Acid and Moisture Uptake into Red Beets during in Vitro Gastric Digestion as Influenced by Gastric pH

Abstract

Acid and moisture diffusion into foods during digestion influence food breakdown and nutrient release. As these mass transport processes can be affected by gastric pH and initial food structure, this study investigated acid and moisture uptake into foods with varying initial structure (raw and canned red beets) during in vitro gastric digestion as influenced by gastric pH. Acid uptake was characterized as the ratio between acid concentration during digestion divided by initial acid concentration and observed to be 4.14 ± 0.06 (canned) and 2.68 ± 0.08 (raw) during digestion at pH 1.8 compared to 1.61 ± 0.10 (canned) and 1.02 ± 0.08 (raw) at pH 4.8. Acid effective diffusivities, estimated following Fick’s second law, ranged from 1.7 × 10−10 m2/s to 1.2 × 10−9 m2/s and moisture effective diffusivities ranged from 6.7 × 10−11 m2/s to 2.1 × 10−10 m2/s. Higher solid loss after 240 min of digestion of red beets was observed at pH 1.8 (6.3% of initial solid content (raw) and 4.3% (canned)), whereas no significant solid loss was observed at pH 3.0 and 4.8. Results indicated swelling of cells and decrease in hardness of raw red beets during digestion at pH 1.8. The results of this study may help to design food products with a tailored particle breakdown and nutrient release during the dynamic pH conditions of the gastric environment.