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Lactase (β-galactosidase) encapsulation in hydrogel beads with controlled internal pH microenvironments: Impact of bead characteristics on enzyme activity

Zhang, Zipei, Zhang, Ruojie, McClements, David Julian
Food hydrocolloids 2017 v.67 pp. 85-93
beta-galactosidase, confocal laser scanning microscopy, encapsulation, enzyme activity, fluorescence, foods, gastric juice, hydrocolloids, hydrogen ions, ingestion, lactose intolerance, magnesium hydroxide, pH, protons, small intestine, stomach
Individuals who suffer from lactose intolerance can alleviate many of their symptoms by ingestion of lactase (β-galactosidase) with lactose-containing foods. However, this enzyme is deactivated when exposed to highly acidic gastric fluids, which reduces the amount reaching the small intestine. Oral delivery systems are therefore needed to protect lactase in the stomach, and then release it in an active form in the small intestine. In this study, carrageenan-based hydrogel beads were fabricated that contained lactase and a buffer (Mg(OH)2). This buffer was selected because it is insoluble under alkaline conditions, but soluble under acidic conditions, and can therefore maintain a neutral pH inside the beads when they are dispersed in a low pH solution (such as acidic gastric fluids). Small (D = 255 μm) and large (D = 2610 μm) hydrogel beads were prepared using two different injection methods to compare the impact of bead dimensions on the retention of lactase activity. A ratiometric fluorescence method based on confocal laser scanning microscopy was developed to measure changes in the internal pH of the hydrogel beads before and after exposure to simulated gastric conditions. After exposure to stomach conditions, the internal pH of buffer-free beads dropped steeply (from around pH 7.0 to below pH 4.0), but that of buffer-loaded beads remained fairly constant (from around pH 7.2 to pH 6.6). When exposed to small intestine conditions, lactase encapsulated in buffer-loaded beads maintained its enzyme activity, whereas lactase encapsulated in buffer-free beads did not. Smaller beads needed a higher amount of Mg(OH)2 to maintain a neutral internal pH throughout the gastric phase, which was attributed to faster diffusion of hydrogen ions (H+) into smaller beads. These results suggest that buffer-loaded hydrogel beads may be useful for encapsulation, protection, and delivery of acid-labile enzymes and other bioactive substances.