la pitaya

Original article
Evaluation of the chemical characteristics and rheological
behavior of pitaya (Hylocereus undatus) peel
Fernanda Robert DE MELLO1*, Cláudia BERNARDO3, Carolinne Odebrecht DIAS3, Luana Carolina BOSMULER ZÜGE1,
Joana Léa MEIRA SILVEIRA4, Edna Regina AMANTE3, Lys Mary BILESKI CANDIDO2
1
Technol. Sector-Fed. Univ.
Paraná, PO Box 19011,
Curitiba PR, Brazil,
[email protected],
[email protected]
2 Dep. Chem. Biol.,
Fed. Technol. Univ. Paraná,
Curitiba PR, Brazil
3
Dep. Food Sci. Technol.,
Cent. Agric. Sci.,
Fed. Univ. Santa Catarina,
Florianópolis SC, Brazil
4 Dep. Biochem. Mol. Biol.,
Fed. Univ. Paraná,
PO Box 19031, Curitiba PR,
Brazil
Evaluation of the chemical characteristics and rheological behavior of pitaya
(Hylocereus undatus) peel.
Abstract – Introduction. Pitaya peel has been applied as a functional ingredient for food
due to the presence of betacyanins. However its polysaccharides can also contribute as a texture agent for food. The aim of this work was to evaluate the chemical characteristics and
rheological behavior of the pitaya peel. Materials and methods. The samples were analyzed
with regard to moisture and mineral content, protein, lipids, sugar, fiber, vitamin C, titratable
acidity, soluble solids content and pH. Rheological measurements were performed on rheometer through flow curve, stress sweep, frequency sweep and the variation of temperature.
Results and discussion. The results showed that pitaya peel is rich in insoluble fibers and
exhibits non-Newtonian behavior, characteristic of a strong gel with a predominance of solid
character. Furthermore, samples showed thermal resistance at the conditions of frequency,
tension and temperature analyzed. Conclusion. Considering our results, in addition to use as
a natural colorant in food, pitaya peel can also contribute to the nutritional value and texture
of the products.
Brazil / Hylocereus undatus / fruits / byproducts / peel / chemical composition /
fibers / rheological properties
Évaluation des caractéristiques chimiques et du comportement rhéologique
de la pelure du pitaya (Hylocereus undatus).
Résumé – Introduction. La pelure du pitaya est utilisée comme ingrédient alimentaire en
raison de la présence de bétacyanines. Cependant ses polysaccharides peuvent également
contribuer à la nutrition en tant qu'agent de texture. Le but de notre travail a été d'évaluer les
caractéristiques chimiques et le comportement rhéologique de la pelure de pitaya. Matériel
et méthodes. Des échantillons de pelure de pitaya ont été analysés quant à leur teneur en
humidité et en sels minéraux, protéines, lipides, sucres, fibres, vitamine C, acidité titrable,
* Correspondence and reprints
matières solides solubles, ainsi que leur pH. Des mesures rhéologiques ont été effectuées
avec un rhéomètre en étudiant la courbe d'écoulement, le balayage du fluage, le balayage de
Received January 4, 2014
fréquence et la variation de température. Résultats et discussion. Les résultats ont montré
Accepted March 4, 2014
que la pelure de pitaya est riche en fibres insolubles et présente un comportement non-newtonien, caractéristique d'un gel avec prédominance d’un caractère solide. En outre, les échantillons ont montré une résistance thermique aux conditions de fréquence, tension et
Fruits, 2014, vol. 69, p. 381–390 température de l’analyse. Conclusion. Compte tenu de ces résultats, en plus d'être appliquée
© 2014 Cirad/EDP Sciences
en tant que colorant naturel dans l'alimentation, la pelure de pitaya pourrait également contriAll rights reserved
buer à la valeur nutritionnelle et à la texture des produits.
DOI: 10.1051/fruits/2014028
www.fruits-journal.org
RESUMEN ESPAÑOL, p. 390
Brésil / Hylocereus undatus / fruits / sous-produit / pelure / composition
chimique / fibre / propriété rhéologique
Article published by EDP Sciences
Fruits, vol. 69 (5)
381
F.R. de Mello et al.
1. Introduction
Pitaya is a tropical fruit and its name, of Antillean origin, means scaly fruit. This fruit
belongs to the Cactaceae family from which
various species of epiphytic cacti of the
genus Hylocereus and Selenicereus, native
to Mexico and Central and South America,
are also cultivated in the countries of Southeast Asia [1, 2].
Hylocereus undatus is the most cultivated
and consumed species of pitaya. The fruits
of this species present market demand, due
to its very attractive sensory characteristics.
Despite considerable research on its
nutritional importance, medicinal and food
value, the pitaya is still a culture not widely
used and exploited [3]. The fruit has a high
nutritional value, and is rich in calcium,
phosphorus, potassium and vitamins. Furthermore, it can also be considered as a
source of carbohydrates and fibers [4, 5].
Studies conducted with the pitaya emphasized its functional properties helping to
reduce the risk of chronic diseases and its
potential to contribute to physical and mental wellness [6–8]. Pulp showed antioxidants
[9, 10], and oligosaccharides with prebiotic
properties [8]. Pitaya peel presented high
quantities of antioxidants [11]. Moreover, its
seeds are rich in essential fatty acids and
phytosterols [12, 13].
The pitaya peel represents up to one third
of the fruit weight; it is considered a residue
of the pitaya processing industry [14, 15].
The waste of fruit and vegetable processing
is traditionally considered an environmental
problem, however it has been increasingly
used for the extraction of compounds such
as pigments [16]. Pitaya peels may be subjected to simple and economical purification
methods to provide extracts and sub-fractions for the formulation of healthcare products and food applications [15].
Aside from being rich in antioxidants [11]
and phenolic compounds [17], pitaya peel
presents high concentration of fibers and
polysaccharides which are responsible of its
texture and rheological behavior, and can
be useful for the food industry as a texture
agent.
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Fruits, vol. 69 (5)
According to Jamilah et al., the total fiber
content of pitaya is very high (69.3%), of
which 56.50% corresponds to insoluble fiber
(IF) and 14.82% to soluble fiber (SF) [14].
The main polysaccharides present are
pectins, hemicelluloses and cellulose, lignin
and starch. Pectin fractions were mainly
composed of arabinose, galactose and
rhamnose, while the hemicellulose fraction
mainly consisted of glucose and xylose [18].
Knowledge of the rheological properties
of raw materials used in the food industry
is essential for the development of new food
products, because different materials will
respond differently to external forces which
they are subjected to [19].
The rheological behavior of fluid food
such as fruit juices and pulps is a factor of
great importance in the design of equipment in the food industry; in addition, it is
one of the factors that helps to evaluate the
quality of the product. The rheological
behavior of these materials, which are
mainly comprised of water and the various
solids, such as soluble and insoluble fibers,
results from the interaction between these
elements contributing alone, or potentiated
when combined [19].
Therefore, pitaya peel presents high
potential as a functional ingredient for food
which can improve its nutritional value and
texture. The aim of our study was to evaluate the chemical composition and rheological behavior of the pitaya peel in order to
provide information which could be helpful
for its application in food products.
2. Materials and methods
2.1. Materials
Samples of pitaya (Hylocereus undatus)
(figure 1) were harvested at Embrapa,
Brasília, Brazil, in 2011 and 2012, January.
The fruits (30 units) were packaged and
transported to the Laboratory of Fruits and
Vegetables of the Federal University of Santa
Catarina, where they were stored at a temperature of 6 °C.
Characteristics and rheological behavior of pitaya
The reagents used were all of analytical
grade. The enzymes α-amylase, protease,
amyloglucosidase were obtained from
Megazyme (Ireland). The other reagents
(sodium hydroxide, ether, sulphuric acid,
anhydrous sodium sulfate, copper sulfate,
boric acid, ethanol, hydrochloric acid,
oxalic acid, ascorbic acid, sodium dichlorophenolindophenol (DCFI), zinc acetate,
copper sulfate, sodium potassium tartrate,
acetone, zinc acetate, potassium ferrocyanide) were obtained from Vetec (Rio de
Janeiro, Brazil). The water used was filtered
through a deionization system (Milli-Q
deionizer, Millipore, Bedford, USA).
2.2. Methods
2.2.1. Sample preparation
The fruits were washed and manually separated in exocarp (dirt, scales and cladode
fragments), mesocarp (peel and endocarp)
and pulp with seeds (figure 2).
Figure 1.
Pitaya fruit (Hylocereus undatus).
The fresh mesocarp was used for chemical analysis. Part of the pitaya peel was
dehydrated in an oven (DLS04, DeLeo,
Brazil) at 45 °C for about 12 h. Samples
were ground in a grinder mill (Q298 A21,
Quimis, Brazil) in order to obtain a homogeneous mixture which was passed through
standard sieves of 100 mesh (150 µm) for
analysis.
For the rheological analysis, dehydrated
pitaya peels were rehydrated with 90%
water and homogenized (L4RT, Silverson
Machines Ltd., U.K.) at 9000 rpm for 3 min.
2.2.2. Chemical characterization
The chemical analysis was performed with
the mesocarp of three fruits of each harvest
(2011 and 2012).
Analyses of fibers (soluble and insoluble)
and sugars (reducing and non-reducing)
were performed in duplicate. All other analyzes were performed in triplicate according
to the standards recommended by the Association of Official Analytical Chemists
(AOAC) [20].
The pH readings were taken with a digital
pH meter (Q-400A, Quimis, Brazil) calibrated with buffers 4.0 and 7.0. The values
of soluble solids (°Brix) were obtained on
a digital refractometer (LLI 58,318, Mettler
Toledo, Switzerland). The titratable acidity
was measured by titration with 0.1 mol⋅L–1
NaOH and acidity expressed as percent
standard solution.
The moisture content was obtained by
oven drying (DLS04, DeLeo, Brazil) at
105 °C until constant weight. The ash was
determined by incinerating the sample at
550 °C in a muffle (Q-318M24, Quimis,
Fruits, vol. 69 (5)
Figure 2.
Preparation of samples for
evaluating chemical
characteristics and rheological
behavior of pitaya (Hylocereus
undatus) peel.
A color figure is available at
www.fruits-journal.org.
383
F.R. de Mello et al.
Brazil) to constant weight. The protein was
analyzed by the Kjeldahl method, based on
nitrogen determination by digestion of
organic matter. Lipids were extracted with
ethylic ether by the Soxhlet method.
The soluble and insoluble fibers were
determined through enzymatic-gravimetric
methods. The non-reducing and reducing
sugars were determined by acid hydrolysis
and the results expressed in reducing carbohydrates into glucose and non-reducing
carbohydrates as sucrose. The vitamin C
content was quantified by the Tillmans
method based on reducing sodium
2,6-dichlorophenolindophenol (DCFI) and
expressed as mg of ascorbic acid.100 g–1 of
the product.
The frequency sweep was then conducted
applying the preselected strain, increasing
the oscillatory frequency over time from (0.1
to 100) Hz at 25 °C.
The rheological behavior of the sample was
also evaluated with variation of temperature,
using a heating program of 3 °C⋅min–1,
increasing the temperature from (5 to
95) °C, at a frequency of 1 Hz. In order to
prevent solvent evaporation, a layer of mineral oil was applied around the rheometer
plate. This temperature range was chosen
due to the storage temperature in the refrigerator, approximately 5 °C, and the pasteurization temperature of fruit juices, approximately 95 °C.
2.2.3. Rheological analysis
Rheological measurements were performed
on rheometer (Mars II, Thermo Electron
GmbH, Germany) coupled to a thermostatic
bath (K15, Haake, Germany), a thermo
circulator water (DC5, Haake, Germany),
and a thermal controller (Peltier, Haake,
Germany), using sensor plate-plate.
The flow curves were obtained applying
shear rates ranging from 0.1 to 300 s-1 at
25 °C, with 100 data acquisition points, in
triplicate. The results obtained from the flow
curve were fitted using the power
law (Ostwald-de-Waele): τ = k (γ)n, and the
Herschel-Bulkley model: τ = τ0 + k (γ)n [21,
22], where τ = shear stress (Pa), τ0 = yield
stress (Pa), γ = shear rate (s–1), K = consistency index (Pa⋅s–1), n = flow behavior index
(dimensionless).
The parameters k and n are widely used
in the characterization of fluids. For a Newtonian fluid, n = 1. When n is different to
1, a non-Newtonian fluid is characterized. In
this case, if n is less than 1, the fluid shows
pseudoplastic behavior, and if n is more
than 1, the fluid shows dilatant behavior.
The k values are related to the resistance to
fluid flow [23].
A stress sweep was performed in the
range of (0.1 to 10) Pa at frequencies of
(1 and 10) Hz at 25 °C, in order to verify the
linear viscoelastic range and to select the
strain that would be used to perform the
frequency sweep and temperature ramps.
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Fruits, vol. 69 (5)
3. Results and discussion
3.1. Chemical characterization
According to our results, pitaya peel has a
high concentration of water (2011 harvest =
90.23%; 2012 harvest = 84.86%) (table I).
Jamilah et al. reported that pitaya peel from
Hylocereus polyrhizus species presents
92.65% moisture content [14].
The samples showed low concentrations of mineral content (2011 harvest,
0.17 g⋅ 100 g–1; 2012 harvest, 0.22 g⋅100 g–1),
proteins (2011 harvest, 0.64 g⋅100 g–1; 2012
harvest, 0.66 g⋅100 g–1) and lipids (2011
harvest, 0.02 g⋅100 g–1; 2012 harvest,
0.07 g⋅100 g–1) (table I). The protein content of pitaya varies considerably from
(0.3 to 1.5) g⋅100 g–1 [24, 25]. This difference can be attributed to the methodologies applied or to the possible interference
of other nitrogen compounds such as
betalains.
Pitaya peel from the 2011 harvest presented less reducing sugars (0.70 g⋅100 g–1)
than that of the 2012 harvest (2.62 g⋅100 g–1)
(table I). Wichienchot et al. reported that
the main reducing sugars of pitaya are glucose and fructose [8].
The non-reducing sugar levels were
lower than 0.5 g.100 g–1 in all samples analyzed. This result is in agreement with
(%)
Lipids
Reducing
sugars
84.86 ± 0.650 0.22 ± 0.180 0.66 ± 0.006 0.07 ± 0.030 2.62 ± 0.020
Protein
2012
Mineral
content
90.23 ± 0.250 0.17 ± 0.005 0.64 ± 0.002 0.02 ± 0.008 0.70 ± 0.000
Moisture
content
2011
Year of
harvest
< 0.5
< 0.5
Non–
reducing
sugars
1.30 ± 0.99 5.70 ± 0.71 7.04 ± 0.88
0.25 ± 0.04
0.22 ± 0.06
Insoluble
Vitamin C Titratable acidity
fiber
(mg.100 g–1)
(mg malic
acid.100 g–1)
2.14 ± 0.00 2.90 ± 0.00 7.62 ± 2.21
Soluble
fiber
pH
12.77 ± 1.01 4.83 ± 0.03
7.15 ± 0.05 5.48 ± 0.06
Soluble
solids
(°Brix)
Table I.
Chemical characteristics of pitaya (Hylocereus undatus) peel from samplings done on the 2011 and 2012 harvests. Data are the average from
three repetitions.
Characteristics and rheological behavior of pitaya
Fruits, vol. 69 (5)
385
F.R. de Mello et al.
Stintzing et al. who reported that the pitaya
juice is devoid of sucrose [25].
Physicochemical properties of dietary
fiber include solubility, viscosity, water and
oil holding capacity, stabilizing, gel-forming
and fermentation. Compared with insoluble
dietary fiber, in food processing, the soluble
fraction demonstrates greater capacity to
provide viscosity, ability to form gels and/
or act as emulsifiers. Insoluble fiber usually
has high water-holding capacity.
Insoluble fiber (IF) was present in greater
quantity than soluble fiber (SF) in all samples. The [IF/SF] ratio was [2.90/2.14] in the
2011 harvest and [5.70/1.30] in the 2012 harvest. Jamilah et al. reported that pitaya peel
presents a relation of [IF/SF] of [3.8/1.0] [14].
According to Horn, the recommended ratio
of [IF/SF] in food is [3/1] [26]. Therefore, the
pitaya peel from the 2012 crop presented a
good [IF/SF] ratio, indicating the presence of
dietary fiber with good physiological effect.
Different values were obtained by
Zhuang et al. that determined the contents
of total fiber (TF), soluble fiber (SF), insoluble fiber (IF) of fiber rich powders (FRP)
from pitaya peels with different particle
size [27]. Dried peels were milled and
meshed through the 80 (FRP 80), 140 (FRP
140) and 250 (FRP 250) meshes. Results
showed that FRP 140 had the highest total
fiber (79.37%) and soluble fiber (33.07%)
with a balanced ratio of [SF/IF] [1.00/1.32].
The [SF/IF] ratios of FRP 80, and FRP 250
were [1.00/1.99], and [1.00/1.41], respectively. The particle size of milled peels
affected the fiber compositions.
From the physiological viewpoint, dietary fiber generally has properties such as
decreased intestinal transit time and
increased stool bulk; it is fermentable by
colonic micro flora; it reduces total blood
and/or LDL cholesterol levels; it reduces
postprandial blood glucose and/or insulin
levels, contributing to reduction in the risk
of chronic disorders, e.g., coronary heart
disease, diabetes, obesity and some forms
of cancer [28, 29].
The soluble fibers present in pitaya peel
can help in the digestive process, neutralize
toxic substances such as heavy metals and
may be associated with the regulation of
386
Fruits, vol. 69 (5)
blood sugar in people with type II diabetes
[5]. Moreover, pitaya peel presents mucilage
that can have a positive influence on cholesterol metabolism [30].
Hadi administered pitaya extracts to
hyperglycemic rats and observed that, after
seven weeks of supplementation, the mice
showed reduced levels of glucose in the
blood, triglycerides and LDL cholesterol,
and increased levels of HDL cholesterol and
antioxidants in the plasma [31].
Pitaya is a fruit with low levels of
vitamin C [4]. Pitaya peel presented (7.62
and 7.04) mg⋅100 g–1 of vitamin C in
the 2011 and 2012 harvests, respectively
(table I). Although low, these levels of
vitamin C are in the same range of other
fruits, such as apple (6.0 mg⋅100 g–1) and
plum (3.0 mg⋅100 g–1) [32]. Choo and Yong
reported that the pitaya pulp with seeds presented 31.1 mg⋅100 g–1 of vitamin C while
pitaya fruit (pulp + seeds + peel) presented
11.6 mg⋅100 g–1 of vitamin C [33].
Pitaya peel has low acidity: (0.22 and
0.25) mg of malic acid⋅100 g–1 of sample
for the 2011 and 2012 harvests, respectively
(table I). The acidity and soluble solids
content of the fruits are considered as
important quality criteria for the flavor classification. The total acidity decreases with
fruit ripening due to the respiration process
and use of organic acids as substrates in
metabolic reactions [34].
Pitaya peel presented (7.15 and
12.77) °Brix for the 2011 and 2012 harvests,
respectively (table I). Chitarra and Chitarra
reported that the fruits in general have a
mean soluble solid between (8.0 and
14.0) °Brix [35]. Junqueira et al. found that
values of soluble solids of pitaya pulp
ranged between 13.0–15.0 °Brix [2].
The pH values for pitaya peel were high
(2011 harvest: 5.48; 2012 harvest: 4.83).
These results are in agreement with Stintzing et al. [25] and Fernandes et al. [36] who
reported that pitaya pulp has a pH of 4.82
and 4.6, respectively.
3.2. Rheological analysis
Our results regarding ground pitaya peel
in water showed that the flow curve
Shear stress (Pa)
Characteristics and rheological behavior of pitaya
Figure 3.
Flow curve of pitaya peel sample representing the
shear rate dependence of the shear stress,
recorded at 25 °C.
Figure 4.
Effect of frequency on storage modules (G':
elastic modulus) and loss (G'': viscous modulus)
of pitaya peel throughout the entire frequency
range (0.1–10 Hz).
obtained exhibited a nonlinear relationship
between the shear stress and shear rate
(figure 3), thus demonstrating non-Newtonian behavior.
The deviation from Newtonian behavior
of the solution of ground pitaya peel can be
justified by the presence of insoluble particles and suspended insoluble materials consisting of pectin and polysaccharides.
Furthermore, pitaya peel is rich in insoluble
fibers (2011 harvest: 2.90 g⋅100 g–1; 2012:
5.70 g⋅100 g–1) which exert a significant
influence on their rheological behavior.
The results obtained with the flow curves
were fitted by power law (Ostwald-deWaele), these being: consistency index (k) =
131.61 ± 0.80, flow behavior index (n) =
0.20 ± 0.00 and R2 = 0.99; and HerschelBulkley model: yield stress (τ0) = 6.36 ± 0.05,
consistency index (k) = 132.14 ± 6.34, flow
behavior index (n) = 0.20 ± 0.01 and
R2 = 0.99. These values confirmed that the
flow curves are typical of pseudoplastic fluids, because the value of (n) is less than 1
(0.20) in both models, with a good correlation coefficient (R2 = 0.99). The HerschelBulkley model shows that the yield stress is
not significant, since its value is lower than
the standard deviation.
Krokida et al. performed a study comparing various rheological data available in
the literature for fruit pulps, including
guava, raspberry, pineapple, apricot, apple,
mango, tamarind, and blackcurrant and
found that all these pulps fruit exhibit pseudoplastic behavior [37].
The effect of the ground pitaya peel in
water sample on the mechanical response
was investigated by dynamic oscillatory
tests. These assessments are sensitive to
changes in chemical composition and in the
physical structure of the samples due to the
characteristics of non-destructive measuring
method. Stress sweep experiments (1.0 Hz
and 10.0 Hz) were carried out to ensure that
the frequency sweep measurements were
performed within the linear viscoelastic
region. Considering the mechanical spectra
of the pitaya peel sample, dynamic oscillatory results showed G’ (elastic modulus) >
G” (viscous modulus) throughout the entire
frequency range (0.1–10 Hz), showing viscoelastic solid behavior with a gel-like structure. The moduli G’ and G’’ are dependent
on the frequency (figure 4). According to
Rao, a weak gel presents G’ and G’’ dependent on the frequency and low range
between G’ and G’’, like that shown for the
pitaya peel sample [38].
Montoya-Arroyo et al. reported that
pitaya peel has high viscosity values at low
concentrations and the shear-thinning flow
behavior showed interesting similarities to
that of commercial thickeners like locus
bean gum and guar gum [18]. Therefore,
pitaya pericarp is suggested to be a promising alternative to these commercial gums.
To evaluate their thermal stability, the
ground pitaya peel in water sample was submitted to temperature variations, from 5 °C
to 95 °C at 3 °C per min. Results show
Fruits, vol. 69 (5)
387
F.R. de Mello et al.
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Effect of increasing
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at 1 Hz.
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and thermo stability at the conditions of frequency, tension and temperature analyzed.
The predominance of insoluble fibers can
justify this rheological behavior of the pitaya
peel at several temperatures.
Acknowledgements
The authors are grateful to Embrapa
Cerrado for providing the pitaya samples
and technical information, and to Dr Nilton
Tadeu Vilela Junqueira for providing scientific information on the pitaya fruit.
388
Fruits, vol. 69 (5)
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Fruits, vol. 69 (5)
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F.R. de Mello et al.
Evaluación de las características químicas y del comportamiento reológico
de la cáscara de la pitahaya (Hylocereus undatus).
Resumen – Introducción. La cáscara de la pitahaya se emplea como ingrediente alimentario, ya que presenta betacianinas. Sin embargo sus polisacáridos pueden contribuir también a
la nutrición como agente de textura. El objetivo de nuestro estudio fue el de evaluar las características químicas y el comportamiento reológico de la cáscara de la pitahaya. Material y
métodos. Se analizaron muestras de cáscara de pitahaya en cuanto a su contenido de humedad y de sales minerales, proteínas, lípidos, azúcares, fibras, vitamina C, acidez valorable,
materias sólidas solubles, así como su pH. Se efectuaron medidas reológicas con un reómetro, para estudiar la curva de flujo, el barrido de la fluencia, el barrido de frecuencia y la
variación de temperatura. Resultados y discusión. Los resultados mostraron que la cáscara
de la pitahaya es rica en fibras insolubles y presenta un comportamiento no Newtoniano,
característica de un gel con predominancia de un carácter sólido. Además, las muestras revelaron una resistencia térmica a las condiciones de frecuencia, tensión y temperatura del análisis. Conclusión. Habida cuenta de estos resultados, además de aplicarse como colorante
natural en la alimentación, la cáscara de pitahaya podría asimismo contribuir al valor nutricional y a la textura de los productos.
Brasil / Hylocereus undatus / frutas / subproductos / piel (vegetal) /
composición química / fibras / propiedades reológicas
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Fruits, vol. 69 (5)