Uses of the HGS

The HGS has been used to investigate the role that ACW dynamics and food material properties have on the structural changes and disintegration profile of different foods during digestion.

Role of ACW Activity on Food Digestion

To investigate the relevance of ACW motility on the digestion behaviour of foods, Kong and Singh (2010) compared the performance of the HGS against the more traditional shaking bath method.

Apple cubes and extra-long white rice kernels were mixed with simulated saliva and exposed to 2 h of digestion in both, the HGS and a shaking bath. It is noteworthy that a batch approach was employed in both cases, with gastric juices being added to the systems only at the beginning of the process. The results clearly illustrated the significant effect that the crushing and squeezing forces generated within the HGS have on the breakdown of both food models during the process. In the case of the apples, 61 % of the total dry matter from the shaking bath was still in particles larger than 6.3 mm, and only 20 % in particles smaller than 2.8 mm. In comparison, only 16 % of the total dry matter from the HGS remained in particles larger than 6.3 mm, with a 69 % of it distributed in particles smaller than 2.8 mm. A similar result was found in the case of rice. Most kernels were intact after digestion in the shaking bath, while 52 % of the dry matter from the HGS was associated with particles smaller 0.8 mm.

Considering that the structural breakdown of the diet will have a significant impact on the rate of nutrient release during digestion, this study confirmed the need to better emulate the fluid mechanical conditions that develop during digestion. To further investigate the role of gastric motility on the disintegration kinetics of foods, Kong and Singh (2010) investigated the disintegration profile of white rice when exposed to two different levels of compression. Unlike the previous study, the HGS was operated under dynamic conditions, where a continuous release of 2.5 mL/min of gastric juice was imposed. In agreement with in vivo data, an exponential decay of the digesta's pH from an initial value of 4.27 to a final constant value of 1.35 was observed within the first 2 h of process. Simulated digesta was continuously removed from the HGS at a rate of 3 mL/min, leading to a 60 % of the total dry mass being emptied after 3 h of process. The HGS was operated under two levels of compression (50 % and 70 %). The higher the compression, the higher the disintegration of the food particles. In particular, a 75 % compression was able to break down 75 % of the rice kernels into particles much smaller than 1.2 mm in size. This study showed once again the need to better understand and mimic the biomechanical functions of the human stomach in order to improve the performance and reliability of in vitro digestive systems.

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