Gastric digestion of α-lactalbumin in adult human subjects using capsule endoscopy and nasogastric tube sampling. Issue 4 (28th August 2014)

• Record Type: Journal Article
• Authors: Sullivan, Louise M.; Kehoe, Joseph J.; Barry, Lillian; Buckley, Martin J. M.; Shanahan, Fergus; Mok, K. H.; Brodkorb, André
• Is Part Of: British journal of nutrition. Volume 112:Issue 4(2014)
• Page Start: 638
• Page End: 646
• Publication Date: 2014-08-28
• Subjects: Nutrition -- Periodicals; 572.4
• DOI: 10.1017/S0007114514001196
• Languages: English
• ISSNs: 0007-1145

Abstract

<abstract abstract-type="normal"> <title> <x content-type="archive" xml:space="preserve">Abstract</x> </title> <p>In the present study, structural changes in the milk protein α-lactalbumin (α-LA) and its proteolysis were investigated for the potential formation of protein–fatty acid complexes during <italic>in vivo</italic> gastric digestion. Capsule endoscopy allowed visualisation of the digestion of the test drinks, with nasogastric tubes allowing sampling of the gastric contents. A total of ten healthy volunteers had nasogastric tubes inserted into the stomach and ingested test drinks containing 50 g/l of sucrose and 25 g/l of α-LA with and without 4 g/l of oleic acid (OA). The samples of gastric contents were collected for analysis at 3 min intervals. The results revealed a rapid decrease in the pH of the stomach of the subjects. The fasting pH of 2·31 (<sc>sd</sc> 1·19) increased to a pH maxima of pH 6·54 (<sc>sd</sc> 0·29) after ingestion, with a subsequent decrease to pH 2·22 (<sc>sd</sc> 1·91) after 21 min (<italic>n</italic> 8). Fluorescence spectroscopy and Fourier transform IR spectroscopy revealed partial protein unfolding, coinciding with the decrease in pH below the isoelectric point of α-LA. The activity of pepsin in the fasting state was found to be 39 (<sc>sd</sc> 12) units/ml of gastric juice. Rapid digestion of the protein occurred: after 15 min, no native protein was detected using SDS–PAGE; HPLC revealed the presence of small amounts of native protein after 24 min of gastric digestion. Mirocam<sup>®</sup> capsule endoscopy imaging and video clips (see the online supplementary material) revealed that gastric peristalsis resulted in a heterogeneous mixture during gastric digestion. Unfolding of α-LA was observed during gastric transit; however, there was no evidence of a cytotoxic complex being formed between α-LA and OA.</p> </abstract>