Plant cell walls as barriers to lipid bioaccessibility in model lipid-rich plant food

337 Pages·2017·7.97 MB·English

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Plant cell walls as barriers to lipid bioaccesibility in model lipid-rich plant food
(almond)

Grundy, Myriam Marie-Louise

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King's College London

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D ownload date: 06. Nov. 2017
Plant cell walls as barriers to lipid
bioaccessibility in model lipid-rich plant food
(almond)

Myriam Marie-Louise Grundy B.Sc. (Hons), M.Sc.

A thesis submitted to King’s College London for the degree of Doctor of Philosophy in
Nutritional Science and Biochemistry

Division of Diabetes and Nutritional Sciences
School of Medicine
King’s College London
September 2014
In loving memory of my dad

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PREFACE
This thesis was submitted to King’s College London for the degree of Doctor of Philosophy. The work
presented herein was undertaken in the Division of Diabetes and Nutritional Sciences (previously the
Nutritional Sciences Research Division), King’s College London, from October 2010 to September
2014.

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ABSTRACT
It is generally assumed that most of the nutrients contained in a food are released (bioaccessible)
during digestion and potentially available for absorption. However, the structure of plant food such
as almonds, in particular the cell walls (‘dietary fibre’), may encapsulate intracellular nutrients,
thereby limiting their bioaccessibility. The main aim of the studies described in this thesis was to
investigate the role played by almond cell walls in the regulation of lipid bioaccessibility and
digestion kinetics using a combination of in vivo, in vitro and in silico methods.
The particle size distributions of masticated whole raw and roasted almonds collected from 15
volunteers were used to predict lipid bioaccessibility from a mathematical model. Predicted values
were compared with experimental measurements of lipid release in the same almond samples.
Samples of masticated almonds were then loaded into a dynamic gastric model followed by a static
duodenal model to determine lipid loss in these compartments. The rate and extent of lipolysis were
measured by pH-stat titration and gas liquid chromatography of released fatty acids on almond
materials with different degrees of bioaccessibility under simulated duodenal digestion conditions.
The effect of processing on lipid losses and almond microstructure was also determined in ileostomy
subjects who consumed two almond meals varying in lipid bioaccessibility. Finally, the potential
penetration of lipase(s) through the cell wall matrix was investigated using notably confocal
microscopy.
The findings of this project indicated that following mastication and gastrointestinal digestion of
whole almonds, only a small proportion of lipid was released from ruptured cells. Depending on the
almond structure and degree of processing, the amount of lipid released from the food matrix and
fatty acids produced from lipolysis varied substantially. This work has provided further evidence that
cell walls act as a physical barrier that limits nutrient digestion.
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ACKNOWLEDGEMENTS
I would firstly like to thank my supervisors, Prof Peter Ellis, Dr Peter Butterworth and Dr Sarah Berry,
as well as Dr Jeremy Sanderson for their invaluable guidance and support throughout my PhD.
Secondly the Diet and Health Research Industry Club (DRINC) of the Biotechnology and Biological
Sciences Research Council (BBSRC), who financed my PhD (BBSRC studentship award no.
BB/H531994/1), and Karen Lapsley from the Almond Board of California for providing the almonds.
I would like to thank all the members of the Biopolymers group, past and present: Dr Frederic
Warren for his support during the early stages of my project, Hamung Patel, Daphne Vasilopoulou
and Dr Terri Grassby; also all the undergraduate project students we have had in the lab, in
particular Bérengère Bayart for her contribution on the lipase and cell wall permeability work.
Special thanks go to Cathrina Edwards who assisted me in many ways throughout those 4 years.
Some of the work reported in this thesis was undertaken in collaboration with different institutes
and universities, in particular the Institute of Food Research (IFR) in Norwich. My special thanks go to
Dr Giusy Mandalari, Prof Keith Waldron and Richard Faulk for their assistance on the design and
running of the DGM/SDM work, and Dr Mary Parker who provided advice on microscopy techniques.
I am also deeply grateful to Prof Peter Wilde and Dr Alan Mackie for sharing with me their
knowledge on interface, emulsion and lipid digestion, and coping with my endless questions.
I would also like to thank Prof Frédéric Carrière for giving me the opportunity of visiting, in two
occasions, the Laboratory of Enzymology at Interfaces and Physiology of Lipolysis (EIPL) in the Centre
National de la Recherche Scientifique (CNRS) in Marseille. I am highly grateful for his advice and
supervision on the enzymology of lipolysis and lipases aspects of my work, and for the excellent
discussions and ideas for this part of the project. Many thanks to Dr Sawsan Amara, Dr Hélène
Gaussier and Eduardo Mateos for helping me with the lipase experiments. Thanks also to the EIPL
team for making me feel so welcome in their lab.
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Many thanks to Dr David Gray and his team at the University of Nottingham who contributed to the
work presented in this thesis and kindly offered their expertise on oil bodies.
Thank you to the dedicated staff at the Clinical Research Facility at St Thomas’ Hospital especially
Dana Navaie. Many thanks to Dr Shuvra Ray, Paula Darroch and the volunteers for their enthusiastic
contribution and effort in the Biogut study, Dr Tracy Nelson and GSTS pathology for blood analyses.
I am very grateful to the technical team at King’s College London, David Lincoln, Anne-Catherine
Perz, Mary-Jo Searle, Robert Gray, Rosie Calokatsia and David Gondi for their fantastic work at
sorting out all the details that were essential for the smooth progression of my PhD.
There are many others notably Prof Willats and his group from the University of Copenhagen who
very kindly did the analysis of the almond cell wall using antibodies; Dr Trevor Blackall for letting me
use the Malvern Mastersizer 2000 at the Geology department at King’s College London; Dr Gema
Vizcay-Barrena and Leanne Glover from the Centre for Ultrastructural Imaging as well as Dr Jan
Soetaert from the Nikon Imaging Centre at King’s College London for their help with some of the
microscopy; and Dr Peter Milligan for his aid with statistical analysis.
Finally, I would like to thank my mum, David, Caroline and the Grundies/Cotons, who supported me
from day one and developed a surprising interest in almonds despite not always understanding what

I was doing with them.

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MEETINGS ATTENDED, PRESENTATIONS AND AWARDS
Oral presentations
(i) 21st and 22nd of June 2012, Science and Technology of Food Emulsions, London, UK. “Role of cell
walls during in vitro duodenal digestion of almond lipids”
(ii) 1st to 5th of July 2012, Food Oral Processing, Beaune, France. “The role of mastication in
determining macronutrient bioaccessibility using almonds as a model food”. Obtained a Conference
Fund Grant from King’s College London Graduate School (£300).
(iii) 10th and 11th of September 2012, Nutrition Society Postgraduate Conference, Newcastle, UK.
“Role of cell walls during in vitro duodenal digestion of almond lipids”
(iv) 8th of May 2013, Biosciences KTN Early Careers Researchers Event, London, UK. “Role of cell walls
during in vitro duodenal digestion of almond lipids”
(v) 24th to 26th of June 2013, Dream conference - From Model Foods to Food Models, Nantes, France.
“Plant cell walls as barriers to lipid bioaccessibility in a model lipid-rich plant food”. Selected among
the 25 best PhD student papers and awarded with free participation at the conference and
reimbursement of travel cost.
(vi) 15th to 18th of July 2013, Nutrition Society Conference within the BBSRC (DRINC) satellite session,
Newcastle, UK. “The role of plant cell walls in regulating lipid bioaccessibility”
(vii) 11th to 14th of March 2014, 3rd International Conference on Food Digestion, Wageningen, the
Netherland. “Investigating the permeability of almond cell walls to digestive enzymes”. Obtained a
Travel Grant from the Nutrition Society (£350).

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Poster presentations
(i) 11th of March 2011, Kings College London Diabetes and Nutritional Sciences Research Division
annual symposium. “The role of plant cell walls in regulating lipid bioaccessibility”
(ii) 13th and 14th of April 2011, 6th DRINC Dissemination Event, Bristol, UK. “The role of plant cell walls
in regulating lipid bioaccessibility”
(iii) 17th of June 2011, Kings College London Medicine School Showcase. “The role of plant cell walls
in regulating lipid bioaccessibility”
(iv) 12th and 13th of October 2011, 7th DRINC Dissemination Event, Manchester, UK. “Lipid
bioaccessibility of almonds: the influence of mastication and simulated digestion”
(v) 15th and 16th of May 2012, 8th DRINC Dissemination Event, Leeds, UK. “Role of cell walls during in
vitro duodenal digestion of almond lipids”
(vi) 5th and 6th of February 2013, 9th DRINC Dissemination Event, Bristol, UK. “In vitro duodenal
digestion of raw and roasted almond lipids”. Winner of first prize for PhD poster presentations.
(vii) 5th to 8th of March 2013, 2nd International Conference on Food Digestion, Madrid, Spain. Poster
and 4 minutes presentation (PhD contest) “Role of food structure during in vitro duodenal digestion
of raw and roasted almond lipids”. Obtained a General Travel Grant from the Biochemical Society
(£348).

Other awards
(i) 22nd to 26th of April 2013, Selected to attend the PhD Training School on “Food Digestion and
Human Health” in Gdansk, Poland organised by InfoGest COST Action.
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(ii) October 2013, One month Short-Term Scientific Mission (STSM) awarded by InfoGest COST
Action (2500 Euros). Worked with Prof Frédéric Carrière for a month in the Laboratory of
Enzymology at Interfaces and Physiology of Lipolysis (EIPL) in the Centre National de la Recherche
Scientifique (CNRS) in Marseille.
(iii) 6th of June 2014, Shortlisted for the Young Lipid Scientist Award organised by the lipid group
AGM of the Society of Chemical Industry (SCI) at the University of Reading. I gave a 15 min
presentation summarising the work performed during my PhD: “Plant cell walls as barriers to lipid
bioaccessibility in a model lipid-rich plant food”.

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