Introduction
Green asparagus (Asparagus officinalis L.), belonging
to the Asparagaceae family, is widely cultivated in
subtropical and tropical regions around the world such
as China, Peru, Thailand, Mexico, etc. [1]. Asparagus is
commonly divided into two categories: green asparagus
and white asparagus. The difference between them,
however, is dependent on the growth of their spears.
White stems are formed when growing below the soil,
whereas green stems are developed when they are
directly exposed to sunlight and become green via
the chlorophyll function [2]. Besides, another rarely
consumed asparagus is purple asparagus which has
a higher anthocyanin content compared to green and
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white asparagus [3]. Asparagus is favorably consumed
in many countries due to its high nutritional value and
low calorie content [1].
Asparagus has a considerably higher protein content
than many other vegetables, but it is low in carbohydrates
and calories [4]. Besides, asparagus has been found
to be a rich source of such bioactive compounds as
vitamin C, flavonoids, polyphenols, and tannins, which
lower cholesterol and have an anti-cancerous effect [4].
Many antioxidants have been identified in green asparagus
including rutin, tocopherol, ferulic acid, and
glutathione [5]. The asparagus aqueous extract was
found to have a 7-fold higher inhibitory effect against
α-glucosidase than that of acarbose used for a highfructose
diet-induced metabolic syndrome in mice [6].
Asparagus extracts were reported to have potential in
immunomodulatory activities [7]. The effectiveness of
antihyperglycemic treatment with an asparagus extract
(500 mg/kg) on STZ-induced diabetic mice was found
to be the same as that of an anti-diabetic drug (glibenclamide,
5 mg/kg) [8].
On the other hand, asparagus is a highly perishable
product due to its high respiration rate, limiting its
shelf-life [9]. Therefore, appropriate methods should
be applied to better maintain the quality of fresh
asparagus or to create innovative asparagus-based
products for long-term use. Asparagus stems are currently
commercialized as fresh, frozen, or canned products [2].
To date, many studies have aimed to develop innovative
products from green asparagus. White asparagus
was successfully employed to produce a spray-dried
asparagus powder by Siccama et al. [10]. Asparagus
powder was used as an additive to improve the elasticity
and rigidity of cheeses and ensure enhanced bioactive
compounds in the final cheese products [11]. Mazaheri
Kalahrodi et al. showed a tendering effect of asparagus
juice on the textural characteristics of beefsteak [12].
Adding asparagus powder into processed cheese was
found to enhance the phenolic content, antioxidant
activity, and proteolysis of the processed cheeses,
as well as to improve the textural characteristics of
processed cheese [11]. The term “herbal drink” is scarcely
mentioned in the studies developing products from green
asparagus. Therefore, we, for the first time, developed
a herbal drink from green asparagus which serves as a
healthy drink due to its nutritional value and bioactive
compounds. Besides, we selected an appropriate drying
method to ease the quality deterioration of fresh asparagus
and prevent its harvest loss. Finally, we evaluated the
process parameters for developing the asparagus herbal
drink to obtain a tea extract with a high solute yield.
Study objects and methods
Materials. Asparagus spears (edible part) of different
length were collected from a local farm in Ea Kar, Dak
Lak province. Anthrone (9,10-Dihydro-9-oxoanthracene),
gallic acid, and vitamin C were purchased from Sigma-
Aldrich (St. Louis, Missouri, USA). Other analytical
chemicals were purchased from standard commercial
suppliers.
Preparation of asparagus herbal drink. Asparagus
spears were washed with distilled water to remove
impurities and then sliced into specimens with varying
lengths (2, 5, 10, 15, and 20 mm). The samples (500 g)
were blanched in hot water (90–100°C), dried at 55°C to
obtain the moisture content of 12%, and roasted at 100°C
for 3 min (SCR301, Barwell, China). The samples with
a suitable length were then used for further experiments.
To investigate the effect of heat pretreatment methods
on the quality of the asparagus herbal drink, the selected
specimens (500 g) were subjected to different heat
pretreatments: without blanching (control sample), hot
water blanching at 70–80°C for 3 min, hot water
blanching at 90–100°C for 1.5 min, and microwave
heating (R-G302VN-S, Sharp Coporation, Osaka, Japan)
for 30 s at 440 W. The pretreated samples were dried at
55°C to the moisture content of 12% and then roasted at
100°C for 3 min. An appropriate pretreatment method was
selected and the samples were prepared for subsequent
evaluations.
The pretreated asparagus samples (500 g) were then
subjected to different drying conditions (convective
drying at 55°C, heat pump drying at 40°C, and microwave
drying) until obtaining the moisture content of 12%
followed by roasting at 100°C for 3 min. A proper drying
method was selected for the herbal drink. Finally, the
dried samples were ground into smaller pieces of different
sizes (< 0.5, 0.5–1.0, 1.0–1.5, 1.5–2.0, and > 2 mm).
The dried asparagus samples (2 g) were packaged into
teabags made of filter paper. Analytical responses were
determined to select the appropriate process parameters,
including total soluble solids, total polyphenol content,
total carbohydrate, vitamin C, and visual appearance
of asparagus samples.
Total polyphenol determination. The total polyphenol
content was determined according to a previous
study by Nguyen et al. [13]. Each sample was extracted
with distilled water at the ratio of 1:10. An aliquot
(1 mL) of the extract was mixed with 5 mL of 10%
Folin-Ciocalteu reagent and 1 mL of 7.5% Na2CO3. The
mixture was kept for 30 min in the dark before reading
absorbance values at 765 nm by using a 722-Visible
spectrophotometer (Yangzhou Wandong Medical Co.,
China). Gallic acid served as a standard solution. The
total polyphend content was expressed as milligrams
of gallic acid equivalent per gram of dry matter (mg
GAE/g DM) by establishing a standard curve or varying
concentrations of gallic acid (0.01–0.09 mg/mL) versus
its absorbance.
Vitamin C determination. The content of vitamin
C was determined by using a high-performance liquid
chromatography (HPLC) system (Waters Corp., Milford,
MA, USA) equipped with a Bischoff prontosil column
(AQ 4×125 mm×5 μm). A gradient of the mobile phase
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Nguyen Q.V. [и др.] Техника и технология пищевых производств. 2022. Т. 52. № 4. С. 640–648
consisting of methanol and 5 mmol/L KH2PO4 was
programed at 0.75 mL/min for 30 min at 30°C. Each
sample extract was injected to the column at the volume
of 20 μL and vitamin C was used as a standard solution.
The detector recorded the absorbance at 254 nm [14].
Total soluble solids and carbohydrate measurements.
Total soluble solids were determined by using
a digital refractometer (PR-101α, 0–45°Brix, Atago Co.
Ltd., Japan). The carbohydrate content was measured
following the Anthrone method [15]. Each sample extract
(2 mL) was mixed with 4 mL of an anthrone solution
and 5 mL of concentrated sulphuric acid. The mixture
was boiled in a water bath for 8 min and immediately
cooled to room temperature. The mixture was allowed
to stand for 30 min in the dark before its absorbance
was taken at 585 nm.
Sensory evaluation. The sensory evaluation of
the asparagus herbal drink followed the Vietnamese
standard TCVN 3218:2012. Four sensory attributes
(appearance, color, flavor, and taste) of the asparagus
infusion were evaluated according to a 5-point scale.
For this, each teabag containing 2 g of dried asparagus
was placed in a glass cup with 100 mL of boiled water
and allowed to stand for 6 min. The sensory evaluation
was conducted by 20 panelists who were assigned to
score each attribute. The importance indexes were as
follows: 1 for appearance, 0.6 for color, 1.2 for flavor,
and 1.2 for taste.
Statistical analysis. Each experiment was conducted
in triplicate and the data were presented as mean ±
standard deviation. The results were analyzed by a
one-way analysis of variance (ANOVA) with the SPSS
software (IBM Corp., Armonk, New York, USA). The
Tukey HSD test was utilized to compare mean values
at the significant level of 5% ( P < 0.05).
Results and discussion
Effect of asparagus size on the solute content
in the extract. Prior to heat pretreatment, green
asparagus needs to be reduced in size to facilitate
further processes of blanching and drying. Table 1
presents the effects of asparagus lengths on the solute
content in the extract. We found that longer samples
had ineffective extraction yields of total soluble solids,
total polyphenol content, and total carbohydrates. On
the other hand, the total soluble solids, total polyphenol
content, and total carbohydrate values of a 2 mm
asparagus extract were the highest, amounting to
33.53 ± 0.21%, 0.74 ± 0.02 mg GAE/g DM, and
13.36 ± 0.32%, respectively. This was because smaller
asparagus samples facilitated the diffusion
of the blanching water to soften the plant tissues,
increasing the extraction efficiency of solutes in
green asparagus [16]. Our results were consistent
with many previous reports that found smaller particle
sizes to achieve higher extraction efficacy [16–18].
According to our analysis, there was no difference in
the total soluble solids, total polyphenol content, and
total carbohydrate values between the 2 and 5 mm
samples. The content of vitamin C, however, showed
an increasing trend at larger sample sizes. Vitamin C
is highly susceptible to environmental conditions
such as light, temperature, and oxygen [19]. The
lowest content (83.57 ± 2.43 mg/100 g) of vitamin C
was found in the 2 mm sample. This was because the
small size contributed to a larger surface exposure to
the hot blanching temperature, causing vitamin C to
decay faster. Moreover, the loss in vitamin C could
possibly be ascribed to the leakage to the blanching
medium [20].
The visual appearance of asparagus specimens at
different sizes is presented in Fig. 1a. As we can see,
the 2 mm asparagus samples had a soft structure after
blanching, with a dark brown color in some of the
specimens. Meanwhile, the other samples showed harder
structures with a greenish color, which were suitable
for further processing. We found that the 5 mm sample
could be suitable for further processing to develop an
asparagus herbal drink.
Table 1. Effect of asparagus lengths on total soluble solids, polyphenol, carbohydrates, and vitamin C in the asparagus
extract
Таблица 1. Зависимость общего содержания растворимых сухих веще ств, полифенолов, углеводов и витамина С в экстракте
от длины нарезанных образцов спаржи
Sample length,
mm
Total soluble solids,
%
Total polyphenol content,
mg GAE/g DM
Total carbohydrate,
%
Vitamin C,
mg/100 g
2 33.53 ± 0.21c 0.74 ± 0.02bc 13.36 ± 0.32d 83.57 ± 1.43a
5 32.77 ± 0.59c 0.72 ± 0.03b 11.39 ± 1.67cd 85.43 ± 1.21ab
10 28.57 ± 0.34b 0.67 ± 0.04ab 10.56 ± 0.65bc 86.33 ± 1.05b
15 26.64 ± 0.82a 0.63 ± 0.03a 9.51 ± 0.34b 88.53 ± 0.67b
20 25.56 ± 0.48a 0.61 ± 0.03a 8.33 ± 0.24a 90.78 ± 0.77c
Values are expressed as mean ± SD. Different letters (a, b, c, d) show significant differences within the same column ( P < 0.05).
Данные представлены как среднее значение ± стандартное отклонение. Буквами a, b, c, d обозначены значительные различия
в пределах одного и того же столбца ( P < 0,05).
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Nguyen Q.V. et al. Food Processing: Techniques and Technology. 2022;52(4):640–648
Effect of blanching methods on the quality of
asparagus herbal drink. Heat pretreatment of the
asparagus samples aims to inactivate the browning
enzymes such as polyphenol oxidase and peroxidase,
as well as to inhibit microbial growth on the material
surfaces. It can also shorten the drying time as it
softens the structure of the material, leading to a
higher water evaporation rate [21]. According to
our results, all the methods of heat pretreatment
showed an increment in total soluble solids and total
polyphenol content but a decline in vitamin C and
total carbohydrates, compared to the control sample
(without blanching). As previously discussed, high
temperature might degrade vitamin C molecules. The
decrease in total carbohydrates could be ascribed
to the leakage to the blanching water, which was
previously mentioned by Xanthakis et al. [20]. High
Temperature Short Time (HTST). Heat treatment can
increase the content of solutes and polyphenols by
causing structural changes in plant cells. In particular,
it can disrupt cell membranes and weaken hemicellulase
and cellulase bonds, thus enhancing the
extraction efficacy [22]. In our study, the microwave
treatment showed the best extraction efficiency in
the total soluble solids (32.67 ± 0.43%) and total
polyphenol content (0.80 ± 0.05 mg GAE/g DM) of
asparagus, while having a lesser effect on the vitamin C
content and total carbohydrates in the extract. It
was noted that the microwave treatment promoted
a thermal gradient between the extracting medium
and plant cells, facilitating the liberation of phenolic
compounds [23]. A similar finding was reported in
the study by Severini et al., where the microwave
blanching showed an increase in phenolic compounds
and impaired the degradation of vitamin C in the
sample, compared to hot water blanching and steam
blanching [24].
As seen in Fig. 1b, the blanching processes caused
noticeable impacts on the color of the dried
asparagus samples. Hot water blanching at 70°C
caused a browning effect, while blanching at 90°C
and microwave heating gave the dried asparagus a
yellow-greenish color. This could be explained by the
fact that blanching at 90°C and microwave heating
showed better efficiency in inactivating polyphenol
oxidase compared to blanching at 70°C [13, 20]. High
Temperature Short Time. Thus, microwave blanching
could be a suitable option to develop a yellow-greenish
color for asparagus tea, as well as to achieve higher
total soluble solids, total polyphenol content, and
vitamin C contents in the extract.
Effect of drying conditions on the quality of
asparagus herbal drink. The effects of different drying
conditions on the extraction yield of the asparagus
herbal drink are presented in Table 3. Microwave
drying had the shortest drying time of 29 min.
However, it considerably reduced the contents of
vitamin C, carbohydrates, and total soluble solids in
the asparagus drink. Meanwhile, convective drying
and heat pump drying resulted in higher total soluble
solids and vitamin C content in the extract. The rapid
degradation of vitamin C by microwave heating
was due to excessive heat generated in the internal
molecular structures of asparagus. As shown in Fig. 1c,
Figure 1. Visual appearance of asparagus samples: a) different lengths; b) blanching methods; c) drying methods;
d) asparagus tea at different particle sizes
Рисунок 1. Внешний вид образцов спаржи: а) нарезки длины; б) ме тоды бланширования; в) методы сушки; г) напиток из спаржи
при разной величине помола
2 mm 5 mm 10 mm 15 mm 20 mm
Microwave drying Converctive drying Heat pump drying
Hot water (70°C) Hot water (90°C) Microwaver Control
a b
c d
< 0.5 mm 0.5 mm–1.0 mm 0.0 mm–1.5 mm 1.5 mm–2.0 mm > 2.0 mm
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convective drying and heat pump drying gave dried
asparagus a yellow-greenish color, whereas microwave
drying induced a brown-yellowish color, reducing the
sensorial attributes of the asparagus herbal drink. The
lower total polyphenol content caused by convective
drying and heat pump drying, as compared to the
microwave-dried asparagus, could be attributed to the
degradation of phenolic compounds when exposed to
an extended drying time (17–22 h). The decrease in
the total polyphenol content could also be due to the
enzymatic processes that occurred during drying [25].
Although the heat generated by microwave drying
was considerably higher than that in the other drying
methods, the microwave drying time was not sufficient
to cause a significant impact on phenolic compounds.
As for sensorial properties, the asparagus samples
Table 2. Effect of blanching methods on total soluble solids, polyphenol, carbohydrates, and vitamin C in the asparagus
extract
Таблица 2. Зависимость общего содержания растворимых сухих веще ств, полифенолов, углеводов и витамина С в экстракте
спаржи от методов бланширования
Blanching method Total soluble solids, % Total polyphenol content,
mg GAE/g DM
Total carbohydrate,
%
Vitamin C,
mg/100 g
Control sample (without
blanching)
27.56 ± 0.32a 0.60 ± 0.03a 12.78 ± 0.54b 72.10 ± 1.51c
Hot water (70°C) 28.31 ± 0.21b 0.68 ± 0.02b 10.40 ± 0.43a 63.52 ± 2.43a
Hot water (90°C) 30.63 ± 0.18c 0.74 ± 0.01c 9.92 ± 0.67a 65.29 ± 2.67a
Microwave 32.67 ± 0.43d 0.80 ± 0.02d 11.56 ± 0.81ab 68.61 ± 1.43ab
Values are expressed as mean ± SD. Different superscripts (a, b, c, d) indicate significant differences within the same column (P < 0.05).
Данные представлены как среднее значение ± стандартное отклонение. Буквами a, b, c, d обозначены значительные различия
в пределах одного и того же столбца ( P < 0,05).
Table 3. Effect of drying methods on total soluble solids, polyphenol, carbohydrates, and vitamin C in the asparagus extract
Таблица 3. Зависимость общего содержания растворимых сухих веще ств, полифенолов, углеводов и витамина С
в экстракте спаржи от методов сушки
Drying method Total soluble solids, % Total polyphenol content,
mg GAE/g DM
Total carbohydrate, % Vitamin C,
mg/100 g
Drying time
Microwave 26.93 ± 1.44a 0.75 ± 0.04b 11.53 ± 0.54a 52.69 ± 2.54a 29 min
Convection 30.46 ± 1.20b 0.61 ± 0.02a 13.58 ± 0.32b 68.36 ± 2.45b 17 h
Heat pump 29.62 ± 2.12b 0.59 ± 0.03a 12.47 ± 0.67b 70.33 ± 3.12b 22 h
Data are expressed as mean ± SD. Different superscripts (a, b, c, d) indicate significant differences within the same column ( P < 0.05).
Данные представлены как среднее значение ± стандартное отклонение. Буквами a, b, c, d обозначены значительные различия
в пределах одного и того же столбца ( P < 0,05).
Table 4. Dried asparagus in the teabag and sensorial properties of asparagus infusion at different particle sizes
Таблица 4. Высушенная спаржа в пакетиках и органолептические св ойства настоя спаржи при разной величине помола
Particle size,
mm
Appearance of dried
asparagus in the teabag
Color Flavor Taste Sensory score
< 0.05 Fine powder Light yellowish color,
presence of many fine
particles
Very light characteristic
flavor of asparagus
Very light sweet 7.40 ± 0.32
0.5–1.0 Homogenous form Presence of particles,
light yellowish color
Light characteristic flavor
of asparagus
Light sweet 9.00 ± 0.23
1.0–1.5 Homogenous form Yellowish color Intense characteristic
flavor of asparagus
Relative sweet 15.40 ± 0.24
1.5–2.0 Homogenous form Yellowish color Intense characteristic
flavor of asparagus
Relative sweet 16.00 ± 0.35
> 2.0 Inhomogeneous form Light yellowish color Very light characteristic
flavor of asparagus
Very light sweet 9.60 ± 0.32
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acquired a yellow-greenish color from convective
drying and heat pump drying and a dark brown color
from microwave drying, which significantly affected
their appearance. Both convective drying and heat
pump drying produced the drinks with the same values
of total soluble solids, total polyphenol content, total
carbohydrate, and vitamin C. However, convective
drying required a shorter time (17 h) to achieve the
desired moisture content (12%) in the asparagus tea.
Therefore, this method proved the most suitable for
developing the asparagus herbal drink.
Effect of asparagus particle sizes on total soluble
solids in the asparagus infusion. After drying, the
asparagus samples were ground to different particle
sizes and packaged into teabags. The effect of particle
sizes on total soluble solids in the tea extract is
illustrated in Fig. 2. We found that the grinding size
from 1 to 2 mm produced the highest total soluble
solids (> 26%), while very fine powder (< 0.5 mm)
produced the lowest total soluble solids (13.37%) in
the asparagus infusion. This agreed with many previous
studies where the small particle size facilitated the
extraction of solute in the solvent medium. However,
very fine particles tended to agglomerate and deposit
at the bottom of the teabag, preventing the diffusion
of solute to the extracting medium sieving and selecting
the optimal granulometry (0.15–0.74 mm) [16].
Table 4 shows a sensorial description of asparagus
tea, while Fig. 1d features the appearance of dried
asparagus at different particle sizes. According to the
sensory evaluation, dried asparagus with 1.5–2 mm
particles produced an asparagus infusion with the
highest score (16) for color, intense taste, and
characteristic flavor. Therefore, this size proved the
most suitable for developing the asparagus herbal
drink since it produced the highest soluble solids
and good sensorial properties.
Conclusion
In this study, we developed an innovative asparagus
herbal drink. The asparagus length of 5 mm was found
to facilitate subsequent steps. Microwave blanching
caused the dried asparagus to acquire a yellow-greenish
color. Unlike hot water blanching, this method produced
higher values of total soluble solids, total polyphenol,
and total carbohydrate, while having a lesser effect on the
content of vitamin C. Of all drying methods, convective
drying proved suitable for higher total soluble solids and
total carbohydrate, as well as better visual appearance of
asparagus tea. Finally, the grinding size of asparagus was
selected at 1.5–2.0 mm to obtain the highest total soluble
solids in the asparagus infusion and the highest sensory
score. The asparagus herbal drink had a yellowish color, an
intense characteristic flavor of asparagus, and a relatively
sweet taste. In addition, we selected the process parameters
for the asparagus teabag to maintain a high content of total
polyphenol and vitamin C in the asparagus herbal drink
to enhance its nutritional value. Further investigations
can be carried out to produce an asparagus herbal drink
with a higher polyphenol content in the infusion. Besides,
a pilot-scale study should be conducted to enhance the
feasibility of the asparagus herbal drink as a commercial
product.
Contribution
The authors were equally involved in writing the
manuscript and are equally responsible for plagiarism.
Conflict of interest
The authors declare that there is no conflict of interest
regarding the publication of this article.

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