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.

中文翻译：

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胃pH值对体外消化过程中红甜菜酸和水分的吸收

消化过程中酸和水分向食物中的扩散会影响食物分解和营养释放。由于这些大量运输过程可能会受到胃液pH值和初始食物结构的影响，因此本研究调查了在体外胃液消化过程中，受胃液pH值影响，酸和水分摄入具有不同初始结构的食物（生甜菜和罐装红甜菜）。酸吸收的特征是消化期间酸浓度除以初始酸浓度之间的比率，在pH 1.8的消化过程中观察到的酸浓度为4.14±0.06（罐装）和2.68±0.08（原始），而1.61±0.10（罐装）和1.02± pH值为4.8时为0.08（原始）。根据菲克第二定律估算的酸有效扩散率范围为1.7×10 ^-10  m ² / s至1.2×10 ^-9  m² / s，湿气有效扩散率为6.7×10 ^-11  m ² / s至2.1×10 ^-10  m ² / s。在pH 1.8（消解甜菜根的原始固体含量的6.3％（原始）和罐装的4.3％）下，消解红甜菜240分钟后观察到较高的固体损失，而在pH 3.0和4.8时未观察到明显的固体损失。结果表明，在pH 1.8的消化过程中，细胞肿胀，生的红甜菜硬度降低。这项研究的结果可能有助于设计在胃pH值动态变化条件下具有特定的颗粒分解和营养释放功能的食品。