Influence of cooking methods on bioactive compounds in beetroot

Abstract

Beetroot is rich in bioactive compounds that may provide health benefits. However, vegetable tissues are physically and chemically damaged by cooking, causing major changes to compounds in cell membranes. The current study aimed to evaluate the influence of several cooking methods on bioactive compounds in beetroot. Four heat treatments were carried out: steam cooking, pressure cooking, baking in an oven, and boiling in water. Beets were matched in uniformity of size, color, and absence of defects. They were washed thoroughly in running water to remove dirt. Next, one of the four cooking methods was applied. After cooking, beets were peeled by hand. Analysis was carried out on both uncooked and cooked beets to evaluate antioxidant activity, content of phenolic compounds, pigments, flavonoids, and betalains. The experiment was completely randomized design (CRD) and carried out in triplicate. Data were subjected to analysis of variance (F test, p < 0.05) and mean values compared by Tukey test at 5% probability. There was no change in antioxidant activity or total phenolic and anthocyanin content by any of the cooking methods compared to that in raw beetroots. However, pressure-cooking resulted in lower carotenoid levels compared to that in raw beet. Furthermore, flavonoid and betalain content decreased by all the cooking methods.

Full text

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Semina: Ciências Agrárias, Londrina, v. 38, n. 3, p. 1295-1302, maio/jun. 2017
Received: Aug. 28, 2016 - Approved: Jan. 30, 2017
DOI: 10.5433/1679-0359.2017v38n3p1295
Inuence of cooking methods on bioactive compounds in beetroot
Compostos bioativos em beterrabas submetidas a
diversas formas de cozimento
Juliana Arruda Ramos1*; Karina Aparecida Furlaneto1;
Veridiana Zocoler de Mendonça1; Flávia Aparecida de Carvalho Mariano-Nasser2;
Giovanna Alencar Lundgren3; Erika Fujita4; Rogério Lopes Vieites5
Abstract
Beetroot is rich in bioactive compounds that may provide health benets. However, vegetable tissues
are physically and chemically damaged by cooking, causing major changes to compounds in cell
membranes. The current study aimed to evaluate the inuence of several cooking methods on bioactive
compounds in beetroot. Four heat treatments were carried out: steam cooking, pressure cooking, baking
in an oven, and boiling in water. Beets were matched in uniformity of size, color, and absence of defects.
They were washed thoroughly in running water to remove dirt. Next, one of the four cooking methods
was applied. After cooking, beets were peeled by hand. Analysis was carried out on both uncooked and
cooked beets to evaluate antioxidant activity, content of phenolic compounds, pigments, avonoids, and
betalains. The experiment was completely randomized design (CRD) and carried out in triplicate. Data
were subjected to analysis of variance (F test, p < 0.05) and mean values compared by Tukey test at
5% probability. There was no change in antioxidant activity or total phenolic and anthocyanin content
by any of the cooking methods compared to that in raw beetroots. However, pressure-cooking resulted
in lower carotenoid levels compared to that in raw beet. Furthermore, avonoid and betalain content
decreased by all the cooking methods.
Key words: Antioxidants. Anthocyanins. Betalains. Beta vulgaris. Carotenoids. Flavonoids.
Resumo
A beterraba é rica em compostos bioativos, que possuem efeitos benécos para o organismo humano.
Porém o cozimento dos tecidos vegetais altera física e quimicamente as propriedades da parede celular,
afetando o teor desses compostos. O objetivo do trabalho foi avaliar os compostos bioativos em beterrabas
in natura e submetidas a diversas formas de cozimento. Foram realizados quatro tratamentos térmicos,
sendo eles cocção a vapor, cocção na panela de pressão, no forno e na água em imersão. As beterrabas
foram selecionadas visando a homogeneização do lote quanto ao tamanho, cor e ausência de injúrias e
defeitos. Foram lavadas em água corrente para tirar as sujidades. Em seguida, levadas às quatro formas
de cocção. Após os tratamentos térmicos, foram descascadas manualmente. As análises realizadas
nas beterrabas in natura e cozidas foram a atividade antioxidante, teor de compostos fenólicos totais,
1 Discentes, Programa de Pós-Graduação em Agronomia- Energia na Agricultura, Universidade Estadual Paulista, UNESP,
Faculdade de Ciências Agronômicas, Botucatu, SP, Brasil. E-mail: ju.a.ramos@globo.com; karina_furlaneto@globo.com;
veridianazm@yahoo.com.br
2 Discente de Pós-Doutorado, Programa de Pós-Graduação em Agronomia, Horticultura, UNESP, Faculdade de Ciências
Agronômicas, Botucatu, SP, Brasil. E-mail: aviamariano1@hotmail.com
3 Discente, Programa de Pós-Graduação em Agronomia, Horticultura, UNESP, Faculdade de Ciências Agronômicas, Botucatu, SP,
Brasil. E-mail: giolundgren@gmail.com
4 Profª, Faculdade de Ensino Superior e Formação Integral, FAEF, Garça, SP, Brasil. E-mail: erikafujita79@hotmail.com
5 Prof. Titular, Departamento de Horticultura, UNESP, Faculdade de Ciências Agronômicas, Botucatu, SP, Brasil. E-mail: vieites@
fca.unesp.br
* Author for correspondence

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Ramos, J. A. et al.
pigmentos, avonoides e betalaínas. O experimento seguiu o Delineamento Inteiramente Casualizado
(DIC) com três repetições. Os dados foram submetidos a análise de variânca, teste F, e as médias
comparadas pelo Teste de Tukey (p < 0,05). Não houve perdas na atividade antioxidante, fenólicos
totais e antocianinas em todas as formas de cocção estudadas em relação à beterraba crua. Somente a
cocção na pressão apresentou menores teores de carotenoides em relação a crua. As concentrações de
avonoides e de betalaínas diminuíram em todas as formas de cozimento.
Palavras-chave: Antioxidantes. Antocianinas. Betalaínas. Beta vulgaris. Carotenoides. Flavonoides.
Introduction
Vegetables are important sources of antioxidant
compounds, such as vitamin C and E, phenolic
compounds, and carotenoids. These compounds
are widely distributed in plants and have biological
properties that promote human health; therefore,
fruits and vegetables have been encouraged for
human consumption (CAMPOS et al., 2008,
MELO et al., 2009). Dark fruits and dark green/
red vegetables (e.g. beets) contain high levels of
phenolic and avonoid compounds (LIN; TANG,
2007), which have shown to have potent biological
effects such as antioxidant, anti-inammatory,
antitumor, and platelet aggregation inhibitory
activities. Flavonoid intake is positively associated
with an increase in life expectancy and a decrease
in incidence of cardiovascular disease (VOLP et al.,
2008). Additionally, dietary intake of carotenoids
and phenolic compounds has been associated with
prevention of numerous degenerative diseases
(SILVA et al., 2010).
Anthocyanins are the pigments responsible
for blue, purple, and red color, and are present
in high concentrations in beet. The antioxidant
potential of anthocyanins could be more than
double compared to that of commercial antioxidants
like vitamin E, and have improved activity
compared with butylhydroxyanisole (BHA) and
butylhydroxytoluene (BHT) (MACHADO et
al., 2013). Betalains are also responsible for the
coloration of beets. This compound is derived
from secondary metabolism of a diverse group of
secondary metabolites that contain nitrogen and is
a powerful antioxidant that scavenges free radicals,
which may suppress the development of malignant
tumors (PICOLI et al., 2010; TIVELLI et al., 2011).
Food processing is crucial from a nutritional
viewpoint, as it can affect the content, activity, and
bioavailability of both nutrients and antioxidants.
Processing may lead to benecial transformations,
compound degradation, or nutrient loss (MELO
et al., 2009). Cooking of vegetable tissues alters
the physicochemical properties of the cell wall,
which in turn affects their performance as dietary
ber (CARVALHO et al., 2003). For example, the
whitening effect from cooking purple cauliower
using heat dramatically decreased the anthocyanin
content, whereas microwave cooking did not show
any difference compared to the raw vegetable (LO
SCALZO et al., 2008).
According to some studies, cooking methods
have inuenced antioxidant content. Galgano et
al. (2007) reported a 34% reduction in vitamin C
content in broccoli after cooking in water for 15
minutes, 22.4% after steam cooking for 23 minutes,
8% after pressure-cooking for 2 minutes; and 9%
after microwave cooking for 11 minutes. In leafy
vegetables, cooking resulted in 12%, 14%, and 20%
reduction of phenolic compounds in kale, spinach,
and cabbage, respectively, after 1 minute of boiling
(ISMAIL et al., 2004). However, Miglio et al.
(2008) observed an increase in antioxidant capacity
in carrots, zucchini, and broccoli after cooking in
water, steaming, and frying. According to this study,
this result was most likely due to the vegetable
matrix softening and increased extractability of
compounds, which could be partially converted
into more antioxidant chemical species. The authors
also mention that treatment by immersion in water
better preserves the carotenoid content in the
three vegetables and ascorbic acid in carrots and
zucchini. Cooking methods that involve immersion
in hot water resulted in an increase in carotenoid

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Influence of cooking methods on bioactive compounds in beetroot
content in pumpkin, taro, and beet (SINGH et al.,
2015). These changes might be due to the increased
extraction capacity of carotenoids in the cellular
system by boiling in water.
Changes induced by heat treatment, whether
benecial or not, depend on the vegetable type as
well as preparation factors, such as slicing, time,
cooking temperature, and cooking method, since
they directly inuence the content of bioactive
compounds; thus, studies should be carried out on
various vegetables to establish the best cooking
method when preparing them. The current study
aimed to evaluate the inuence of several cooking
methods on bioactive compounds of both uncooked
and cooked beetroot.
Material and Methods
The hybrid Borus cultivar was used, purchased
from the Dalbon farm in São José do Rio Pardo,
São Paulo State, Brazil (geographical coordinates
21°35’45”S and 46°53’23”W). Immediately after
purchase, they were transported by road to the
Laboratory of Nutrition and Dietetics in the Institute
of Biosciences of the Sao Paulo State University,
Botucatu. Subsequently, the lots were homogenized
manually. Plants were selected according to
uniformity of size, color and absence of defects.
They were then washed thoroughly in running water
to remove soils.
All cooking methods were tested beforehand
to establish the correct cooking time for beets to
be “al dente” (COPETTI et al., 2010). The times
applied in the current study are shown in Table 1.
Four heat treatments were carried out: steaming,
pressure-cooking, oven-baking using aluminum foil
wrap to cook evenly at 200°C, and water immersion
cooking. For each cooking method, eight beets were
used, weighing around 2 kilograms. After cooking,
the beets were manually peeled using a knife. Once
peeled, they were frozen in liquid nitrogen; they
were then macerated and frozen for biochemical
analysis.
Table 1. Cooking times for each treatment for the beetroots.
TREATMENT COOKING TIME (hour:min)
Steaming 01:18
Pressure 00:30
Oven-baked 03:00
Water immersion 01:05
The antioxidant activity of both uncooked and
cooked beet was measured by DPPH (MENSOR et
al., 2001) and expressed as reduction of %DPPH. The
total phenolic compound content was determined
by Folin-Ciocalteau’s spectrophotometric method
(SINGLETON et al., 1999) and expressed in mg of
gallic acid/100 g-1 of sample. The pigment content
was determined as described by Linder (1974),
expressed in mg 100 g-1 of beetroot. Flavonoid
content was determined by the spectrophotometric
method adapted from Santos and Blatt (1998); 4 ml
of acidied methanol solution was added to 0.1 g
of sample, homogenized and placed in an ultrasonic
bath for 30 minutes. 1 ml of 5% aluminum
chloride solution in methanol was added and left
to stand in the dark for 30 minutes. Afterwards, the
solution was centrifuged for 20 minutes at 6000
× g and the absorbance at 425 nm read using a
spectrophotometer. Results are expressed in mg of
rutin 100 g-1. Betalain content was determined as
described by Stintzing et al. (2005) and expressed
in mg 100 g-1.
The experiment was a completely randomized
design (CRD) with three replicates. Data were
subjected to analysis of variance (F test, p <0.05) and
means compared by Tukey test at 5% probability.

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Ramos, J. A. et al.
Results and Discussion
Antioxidant activity of raw beetroot was
57.63%, with no statistically signicant difference
(p>0.05) between any of the cooking methods
(Table 2). Monreal et al. (2009) analyzed the
inuence of cooking methods on antioxidant
activity in vegetables and showed that beet retained
its antioxidant activity when assessed by several
antioxidant activity quantication methods. This
result is similar to that of the current study that
showed that antioxidant capacity was maintained
in all treatments. Lin and Chang (2005) reported
that cooking broccoli for 10 minutes at 50°C or
for 8 minutes at 100°C did not alter antioxidant
capacity by DPPH method; similar to other studies,
the current study showed that various cooking
methods did not alter antioxidant properties of
beets. Melo et al. (2009) studied the antioxidant
activity of a variety of vegetables subjected to
heat treatment and showed that cooking did not
drastically affect their antioxidant properties. This
may be due to compensation by newly formed
compounds, such as those of the Maillard reaction,
or because a compound having partial oxidation to
donate hydrogen atom to the hydroxyl radical and/
or the polyphenol aromatic structure to tolerate the
displacement of unpaired electron around the ring
(NICOLI et al., 1999).
Table 2. Mean values of antioxidant capacity in percentage of reduced DPPH (%) and phenolic compounds (mg 100
g-1) in raw and cooked beetroots.
Cooking method DPPH Phenolic compounds
Steaming 61.57 a 84.06 a
Pressure 46.32 a 64.20 a
Oven-baked 44.07 a 64.82 a
Water immersion 43.58 a 57.46 a
Raw 57.63 a 77.81 a
CV% 14.90 16.64
Means followed by equal letters in the column do not differ from each other by the Tukey test (p <0.05).
There was no signicant difference in the
concentration of phenolic compounds between
uncooked and cooked beets. This can be explained
by the increased extraction of phenolic compounds
from the cellular matrix, due to changes in texture
that occur during cooking (BLESSINGTON et
al., 2010). Campos et al. (2008) reported that
extracting phenolic compounds in raw vegetables
is still a barrier when evaluating the inuence of
heat treatments on them, because some studies have
shown higher extraction in cooked vegetables.
The concentration of anthocyanins (Table 3)
found in raw beet was 85.2 mg 100 g-1, consistent
with reports by Macagnan et al. (2015) (83.7 mg
100 g-1), both expressed on a wet basis. There was no
inuence of the treatments (p> 0.05) on anthocyanin
concentration in beets. In a study on fruits and
vegetables cooked at different temperatures for
different periods of time, Machado et al. (2013)
showed a positive correlation between exposure
time and temperature (50ºC) for anthocyanin
concentration in all samples, probably due to the
higher extraction of anthocyanin pigments.
There was a 54.9% decrease in the carotenoid
concentration of pressure-cooked beets compared to
that of raw beets (13.1 mg 100 g-1); however, there
was no signicant difference compared to other
cooking methods (Table 3). Some previous studies
have stated that carotenoids are lost during cooking,
whereas others have found opposite responses, such
as no loss or an increase in carotenoid concentration,
making it difcult to evaluate carotenoid retention
in cooked foods (CAMPOS, 2008).

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Influence of cooking methods on bioactive compounds in beetroot
Table 3. Mean values of anthocyanins and carotenoids (mg 100 g-1) in raw and cooked beetroots.
Cooking method Anthocyanins Carotenoids
Steaming 69.8 a 10,0 ab
Pressure 40.3 a 5.9 b
Oven-baked 48.8 a 7.6 ab
Water immersion 49.8 a 7.7 ab
Raw 85.2 a 13.1 a
CV% 28.81 25.89
Means followed by equal letters in the column do not differ from each other by the Tukey test (p <0.05).
The concentration of avonoids (Table 4) in raw
beet was higher (290.64 mg rutin 100 g-1) than that
in cooked beets. Pressure-cooked beets showed
the largest reduction in avonoid content (70.8%).
There was no signicant difference in avonoid
content among steamed beets, oven-baked beets,
and those immersed in water. Pellegrini et al. (2010)
showed similar results, observing a 50% decrease
in the concentration of avonoids in broccoli when
cooked in boiling water.
Table 4. Mean values of avonoids (mg rutin 100 g-1) in raw and cooked beetroots.
Cooking method Flavonoids
Steaming 141.81 b
Pressure 84.79 c
Oven-baked 122.37 bc
Water immersion 109.34 bc
Raw 290.64 a
CV% 11.15
Means followed by equal letters in the column do not differ from each other by the Tukey test (p <0.05).
Table 5 shows the betalain concentration,
which is the sum of betacyanin and betaxanthin.
The concentration of betalain found in raw beets
was 49.51 mg 100 g-1. This result is similar to that
found by Picoli et al. (2010), who reported betalain
concentrations between 30 and 48 mg 100 g –1 in
raw whole beets. It is known that betalains are lost
at high temperatures, which explains the decrease
in betalain concentration by all cooking methods
(CONSTANT et al., 2002). Beets cooked in a pressure
cooker had the highest loss (59.5%) compared to
raw beet (49.51 mg 100 g-1); however, there was no
statistically signicant difference compared with
oven-baked beets (40.4%). Cooking methods that
best preserved betalain content in beets were those
immersed in water and steamed (31.74 and 32.21 mg
100 g-1, respectively). In a previous study conducted
with blanched beets, there was a decrease of almost
10% in betalain concentration compared to that in
raw beets (ZABOTTI et al., 2013). In the current
study the betalain content decreased by 35% when
immersed in water, probably due to the longer time
when compared with blanching.

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Ramos, J. A. et al.
Table 5. Mean betalain values (mg 100 g-1) in raw and cooked beetroots.
Cooking method Betacyanin Betaxanthin Betalain
Steaming 20.98 b 11.23 b 32.21 b
Pressure 13.25 c 6.78 c 20.02 c
Oven-baked 17.56 bc 11.90 b 29.46 bc
Water immersion 20.56 b 11.19 b 31.74 b
Raw 31.63 a 17.88 a 49.51 a
CV% 12.87 10.2 11.81
Means followed by equal letters in the column do not differ from each other by the Tukey test (p <0.05).
Conclusion
There was no signicant difference in antioxidant
activity, and total phenolic and total anthocyanin
content by any of the cooking methods compared to
raw beetroots. However, pressure-cooking lowered
carotenoid levels compared to raw beets. Flavonoid
and betalain content decreased by all the cooking
methods.
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