• Dairy food structures influence the rates of nutrient digestion through different in vitro gastric behaviour

      Mulet-Cabero, Ana-Isabel; Rigby, Neil M.; Brodkorb, Andre; Mackie, Alan; Irish Dairy Levy Research Trust; BBSRC UK; Teagasc Walsh Fellowship Programme; BB/J004545/1 (Elsevier, 31/12/2016)
      The purpose of this study was to investigate in vitro the extent to which specific food structures alter gastric behaviour and could therefore impact on nutrient delivery and digestion in the small intestine. Results obtained from a specifically developed gastric digestion model, were compared to results from a previous human study on the same foods. The semi-dynamic model could simulate the main gastric dynamics including gradual acidification, lipolysis, proteolysis and emptying. Two dairy-based foods with the same caloric content but different structure were studied. The semi-solid meal comprised a mixture of cheese and yogurt and the liquid meal was an oil in water emulsion stabilised by milk proteins. Our findings showed similar gastric behaviour to that seen previously in vivo. Gastric behaviour was affected by the initial structure with creaming and sedimentation observed in the case of liquid and semi-solid samples, respectively. Lipid and protein digestion profiles showed clear differences in the amount of nutrients reaching the simulated small intestine and, consequently, the likely bioaccessibility after digestion. The semi-solid sample generated higher nutrient released into the small intestine at an early stage of digestion whereas nutrient accessibility from liquid sample was delayed due to the formation of a cream layer in the gastric phase. This shows the strong effect of the matrix on gastric behaviour, proteolysis and lipolysis, which explains the differences in physiological responses seen previously with these systems in terms of fullness and satiety.
    • Structural mechanism and kinetics of in vitro gastric digestion are affected by process-induced changes in bovine milk

      Mulet-Cabero, Ana Isabel; Mackie, Alan R.; Wilde, Peter J.; Fenelon, Mark A.; Brodkorb, Andre; Irish Dairy Levy Research Trust; Teagasc Walsh Fellowship Programme; BBSRC; 2014029; BB/J004545/1 (Elsevier, 2018-03-20)
      Bovine milk is commonly exposed to processing, which can alter the structure, biochemical composition, physico-chemical properties and sensory quality. While many of these changes have been studied extensively, little is known about their effect on digestive behaviour. In this study, heat treatments of pasteurisation at 72 °C for 15 s or Ultra-High-Temperature (UHT) treatment at 140 °C for 3 s and homogenisation at pilot-plant scale were applied to whole milk. The gastric behaviour was investigated using a recently developed semi-dynamic adult in vitro model. The emptied digesta were analysed to assess the nutrient delivery kinetics, changes in microstructure and protein digestion. All samples showed protein aggregation and coagulum formation within the first 15 min of gastric digestion at which time the pH ranged from 5.5 to 6. Homogenised samples creamed regardless of heat treatment, whereas all non-homogenised samples exhibited sedimentation. The consistency of the coagulum of the heated samples was more fragmented compared to those of the non-heated samples. Rheological analysis showed that the higher the temperature of the heat treatment, the softer the obtained coagulum and the higher the protein hydrolysis at the end of digestion. The study also confirmed that gastric emptying of caseins from milk is delayed due to coagulation in the stomach, while β-lactoglobulin was emptied throughout the gastric phase, except for UHT-treated milk. The gastric behaviour also had an impact on the lipid and protein content of the emptied chyme. The homogenised samples seemed to release more nutrients at the end of gastric digestion.