Abstract:
Although general instructions regarding the preparation of milk powder are provided by the manufacturer, the effects of water temperature used to reconstitute milk powder on the hydrolysis of protein and the survival of probiotics during human digestion process still need to be further understood. The current study therefore aimed at investigating the influence of reconstitution water temperature (40℃, 55℃, 70℃) on the digestive behaviours of milk powder in the novel Dynamic Human Stomach-Intestine IV (DHSI-IV) model.
The in vitro gastrointestinal digestion was conducted for 180 min. The pH profile, gastric emptying, particle size distribution and appearance of the digestive products were characterised. Protein hydrolysis was evaluated using polyacrylamide gel electrophoresis (SDS-PAGE) and biuret reaction test. The survival of probiotics (Bifidobacterium) was determined by enumerating the viable count. The digested products and the potentially survived probiotics before and after the digestion were assessed by scanning electron microscope (SEM).
By properly mimicking the human gastrointestinal digestion, all the milk samples showed buffering capacity against the low pH in the stomach and their gastric emptying behaviours were adequately close to those in vivo data. Visible distinction was observed among the undigested and digested samples with a great number of protein aggregations presented in the gastric chyme. Particle size distribution was found to be greater in the stomach than in the small intestine especially during the prior 120 min of digestion for samples of 40℃ and 55℃. The hydrolysis of protein was complete after 180-min digestion while the generation of peptides was found to show some variances among the temperatures. The probiotics no longer survived in the stomach at 120 min except for the sample of 55℃, while they presented at a low survival rate in the small intestine with a gradual reduction in the viable count along with the digestion time. Overall, the water temperature used for reconstitution of the probiotic enriched milk powder influenced the digestion process and probiotics survival.
