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The glycemic index of pigmented potatoes is related to their polyphenol content

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Polyphenol extracts from coloured fruits and vegetables inhibit α-glucosidase in vitro, however it is not known whether this translates into an attenuation of blood glucose response in vivo. We examined this relationship in a GI study by feeding coloured potatoes to 9 healthy volunteers. We also examined the in vitro inhibitory activity of potato anthocyanin extracts on rat intestinal α-glucosidase. Potatoes (Purple Majesty; Red-Y38; Yukon Gold and Snowden) were fed with skin after cooking in a convection oven, using a random block design and 50 g available carbohydrate. Glucose was used as the standard and venous blood collected at 0, 15, 30, 45, 60, 90, 120 min. Areas under the curve (AUC) for glucose and insulin were calculated, and GI and Insulin Index derived. Neither AUC for blood glucose response nor insulin was significantly different among the various potatoes studied. Although the mean GI (±SE) values for the potato types varied (purple = 77.0 ± 9.0; red = 78.0 ± 14.0; yellow = 81.0 ± 16.0; and white = 93.0 ± 17.0), these differences were not significantly different. The mean (±SE) polyphenol content (mg GAE/100 g DW) was 234 ± 28; 190 ± 15; 108 ± 39; 82 ± 1 for purple, red, yellow and white potatoes, respectively. There was a significant inverse correlation between polyphenol content and GI of the potatoes (r = -0.825; p < 0.05; n = 4). In vitro, polyphenol extracts of red and purple potatoes inhibited α-glucosidase by 37.4 ± 2.2% and 28.7 ± 3.2%, respectively. The GI of coloured potatoes is significantly related to their polyphenol content, possibly mediated through an inhibitory effect of anthocyanins on intestinal α-glucosidase.
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The glycemic index of pigmented potatoes is
related to their polyphenol content
D. Dan Ramdath,*Emily Padhi, Aileen Hawke, Theva Sivaramalingam and Rong Tsao
Polyphenol extracts from coloured fruits and vegetables inhibit a-glucosidase in vitro, however it is not
known whether this translates into an attenuation of blood glucose response in vivo. We examined this
relationship in a GI study by feeding coloured potatoes to 9 healthy volunteers. We also examined the in
vitro inhibitory activity of potato anthocyanin extracts on rat intestinal a-glucosidase. Potatoes (Purple
Majesty; Red-Y38; Yukon Gold and Snowden) were fed with skin after cooking in a convection oven,
using a random block design and 50 g available carbohydrate. Glucose was used as the standard and
venous blood collected at 0, 15, 30, 45, 60, 90, 120 min. Areas under the curve (AUC) for glucose and
insulin were calculated, and GI and Insulin Index derived. Neither AUC for blood glucose response nor
insulin was signicantly dierent among the various potatoes studied. Although the mean GI (SE) values
for the potato types varied (purple ¼77.0 9.0; red ¼78.0 14.0; yellow ¼81.0 16.0; and white ¼
93.0 17.0), these dierences were not signicantly dierent. The mean (SE) polyphenol content
(mg GAE/100 g DW) was 234 28; 190 15; 108 39; 82 1 for purple, red, yellow and white
potatoes, respectively. There was a signicant inverse correlation between polyphenol content and GI of
the potatoes (r¼0.825; p< 0.05; n¼4). In vitro, polyphenol extracts of red and purple potatoes
inhibited a-glucosidase by 37.4 2.2% and 28.7 3.2%, respectively. The GI of coloured potatoes is
signicantly related to their polyphenol content, possibly mediated through an inhibitory eect of
anthocyanins on intestinal a-glucosidase.
Introduction
Type 2 diabetes mellitus (T2DM) is a signicant global health
problem, characterized by abnormal glucose tolerance and
insulin resistance, and is oen associated with signicant long
term complications, and poor quality of life.
1,2
T2DM is asso-
ciated with diets high in calories and reduced physical activity;
consequently many dietary interventions have been advocated
for the management and prevention of T2DM.
3
The glycemic
index (GI) of foods has been proposed as evidence based guid-
ance in choosing carbohydrate rich foods on the basis of their
post prandial blood glucose raising potential.
4,5
Potatoes have
been characterized as being a medium to high GI food,
although this varies among dierent varieties
6,7
and by cooking
and processing methods
810
as well as starch digestibility.
9,11
Potatoes are the third largest food crop worldwide following
rice and wheat, and as such play a signicant role in human
health.
12
Potatoes with pigmented esh are becoming more
readily available in the market place and there is growing
interest in their potential health benets. Pigmented red and
purple esh potatoes contain two to three times more
antioxidants than white-esh potatoes.
13,14
The antioxidant
properties of pigmented potatoes are accounted for by the
presence of polyphenols, specically anthocyanins, phenolic
acids and carotenoids.
13,15
Further, consumption of purple and
yellow pigmented potatoes has been associated with a reduction
in inammation and oxidative damage in healthy adult males
when compared to white potatoes.
16
Despite their nutritional
and antioxidant properties, potatoes have been implicated in
contributing to T2DM due to their higher GI values; however, the
GI of pigmented potatoes has not been previously determined.
Foods rich in polyphenols, especially anthocyanins and
condensed tannins, have been associated with reduced glyce-
mic response, with a negative correlation observed between
polyphenol content of leguminous foods and non-leguminous
cereals and blood glucose response.
17
Further, polyphenol-rich
extracts from fruits have also been shown to inhibit the activity
of a-glucosidase, the main enzyme responsible for intestinal
starch digestion.
18
The eect of polyphenol content on the
digestibility of starch in newer cultivars of pigmented potatoes
and blood glucose response has not been studied. We reasoned
that the GI of pigmented potatoes may be lower than that of
white potatoes and that this may be related to the inhibitory
eect of anthocyanins on intestinal a-glucosidase. Further, with
pigmented potatoes emerging in the market place with
increasing frequency, the availability of GI values would be
Guelph Food Research Centre, Agriculture and Agri-Food Canada, 93 Stone Road West,
Guelph, ON N1G 5C9, Canada. E-mail: dan.ramdath@agr.gc.ca; Fax: +1 226-217-
8181; Tel: +1 226-217-8082
Cite this: DOI: 10.1039/c3fo60395d
Received 6th September 2013
Accepted 25th January 2014
DOI: 10.1039/c3fo60395d
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benecial in making informed dietary choices. The objectives of
this study were to determine the GI values of commonly avail-
able pigmented Canadian potatoes, to dene the relationship
between potato polyphenol content and GI, and to assess the in
vitro inhibitory eect of crude anthocyanin extracts from
pigmented potatoes on intestinal a-glucosidase activity.
Methods
Potatoes
Potato cultivars of Purple Majesty with purple skin and esh,
Y38 with red skin and esh, Yukon Gold with white skin and
yellow esh, and Snowden with white skin and white esh, were
obtained as mature potatoes at fall harvest from the Elora
Research Station, University of Guelph (Elora, Ontario, Canada
43410N, 80260W) on a Conestoga silt loam soil in 2009.
Food analysis
Detailed proximate and dietary bre analysis was performed
commercially (Maxxam Analytics International Corporation,
Mississauga, ON, Canada) using standard AOAC methods for
total fat (AOAC 922.06), protein (AOAC 992.15), total dietary
bre (AOAC 985.29) and moisture (AACC 44-15A). Energy and
total carbohydrates were derived and available carbohydrate
was calculated as the dierence between total carbohydrate and
total dietary bre.
Test foods
Fresh whole potatoes were washed in tap water, air dried,
packaged into 50 g available carbohydrate portions and stored
at 20 C. On test days, the potatoes were quickly defrosted in a
microwave oven, cut into 2 cm
3
cubes and baked in a convection
oven for 40 min until sowhen prodded with a fork. Potatoes
were served with skin on, a pinch of salt and pepper and about 5
g of margarine, if desired. Flavourings remained constant for
each participant, for all test foods. The potatoes as well as the
standard glucose solution were served with 300 mL of water.
Participants consumed the foods within 15 minutes.
GI study
This study was conducted according to the guidelines set by the
Declaration of Helsinki and all procedures involving human
participants were approved by the Canadian Shield Ethics Review
Board. Written informed consent was obtained from all partici-
pants. The study protocol was based on the method of Wolever
et al. (1991),
19
was approved by the Canadian Shield Ethics
Review board and registered at http://www.clinicaltrials.gov
(#NCT01053793). The following exclusion criteria were applied:
BMI > 30 kg m
2
, history of drug abuse, pregnancy or lactation,
allergy to potatoes, and abnormal fasting glucose ($5.56 mmol
L
1
), and nine healthy Caucasian adults (3 males, 6 females)
were recruited. On the day prior to testing, participants were
asked to refrain from alcohol, intense physical activity and high
bre foods at dinner. On each study day participants arrived at
the human trial facility (Nutrasource Diagnostics Inc., Guelph,
ON, Canada) in a fasted state (12 h). On the rst visit participants
were given a 50 g standard glucose solution. At subsequent study
visits participants consumed one of the four potato varieties or a
second standard glucose solution in a randomized block design.
Before consumption of the test meal or standard a fasting blood
sample was obtained using an indwelling catheter and addi-
tional blood samples collected at 15, 30, 45, 60, 90, and 120 min
aer the rst bite was taken. Participants remained seated
quietly during the test period. Whole blood samples were
collected into lithium heparin tubes and an aliquot was stored at
80 C pending glucose analysis on a YSI model 2300 STAT
analyzer (Yellow Springs, OH), with fasting samples measured in
duplicate. The remainder of the whole blood was centrifuged to
obtain plasma which was stored at 80 C pending analysis for
insulin using a commercial ELISA kit and multi-level quality
control material (Invitrogen, CA, USA).
Plasma antioxidant status
The oxygen radical antioxidant assay (ORAC) and ferric
reducing antioxidant power (FRAP) assays were used to deter-
mine total antioxidant capacity of serum as outlined by Li
et al.
20,21
Polyphenol analysis
Total polyphenol content (TPC) of ground freeze dried potato
powders was determined in triplicate using an adapted 96-well
micro plate FolinCiocalteu method
20,21
and expressed as milli-
gram gallic acid equivalent (GAE)/100 g dry weight basis (mg
GAE/100 g DW). Crude anthocyanin rich extracts were prepared
from 50 g ground freeze dried potato powders that were double
extracted with 500 mL acidied methanol (85% MeOH: 14%
H
2
O: 1% HOAc) and partially puried using ash chromatog-
raphy (Isolera One, Biotage, Sweden, AB). Methanol was
removed by rotary evaporation and the resulting extracts were
freeze dried and stored at 20 C until use. Total anthocyanin
concentration (TAC) was determined in triplicate using a
modied pH dierential method
20,21
and expressed as mg cya-
nidanin-3-glucoside equivalent/100 g (mg CyGE/100 g DW). All
general purpose chemicals were of analytical or HPLC grade and
were purchased from Sigma-Aldrich Chemical Co. (St Lois, MO).
a-Glucosidase inhibition assay
Experiments were carried out with crude a-glucosidase from rat
intestinal powder (Sigma I1630: 25 mg mL
1
in 0.1 M phosphate
buer, pH 6.9) as previously outlined.
18
Anthocyanin extracts
were dissolved in buer and serial dilutions prepared. Acarbose
(Sigma A8980) was used as a positive control. The assay was
carried out in a 96-well microplate and contained: 100 mLof
extract, acarbose or buer and 100 mL of enzyme solution. The
reaction was initiated by the addition of 100 mL of enzyme
substrate (5 mM p-nitrophenyl a-D-glucopyranoside; Sigma
N1377), and monitored at 405 nm at 30 C for 1020 minutes.
Assays were performed in triplicate on three separate days for
each extract. The reaction rates of the assays with and without
extracts were compared, and the a-glucosidase inhibitory
activity determined.
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Data analysis
The incremental AUC for blood glucose response, excluding
area below fasting, was calculated for each potato tested by each
participant using the trapezoid method.
19
GI values were
derived by expressing the AUC as a percentage of the mean AUC
for the reference food; the mean of the resulting values for each
participant was used to determine the food GI. The incremental
area under the blood insulin response curve was calculated and
the insulin index (II) derived in the same manner as for GI
values. Data were entered into Excel, 2007 (MicrosoCorpora-
tion, Washington, USA), veried and then imported to STATA
23
(version 10.0, STATA Corporation, Texas, USA). Dierences in
AUC, II and glycemic index were compared by potato type and
time using two-way ANOVA, with post-hoc analysis when
applicable. Spearman rank correlation was used to determine
the relationship between potato GI and polyphenol content.
Dierences were considered statistically signicant at p< 0.05.
Results
Table 1 shows the nutritional composition of 50 g available
carbohydrate portions of the test meals. As eaten, the poly-
phenol content of purple and red pigmented potatoes were at
least twice as high as that of yellow and white potatoes,
respectively. Corresponding total anthocyanin (TAC) for purple
and red pigmented potato powders were 152 and 179 (mg CyGE/
100 g DW); no signicant amount of anthocyanin was detected
in the yellow and white potatoes.
Participants (3 males; 6 females) involved in the GI study
were all Caucasian with ages ranging from 23 to 36 years with a
mean (SE) BMI of 25.2 1.1 Kg m
2
and normal fasting blood
glucose levels (4.8 0.2 mmol L
1
). The mean blood glucose
AUC following consumption of purple, yellow, red, and white
potatoes and standard glucose solution were (mmol min L
1
):
90 17, 100 30, 101 26, 116 27 and 125 23, respectively.
One way repeat measures ANOVA revealed that among the
potatoes, blood glucose response at dierent time points was
similar, but this diered signicantly from the glucose standard
(Fig. 1). At 15 min all potato types showed signicantly lower
blood glucose values (p< 0.005) than the glucose standard;
however at 120 min white, red, and yellow potato types had
signicantly higher blood glucose values than the glucose
standard (p< 0.001).
The blood insulin response aer consumption of potatoes,
shown in Fig. 2, was similar to the glucose response curve with
insulin levels peaking around 45 min. One way ANOVA on ranks
indicated a signicant dierence in the blood insulin AUC
between the glucose standard and red potato (H¼10.2; df ¼4;
p¼0.039). However, there were no signicant dierences in the
blood insulin concentration between the glucose standard and
potato types at any of the time points. The insulin index (%) for
red, purple, white, and yellow potatoes were: 52 7; 76 10; 78
14 and 81 10, respectively; these were not signicantly
dierent by one-way ANOVA.
The mean (SE) glycemic index values were 77 9, 78 14,
81 16 and 93 17 for purple, red, yellow and white potatoes,
respectively (Table 1). Neither blood glucose AUC nor glycemic
index diered signicantly among the potato types when
assessed either by repeat measures ANOVA or by one way
ANOVA on ranks.
Plasma antioxidant status (Fig. 3A and B) as measured by
ORAC remained relatively unchanged following the consump-
tion of the dierent potatoes however, the pattern observed with
FRAP suggested a trend towards decreasing antioxidant status.
Table 1 Nutritional composition of test meals (per 50 g available carbohydrate)
Food
Weight
(g)
Energy
(KJ)
Fat
(g)
Protein
(g)
Total
CHO (g)
Fibre
(g)
Moisture
(%)
Anthocyanin
(mg CyGE)
a
Polyphenol
(mg, GAE)
b
Glycemic
index (%)
Purple potato (Purple
Majesty)
289.0 1020 0.3 6.3 53.8 3.8 78.5 16.4 1.5 145 17 77 9
Red potato (Y38) 375.9 1056 0.5 7.8 54.1 4.1 82.8 15.4 1.2 123 10 78 14
Yellow potato (Yukon
Gold)
267.4 1027 0.3 7.2 54.0 4.0 76.3 nd 68 25 81 16
White potato (Snowden) 274.4 1029 0.3 7.4 53.5 3.6 76.8 nd 52 19317
a
Total anthocyanin (milligram cyanidanin-3-glucoside equivalent/100 g dry weight (mg CyGE)/100gDW).
b
Total polyphenol (milligram gallic acid
equivalent/100 g dry weight (mg GAE/100 g DW)), nd ¼not detected.
Fig. 1 Blood glucose response elicited from dierent colour potatoes.
Values are means with standard errors represented by vertical bars.
Standard glucose ¼C; yellow potato ¼; white potato ¼B; purple
potato ¼A; red potato ¼:,*- at 15 min, mean blood glucose after
consumption of glucose standard signicantly dierent from all 4
potato types (p< 0.01). **- at 120 min, mean blood glucose after
consumption of glucose standard signicantly dierent from red (p¼
0.007), yellow (p¼0.013) and white potatoes (p¼0.001).
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Polyphenol
Overall, the highest polyphenol concentration was found in
purple potato, whereas the glycemic index of this potato was
lowest compare to the other potato varieties (Table 1). Ranked
correlation showed that there was a signicant inverse rela-
tionship between the total polyphenol content and glycemic
index among dierent coloured potatoes (r¼0.825; n¼4;
p< 0.05). Crude anthocyanin-rich extracts from red potato and
purple potato, at a concentration of 1.67 mg mL
1
, inhibited the
in vitro action of rat intestinal a-glucosidase by (mean and SE)
37.4 2.2% and 28.7 3.2%, respectively. The same concen-
tration of acarbose, a synthetic a-glucosidase inhibitor used to
manage postprandial blood glucose levels, resulted in 100%
inhibition.
Discussion
Potato consumption is signicant in many dierent cultures
globally
12
so it is important to provide evidence based guide-
lines on the choice of potatoes. Potatoes have long been regar-
ded as being a high GI food, but more recently the increasing
availability of potatoes with pigmented esh has generated
interest in their potential health benets. Pigmented potatoes
contain signicant amounts of antioxidant due to the presence
of anthocyanins,
14,15,24
and their consumption is associated with
a reduction in inammation and oxidative damage.
16
Given that
anthocyanin extracts from fruits have been shown to inhibit
intestinal a-glucosidase in vitro,
18
it was hypothesized that pig-
mented potatoes would have lower in vivo GI values compared
to white potatoes.
In the present study, consumption of the various pigmented
potatoes resulted in blood glucose AUC that were not signi-
cantly dierent. However, compared with the glucose standard
all potato varieties showed signicantly lower blood glucose
values 15 min aer consumption. At 120 min white, red, and
yellow potatoes had signicantly higher blood glucose values
than the glucose standard, indicating that the potatoes were
digested slower, as expected. Among the potatoes studied the
resulting GI values were not signicantly dierent. Importantly,
the potatoes used in this study had GI values ranging from mid-
high (purple) to very high (white). Variations in the GI of potatoes
have been accounted for by dierences in the starch fractions
and digestibility,
911
and by cooking and storage methods.
8,10,24
According to Foster-Powell et al. (2002),
25
dierences in GI
values of the same type of foods may be explained by method-
ological dierences in processing, in determining the digestible
carbohydrate content of the test foods and in GI testing, and
inherent botanical dierences. The varieties of potatoes used in
the present study had similar total dietary bre levels so their
digestible carbohydrate content was similar. The GI testing
method used in the present study is widely used and utilized key
Fig. 2 Insulin response elicited from dierent colour potatoes*values
are means with standard errors represented by vertical bars. Standard
glucose ¼C; yellow potato ¼; white potato ¼B; purple potato ¼
A; red potato ¼O,*blood insulin AUC between the glucose standard
and red potato is signicantly dierent (H¼10.2; df ¼4; p¼0.039).
Fig. 3 (A) Plasma ferric reducing antioxidant power (FRAP) values and
(B) oxygen radical absorbance capacity (ORAC) following consump-
tion of potatoes. Mean and SEM; n¼3.
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improvements in human GI studies as recommended by
Wolever et al. (2008).
26
Further, the GI values obtained in the
present study for Red, White and Yellow are similar to values
obtained for same-day cooked and eaten, peeled, boiled or
baked potatoes.
8,10
Most GI studies on potatoes have used boiling as the
preferred cooking method. In the present study frozen potatoes
were thawed via microwave, cooked with skin in a convection
oven and consumed immediately. Fernandes et al. (2005)
7
reported that the mean AUC elicited by day-cooked Russet
Burbank potatoes did not dier signicantly whether baked in a
microwave or conventional oven. In addition, Soh and Brand-
Miller (1999)
10
found no dierences in GIs when they compared
cooking methods (peeled and boiled; peeled, boiled and
mashed; peeled and microwaved; peeled and baked). However,
the eect of freezing whole potatoes and microwave thawing
must be considered since ice crystal formation during initial
freezing could have disrupted cells walls and physically separate
starch from amylases through shrinking of gelled starch gran-
ules and cell distortion.
27
On the other hand, microwave heating
increases hydration and consequently reverses retrogradation
of starch. Mulinacci et al.
24
have shown that microwave heating
of potatoes results in a higher level of resistant starch in both
pigmented and white varieties. In the present study there could
have been some resistant starch formation in the cooked
potatoes, although this would have occurred in all potato types.
It would have been ideal to use fresh potatoes in this study and
it is likely that their GI values would have been lower, given the
cell wall disruption and starch separation associated with
freezing. However, this approach would have led to variation in
the batch of potatoes studied.
A study on GI values for commercially available potatoes in
Great Britain also showed that there was no signicant dier-
ence in GI values between dierent potato types, although the
GI values ranged from 56 to 94.
6
There were no pigmented
potatoes in that study and the variation was accounted for by
dierences in the texture of the potato types: waxy texture
produced low GI, whereas oury potatoes had high GI values.
6
It
has been suggested that the latter could be partially explained
by an increased amylopectin content of the oury, more mature
potatoes.
10
Fernandes et al.
7
reported a GI of 89 for boiled red
potatoes and showed that precooking and reheating, or
consuming cold potatoes resulted in a lowering of the GI, which
was accounted for by an increased formation of resistant starch.
It is possible that the GI values obtained in the present study
may be even lower if the pigmented potatoes were consumed
cold or aer precooking and reheating. It has been suggested
that the glycemic responses to consumption of carbohydrate
foods is also inuenced by particle size and the presence of
other macronutrient components, including fat, protein and
dietary bre.
28
However, the role of bioactive minor food
components such as polyphenols, particularly anthocyanins, on
blood glucose response and glycemic index has not been
explored.
It is well known that anthocyanin-rich extracts from fruits
and vegetables exhibit varying but signicant in vitro inhibitory
activity towards a-glucosidase, the main enzyme responsible for
intestinal starch digestion.
18,22
However, few human studies
have explored the relationship between the polyphenol content
of foods and glycemic response in vivo. In a GI study that
examined various leguminous and non-leguminous foods,
Thompson et al.
17
reported a negative correlation between GI
and polyphenol content. Results from the present study show
that within a given food crop GI values are inversely related to
the polyphenol content. Further, results of in vitro studies show
that anthocyanin extracts from the pigmented potatoes display
signicant inhibition of a-glucosidase, and oers an explana-
tion for the lower blood glucose response and GI values
observed for pigmented potatoes. Many of these in vitro studies
have reported that cyanidin 3-glucoside is a potent inhibitor of
a-glucosidase.
17,29
In the present study, no attempt was made to
identify the individual anthocyanin(s) that may account for
a-glucosidase inhibition. However, Li et al.
21
have shown that
the major anthocyanins in Purple Majesty and Y38 varieties of
potatoes (used in the current study), were petunidin and
pelargonidin, respectively. As such, it is unlikely that the inhi-
bition of a-glucosidase by anthocyanin extracts from these
potatoes is due to cyanidin 3-glucoside.
Several studies have shown that purple potatoes contain
more total antioxidant capacity, total phenolics and total
anthocyanins content than yellow, and white potatoes.
13,15,24,30
Further, Kaspar et al.
16
have shown that consumption of purple
potatoes is associated with a reduction in inammation and
oxidative damage. In the present study, we found that there was
very little change in plasma ORAC and FRAP. This suggests that
the GI values obtained were independent of the antioxidant
eects of polyphenols. Kasper et al.
31
reported that although
consumers ranked the aroma and appearance of white and
yellow potatoes higher than purple there were no signicant
dierences in overall acceptance of the potato cultivars. It
appears that consumers may be willing to consume pigmented
potatoes, which are perceived to be benecial to health.
31
Taken
together with the lower GI values, the available evidence
suggests that pigmented potatoes (purple and red) may be
healthier choices than white potatoes. These ndings could
lead to greater awareness of consumers and breeders to
increase the availability and usage of pigmented potatoes.
Conclusion
The GI values derived for the potatoes studied could be used to
guide choices of potatoes in order to lower the overall GI and
glycemic load of the diet. Further, with pigmented potatoes
emerging in the market place with increasing frequency the
availability of GI values would be benecial in making informed
dietary choices. Among the four potatoes studied, there was a
highly signicant inverse correlation between polyphenol
content and in vivo GI suggesting a possible inhibitory eect on
intestinal a-glucosidase. Compared to white potatoes, antho-
cyanin rich extracts from the pigmented potatoes displayed
moderate inhibitory activity towards intestinal a-glucosidase in
vitro. Further research is necessary to identify the mechanism
by which polyphenol rich starchy foods inuence blood glucose
response.
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Conict of interest statement and
contributions
All authors declare no conict of interest. DDR conceptualized
the study, managed the human trial, analyzed the data and
prepared the nal manuscript. AW, EP contributed to the
human trial, laboratory analyses and data analysis; TS assisted
with data analysis and manuscript preparation. RT oversaw
analyses of polyphenols and contributed to the nal
manuscript.
Abbreviations
GI Glycemic index
AUC Area under the curve
II Insulin index
GAE Gallic acid equivalent
TAC Total anthocyanin
CyGE Cyanidanin-3-glucoside equivalent.
Acknowledgements
The authors thank Professors Al Sullivan and Mary Ruth
McDonald of the Department of Plant Agriculture, University of
Guelph for providing the potato samples, Dr Ronghua Liu for
assistance with polyphenol, anthocyanin and antioxidant
analysis, and the NDI staand volunteers for their involvement
in the human trial. This work was supported in part by the
A-base research program of Agriculture & Agri-Food Canada
(RBPI #1343 and #109).
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... Pigmented red-and purple-flesh potatoes contain two to three times more antioxidants than white-flesh potatoes. The antioxidant properties of pigmented potatoes are accounted for by the presence of polyphenols, specifically anthocyanins, phenolic acids, and carotenoids [67]. Potato peel and neighboring tissues also contain about 50% of the polyphenols, while its amount slowly and gradually decreases towards the center of the potato tubers. ...
... The intake of purple-fleshed potatoes may prevent diabetes by improving serum insulin levels as was shown in diabetic rates [91]. A study evaluated the GI of white, yellow, red, and purple potatoes in healthy adults: the GI of red potatoes was 78, purple potatoes were 77, yellow potatoes were 81, while white potatoes were recorded as 93 [67]. The polyphenols in red potatoes were 190 mg/100 g DW, in purple potatoes were 234 mg/100 g DW, in yellow potatoes were 108 mg/100 g DW, while in white potatoes were 82 mg/100 g DW. ...
... The polyphenols in red potatoes were 190 mg/100 g DW, in purple potatoes were 234 mg/100 g DW, in yellow potatoes were 108 mg/100 g DW, while in white potatoes were 82 mg/100 g DW. These findings suggest that colored potatoes with high polyphenols have low values of GI which is basically due to the inhibition of α-glycosidase with the help of anthocyanins [67]. Additionally, highly pigmented potatoes tend to reduce glucose responses and GI values compared to white or yellow varieties [23,67]. ...
Article
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Polyphenol is one of the most essential phytochemicals with various health benefits. Potato (Solanum tuberosum L.) is known as a potential source of polyphenols, and also has health benefits in which phenolic acids, such as chlorogenic, ferulic acid, caffeic acid, and flavonoids, such as anthocyanins, sustainably play the most significant role. Almost every polyphenol contributes to various biological activities. In this review, we collected comprehensive information concerning the diversity of polyphenols in potatoes, and the effects of post-harvest processing and different cooking methods on the bioavailability of polyphenols. To achieve maximum health benefits, the selection of potato cultivars is necessary by choosing their colors, but various cooking methods are also very important in obtaining the maximum concentration of polyphenolic compounds. The health properties including major biological activities of polyphenols, such as antioxidant activity, anticarcinogenic activity, anti-inflammatory activity, anti-obesity activity, and antidiabetic activity, have also been summarized. All these biological activities of polyphenols in potatoes might be helpful for breeders in the design of new varieties with many health benefits, and are expected to play a vital role in both pharmaceutical and nutraceutical industries.
... Ramdath et al. studied the glycemic indices of purple, red, yellow, and white potato varieties, and no statistically significant differences were found. However, a significant inverse correlation between the glycemic indices and polyphenol content was found (Ramdath et al., 2014). ...
... An acute dose (50 g of available carbohydrates, 290−380 g of potato) of oven-baked purple (cultivar Purple Majesty) and red potatoes (cultivar Y38), with 16 and 15 mg/100 g DW of anthocyanins, decreased the postprandial glucose of healthy volunteers (n = 9) 15 min after the intake compared to a control dose of glucose which had no effect on AUC120 min or insulin (Ramdath et al., 2014). Another study in which healthy volunteers (n = 13) consumed a meal of 350 g steam-cooked and mashed purple potatoes (140 mg of anthocyanins and 71 g of available carbohydrates) showed that purple potatoes decrease postprandial blood glucose at 40 min and iAUC of insulin (120 and 240 min) (Linderborg et al., 2016). ...
... However, contradictory results exist (Garcia-Alonso et al., 2009;Jin et al., 2011;Mathison et al., 2014). Considering acylated anthocyanins, a meal of purple potatoes did not increase the plasma antioxidant capacity of healthy volunteers (Moser et al., 2018;Ramdath et al., 2014). A meal of purple potatoes raised the plasma antioxidant capacity in a mixed study population of normal weight (n = 5), overweight (n = 2), and obese (n = 1) volunteers first at 30 min and then at 2 h, and further increased it toward the last sampling point, from 4 to 8 h (Vinson et al., 2012). ...
Article
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Anthocyanins, the natural red and purple colorants of berries, fruits, vegetables, and tubers, improve carbohydrate metabolism and decrease the risk factors of metabolic disorders, but their industrial use is limited by their chemical instability. Acylation of the glycosyl moieties of anthocyanins, however, changes the chemical properties of anthocyanins and provides enhanced stability. Thus, acylated anthocyanins are more usable as natural colorants and bioactive components of innovative functional foods. Acylated anthocyanins are common in pigmented vegetables and tubers, the consumption of which has the potential to increase the intake of health-promoting anthocyanins as part of the daily diet. For the first time, this review presents the current findings on bioavailability, absorption, metabolism, and health effects of acylated anthocyanins with comparison to more extensively investigated nonacylated anthocyanins. The structural differences between nonacylated and acylated anthocyanins lead to enhanced color stability, altered absorption, bioavailability, in vivo stability, and colonic degradation. The impact of phenolic metabolites and their potential health effects regardless of the low bioavailability of the parent anthocyanins as such is discussed. Here, purple-fleshed potatoes are presented as a globally available, eco-friendly model food rich in acylated anthocyanins, which further highlights the industrial possibilities and nutritional relevance of acylated anthocyanins. This work supports the academic community and industry in food research and development by reviewing the current literature and highlighting gaps of knowledge.
... In total, the meta-analysis involved fifty-seven articles, as exhibited in Figure 1. According to the Cochrane Collaboration tool, eleven trials [6,24,29,32,33,37,38,42,48,51,54] were categorized as being at a low risk of bias, while forty-four were categorized as unclear [17,[19][20][21][22][23]25,27,28,30,31,[34][35][36][39][40][41][43][44][45][46][47]49,50,52,53,[55][56][57][58][59][60][61][62], and two were categorized as being at a high risk of bias [18,26]. Details about the risk of bias are supplied in Figures 2 and 3. ...
... Fifty-seven studies, involving 936 participants, were published from 2002 to 2019. Twenty-six studies [9][10][11][12]17,18,20,21,26,31,35,39,[43][44][45][46][47]49,[54][55][56][57][59][60][61][62] used an in vitro experiment, while thirty-two studies involved in vivo experiments. Only one study used both in vitro and in vivo data experiments [11]. ...
... Among fifty-seven included studies, forty-eight were selected for discussion of the relationship between chemical properties and GI value . The remaining studies were used for the selection of low-GI carbohydrate-based foods [55][56][57][58][59][60][61][62]. All studies reported changes in glycemic index, four studies [7,[17][18][19] reported changes in amylose content to GI, ten studies [9][10][11][12][13][20][21][22][23][24] reported changes in resistant starch (RS) content to GI, fifteen studies reported a change in dietary fibre content to GI, fifteen studies reported a change in fat content to GI, fifteen studies reported a change in protein content to GI, twelve studies reported a change in phenol content to GI, ten studies reported a change in flavonoid content to GI, five studies reported a change in cereal type to GI, six studies reported a change in tuber type to GI, two studies reported a change in fruit type to GI, and four studies reported a change in legume type to GI. Detailed characteristics of eligible studies are presented in Tables 2 and 3. Thiranusornkij et al. 2019 [12] Odenigbo et al. 2012 [24] Ek et al. 2013 [45] Hidayat et al. 2017 [46] Singh et al. 2011 [47] Kumar et al. 2019 [10] Srikaeo and Sangkhiaw 2014 [11] Darandakumbura et al. 2013 [14] Ayerdi et al. 2005 [13] Oboh and Ogbebor 2010 [48] Vahini et al. ...
Article
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The chemical properties that serve as major determinants for the glycemic index (GI) of starchy food and recommended low-GI, carbohydrate-based foods have remained enigmatic. This present work performed a systematic assessment of linkages between chemical properties of foods and GI, and selected low-GI starchy foods. The data were sourced from literature published in various scientific journals. In total, 57 relevant studies and 936 data points were integrated into a database. Both in vitro and in vivo studies on GI values were included. The database was subsequently subjected to a meta-analysis. Meta-analysis from in vitro studies revealed that the two significant factors responsible for the GI of starchy foods were resistant starch and phenolic content (respectively, standardized mean difference (SMD): −2.52, 95% confidence interval (95%CI): −3.29 to −1.75, p (p-value) < 0.001; SMD: −0.72, 95%CI: −1.26 to −0.17, p = 0.005), while the lowest-GI crop type was legumes. Subgroup analysis restricted to the crop species with significant low GI found two crops, i.e., sorghum (SMD: −0.69, 95%CI: −2.33 to 0.96, p < 0.001) and red kidney bean (SMD: −0.39, 95%CI: −2.37 to 1.59, p = 0.001). Meta-analysis from in vivo studies revealed that the two significant factors responsible for the GI of starchy foods were flavonoid and phenolic content (respectively, SMD: −0.67, 95%CI: −0.87 to −0.47, p < 0.001; SMD: −0.63, 95%CI: −1.15 to −0.11, p = 0.009), while the lowest-GI crop type was fruit (banana). In conclusion, resistant starch and phenolic content may have a desirable impact on the GI of starchy food, while sorghum and red kidney bean are found to have low GI.
... Though potatoes are full of antioxidants and are a nutritious food, worldwide people are concerned with their role in diabetes type-2 development due to the high glycemic index of potatoes. [1] Potatoes are generally consumed in boiled, microwaved, and fried forms. The method of processing alters the composition as well as the nutritional quality of the food. ...
Article
The study was carried out with the objective to estimate the resistant starch, amylose and sugar concentrations as affected by cooking methods (boiling, microwave cooking and pressure cooking) and storage conditions (-20, 4 and 12°C) in the tuber of Indian cultivars viz. Kufri Pukhraj and Kufri Chipsona-1. There was a significant decrease in starch content of Kufri Pukhraj and a non-significant decrease in Kufri Chipsona 1 with a concomitant significant increase in reducing sugars and sucrose concentrations in potatoes cooked by different methods. Storage of microwave cooked tubers at 4°C for 48 h resulted in a 4–6% reduction in starch content with a concomitant increase in reducing sugars (66-109%) and sucrose (16-18%) in the two cultivars. Increase in RS content at -20°C, 4°C and 12°C after 48h was 14, 21 and 27% after microwaving, 12, 25 and 23% after boiling and 13, 15 and 20%, respectively after pressure cooking. Amylose showed the highest positive correlation with resistant starch at 4°C temperature (R = 0.756) and 12h storage duration (R = 0.924) The study revealed that storage of microwaved potatoes at 12°C for 48h increased the resistant starch concentration to a higher extent, therefore, these cooking and storage conditions may be used by potato consumers. For estimation of glycemic index, live human subjects are required which is a difficult task and beyond the reach of general researchers. The study showed that the resistant starch and amylose content being inversely related to the glycemic index can be used to estimate the indirect glycemic index of potatoes. This article is protected by copyright. All rights reserved
... 22 Not to forget that potatoes have a high glycaemic index which increases the glucose level in the bloodstreams. 23 The glycaemic index of glucose is taken to be 100. So, the GI value of potatoes generally ranges from 53-111 as compared to white potatoes which typically show lower values in the index. ...
... Polyphenols are known to inhibit α-glucosidase, an enzyme present in the brush border of the small intestine and are involved in the release of glucose from more complex carbohydrates. To establish the relationship between polyphenols, GI, and α-glucosidase, Ramdath et al. (2014) evaluated GI of white and colored potatoes in healthy adults. GI of white-fleshed potatoes was around 93, yellow was 81, while in red and purple-fleshed potatoes GI were 78 and 77, respectively. ...
Chapter
Potatoes are widely consumed and are a highly popular food due to their preparation in many ways such as boiled, microwaved, fried, roasted, dehydrated, etc. Methods of processing and storage are known to affect its nutritional quality. Glycemic index of potato is affected by various factors, which include the genetic makeup of variety, amylose content, type and ratio of starches, cooking method, and the presence of other ingredients consumed with them including fiber, fat, and protein. Potatoes contain three types of starches, i.e. rapidly digestible starch, slowly digestible starch, and resistant starch. These starches affect blood glucose levels to different extents and hence the glycemic index. Processing method significantly affects the concentration of these starch types. Potato resistant starch has attracted the attention of nutritionists due to its various health benefits. Potato contains resistant starch type III in most cooked forms. Potato carbohydrates are affected by factors including cultivation practices, temperatures during crop growth, storage durations and temperatures, and processing. Various biochemical procedures are available to evaluate potato carbohydrates. This chapter deals with the types of starches present in potato, effect of cultivation practices, processing and storage on carbohydrates, methods used for evaluation, glycemic index, and genetic modifications carried out to alter the structure and function of potato carbohydrates.
... As the study was designed to observe the impact of preload GI on acute postprandial GR and satiety, we attempted to eliminate as much confounders as possible, including the protein, fat, dietary fiber, and phytochemical [33][34][35][36] contents of the test meals. In light of the fact that potato foods could either be a good source of resistant starch or a food high in rapid digest starch, depending on the cooking treatment [13], we successfully manipulated the glycemic characteristics (either a high GI or a medium GI food) of potato samples by modifying the microwave treatment while keeping the nutrient composition unchanged. ...
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This study investigated the preload effect of the medium and high glycemic index (GI) potato, as well as the combination of partially hydrolyzed guar gum (HG) and potato, when ingested prior to a rice meal, on the iso-carbohydrate basis. In a randomized crossover trial, 17 healthy female subjects consumed (1) rice; (2) co-ingestion of highly cooked potato (HP), and rice (HP + R); (3) co-ingestion of minimally cooked potato (MP) and rice (MP + R); (4) preload HP prior to rice meal (PHP + R); (5) preload MP prior to rice meal (PMP + R); (6) co-ingestion of partially hydrolyzed guar gum (HG), HP and rice (HG + HP + R); (7) preload HG prior to co-ingestion of HP and rice (PHG + HP + R); (8) co-preload of HG and HP prior to rice (PHG + PHP + R); and (9) preload of HP prior to co-ingestion of HG and rice (PHP + HG + R). Postprandial glycemic response (GR) tests and subjective satiety tests were conducted for each test food. Cooked potato as a preload to a rice meal could significantly cut the acute postprandial glycemic excursion by around 1.0 mmol/L, irrespective of the GI of the preload. Co-preload of partial hydrolyzed guar gum and highly cooked potato (PHG + PHP + R) resulted in improved acute GR in terms of peak glucose value and glycemic excursion compared with either HG preload or HP preload. All the meals with preload showed comparable or improved self-reported satiety. Within an equicarbohydrate exchange framework, both high-GI and medium-GI potato preload decreased the postprandial glycemic excursion in young healthy female subjects. The combination of HG and HP as double preload resulted in better GR than both single HG or HP preload did.
Article
Potatoes (Solanum tuberosum L.) are one of the most valuable agricultural crops, and the flesh of these tubers provides various classes of healthy compounds important for human nutrition. This work presents the results of a joint analysis of different chemical classes of compounds which provided insights on the metabolic characterization of pigmented and non-pigmented potato varieties collected from Italy. The identification of common or individual metabolic characteristics across the omic datasets (antioxidants, total polyphenolic content, polyphenols, and sugars) is conducted by Joint and Individual Variation Explained (JIVE), a data fusion multivariate approach. The common part of the multivariate model allowed the separation between non-pigmented and pigmented samples. Polyphenolic compounds were mainly responsible for the separation between purple-fleshed and red-skinned potatoes. An additional detailed analysis of the anthocyanin composition, including the acylated anthocyanins, allowed to pinpoint the diversities between the pigmented potato groups. Furthermore, the presence of an appreciable amount of hydroxycinnamic acids and anthocyanins in the purple-fleshed varieties, which are also characterized by a lower content of sugars, is found. Our results provide scientific evidence for the promotion of promising potato cultivars, which are characterized by a remarkable amount of various health benefit compounds.
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Potatoes are one of the main sources of carbohydrates in human diet, however they have a high glycaemic index (GI). Hence, developing new agricultural and industrial strategies to produce low GI potatoes represents a health priority to prevent obesity and related diseases. In this work, we investigated whether treatments of potato plants with elicitors of plant defence responses can lead to a reduction of tuber starch availability and digestibility, through the induction of cell wall remodelling and stiffening. Treatments with phosphites (KPhi) and borate were performed, as they are known to activate plant defence responses that cause modifications in the architecture and composition of the plant cell wall. Data of suberin autofluorescence demonstrated that potato plants grown in a nutrition medium supplemented with KPhi and borate produced tubers with a thicker periderm, while pectin staining demonstrated that KPhi treatment induced a reinforcement of the wall of storage parenchyma cells. Both compounds elicited the production of H2O2, which is usually involved in cell-wall remodelling and stiffening reactions while only KPhi caused an increase of the total content of phenolic compounds. A two-phase digestion in vitro assay showed that treatment with KPhi determined a significant decrease of the starch hydrolysis rate in potato tubers. This work highlights the ability of cell wall architecture in modulating starch accessibility to digestive enzymes, paving the way for new agronomic practices to produce low GI index potatoes.
Chapter
The intended end uses of new cultivars determine the quality criteria that need to be added as breeding objectives to yield in the production environments. Nutritional value will be important for the potato as a staple food; cooking quality, texture, taste and flavour will be important for the potato as a vegetable sold for cash; processing quality will be defined by the manufacturers of French fries, chips (crisps) and other processed products and the composition of the potato starch will determine its value for different uses in the starch industry. This chapter considers the challenges of translating these breeding objectives into selection criteria and methods of measurement for use on the tubers from assessment plots and yield trials, both immediately after harvest and after storage. Tuber appearance and freedom from internal defects are also selection criteria. Mineral and vitamin biofortification, beneficial phytochemicals, steroidal glycoalkaloids and acrylamide formation are also considered.
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Pigmented potato cultivars were ranked by a consumer panel for overall acceptance, and acceptance of aroma, appearance, and flavor. Potatoes were analyzed for total phenolics, anthocyanins and carotenoids. Concentrations of total phenolics in yellow and purple potato cultivars were 2-fold greater (P P P
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Potatoes regarding their consumption are a significant antioxidant source in human nutrition. The main potato an - tioxidants are polyphenols, ascorbic acid, carotenoids, tocopherols, α-lipoic acid, and selenium. The most contained polyphenolic antioxidants in potatoes are L-tyrosine, caffeic acid, scopolin, chlorogenic and cryptochlorogenic acid and ferulic acid. In red and purple potatoes are in addition contained acylated anthocyanins and pigmented potatoes display two to three times higher antioxidant potential in comparison with white-flesh potato. Red potato tubers con - tain glycosides of pelargonidin and peonidin, purple potatoes glycosides of malvidin and petunidin. New red and purple flesh potato varieties are breeded for their use in food and in the non-food industry. Anthocyanins of potatoes are also useful in the protection against potato blight.
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Three major studies have made a brave attempt to quantify mortality and disability worldwide from 289 diseases and their sequelae. Striking data are presented that confirm the rising tide of noncommunicable diseases, particularly diabetes mellitus. The predictions for diabetes mellitus are, however, probably underestimated owing to underdiagnosis and under-reporting. Alberti, K. G. M. M. & Zimmet, P. Nat. Rev. Endocrinol. 9, 258-260 (2013); published online 12 March 2013; doi:10.1038/nrendo.2013.54
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The aim of the research was to determine contributions of moisture and carbohydrate digestibility to the glycemic impact of potatoes. Five potato cultivars, including low dry matter, low glycemic index ‘Almera’ and high dry matter ‘Moonlight’ were boiled and subsamples taken for dry matter and simulated digestion in vitro. Digestion-time profiles of the different cultivars were of very similar shape, although the quantity of carbohydrate released differed between cultivars. ‘Moonlight’ gave the highest rapidly available (20 min) carbohydrate (16.2 ± 0.9 g/100 g) and ‘Almera’ the lowest (11.1 ± 2 g/100 g). The cultivars also differed in dry matter content, ‘Almera’ having the lowest (14.4 ± 0.4%) and ‘Moonlight’ the highest (23.3 ± 0.5%). However, adjusted to an equivalent 20% dry matter, digestion profiles of all cultivars were almost identical. We conclude that values reflecting solely the digestibility of carbohydrate in potatoes cannot be accurately or easily used by consumers to guide intakes of potato in terms of customarily consumed portions, for blood glucose management. Taking into account water content and serving size, glycemic impact per standard serving of potato was moderate compared with other starchy foods.
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Twelve highly pigmented (red or purple) vegetables (carrots, cabbage, cauliflower, potatoes, onions, asparagus and eggplant) were investigated for their total anthocyanin contents (TAC) and compositions of the individual anthocyanins and anthocyanidins by UPLC and LC–DAD–ESI–MS, and their antioxidant activities by DPPH, FRAP (ferric reducing antioxidant power) and ORAC (oxygen radical absorption capacity) assays. While a total of 26 anthocyanins were identified, the main aglycones were only found to be limited to 4 anthocyanidins (cyanidin, petunidin, pelargonidin and delphinidin). The TAC ranged from 0.08 to 2.01 mg Cyanidin-3-glucoside (C3G)/g DW and the total phenolic contents (TPC) was from 1.30 to 2.19 mg GAE/g DW suggesting that anthocyanins were the main phenolics in certain vegetables but not others. DPPH radical scavenging activities were 54.91–81.94%, FRAP values 10.00–70.07 μmol AAE/g DW and ORAC values were 3.74–189.32 μmol TE/g DW. The two cruciferous vegetables (purple cauliflower and cabbage) showed the highest TPC, TAC, DPPH and FRAP values, and the onions the lowest. The antioxidant activities in the DPPH and FRAP assays correlated well with the TPC and TAC, but ORAC did not. Results of this study are comparable and provide a rapid and effective method for the identification and quantification of all major anthocyanidins and their glycosides (anthocyanins), and how they might contribute to the antioxidant activity, therefore important information in developing anthocyanin-rich nutraceuticals and functional foods.
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Pigmented potato (Solanum tuberosum L.) varieties are a rich source of anthocyanins, in particular acylated derivatives. From potato cultivars “Hermanns Blaue”, “Highland Burgundy Red”, “Shetland Black”, and “Vitelotte” the major anthocyanins were isolated and characterised. Sliced potatoes were blanched to minimise enzymatic reactions which cause degradation of anthocyanins.By means of solid phase extraction, countercurrent chromatography and preparative HPLC, it was possible to separate coumaric acid derivatives (i.e. 3-p-coumaroylrutinoside-5-glucosides of petunidin, pelargonidin, peonidin and malvidin) from non-acylated anthocyanins as well as chlorogenic acids. Identity of the isolated compounds was determined by combination of HPLC-DAD and LC-ESI-MS2 measurements.Petunidin derivatives were detected in all varieties except Highland Burgundy Red, where pelargonidin was found to be the only anthocyanidin. Malvidin was the predominant aglycon of the variety Vitelotte. Of the four selected cultivars, Shetland Black was the only one containing minor amounts of peonidin derivatives.
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Potato (Solanum tuberosum L.) is one of the most important food crops in the world and provides essential nutrients. With an aim to develop potato varieties for functional food or nutraceutial applications, we have conducted metabolomic profiling, total phenolics, chlorogenic acid, anthocyanins, and glycoalkaloids analyses on 20 selected potato clones within the Canadian potato breeding program of Agriculture and Agri-Food Canada. Pigmented potatoes in general contain higher levels of phenolic components, including chlorogenic acid and anthocyanins. Levels of phenolics were retained with granulation processing of pigmented potato tubers, but glycoalkaloids were significantly reduced with granulation. The pigmented potatoes also have higher antioxidant activity reaching up to 35% of that for berries, measured as their potency in scavenging DPPH radicals. Extracts of the 20 potato clones (peel, tuber, and granule) were also evaluated for in vitro effects on liver LDL cholesterol uptake and protection of cortical neurons from cell death caused by oxygen glucose deprivation (OGD). These potato extracts in general showed mild activity in enhancing LDL cholesterol uptake in liver HepG2 cells, and also protected cortical neurons against OGD induced cell death, with extracts from granules of six of the potato clones showing significant neuroprotective effects. The bioactive components are not dependent on pigmentation of potato clones. These novel bioactivities identified in potatoes warrant in-depth investigations in the future. Taken together, our results provide further evidence for the enhanced health beneficial components in potato.
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Background: There is evidence that reducing blood glucose concentrations, inducing weight loss, and improving the lipid profile reduces cardiovascular risk in people with type 2 diabetes. Objective: We assessed the effect of various diets on glycemic control, lipids, and weight loss. Design: We conducted searches of PubMed, Embase, and Google Scholar to August 2011. We included randomized controlled trials (RCTs) with interventions that lasted ≥6 mo that compared low-carbohydrate, vegetarian, vegan, low–glycemic index (GI), high-fiber, Mediterranean, and high-protein diets with control diets including low-fat, high-GI, American Diabetes Association, European Association for the Study of Diabetes, and low-protein diets. Results: A total of 20 RCTs were included (n = 3073 included in final analyses across 3460 randomly assigned individuals). The low-carbohydrate, low-GI, Mediterranean, and high-protein diets all led to a greater improvement in glycemic control [glycated hemoglobin reductions of −0.12% (P = 0.04), −0.14% (P = 0.008), −0.47% (P < 0.00001), and −0.28% (P < 0.00001), respectively] compared with their respective control diets, with the largest effect size seen in the Mediterranean diet. Low-carbohydrate and Mediterranean diets led to greater weight loss [−0.69 kg (P = 0.21) and −1.84 kg (P < 0.00001), respectively], with an increase in HDL seen in all diets except the high-protein diet. Conclusion: Low-carbohydrate, low-GI, Mediterranean, and high-protein diets are effective in improving various markers of cardiovascular risk in people with diabetes and should be considered in the overall strategy of diabetes management.
Article
Background: Legumes, including beans, chickpeas, and lentils, are among the lowest glycemic index (GI) foods and have been recommended in national diabetes mellitus (DM) guidelines. Yet, to our knowledge, they have never been used specifically to lower the GI of the diet. We have therefore undertaken a study of low-GI foods in type 2 DM with a focus on legumes in the intervention. Methods: A total of 121 participants with type 2 DM were randomized to either a low-GI legume diet that encouraged participants to increase legume intake by at least 1 cup per day, or to increase insoluble fiber by consumption of whole wheat products, for 3 months. The primary outcome was change in hemoglobin A1c (HbA1c) values with calculated coronary heart disease (CHD) risk score as a secondary outcome. Results: The low-GI legume diet reduced HbA1c values by -0.5% (95% CI, -0.6% to -0.4%) and the high wheat fiber diet reduced HbA1c values by -0.3% (95% CI, -0.4% to -0.2%). The relative reduction in HbA1c values after the low-GI legume diet was greater than after the high wheat fiber diet by -0.2% (95% CI, -0.3% to -0.1%; P < .001). The respective CHD risk reduction on the low-GI legume diet was -0.8% (95% CI, -1.4% to -0.3%; P = .003), largely owing to a greater relative reduction in systolic blood pressure on the low-GI legume diet compared with the high wheat fiber diet (-4.5 mm Hg; 95% CI, -7.0 to -2.1 mm Hg; P < .001). Conclusion: Incorporation of legumes as part of a low-GI diet improved both glycemic control and reduced calculated CHD risk score in type 2 DM.