Food Biophysics

, Volume 9, Issue 3, pp 292–300 | Cite as

Gastric pH Distribution and Mixing of Soft and Rigid Food Particles in the Stomach using a Dual-Marker Technique

  • Gail M. Bornhorst
  • Shane M. Rutherfurd
  • Maxine J. Roman
  • Betty J. Burri
  • Paul J. Moughan
  • R. Paul Singh


Mixing of a particle-laden material during peristaltic flow in the stomach has not been quantified in vivo. Gastric mixing plays a key role in the digestion process; it determines the availability of acid and enzymes to individual food particles and controls the length of time particles will spend in the antral region, where they are subjected to mechanical breakdown from antral contraction waves. Solid particle mixing has been quantified using a dual-indigestible marker technique (TiO2 and Cr2O3) in soft (cooked brown and white rice) and rigid (raw and roasted almonds) particle meals fed to growing pigs. All meals consisted of two portions. Each portion was separately marked by one of the two indigestible markers, and the portions were sequentially fed to the pigs. At time periods ranging from 20 to 720 min after completion of the meal, ten intragastric chyme samples were taken from each pig to determine the marker concentration and pH value. Gastric pH was not homogeneous throughout the stomach and varied over time, with differences observed between soft and rigid meals (p < 0.0001). The total percentage of each meal that was mixed was calculated using a statistically-based mixing index (M). White rice had the greatest amount of mixing, becoming 94 % mixed after 480 min of digestion compared to 72 % mixing for brown rice. Rigid particles underwent a slower mixing process and only arrived at 65 and 71 % mixing after 720 min for raw and roasted almonds, respectively. Meal composition plays a role in the overall meal mixing during gastric digestion.


Mixing pH Gastric digestion In vivo Particle movement Mixing index 



The almonds used in this trial were generously donated by the Almond Board of California. The authors would like to acknowledge Trent Olson, Sharon Henare, and Carlos Montoya (Riddet Institute, Massey University) for their assistance in animal handling and sample procurement, and Carlos Montoya for his assistance in the statistical analysis. We also thank Leslie Woodhouse and Erik Gertz (USDA Western Human Nutrition Research Center) for their assistance in the ICP-AES analysis.

This project was partially supported by the Agriculture and Food Research Initiative grant 2009–35503-05195 from the USDA – National Institute of Food and Agriculture.

Mention of trade names in this publication is solely for the purpose of providing scientific information and does not imply recommendation of endorsement by the U.S. Department of Agriculture. The USDA is an equal opportunity provider and employer.


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Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  • Gail M. Bornhorst
    • 1
  • Shane M. Rutherfurd
    • 2
  • Maxine J. Roman
    • 1
  • Betty J. Burri
    • 3
  • Paul J. Moughan
    • 2
  • R. Paul Singh
    • 1
    • 2
  1. 1.Department of Biological and Agricultural EngineeringUniversity of CaliforniaDavisUSA
  2. 2.Riddet InstituteMassey UniversityPalmerston NorthNew Zealand
  3. 3.Western Human Nutrition Research CenterUnited States Department of AgricultureDavisUSA

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