rho = 0.8) and decreases in entropy (rho = -0.82) and slope (rho = -0.85) corresponded with increasing starch digestibility. These findings show the capacity of US imaging for quantifying bolus degradation in vitro. Future work should explore this novel application of US imaging in dynamic in vitro models and in vivo.