Dietary Phenolic Phytochemicals - Oxford Brookes …€¦ · · 2012-12-03Dietary Phenolic Phytochemicals ... activity, modulation of ... Antidiabetic Role of Polyphenols?
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IntroductionThe prevalence of type 2 diabetes is rising exponentially
Current treatment of the metabolic syndrome & prevention of type 2 diabetes – lifestyle modification
Dietary recommendations emphasise the intake of plant food sources
These foods are a great source of fibre but also of phenolic phytochemicals which may be able to influence glucose metabolism by several mechanisms
PhytochemicalsNatural plant compounds that provide a variety of health benefits
Fruits and vegetables are known to contain carbohydrates, vitamins and minerals, usually very low in proteins & fat – however also a rich source of phytochemicals
May act as antioxidants or enhance the effects of antioxidants
Oxidative Stress & Free Radicals
Free radicals are highly reactive molecules (contain one or more unpaired electron)
Ex. Reactive Oxygen Species (ROS)
They are produced through a no. of different processes
Our bodies have developed different mechanisms to cope
When the body’s natural antioxidant mechanism is overwhelmed = Oxidative Stress
Cellular Targets of Free RadicalsReactive free radicals react with a non radical
Lipid peroxidation occurs in blood vessel walls contributing to the development of atherosclerosis (CHD)
Radicals may attack DNA and cause mutations (cancer)
Free radicals can result in inactivation of enzymes & denaturation of proteins
Increasing evidence suggests that oxidative stress plays a role in both types of DM
PhytochemicalsPotential Role in:
GI/GR – preventing postprandial hyperglycaemia
Insulin signalling
Energy Expenditure
Many different types of phytochemicals
Carotenoids have been extensively studied however relatively little known about polyphenols & other plant extracts
Polyphenols
StilbenesFlavonoids*Phenolic acids
Isoflavones Flavanones Flavonols
Flavones Flavanols Anthocyanins
Flavan-3-ols Proanthocyanidins
FlavonoidsPhenolic phytochemicals; contain aromatic rings
Many occur in nature with a sugar group attached (water soluble)
Phenolics are plant secondary metabolites
Often found in the epidermis of leaves & fruits
Onions, apples, black tea are rich sources
Roles include:Pigmentation
Protect the plant from UV damage
Confer resistance to disease
Health Benefits of Flavonoids
Reduction in CVD risk (consistent)
Reduction in cancer risk (inconsistent)
Reduced diabetes risk (inconsistent)*
Weight management (emerging)
Cognitive function (emerging)
Gut & oral health (emerging)
Anthocyanins
Responsible for the red, purple & blue colours of many fruits, veg., cereal grains & flowers
Over 300 structurally distinct anthocyanins have been identified
Diverse range of physiological activities
Potent antioxidant
Physiological effects may be due to antioxidant activity, modulation of cellular biochemical processes or alteration of gene expression
Preventative role in cancer, diabetes, CVD, obesity, inflammation, cognitive decline
Antidiabetic Role of Polyphenols?Polyphenols may influence glucose metabolism by several mechanisms:1) inhibition of CHO digestion and glucose absorption in the intestine2) stimulation of insulin secretion from the pancreatic β–cells3) modulation of glucose release from liver4) activation of insulin receptors and glucose uptake in the insulin-sensitive tissues5) modulation of hepatic glucose output
FFC & Phenolic PhytochemicalResearch
‘undertake leading edge research focussed on tackling obesity, improving glycaemic control and reducing inflammation, thereby
helping to improve the health and well-being of the global population’
Polyphenol Content of Extracts
* p < 0.05, denotes significantly greater in polyphenol content as measured by FCR. Values reported as mg Gallic acid equivalents (GAE)/ gram extract
* * *
Bioavailability vs Bioaccessibility
OH
OH
?Intestine
Bioaccessibility
Bioavailability
inflammation
triglyceridesglycaemia
Inte
stin
al
bo
rder Blood
Bioaccessibility of Baobab
Polyphenols
Baobab 1 Baobab 2 Baobab 3 Baobab 4 Baobab 5 Baobab 6
Baseline 23.3 ± 0.6 21.2 ± 0.5 27.7 ± 0.2 26.5 ± 0.2 24.0 ± 0.3 28.2 ± 0.3
Gastric 63.0 ± 0.6* 62.0 ± 0.6* 61.6 ± 0.7* 63.5 ± 0.5* 60.5 ± 0.5* 63.2 ± 0.6*
Duodenal 76.9 ± 1.3* 76.4 ± 0.9* 76.0 ± 0.7* 77.3 ± 0.9* 71.8 ± 0.7* 75.9 ± 0.5*
* p < 0.05, denotes significant increase from the FCR values prior to in vitro
digestion. Values reported as mg Gallic acid equivalents (GAE)/ gram extract
What is the Glycemic Index
A ranking of food carbohydrates –based on the incremental area under the blood glucose curve
Comparing equal amounts of carbohydrate: reference food = glucose or white bread
Plasma glucose response to ingestionof 50 g CHO
-20
0
20
40
60
80
100
120
140
160
0 50 100 150 200 250 300
Minutes after meal
mg
/dl
Glucose Lentils
Kidney beans Potato
Bread Oatmeal
Rice
(Krezowski et al., 1987)
In vitro digestion
Food Sample
Oral phase
Gastric phase
Ileal phase
Salivary amylase
Pepsin
Pancreatic amylase
Betalains
Water-soluble pigments, replace anthocyanins in most plants of the order Caryophyllales (also found in some fungi)
Less well used in food processing than anthocyanins& carotenoids
These pigments are stable between pH 3-7, suitable for use in low acid food
Two main types, betacyanins & betaxanthins
Beetroot juice has been shown to contain high levels of polyphenols, betalains, as well as other bioactive phytochemicals
DesignIn a randomised, cross-over design, 20 healthy adults (8 male / 12 female) consumed one of three test beverages each containing 50g of available CHO (following on from pilot study)
The meals consisted of 225 mL of beetroot juice (Beetroot), 225 mL of a matched control beverage (Control), or 225 mL glucose as a positive control
On each test day postprandial finger prick blood samples were taken at baseline (-5, 0) 5, 15, 30, 45, 60, 90, 120 and 150 minutes to measure both blood glucose (5 µL) and plasma insulin (300 µL)
Food frequency questionnaires were analysed using the phenol explorer database (Neveu et al., 2010) to estimate habitual polyphenol intake
Glucose (segmental area under the curve)
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
160.00
180.00
200.00
0-30 0-45 0-60 0-90 0-150
Time (minutes)
sAU
C G
luco
se
MCON
BEET
GLUC
Glucose (area under the curve)
3.00
3.50
4.00
4.50
5.00
5.50
6.00
6.50
7.00
7.50
0 5 15 30 45 60 90 120 150
Time (minutes)
Blo
od
Glu
co
se (
mm
ol/
L)
MCON
BEET
GLUC
Insulin (segmental area under the curve)
200.00
700.00
1200.00
1700.00
2200.00
2700.00
0-30 0-45 0-60 0-90 0-150
Time (minutes)
Insu
lin
sA
UC
MCON
BEET
GLUC
Insulin (area under the curve)
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
0 5 15 30 45 60 90 120 150
Time (minutes)
Insu
lin
(µ
IU/m
L)
MCON
BEET
GLUC
ResultsSegmental area under curve analysis revealed a significantly lower postprandial glycaemic response at 0-30 minutes and a significantly lower insulin response at 0-30, 0-45, 0-60 for the beetroot juice drink compared to the control (P < 0.05)
This suggests an effect of beetroot phytochemicals or nitrate on insulin secretion, insulin receptor sensitivity or insulin utilisation
In vitro digestion of flatbreads with HMW barley β-glucan
0
50
100
150
200
250
300
350
400
0 20 40 60 80 100 120 140
Digestion time (min)
Glu
cose rele
ase (m
g/g
sam
ple
)
0% beta glucan 4% beta glucan8% beta glucan
Thondre et al., Food Research International (2010)
0
50
100
150
200
250
300
350
400
0 50 100 150
Digestion Time (min)
Glu
co
se
re
leas
ed
(m
g/g
sa
mp
le)
0% beta glucan 4% beta glucan 8% beta glucan
In vitro digestion of flatbreads with LMW barley β-glucan
Thondre & Henry, Int J Food Sci Nutr (2011)
In vivo study using β-Glucan
Randomised cross-over design
Unleavened flat breads with β-Glucan
Healthy subjects
-5 0 15 30 45 60 90 120
Glucose Analysis
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
0 15 30 45 60 90 120
Time (minutes)
De
lta g
luc
ose
(m
mo
l/l)
Glucose 0 g beta glucan
4 g beta glucan 8 g beta glucan
Thondre & Henry, Nutr Research, 2009
Glycemic response to flatbreads with HMW barley β-Glucan
GI of flatbreads with HMW barley β-Glucan
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
0 4 8
Amount of beta glucan (g)
Gly
cem
ic I
nd
ex
Thondre & Henry, Nutr Research, (2009)
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
0 15 30 45 60 90 120
Time (min)
Delta g
lucose (m
mol/l)
Glucose 0 g beta glucan
4 g beta glucan 8 g beta glucan
Glycemic response to flatbreads with LMW barley β-Glucan
Thondre & Henry, Int J Food Sci Nutr (2011)
0
10
20
30
40
50
60
70
0 4 8
Amount of beta glucan (g)
Gly
ce
mic
In
de
x
GI of flatbreads with LMW barley β-glucan
Thondre & Henry, Int J Food Sci Nutr (2011)
Polyphenol content of β-Glucan extracts
Thondre et al., Food Chemistry (2011)
0
200
400
600
800
1000
1200
1400
75% BG 25% BG 30% BG
70% Acetone 70% Methanol 70% Ethanol Acidified Methanol
Po
lyp
he
no
l c
on
ten
t ( µµ µµ
g/g
sa
mp
le)
75% BG – LMW; 25 and 30% BG - HMW
Comparison of β-Glucans with other antioxidants
0
10
20
30
40
50
60
70
80
90
100
GA FA Trolox AA BB BFRF
Antioxidant source
Inh
ibit
ion
(%
)
Thondre et al., Food Chemistry (2011)
HMW Beta glucan
0
100
200
300
400
500
600
Cra
nber
ryA
pple
Red
gra
pe
Straw
berry
BF
RF
BB
Bro
ccol
iS
pinac
hP
each
Oni
on
Red
pep
perB
anan
aO
range
Pea
r
Gra
pefru
itP
inea
pple
Car
rot
Glu
cag
elC
abba
ge
Co
rnR
ice
Whea
tPo
tato
Lettu
ce
Oat
sC
eler
yC
ucu
mbe
r
Source
Fre
e p
hen
olics (
mg
GA
E/1
00g
sam
ple
)
Thondre et al., Food Chemistry (2011)
Comparison of β-Glucans with common sources of polyphenols
HMW beta glucan
Influence of polyphenols on in vitro starch digestibility of porridge oats
y = -0.7455x + 1946.1
R2 = 0.8762
1400
1450
1500
1550
1600
1650
1700
1750
1800
1850
0 100 200 300 400 500 600 700
Rapidly digested starch (mg/g sugars released)
Po
lyp
he
no
l co
nte
nt
(ug/g
GA
E)
0
200
400
600
800
1000
1200
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Sample no.
Su
ga
rs r
ele
as
ed
(m
g/C
HO
in
sa
mp
le)
0 min gastric 20 min 60 min 120 min 180 min
0
200
400
600
800
1000
1200
1400
1600
1800
2000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Oats porridges
Po
lyp
he
no
l co
nte
nt
(ug
/g G
AE
)
Thondre et al, 2011, Proceedings of the Nutrition Society, 70 (OCE4), E138
Future Work
Currently investigating the effect of adding different plant extracts and pure polyphenols to different food systems with a particular focus on
Insulin signalling
Energy Expenditure
Satiety
SummaryPhenolic Phytochemicals as functional ingredients represent an exciting & developing area of nutrition
Foods that can attenuate the postprandial glycaemic response may help to control BMI, blood glucose control and ultimately protect against the development of Diabetes …
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