Effect of thickening agent and fat in custard microstructure upon in vitro enzymatic digestion.

摘要

Custard desserts with and without fat were prepared using either tapioca modified starch or carboxymethylcellulose (CMC) as thickening agents and the changes in their microstructure upon in vitro simulation of mouth, stomach and small intestine conditions were evaluated by light microscopy. A completely different pattern of behaviour was found between starch and CMC custards. After mouth incubation, partially gelatinized tapioca granules were completely disintegrated by the action of saliva, while the CMC custard was practically unaffected. Fat incorporation did not influence the breakdown of gelatinized starch. Coagulation of milk proteins was observed after stomach incubation. In the starch custards, the fat globules aggregated with the milk proteins, whereas in the CMC custard they were still embedded in the unaltered network. Intestine incubation completely digested the remaining structures after stomach incubation, although in the CMC custard particles of undigested hydrocolloid were observed. In the presence of fat, micelles were visualized in both custards, which favoured the bioaccessibility of lipophilic compounds. The higher digestive resistance of the CMC custards implied the existence of a higher barrier against the release of active compounds from the custard matrix and therefore a higher barrier against bioaccessibility.