Post on 14-Sep-2019
Food Structures: processing, digestibility and nutrient bioavailability
Professor Harjinder Singh
Riddet Institute, Massey University, Palmerston North, New Zealand
Food structures and assemblies
> All foods come from living organisms (plants and
animals) where various components interact to
produce biological systems
> These interactions and the constituent matrix
become relevant when these organisms are
consumed as food
> Nutrients are contained in these biological
systems - human digestive processes
> Fibrous structures (e.g. muscle); Fleshy materials
(e.g. fruits, tubers, vegetables); Encapsulated
embryos (e.g. grains and pulses); Complex fluids
(e.g. milk)
Structure anatomy of plant foods
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Hierarchical composites of hydrated cells that are bound together at cell walls and middle lamella, and exhibit turgor pressure
Dispersion of starch, protein, lipids assembled into discrete pockets
Tubers Fruits Vegetables Cereals Legumes Tree nuts
Fleshy structures Encapsulated embryosClassification
Description
Microstructure
Examples of plant foods
Hierarchical assemblies of foods in nature
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1Å
1nm
1onm
100nm
1µm
100µm
1mm
10µm
Water ~ 3ÅGlucose
molecules ~ 1.5nm
Lipid bodies ~ 0.5-2.5µm
Primary cell walls ~100nm thickness
Protein bodies ~ 0.1-25µm
Starch granules ~ 1-100µm
Parenchyma cells ~ 10-200µm
Plant organs order of 1mm
Cellulose microfibrils ~ 3-4nm
Tissues ~100µm to few mm
Molecules
Polymers
Cell wall
Cell
Tissue
Organ
Organelle
Food structure and processing
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Plant food organ
Particles
Tissues
Cell separation
Cell rupture
Bean paste
Starch gelatinisation, protein denaturation,
separation of cells
Particle size reduction
Disruption of cell walls, release of nutrients
Wheat flour
Ground almond meal
Mechanical processing (milling)
Thermal cooking and mashing
Mechanical processing (grinding)
Starch gelatinisation in cooked potatoes
𝟏𝟎−𝟏 −𝟏𝟎−𝟐 𝐦
𝟏𝟎−𝟐 − 𝟏𝟎−𝟑𝐦
𝟏𝟎−𝟑 − 𝟏𝟎−𝟒𝐦
𝟏𝟎−𝟒 − 𝟏𝟎−𝟔𝐦
Food structure and digestionDisassembly of food structure during mastication
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Ingested food (raw or processed)
Particles
Tissues
Cell separation
Cell rupture
Particle size reduction, lubrication (bolus)
Disruption of cell walls, release of nutrients, partial starch
degradation, lipid flocculation
Oral mastication
Cells of hard raw nuts, fruits and vegetables
Separation of cells, encapsulated nutrients
Cells of cooked legumes and
tubers
Food structure and digestionDisassembly of food structure during gastric-intestinal digestion
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Particles
Tissues
Cell separation
Cell rupture
Digestion in stomach and small intestine• Erosion of food particles• Enzymatic hydrolysis of
starch and protein• Lipid emulsification and
digestion
Nutrient releasedEnzyme degradation
Nutrient encapsulatedEnzyme diffusion
CO2, H2, CH4, SFCA
Fermentation in large intestine by bacteria and faecal excretion
Food Matrix/Structure and Nutrient Delivery
> Changes in food matrix/structures during processing and
digestion influence the release of nutrients in the GIT
> Bioavailability of nutrients:
-availability in the intestinal lumen
-absorption and/or retention in the body
-utilization by the body
> Food matrix will the availability of nutrient (the kinetics of
release and absorption of nutrients) - influence
physiological process – human health
> Designing food structures/matrices to develop new types
of healthy foods
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Lipids in Foods
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> Lipids in natural foods occur in many different forms; in
many cases - triglycerides are coated with a
stabilising layer or multilayer of membrane
phospholipids
> Lipids in processed foods – in the form of oil-in-water
or water-in-oil emulsions
> Emulsions are stabilised by proteins, phospholipids,
monoglycerides and/or diglycerides
> Surrounding structures (cells, seed oil bodies etc)
have important influence on lipid digestion and
bioavailability
Natural Food Emulsions: Milk
> The diameter of the fat globules: 0.1-10 m.
> Milk fat globule membrane (MFGM): proteins, phospholipids
10 nm thick
> Lipids stored in oil bodies or “oleosomes”
> Oil droplet surrounded by a monolayer of phospholipids
embedding proteins.
Schematic representation of the surface layer of an oil body. Not to scale. Adapted from Huang, A. H. C. (1994).
"Structure of plant seed oil bodies.” Current Opinion in Structural Biology,4(4): 493-498.
Lipids in Natural Foods: Plant Seed/Nut Oil Bodies
Aggregated
protein
Multi-layers
Protein molecules
Solid particles
Multi-lamellae
layer
Oil
Monomeric
surfactant
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Ice cream
Mayonnaise
Food Emulsions
Surrounding structures have important effect on food properties
Factors that Influence Lipid Digestion in Emulsified Systems
> Droplet size and state of flocculation in the GIT
> Nature of the interfacial layers
> Physical state of lipids; solid/liquid fat content
> Food matrix effects, e.g. fibres
(Berry S E et al. Am J Clin Nutr (2008) 88, 922-929)
©2008 by American Society for Nutrition
TAG levels after test meals containing 50 g test fat from whole almond seed
macroparticles (▴), almond oil and flour (○), or sunflower oil (control,▪).
Examples: Postprandial Lipid Response
Initial Stomach Intestine
Simulated
in-vivo – plasma TAG
StablePartially Coalesced
1.4
1.2
1.0
0.8P
lasm
a T
AG
(m
g/m
l)
6543210
Ingested Time (hours)
Impact of Emulsion Structure on Lipid Digestion
(From Golding et al, 2010)
Emulsion gels
Green represents protein
Red represents oil
Black represents water or air
Whey protein oil-in-water emulsion (10 wt% protein, 20 wt% soya oil, d4,3: 0.45 μm)
Add NaCl
Emulsions containing 10, 25, 100 and 200 mM NaCl
Heated in 90 °C for 30 min
Cooled to 4°C
Gels with different structures
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Characterization of emulsion gel
Gel type Gel strength (kPa) Hardness before fracture (N) Fracture force (N)
10 mM NaCl 7.3±1.8* 19.2±0.6* 3.9±0.3*
25 mM NaCl 23.0±1.8** 56.5±1.3** 7.0±0.1**
100 mM NaCl 107.0±5.2**** 77.8±0.4**** 12.9±1.4***
200 mM NaCl 91.0±1.1*** 69.9±0.3*** 17.2±1.9****
Absorbable nutrients
Gastric emptying; rate of lipid digestion and absorption
Structures/physical properties
Not all proteins are created equal nutritionally
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c
Differences in bioavailability of amino acids from different proteins
Composition:
cni
Plant-based proteins are generally of lower quality than animal-based proteins
> fibre
> anti-nutritional factors
> different structures
> Differences in bioavailability and
digestibility of amino acids
Food Chemistry 143 (2014) 1–8
Structure of dairy products affect the kinetics ofprotein digestion and amino acid bioavailability
Plasma leucine concentration (lmol/L) over a 7 h-period after ingestion of acid gel (AG)
and rennet gel (RG), in minipigs. At a given time, differences between matrices are
evidenced by different letters a, b (P < 0.05).
Ovalbumin aggregates formed under different conditions
Linear
pH 9/ IS 0,03 M
Size: 10 to 140 nm
(average 33 nm)
Linear-branched
pH 7/ IS 0,03 M
Size: 7,5 to 140 nm
(average 16 nm)
Spherical
pH 7/ IS 0,3 M
Size: 10 to 80 µm
(average 30 µm)
Spherical-agglomerated
pH 5/ IS 0,8M
Size: 20 to 250 µm
(average 80 µm)
Microstructure of OVA aggregates analyzed by TEM
Aggregate particle size distributions obtained by SLS and DLS
Nyemb et al., Food Chemistry, 2014
Protein digestion is affected by the aggregate
morphology
0
20
40
60
80
100
0 20 40 60 80
OV
A (
%)
(45
kD
ab
and
)
Digestion time (min)
Linear
Linear-branched
Spherical
Spherical-agglomerated
Non-aggregated OVA
Gastric conditions
(pH 2.5)
Intestinal conditions
(pH 6.5)
Nyemb et al., Food Chemistry, 2014
Structural aspects of carbohydrate digestion
Juntunen K S et al. Am J Clin Nutr (2002) 75, 254-262
Mean fasting and postprandial responses to rye and wheat products over 180
min (n = 20). Postprandial responses to whole-kernel rye bread (a), ß-glucan rye
bread (b), and pasta (c) were significantly different from those to white wheat
bread, P < 0.05.
Rice Processing and Starch DigestionStarch Hydrolysis Differs for Fully Cooked, Partially Cooked and Uncooked Rice
Starch Hydrolysis Differs for Cooked Whole Rice and Cooked Rice Paste
Changes in starch hydrolysis (%) of homogenised (a) and non-homogenised (b) uncooked and cooked rice during in vitro gastro-small intestinal starch digestion. U (uncooked), PC (partially cooked), FC (fully cooked) Tamura et al., 2016
Whole Navy Beans
Navy Beans Flour
Navy Beans Starch
Native Microstructure of Beans and In vitro Starch DigestionStarch Hydrolysis Differs for Whole Beans, Bean Flour and Bean Starch
Raw Navy Beans Cooked Beans Navy Bean Flour
Navy Bean Starch
Berg et al., 2012
Microstructure of Bean Cotyledon Cells During and After DigestionIntact Cotyledon Cells in Whole Navy Beans
Un-digested
a b
30 min Gastric
a b
10 min Small Intestine
a b
120 min Small Intestine
ba
Berg et al., 2012
Preliminary resultsMorphology of isolated legume cells by light microscopy
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Chickpea
Lentil
Lima bean
Adzuki bean
Navy bean
Preliminary results
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▪ Starch content (w/w)
✓ Lima bean 56.53 ± 1.02
✓ Navy bean 51.44 ± 2.24
✓ Chickpea 60.97 ± 1.08
▪ Moisture content, protein, lipids, carbohydrates, ash
▪ Cell wall
✓ Cellulose
✓ Xyloglucan
✓ Pectin
Chemical composition of legume cells
Preliminary resultsIn vitro starch digestion of navy bean cotyledon cells
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0
10
20
30
40
50
60
70
80
90
100
G0 G15 G30 I0 I5 I10 I15 I30 I60 I90 I120
Sta
rch
Hy
dro
lysi
s (%
)
Time (min)
Gastric digestion Intestinal digestion
Waxy corn starch
Cooked potato starch
Cooked cotyledon cell
Cooked navy bean
Uncooked cotyledon cell
Concluding Remarks
> Further establish the role of food matrix in nutrition (consider food matrix as
a variable in nutrition studies)
> Understanding the behaviour of food structures /matrices in the GIT
> Establish responses of GIT to different material structures, including
modelling
> Develop more complex in vitro models for studying digestion and nutrient
liberation
> Validation of in-vitro models using in-vivo studies
> Strong inter-disciplinary approach, involving physics, chemistry, colloid
science, process engineering, biology and nutrition.
Acknowledgements
Thomas Do
Dr Jaspreet Singh
Dr. Aiqain Ye
Dr. Qing Guo
Dr. Sophie Gallier
Financial Support
Tertiary Education Commission, NZ Ministry of Education
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Bioavailability of dietary AA is defined as the proportion of ingested dietary AA that is absorbed in a chemical form that renders these AA potentially suitable for metabolism or protein synthesis (Lewis and Bayley, 1995).
Amino acid digestibility reflects enzymatic hydrolysis and microbial fermentation of ingested proteins and peptides and absorption of AA and peptides from the gastrointestinal lumen (Fuller, 2003).
STEP 5
Chylomicrons form and travel
through lymphatics
STEP 3
Liver releases bile acids
to solubilize lipid products
in mixed micelles
STEP 2
Pancreas releases:
Lipase (+colipase)
cholesterol esterase
phospholipase A2
Lipids:
Triacylglycerol
Cholesterol esters
Phospholipids
pancreas
liver
STEP 4
Lipids absorbed from micelles
into epithelial cells
Gastric Lipase
Key Steps of Lipid Digestion and Absorption
small intestine
stomach
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