Black garlic: Transformation effects, characterization and consumer purchase intention

Abstract

Black garlic is produced from chemical and biochemical reactions when the fresh garlic bulb is submitted to specific temperature and moisture conditions. The aim of this study was to evaluate quality and nutritional changes on bulbs before and after the transformation in black garlic, presenting the new product for the consumer, evaluating the purchase intention. Commercial garlic bulbs cv. Amarante were obtained and transformed in black garlic. The color, proximate composition (moisture, crude lipid, crude protein, crude fiber, ash and nitrogen-free extract), total sugars, total phenolics content and antioxidant activity were evaluated on fresh and black garlic bulbs. The transformation of garlic in black garlic resulted in an increase on crude lipid, crude protein, total sugars, antioxidant activity and total phenolic content. A multivariate analysis was performed and the characteristics of nutritional interest were positively related to the black garlic samples and a completely separation of the products before and after processing can be observed, affirming the physical, chemical, nutritional and sensory attributes difference. Only 20% of the surveyed consumers affirmed that they already knew the product and 55% classified the product after visual evaluation between “liked slightly” and “liked very much”, with 62% of purchase intention by the interviewed consumers.

Full text

DOI: 10.14295/CS.v8i3.2251
444
Comunicata Scientiae 8(3): 444-451, 2017
e-ISSN: 2177-5133
www.comunicatascientiae.com
Received: 29 July 2016
Accepted: 15 January 2017
Black garlic: transformation effects, characterization
and consumer purchase intention
Rita de Cássia Mirela Resende Nassur1*,
Eduardo Valério de Barros Vilas Boas2,
Francisco Vilela Resende3
1Bahia State University, Juazeiro, BA, Brazil
2 Federal University of Lavras, Lavras, MG, Brazil
3 Embrapa Vegetables, Brasília, DF, Brazil
*Corresponding author, e-mail: ritarnassur@hotmail.com
Article
Abstract
Black garlic is produced from chemical and biochemical reactions when the fresh garlic bulb is
submitted to specific temperature and moisture conditions. The aim of this study was to evaluate
quality and nutritional changes on bulbs before and after the transformation in black garlic, presenting
the new product for the consumer, evaluating the purchase intention. Commercial garlic bulbs cv.
Amarante were obtained and transformed in black garlic. The color, proximate composition (moisture,
crude lipid, crude protein, crude fiber, ash and nitrogen-free extract), total sugars, total phenolics
content and antioxidant activity were evaluated on fresh and black garlic bulbs. The transformation
of garlic in black garlic resulted in an increase on crude lipid, crude protein, total sugars, antioxidant
activity and total phenolic content. A multivariate analysis was performed and the characteristics of
nutritional interest were positively related to the black garlic samples and a completely separation of
the products before and after processing can be observed, affirming the physical, chemical, nutritional
and sensory attributes difference. Only 20% of the surveyed consumers affirmed that they already
knew the product and 55% classified the product after visual evaluation between “liked slightly” and
“liked very much”, with 62% of purchase intention by the interviewed consumers.
Keywords: Allium sativum, antioxidant activity, chemical composition, consumer acceptance
Introduction
Garlic has played an important role in
cooking as a condiment and food throughout
the human history. For over 3000 years, this
vegetable has been consumed as food or used
as a medicine in Asian countries (Queiroz et
al., 2009). Nevertheless, black garlic has been
produced recently and it is not yet well-known
by consumers, especially in the west side of the
world.
The black garlic is produced by chemical
and biochemical reactions that occur in the
bulb when it is submitted to specic temperature
and humidity conditions. No additives or other
substances are used or added in the transformation
of garlic to black garlic, which consists of a
simple fermentation of the common vegetable
in controlled temperature and humidity. Black
garlic flavor is unique and distinctive (sweet), with
balsamic notes, sugar cane molasses or plum-
black, with the advantage that this consumption
does not cause undesirable bad breath after
consumption. This fact has been reported as a
result from the destruction of some compounds
during the thermal treatment (Fante & Noreña,
2012)
Black garlic has been named as the
"ingredient of the moment" at gastronomic area
and it has aroused the curiosity and the taste of
consumers. It is a golden skin material with dark

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Com. Sci., Bom Jesus, v.8, n.3, p.444-451 Jul./Set. 2017
colored bulbs, differing from the garlic and any
other raw material. Recently, it has been used in
haute cuisine as an ingredient in savory or sweet
dishes, with great acceptance, especially when
combined with pasta. In Brazil, their production
in a larger scale and even craft production is
still limited by the lack of specific methodology,
product disclosure and technical knowledge.
It is possible to find reports about
black garlic with pharmacological, nutritional
and antioxidant properties (Wang et al, 2012;
Gardner et al, 2007; Lee et al, 2009) and the
influence on temperature on black garlic quality
characteristics (Zhang et al., 2015), mainly in
eastern countries, where the product is better
known by scientists and consumers. Studies about
the quality characteristics and nutritional value of
black garlic produced in Brazil as well as changes
that can occur during its transformation are still
scarce. On this way, the aim of this study was
to evaluate quality and nutritional changes on
garlic bulbs before and after the transformation
in black garlic, presenting the new product for
the consumers and evaluating their purchase
intention.
Material and Methods
Commercial bulbs of cv. Amarante
garlic were obtained and transformed in black
garlic. The cultivar Amarante was selected due
to its higher number of bulblets and a higher mass
per bulb, resulting in higher production of the final
product. The bulbs were selected according
to homogeneity of mass and size (mean of 40
grams per bulb and diameter above 40mm),
avoiding those visibly injured and diseased at
Postharvest Laboratory at the Federal University
of Lavras (UFLA), Brazil. Three replicates of 500
grams each were separated for the analysis
before transformation of the garlic in black garlic.
Bulbs for black garlic production (three replicates
of 500 grams each) were placed in an oven
set at 67 °C and 90 %RH ± 2.1 for 22 days. The
relative humidity (RH) was achieved with a water
container placed into the oven and replaced
when necessary to maintain the RH and the time
was set according to the product characteristics
(golden skin and black bulbs). After obtaining
the black garlic, each portion was separated
in three parts, resulting in nine repetitions after
drying. Nine repetitions of the raw garlic was also
separated.
The following analyses were performed
on fresh material (white garlic) and on black
garlic (after transformation) with the objective of
results comparison, in order to verify the effects of
transformation on garlic characteristics.
The garlic color was evaluated in nine
replicates per bulb, for the nine repetitions
per treatment (white and black garlic) with a
Minolta CR-400 colorimeter with a CIE L*a*b*
determination. The L* coordinate represents how
darker is the sample, with values from 0 (totally
black) to 100 (totally white) and it is normally used
to indicate browning; the a* coordinate can vary
from -80 to +100 where the extremes correspond
to green and red, respectively; the b* coordinate
indicates the color from blue to yellow and can
vary from -50 (totally blue) to +70 (totally yellow).
This variables are used to calculate the cylindrical
coordinates of color named Hue angle (°Hue)
that indicates the color in a 360° angle and
Chroma (C*) that represents color purity. In this
study, the results will be expressed in L*, Chroma
and Hue values.
The proximate composition of garlic and
black garlic was performed according to the
methodology proposed by the AOAC (2012).
The moisture was determined by the gravimetric
method with heat, based on the sample mass
loss when submitted to 105°C, the crude lipid
was quantified by the Soxhlet gravimetric
method based on the mass loss of the material
submitted to ether extraction. The crude protein
was determined by Kjeldahl (total nitrogen).
To determine the fixed mineral residue, the
sample was incinerated in a muffle furnace at
550°C. The determination of dietary crude fiber
was performed according to the techniques
proposed by AOAC (2012) and the nitrogen free
extract (NNE) was determined subtracting the
values obtained in previous analyses of 100g of
the product, in fresh mass.
The pH of the black and raw garlic
were determined by a potentiometric method
according to AOAC (2012) methodology.
The total sugar content was evaluated by
spectrophotometry at 620 nm, according to

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antrona method (Dische, 1962), and the results
were given as grams of glucose per 100g of the
garlic tissue.
The total phenolic content was
determined according to Folin-Ciocalteau
method, which involves the phenolic compounds
with concomitant formation of a blue complex
whose intensity increases linearly at 760 nm,
as described by Rumbaoa et al., (2009). The
aqueous and ethanolic extracts of bulbs were
dissolved in methanol in order to achieve a
concentration of 0.5 mg.solids.mL-1. The total
phenolic compounds level for each extract were
then quantified according to the standard curve
prepared with gallic acid, and the results were
expressed as gallic acid equivalents (GAE).
The antioxidant activity was measure by
two different methods, in order to perform a better
information about the black and white garlic
antioxidant activity, since each method measure
different forms of the radical scavenging. For
the DPPH method, the determination was based
on the free DPPH (2,2-Diphenyl-1-picrylhidrazil)
radical scavenging, that led to an absorbance
increase at 515 nm (Runo et al., 2007a) with
previous tests for raw and black garlic and
results expressed in percentage of free radical
scavenge (%FRS), according to control. For the
ABTS method, the ABTS assay was performed
according to a method developed by Rufino et
al. (2007b). ABTS radical cations were produced
by the reaction of 7 mM ABTS stock solution with
145 mM potassium persulfate. The ABTS solution
was diluted with ethanol until it reaches 0.70±0.02
of absorbance at 734 nm. After the addition of 30
μl of sample or trolox standard to 3 ml of diluted
ABTS solution, absorbances were recorded at 6
min after mixing. Ethanolic solutions with fixed
trolox concentrations were used as a standard
and results were expressed as μM trolox g-1 garlic.
After the transformation, the black
garlic was submitted to a visual evaluation and
purchase intention by consumers. The black
garlic was placed on a white tray where black
garlic samples of bulbs and bulblets, peeled
and unpeeled were presented to consumers as
well as the hedonic scale with answers to the
questions asked. The survey was conducted
in cities of the South of Minas Gerais state, with
60 garlic consumers. Product appearance was
evaluated according on 9-point hedonic scale
(9 = liked very much to 1 = disliked very much)
and the purchase intention was made by visual
assessment through a hedonic scale of 5 points,
with the value 5 corresponding to 'certainly buy
'and 1 to 'certainly would not buy ' the product,
according to Lawless and Heymann (2010).
The experiment was conducted in
a completely randomized design with two
treatments (fresh and black garlic), with nine
repetitions each. The laboratory analysis was
carried out in triplicate for each repetition. The
results were submitted to variance analysis and
the means were compared according to Tukey´s
test at 5% of probability using the software
Sisvar®. For a better visualization of the results, a
multivariate analysis was also performed with the
aid of the XLStat® software.
Results and Discussion
The quality of a new product can
be evaluated according to its nutritional
compounds, its chemical, physical and physic-
chemical characteristics. The means for the
evaluated garlic characteristics, before and after
the black garlic transformation are presented in
Table 1.
The L* coordinate indicates the lightness
of the sample and it can vary from 0 to 100. Higher
the number, whiter the sample. So this variable
can just inform us how black or white is the
sample, and according to the results, it is possible
to confirm that the garlic before transformation
had a high lightness and after the transformation
in black garlic, the L* value decreases, indicating
that the product became darker. During the
transformation of garlic, the development of
black color is related to the temperature that will
lead to non-enzymatic browning reactions. There
were melanoidins forming in Maillard reaction.
Color of melanoidins might be connected with
the enolization of sugars and racemization of
amino acids (Kim & Lee, 2008).
When the Chroma and the Hue angle
were evaluated, the black garlic samples
presented lower values. Chroma presents the
quality of a color's purity, intensity or saturation
and lower the chroma value, more neutral is the

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color, indicating that the black garlic has a lower
saturation when compared to raw garlic. The
Hue angle is the common distinction between
colors positioned around a color wheel and it
makes sense only when evaluated with other
color variables (L*and Chroma). It is possible to
observe that L* has a strong influence on the
sample color, since the Hue angle did not vary
too much, even with a significant statistical
difference. With the global color evaluation, it
is possible to notice a big change in garlic color
before and after transformation.
According to Table 1, black garlic
presented a higher moisture content when
compared to raw/white garlic, emphasizing the
presence of a high relative humidity during the
adopted process. Zhang et al., (2015) observed
that when the temperature increase during
black garlic transformation, the product moisture
content decreases and the authors affirmed
that the decrease rate of moisture content was
faster with the temperature increase during the
transformation.
The moisture content can have a direct
influence on black garlic quality. Zhang et al.
(2015) during their study on the temperature
effect in black garlic, demonstrated that when
the black garlic moisture content achieved 35 to
40%, the black garlic was drier and its elasticity
was not good, and when the moisture content
achieved below 35%, the product became much
harder, which is also undesirable. With a higher
moisture content, the product can be more
susceptible to deterioration by microorganisms,
otherwise this fact was not observed in the
present study and possibly an increase of 9.66%
of this content may not be sufficient to the
deterioration process beginning.
The crude lipid content (%) increased
almost four times when the bulbs were submitted
to the transformation process and it was possible
to feel an oiliness characteristic on black garlic.
Since the moisture content of black garlic was
higher than the one on fresh garlic, it is not
possible that a concentration in lipids level
happened. There are no papers discussing the
lipid content on black garlic and future studies
should be carried out to elucidate the synthesis or
changes in lipid content in black garlic, including
quantitative, metabolic and qualitative analysis.
No differences on the percentage
of crude fiber in the evaluated samples were
Table 1 – Means for color, proximal composition, pH, total sugars, phenolic compounds and antioxidant activity on
fresh and black garlic.
Variable Fresh garlic Black garlic
L* 81.57 a 24.55 b
Chroma 21.26 a 2.67 b
Hue 94.74 a 69.35 b
Moisture (%) 72.42 b 79.42 a
Lipids (%) 0.11 b 0.43 a
Fiber (%) 6.32 a 5.59 a
Ash (%) 3.01 b 3.36 a
Protein (%) 10.62 b 11.75 a
Nitrogen-free extract (%) 7.50 a 0.56 b
pH 6.14 a 4.61 b
Total sugars (g 100g-1) 2.24 b 35.29 a
Total phenolics (mg EAG.100g-1) 35.98 b 52.20 a
Antioxidant activity - DPPH - (%SRL) 10.40 b 56.87a
Antioxidant activity – ABTS - µM Trolox g-1 19.65 b 31.50 a
Same letter for the same attribute: means are not different according to Tukey´s test at 5% of probability

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noticed, according to statistical analysis, with
the mean of the samples varying from 6.32% for
fresh garlic to 5.59% for black garlic. For ash and
crude protein content, black garlic presented
statistically higher values. Garlic is considered a
vegetable with higher mineral content. Minerals
can be co-factors during vegetable biochemical
reactions and their absence in human body can
be related to diseases, if the food intake does not
provide the necessary mineral level.
The protein level in fresh garlic is
important because it is used as a substrate
to Maillard reaction that occurs during black
garlic transformation. Otherwise, it can be seen
(Table 1) that black garlic presented higher
protein amount than raw garlic, even with small
difference in their content. The melanoidin
pigment, formed during Maillard reaction, might
be connected with racemization of amino acids
(Kim and Lee, 2008). The author’s initial hypothesis
was that the Maillard reaction could consume
amino acids and the protein level of black garlic
would be lower than the same level on fresh
garlic. It was not proved in the present study and
new studies should be carried out to investigate
protein dynamics on black garlic and during the
process.
The nitrogen-free extract is concerned
to carbohydrates of the food, except the fiber
portion and it is composed mainly by sugars
and starch. Most part of it can be digested and
used as an energy source. Since the total sugar
content in black garlic is higher (Table 1) when
compared to fresh garlic, the nitrogen-free
extract was probably used as an energy source
for the sugar metabolism, justifying the difference
of free-nitrogen extract between the samples
(carbohydrate content on fresh garlic is 13 times
higher and the sugar concentration on black
garlic is almost 16 times higher).
A lower pH can be observed for the
black garlic, which can be associated to a
higher acidity. According to Liang et al., (2015)
the organic acids profile is different for garlic
extracts before and after processing and they
affirm that is possible to observe changes on
pH during the thermal processing . Acetic acid
and succinic acid were observed for the same
authors on black garlic, but the presence was not
observed in fresh garlic samples, indicating that
the presence of these acids can be associated
to a lower pH on black garlic samples.
Liang et al (2015) also found a reduction
on pH values when comparing the means for
fresh and black garlic, assenting with the results
of this present study, and the authors attributed
the reduction to a decrease in allicin content,
resulting in a final product with a ‘smoother’
taste, since this compound is responsible for the
strong garlic odor. Zhang et al. (2015) reported
that an increase in acidity on garlic samples
submitted to heat can partly be associated with
browning substances formed and is reported that
the formation of carboxylic acids substances can
lead to an increase in acidity.
The total sugars content is about 60%
higher on black garlic samples, when comparing
to fresh garlic, and comparing the same materials,
an increase in 15.75 times was observed for the
total sugars content evaluated by spectroscopy.
According to Zhang et al. (2015), polysaccharide
in garlic is degraded to reducing sugar, but
these sugars can be consumed during Maillard
reaction. The same authors observed that,
when submitted to temperatures about 70°C,
the garlic can form reducing sugars faster than
its consumption rate and that this temperature
in the process provided a better processed
product, with an abundant sweet avor.
Garlic is a vegetable rich in a number of
phenolic compounds (Bozin et al., 2008) and it
is suggested that phenolic compounds content
can increase about 4 to 10 times when the fresh
garlic is processed to obtain the black garlic
(Kim et al., 2013; Choi et al., 2008). In the present
study, an increase in 45% was observed for the
total phenolics content when the garlic was
submitted to the transformation, ranging from
35.98 mg EAG.100g-1 to 52.20 mg EAG.100g-1, as
can be observed on Table 1. These results are in
accordance to Zhen et al., (2015), that observed
an increase in the phenolics content when the
black garlic was obtained.
According to Choi et al. (2008), an
increase of total phenols content improves total
antioxidant capacity of black garlic. The Folin
Ciocalteu method for determination of phenolic
compounds is similar to antioxidant activity

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Com. Sci., Bom Jesus, v.8, n.3, p.444-451 Jul./Set. 2017
determination; therefore, the values should at
least partially express antioxidant activity (Prior et
al., 2005). Tsai et al. (2005) demonstrated that a
signicant correlation (P<0.05) existed between
antioxidant activity and total phenolics content.
It is important the evaluation of the
antioxidant activity by different chemical
assays, since it validated the problems of using a
single one-dimensional method to evaluate this
activity and multifunctional food and biological
antioxidants. In the present study, we evaluated
the garlic antioxidant activity by two different
methodologies that, together, can explain part
of the garlic antioxidant capacity. For the DPPH
method, the antioxidant capacity increased
about 5 times during the processing of the garlic
and for the ABTS methodology, an increase of
the antioxidant capacity from 16.65 to 31.50 µM
Trolox g-1 was also observed (Table 1). The trend
observed here for results of the two chemical
assays for antioxidant activity determination
was also observed in previous vegetable studies
(Strail et al., 2006). Lee et al. (2009) also observed
a higher antioxidant activity on black garlic
and suggested the insertion on diabetics diets,
without problems with the disease indexes.
Previous studies conrmed that the
phenolic is an important component of garlic.
Queiroz et al. (2014) studied ready-to-eat garlic
products and found that there was a signicant
decrease in the total phenolics content due
to storage halfway to the expiration date. This
relationship was conrmed with processed
vegetables in Somman and Siwarungon (2015)
study, that observed the fresh garlic with 1.76 of
phenolic content increase to 19.48 at 10 days
after processing and also observed antioxidant
activity from the DPPH method of 25.53% for
the fresh garlic. The total antioxidant activity
of vegetables and fruits has been extensively
studied using various chemical-based assays
including 2.2-diphenyl-picrylhydrazyl (DPPH) (Lu
et al., 2011).
Rahmam et al. (2012) studied garlic
and concluded that the vegetable has a strong
antioxidant activity, evaluating the product by
the DPPH scavenging method and suggested
that the product can be a source of antioxidant,
even fresh or processed. Gardner et al (2007),
studying the black garlic, afrmed that it is
more powerful for therapeutic and antioxidant
properties when compared to fresh garlic.
In addition, according to the literature,
increments in the polyphenols and avonoids
content (Kim et al., 2012) were observed in black
garlic after the process. Other reports conrmed
the potential health benets of black garlic by
chemical analysis (Kim et al., 2012; Sato et al.,
2006).
According to the results of the chemical
and nutritional properties of the fresh and black
garlic, it is possible to conclude that the black
garlic is a processed food obtained by subjecting
the fresh garlic to higher temperatures and
relative humidity, resulting in chemical reactions,
such as the Maillard reaction, which change
the composition of the garlic (Liang et al., 2015),
being possible to obtain a whole new product,
with a completely different and interesting
characteristics.
For a better visualization of the results,
a multivariate analysis was performed with the
chemical analysis for the fresh and black garlic,
which can be observed on Figure 1. Each point
for the fresh or black garlic is a mean of three
evaluations for each analysis. The samples before
and after processing were clearly separated
and the most interesting characteristics for
human nutrition are positively correlated to the
black garlic samples, such as fiber, antioxidant
capacities, etc, being possible to conclude that
the composition of the product was completely
changed and a new product for the consumer,
that have no chemical, physical and sensorial
relation with the fresh garlic.
After processing, the antioxidant
capacity, total soluble solids and total sugars,
fiber and protein contents increase its content,
due to the compounds changes, discussed
before. Since the luminosity (L*) range from 0 to
100 and higher the L* value, brighter the sample,
it is clear that this variable is positively correlated
with fresh garlic, and negatively correlated to
black garlic samples.
The purchase intention evaluation was
performed in three municipalities of the South
of the Minas Gerais State, Brazil with a total of 60
consumers, being 44 women and 16 men with

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ages varying from 15 to 70 years old. According
to the results, only 20% of the interviewed
consumers knew the product and 55% of the
consumers evaluated the product from ‘like
slightly’ to ‘liked very much’. For the purchase
intention, the notes ranged from ‘would not buy’
to ‘would buy’ and about 62% of the consumers
presented some intention to buy the product, but
only 28% afrmed that would ‘certainly buy’ the
black garlic. Thirty-eight (38%) of the consumers
provided answers from ‘I am not sure if I would
buy’ from ‘certainly not buy’. It is possible to
conclude that the black garlic is not well-known
by consumers and this fact could explain the low
means of consumers that would ‘certainly buy’
the product. New sensory tests with avor, aroma,
taste and appearance evaluations should be
carried out and are necessary in order to obtain
a better prole of the black garlic consumers.
Conclusions
With the processing of the fresh garlic to
obtain the black garlic the chemical and physical
composition of the product was completely
changed, with statistical increase for the contents
of lipids, minerals, total soluble solids, total sugars,
phenolic content and antioxidant activity,
evaluated by two different methodologies.
The black garlic is a product that about
20% of the interviewed consumers already known,
but most of them confirmed their intention to buy.
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