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Food Hydrocolloids 77 (2018) 646e658
Contents lists avai
Food Hydrocolloids
journal homepage: www.elsevier .com/locate/ foodhyd
Eriobotrya japonica seed as a new source of starch: Assessment of
phenolic compounds, antioxidant activity, thermal, rheological and
morphological properties
Rafaela Cristina Turola Barbi, Gerson Lopes Teixeira, Polyanna Silveira Hornung,
Suelen �Avila, Rosemary Hoffmann-Ribani*
Food Engineering Graduate Program, Federal University of Paran�a, Polytechnic Center, 81531-980, Curitiba, Brazil
a r t i c l e i n f o
Article history:
Received 9 August 2017
Received in revised form
1 November 2017
Accepted 3 November 2017
Available online 16 November 2017
Keywords:
Loquat seed
Starch
Rheological behaviour
Antioxidant activity
Thermal analysis
Microstructure
* Corresponding author.
E-mail address: ribani@ufpr.br (R. Hoffmann-Riba
https://doi.org/10.1016/j.foodhyd.2017.11.006
0268-005X/© 2017 Elsevier Ltd. All rights reserved.
a b s t r a c t
Investigating non-conventional starch sources is essential because different chemical compositions,
granular sizes and shapes, and amylose and amylopectin ratios, reveal new technological features. The
loquat (Eriobotrya japônica), which is from the Rosaceae plant family, has a high amount of starch in its
seeds (y 20%). Thus, this study aimed to characterise the physicochemical, thermal, rheological and
structural properties, as well as the bioactive compounds, of loquat seed starch (LSS) derived from urban
afforestation and commercial fruits at two stages of maturity: ripe (RI) and unripe (UN). Scanning
electron micrographs showed oval- and cylindrical-shaped LSS granules. Using X-ray diffraction patterns
it was possible to classify the LSS as having a C-type crystalline structure. The LSS (RI and UN) exhibited a
higher thermal stability range in relation to degradation than conventional starches in the thermogra-
vimetric assays (TG/DTG). Using differential scanning calorimetry it was possible to suggest a correlation
between the peak temperatures with the gelatinisation temperatures obtained by the oscillatory shear
test of the LSS. The rheological assays revealed that the LSS gels present pseudoplastic behaviour, with a
high degree of thixotropy. Furthermore, higher content of polyphenols and higher antioxidant capacity
were observed for the UN unpurified starch samples. Seven bioactive compounds were quantified in the
raw starches by Ultra-High Performance Liquid Chromatography, with major concentrations of kaemp-
ferol (up to 330.46 mg/kg) and 5-caffeoylquinic acid (up to 135.00 mg/kg). The LSS showed compatible
characteristics for industrial usage as an alternative to chemically modified starches.
© 2017 Elsevier Ltd. All rights reserved.
1. Introduction
Starch is the main source of carbohydrates in the human diet
and it has great nutritional and technological importance in the
food industry. It also has several applications in non-food industries
including pharmaceuticals, fertilisers, paper and adhesives (Albano,
Franco, & Telis, 2014).
The industrial use of starch is defined according to its features
such as gelatinisation temperature, gel formation and paste vis-
cosity. Starch is found in plant tissues in granular form and it is
composed of amylose and amylopectin molecules. Every botanical
source of starch has different particularities that affect its techno-
logical behaviour and, consequently, its potential for industrial
ni).
usage (Hoover, 2001).
Starch is mostly employed in industries in a modified form
because native starch does not always provide the appropriate
properties to meet the requirements of industrial processes (e.g.
acidity, high temperature resistance etc.). However, interest in the
replacement of chemically modified starches is increasing due to
environmental concerns and the increased consumption of natural
products. Therefore, new non-conventional amylaceous sources are
being studied in order to provide alternatives for food production
(Przetaczek-Ro _znowska, 2017).
The starch derived from loquat seeds represents an alternative
starch source. The loquat (Eriobothrya japonica) plant belongs to the
Rosaceae family, which also includes the common or European
plum (Prumus domestica L.) and other popular fruits such as
strawberries and peaches, which are found worldwide. The loquat
is an exotic subtropical fruit that develops well in regionswhere the
annual average temperature is above 15 �C. The commercial
mailto:ribani@ufpr.br
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R.C. Turola Barbi et al. / Food Hydrocolloids 77 (2018) 646e658 647
production of loquats is concentrated in more than 20 countries
including China, Japan, India, Australia, Brazil, Israel, Italy, Spain,
Turkey and the United States (Tian, Qin, & Li, 2011).
Previous studies about the skin, pulp and seed of the loquat
evaluated its phenolic extract in order to identify bioactive com-
pounds that could benefit human health when consumed (Koba,
Matsuoka, Osada, & Huang, 2007). Delfanian, Kenari, and Sahari
(2016) reported on the antioxidant activity of the leaves and skin
of the loquat and the viability of its application in soybean oil in
order to replace synthetic antioxidants by natural sources. Zheng,
Xia, and Lu (2015) evaluated drying methods and their possible
influence on the content of components in loquat flowers when
used as tea.
Despite the fact that the loquat fruit has been the subject of
several studies in recent years, as well as the fact that the presence
of bioactive compounds in its composition (skin, pulp, flowers and
seeds) has been proven, no detailed studies of its seed starch fea-
tures were found.
The properties of starches, particularly gelatinisation and paste
behaviour, are of great interest to the food industry and to other
industrial segments. Taking into consideration the scarcity of sci-
entific data regarding the starch properties of loquat seeds, the
present study aimed to characterise this non-conventional starch
source obtained from fruits of urban afforestation and commercial
cultivars in terms of its physicochemical, thermal, rheological,
morphological and functional properties in order to enable future
industrial applications.
2. Materials and methods
2.1. Materials
The loquat (Eriobothrya japonica) seeds were harvested in an
area of urban afforestation at two stages of maturity: ripe (RI) and
unripe (UN). Because no commercial UN sample was available, only
a RI sample was purchased in the local market of Curitiba (Paran�a
State, Brazil). The loquat fruit samples codified as “A” (RI and UN)
were collected in the area surrounding the “Major Antônio Couto
Pereira” football stadium (25�25017.800S 49�15040.000W). The sam-
ples codified as “B” (RI and UN) were harvested at the Federal
University of Paran�a, Polytechnic Campus, Curitiba, Paran�a, Brazil
(25�27006.100S 49�13058.700W), and the samples codified as “C” (RI
and UN) were collected from “Senador Batista de Oliveira” Street,
Curitiba, Paran�a, Brazil (25�27014.000S 49�13057.400W). The loquat
seed starch properties derived from urban afforestation were
compared to the commercial sample codified as “D” only at the ripe
(RI) stage, and to conventional starches found in the literature.
2.2. Starch extraction
The loquat seed starch was extracted using the methodology
described by Hornung et al. (2017) with modifications. The loquat
seeds were removed from the fruit pulp, dried in an air-forced oven
(40 �C/48 h), and then ground in a knife mill (60 mesh) to obtain a
flour. The starch was extracted from the seed flour suspended in
distilled water (1:15) and then homogenised by stirring in amagnet
plate for three minutes. The slurry was sieved (320 mesh)http://refhub.elsevier.com/S0268-005X(17)31379-6/sref33
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	Eriobotrya japonica seed as a new source of starch: Assessment of phenolic compounds, antioxidant activity, thermal, rheolo ...
	1. Introduction
	2. Materials and methods
	2.1. Materials
	2.2. Starch extraction
	2.3. Physicochemical characterization
	2.4. Morphological properties
	2.5. Thermal analysis
	2.6. Rheological measurements
	2.6.1. Steady-state rheology
	2.6.2. Oscillatory shear
	2.7. Extraction of phenolic compounds
	2.7.1. Quantification of total phenolic compounds
	2.7.2. DPPH• radical scavenging capacity
	2.7.3. Ferric reducing antioxidant power (FRAP)
	2.7.4. ABTS•+ radical scavenging capacity
	2.7.5. Determination of phenolic acids by UHPLC-DAD
	2.7.6. Statistical analysis
	3. Results and discussions
	3.1. Chemical composition of starch extracts
	3.2. Granule morphology
	3.3. Thermal properties
	3.3.1. Differential scanning calorimetry (DSC)
	3.3.2. Thermogravimetric (TG) and differential thermogravimetric analysis (DTG)
	3.4. Rheological behaviour
	3.4.1. Steady shear
	3.4.1.1. Rheological models
	3.4.2. Oscillatory shear
	3.5. Total phenolic content and antioxidantcapacity
	3.6. Phenolic acids and flavonoid profile
	4. Conclusion
	Appendix A. Supplementary data
	Referencesand left
to decant at 4 �C for 24 h. The supernatant was discarded and the
starch was vacuum filtered and washed with distilled water, dried
at 40 �C for 24 h, sieved (150 mesh) and kept in amber glasses in a
desiccator until the moment of analysis. No further purification
process was applied.
2.3. Physicochemical characterization
The moisture content was determined by desiccation at 105 �C
(oven); total proteins by the Kjeldahl method; total lipids by
exhaustive extraction with petroleum ether in Soxhlet apparatus;
and fixed mineral residue by incineration in a muffle at 550 �C
using the AOAC (2000) protocols 930.15, 990.03, 920.39 and 942.05,
respectively. The total carbohydrate content was obtained by dif-
ference to 100%. The apparent amylose content was determined
according to the methodology described by Martinez & Cuevas
(1989) by colorimetry.
2.4. Morphological properties
The LSS granules were examined by scanning electron micro-
scopy (SEM) through a Tescan Vega 3 (Kohoutovice, Czech Repub-
lic) microscope. The starch was scattered on double adhesive tape
adapted in a metallic support. The micrographs (magnification
1000 �) were obtained with an acceleration of 15 kV under low
vacuum. The average sizes of the starch granules were calculated
using ImageJ free software (version 1.49 v).
The X-ray diffraction powder patterns (XRD) of the samples
were investigated using a X-ray diffractometer (Bruker emodel D8
Advance) employing Cu Ka radiation (l ¼ 1.5406 Å) and settings of
40 kV and 20 mA. The scattered radiation was detected in the
angular range of 5e80� (2q) with a scanning speed of 2� min�1 and
a step of 0.041�. The relative crystallinity was estimated using
Origin 8.6 software (OriginLab Corporation, Massachusetts, USA).
2.5. Thermal analysis
The thermogravimetric curves (TG/DTG) were obtained using a
TGA 4000 Perkin Elmer thermal analysis system (Perkin Elmer Inc.,
Waltham, Massachusetts, USA) following the proceedings
described by Hornung, do Prado Cordoba et al., (2016) and
Hornung, Oliveira, and Rosa (2016) with some alterations.
Approximately 6 mg of the samples were heated from 30 to 600 �C
(10 �C/min) in open aluminum crucibles under synthetic air at-
mosphere (50 mL/min). Using differential scanning calorimetry
(DSC), the gelatinisation curves were recorded in DSC 8000 (Perkin
Elmer Inc., Waltham, Massachusetts, USA) equipment. The starch
samples were suspended in ultrapure water (1:4, m/m) and heated
(30e100 �C; 10 �C/min) under a nitrogen atmosphere (20 mL/min)
in sealed aluminum crucibles. The results from the TG/DTG and DSC
curves were acquired using Pyris software (Perkin Elmer Inc.,
Waltham, Massachusetts, USA).
2.6. Rheological measurements
2.6.1. Steady-state rheology
The starch gels were prepared at a concentration of 6 g starch/
100 g suspension in distilled water. Measurements of the rheo-
logical deformations of the LSS gels were performed on a Haake
Mars II rheometer (Thermo Electron GmbH, Germany), connected
to a thermostatic bath (Haake K15), thermo-circulator water unit
(Haake DC5B3) and a Peltier temperature control (Haake TC 81),
using a cone-plate sensor with a diameter of 60 mm (cone angle of
2�). The flow curves were obtained at rates of 0.1e500 s�1 for 300 s,
following the methodology of Albano et al. (2014) with modifica-
tions described in detail by Teixeira, Züge, Silveira, Scheer, and
Ribani (2016). Analysis was performed at different temperatures
(30, 50 and 70 �C). The experimental data obtained from the flow
curves were adjusted according to the Ostwald-de Waele (Eq. (1))
and Herschel-Bulkley (Eq. (2)) models:
R.C. Turola Barbi et al. / Food Hydrocolloids 77 (2018) 646e658648
t ¼ K _gn (1)
t ¼ t0H þ KHð _gÞH (2)
where: t is the shear stress (Pa); _g is the shear rate (s�1); t0H is the
Herschel-Bulkley yield stress (Pa); K and KH are the consistency
indices, (Pa.sn); and n and nH are the flow behaviour indices
(dimensionless).
To evaluate the fit of each model, the coefficient of determina-
tion (R2) and chi-square (c2) methods were used. The data from the
apparent viscosity curves at 1.0 s�1 was used to calculate the effect
of temperature (30e70 �C) on the starch gels by using the Arrhe-
nius equation (Eq. (3)):
h ¼ h0exp
�
Ea
RT
�
(3)
where h is the apparent viscosity at a specific shear rate; h0 is the
pre-exponential factor; Ea is the activation energy (J/mol); R is the
gas constant (8.31 J/K.mol�1); and T is the absolute temperature (K).
2.6.2. Oscillatory shear
The frequency sweeps were performed between 0.1 Hz and
10.0 Hz at different temperatures (25 �C, 35 �C, 55 �C and 75 �C) to
obtain the mechanical spectra of the starch gels. In order to
determine the gelatinisation temperatures of the starches, sus-
pensions containing 6% (w/w) LSS were prepared and submitted to
temperature ramps of 50e90 �C at a constant frequency of 0.1 Hz
and a tension of 0.1 Pa, with a heating rate of 2 �C/min (Albano et al.,
2014; Teixeira et al., 2016).
2.7. Extraction of phenolic compounds
The phenolic extracts of the raw LSS were obtained according to
the methodology described by Panteli�c et al. (2016), with modifi-
cations. A quantity of 2 g of each sample was dissolved in 20 mL of
water-methanol (20:80, v/v) and gently stirred for one hour. The
mixture was subsequently centrifuged at 5000 rpm for 15 min and
the supernatant was collected and stored at 4 �C in amber flasks for
further analysis.
2.7.1. Quantification of total phenolic compounds
The total phenolic compound content was determined using the
Folin-Ciocalteu colorimetric method as described by Singleton and
Rossi (1965) with some alterations. An appropriately diluted sam-
ple (12 mL) was added to 144 mL of distilled water and to 48 mL of
freshly prepared Folin-Ciocalteu reagent in a 96-well microplate.
After three minutes, 36 mL of saturated sodium carbonate solution
was added and the samples were kept in the dark for 1 h at room
temperature. The absorbance was measured at 720 nm in an
Infinite M200 NanoQuant microplate reader (Tecan Trading AG,
Switzerland). A gallic acid (2.5e450 mg/mL) standard curve was
used. The results were expressed as mg of gallic acid equivalents
(GAE) per 100 g of the samples.
2.7.2. DPPH� radical scavenging capacity
The DPPH assay was carried out according to Brand-Williams,
Cuvelier, and Berset (1995). Briefly, 5 mL of the sample extracts or
standards were added to 195 mL of DPPH radical solution (125 mmol/
l), which was freshly made in methanol. After 30 min incubation in
the dark at room temperature, the absorbance was obtained at
517 nm using an Infinite M200 NanoQuant microplate reader
(Tecan Trading AG, Switzerland). The DPPH radical scavenging ac-
tivity of the extracts were expressed as mmol of Trolox equivalents
(TE) per milligram of the sample (dry weight basis) using a stan-
dard curve of Trolox ranging from 0.2 to 1 mmol/L.
2.7.3. Ferric reducing antioxidant power (FRAP)
The total antioxidant determination of the loquat starch was
performed using the FRAP assay according to the method proposed
by Benzie and Strain (1996). The assay was performed on a
microplate by adding 10 mL of the diluted sample and 300 mL of the
FRAP reagent. After 30 min of incubation at room temperature in
the dark, the absorbance was measured at 593 nm using a spec-
trophotometer with a microplate reader. The results were
expressed in mmol trolox equivalent/100 g.
2.7.4. ABTS�þ radical scavenging capacity
The ABTS�þ scavenging activity was performed using the
method described by Re et al. (1999) with modifications. The
ABTS�þ cationic radical was prepared with a stock solution of
7mmol/L of ABTS and 2.45mmol/L of potassium persulfate solution
(1:1, v/v). The working solution was stored for 12e16 h at room
temperature in the dark. The mixture was then diluted with
methanol and the absorbance was adjusted to 0.700 ± 0.020 at
734 nm. Then, 300 mL of the ABTS solution and 3 mL of the sample
were added to the microplate. The mixture was subjected to gentle
agitationand stored in the dark for 30 min; the absorbance was
measured at 734 nm using a microplate reader spectrophotometer.
The results were expressed in mmol trolox equivalent/100 g.
2.7.5. Determination of phenolic acids by UHPLC-DAD
The chromatographic separation of phenolic acids from the LSS
was performed using an Acquity UPLC H-Class ultra-high perfor-
mance liquid chromatograph (Waters, Miliford, MA, USA) with
diode array detector (Waters, Miliford, MA, USA), a quaternary
pump and an automatic sampler. Phenolic acid standards were
used to compare the results. The analytical column was a
2.1 mm � 50 mm �17 mm C18 Acquity BEH (Waters, Miliford, MA,
USA) kept at 30 �C. The mobile phase consisted of A (0.1% formic
acid in ultra-pure water) and B (0.1% formic acid in methanol). The
best chromatographic separation of the standards was obtained
using a flow rate of 0.4 mL/min and an elution gradient of 0e15% B;
5 min - 60% B; 5.50 min - 90% B; 7.5 min - 15% B; 9 min-15% B,
isocratic elution with 15% B until 20 min, following the method
described by Galani et al. (2017). The chromatograms were moni-
tored at 260, 270, 280 and 300 nm.
2.7.6. Statistical analysis
All the experimental data were analysed for variance (ANOVA).
The Duncan test was used to compare the significance of the
samples with a 95% confidence level (ponce the average particle size provides an idea of the starch gran-
ules homogenisation degree.
Although the starch extraction was efficient, expressed in the
results of centesimal contents (Table 1) as low amount of ash, lipids
and proteins, some granules presented aggregated particles on
their surface, which were believed to be fibres, therefore support-
ing the need for extra purification of the starch (Andrade-Mahecha,
Tapia-Bl�acido, & Menegalli, 2012).
The X-ray diffraction (XRD) patterns of the starch samples
extracted from the loquat seeds are shown in Fig. 2a and the
determined relative degree of crystallinity is shown in Table 2. The
XRD results of the LSS show that the samples (A-D) had high values
Fig. 1. Scanning electron microscopy micrographs of starch granules from loquat seed at 1000� magnification. UN: unripe; RI: ripe.
Table 2
DSC, SEM and XRD results of starches isolated from seed of loquat.
Samples DSC Results SEM Results XRD Results
To (�C) Tp (�C) Tc (�C) DHgel (J/g) Average size (mm) Degree of relative cristallinity (%)
A (UN) 54.41 ± 0.06f 57.89 ± 0.00e 62.67 ± 0.05c 1.25 ± 0.04ab 40.48 ± 5.94a 24.30 ± 0.04e
A (RI) 52.26 ± 0.03g 56.54 ± 0.00g 59.95 ± 0.08d 1.04 ± 0.06c 39.19 ± 4.33ab 23.59 ± 0.04g
B (UN) 54.79 ± 0.02e 57.89 ± 0.00f 62.45 ± 1.81bc 1.06 ± 0.03c 29.05 ± 2.04c 23.82 ± 0.05f
B (RI) 58.08 ± 0.01b 59.48 ± 0.00c 62.56 ± 1.67bc 0.73 ± 0.02d 35.74 ± 6.17b 24.58 ± 0.02c
C (UN) 55.13 ± 0.03d 58.49 ± 0.00d 65.59 ± 1.97abc 1.41 ± 0.07a 30.86 ± 4.14b 24.40 ± 0.02d
C (RI) 57.79 ± 0.09c 59.92 ± 0.01b 65.64 ± 0.04ab 0.83 ± 0.06d 25.49 ± 4.41c 24.99 ± 0.02a
D (RI) 59.17 ± 0.17a 62.80 ± 0.00a 66.52 ± 0.09a 1.18 ± 0.13bc 43.66 ± 3.95a 24.84 ± 0.03b
To,“onset” initial temperature; Tp, peak temperature; Tc,“endset” final temperature; DH, gelatinisation enthalpy. Different lowercase letters mean significant differences be-
tween samples by the Duncan test (pthe unripe samples presented higher areas in the first
ramp than the ripe ones, except for the commercial sample, which
showed the highest area among all the LSS gels, and the highest
hysteresis loops in the three temperature tested (30, 50, and 70 �C).
It could be stated that the LSS gels were strongly impacted by the
maturation stage and the places where the samples were collected.
The studied conditions caused modifications in the characteristics
of the LSS gels, causing thixotropy as a consequence and thereby
collaborating with the decrease in the viscosity of the starch (Steffe,
Fig. 3. TG and DTG curves (aeg) of loquat seed starches measured from 30 to 650 �C, and DSC curves (h) of loquat seed starches obtained from 30 to 90 �C.
R.C. Turola Barbi et al. / Food Hydrocolloids 77 (2018) 646e658652
Table 3
TG and DTG results of Loquat seed starch.
Samples TG results DTG results
Step Dm (%) DT (�C) Tp (�C)
A (UN) 1st 5.14 30e119 66.66
Stability e 119e264 e
2nd 52.26 264e368 319.09
3rd 11.72 368e533 494.78
A (RI) 1st 4.12 30e113 61.25
Stability e 113e266 e
2nd 51.28 266e365 315.73
3rd 10.58 365e547 502.07
B (UN) 1st 4.96 30e112 64.61
Stability e 112e265
2nd 51.58 265e364 316.01
3rd 9.97 364e554 509.93
B (RI) 1st 5.04 30e117 63.36
Stability e 117e255 e
2nd 51.14 255e366 319.33
3rd 10.59 366e538 495.85
C (UN) 1st 5.31 30e117 64.51
Stability e 117e272 e
2nd 53.55 272e380 317.46
3rd 11.53 380e561 516.66
C (RI) 1st 5.05 30e117 60.71
Stability e 117e258 e
2nd 55.27 258e381 320.99
3rd 10.78 381e560 513.74
D (RI) 1st 5.44 30e114 63.12
Stability e 114e261 e
2nd 50.72 261e367 315.82
3rd 10.58 367e546 497.74
Dm mass loss (%); DT, temperature range; Tp, peak temperature.
R.C. Turola Barbi et al. / Food Hydrocolloids 77 (2018) 646e658 653
1996). Similar behaviour was observed for carrot starch gel at a 6%
concentration (Albano et al., 2014).
The activation energy (Ea) of the LSS samples is presented in
Table 4, while the apparent viscosity (h) is shown in Table 4 and
Fig. 4eef. The effect of temperature on the h of the LSS gels was
fitted by the Arrhenius equation (Eq. (3); Fig. S1), resulting in the Ea,
whose values ranged from 8.35 to 20.60 kJ/mol.
The Ea values of the LSS samples derived from unripe fruits were
higher than those obtained from ripe samples. An explanation for
this behaviour is that the gels formed by UN samples exhibited
stronger intermolecular interactions between the granules than the
ones from RI samples, requiring a high Ea (Guinesi et al., 2006). On
the other hand, the commercial sample (D) exhibited the lower Ea,
i.e., this sample needs small energy inputs to its flow.
The temperature and the time employed in the molecular
structure of the starches during industrial processing have an in-
fluence on their physical properties and technological applications
(Teixeira, R�oz, Carvalho, & Curvelo, 2005). Starch with low Ea, such
as samples A (RI), B (RI), C (RI) and D (RI), can be considered as a
potential starch source to be applied in food processing because it
needs a small amount of energy to start the flow of a process, like in
a pumping unit in the industry.
As expected, with increasing temperature, the h of the starches
decreased (Table 4). When a starch suspension is exposed to
heating, the hydrogen bonds are broken, the water molecules
associate with the released hydroxyl groups, and the granules
continue to swell. However, in some cases the friction is intense,
causing the most brittle swollen granules to break into fragments
and leading to a reduction in viscosity (Damodaran et al., 2010).
3.4.1.1. Rheological models. The analysed LSS gels showed a non-
Newtonian flow behaviour; none of the samples presented a
linear relationship between the shear rate and the shear stress. The
Ostwald-de Waele (OW) and Herschel-Bulkley (HB) rheological
models were used to evaluate the flow behaviour of the gels, which
allowed the estimation of empirical rheological parameters. As
shown in Table S1, the starch samples presented high coefficient of
determination values (R2 > 0.97 for OW and R2 > 0.99 for HB), and
low values for chi-square (c2 G00),
indicating the onset temperature of gelatinisation (Tgel) of the
studied starches. The Tgel values measured during the rheological
assays ranged from 63.48 to 70.57 �C (Table 4), while in the DSC
analysis the variation was in the range of 59.95e66.52 �C.
Comparing both methods, the LSS sample D (RI) showed the
Fig. 4. Flow curves (aed) showing thixotropy for 6% gels of loquat seed starches at temperatures of 30 �C, 50 �C, and 70 �C, and the apparent viscosity of the gels measured at 30 �C
(e), 50 �C (f), and 70 �C (g). Closedsymbols: unripe; open symbols: ripe.
R.C. Turola Barbi et al. / Food Hydrocolloids 77 (2018) 646e658654
smallest variation in Tgel, followed by C (RI) and B (UN). Although
some discrepancy amongst the Tgel values for the LSS samples were
found, it was noted that rheological analysis was also suitable to
estimate this parameter. For this reason, this technique can be
chosen as an alternative method to determine Tgel. Samples A (UN),
A (RI), B (UN) and D (RI) showed sol-gel changes comparable to
those of potato starch (65.49 �C) (Hornung et al., 2017) and waxy
rice starch (67.1 �C) (Jacquier, Kar, Lyng, Morgan,&McKenna, 2006).
The low Tgel values of LSS in its unripe and ripe stages contributes to
easy cooking and high digestibility.
As proposed by Cox and Merz (1958), dynamic rheological
properties can be compared with steady shear properties, as
expressed in the following equation:
h*ðuÞ ¼ hað _gÞu ¼ _g (4)
where ha is the apparent viscosity, h
�is the complex viscosity, and _g
is the shear stress.
The purpose of this relationship is to provide information
regarding the structure of food materials. Fig. S2 demonstrates that
Table 4
Comparison between activation energy (Ea), temperature of gelatinisation (Tgel), the apparent viscosity (h), and the area under flow curves of 6% starch gels from loquat seed at
different temperatures.
Sample Ea (kJ/mol) Tgel h (Pa.s)a Rampb Area under flow curve (Pa.s�1)c
30 �C 50 �C 70 �C 30 �C 50 �C 70 �C
A (UN) 20.60 66.98 4.7206 2.7150 1.8242 1st 18.840 18.110 15.280
2nd 16.360 (86.84%) 16.480 (91.00%) 14.410 (94.31%)
A (RI) 15.65 66.16 4.7823 2.3390 2.2519 1st 17.600 14.050 13.160
2nd 15.980 (90.80%) 13.240 (94.23%) 12.490 (94.91%)
B (UN) 21.77 65.27 5.9948 2.8033 2.2113 1st 20.260 12.740 13.230
2nd 18.250 (90.08%) 11.950 (93.80%) 12.510 (94.56%)
B (RI) 14.71 70.57 3.1584 1.5517 1.4231 1st 11.600 11.500 12.220
2nd 9.781 (84.32%) 10.270 (89.30%) 11.390 (93.21%)
C (UN) 37.52 60.76 7.8409 2.4745 1.3964 1st 21.640 11.500 8.997
2nd 19.340 (89.37%) 10.730 (93.30%) 8.857 (98.44%)
C (RI) 14.20 63.48 1.7996 1.9888 1.0972 1st 12.070 9.592 13.820
2nd 10.730 (88.90%) 8.991 (93.73%) 13.510 (97.76%)
D (RI) 8.35 66.13 17.2179 13.0246 11.7414 1st 39.630 32.140 34.220
2nd 32.240 (81.35%) 25.520 (79.40%) 28.320 (82.76%)
a Measured at the shear rate of 1.0 s-1.
b 1st ¼ upward ramp; 2nd ¼ downward.
c The area under the first upward flow curve was taken as 100%.
R.C. Turola Barbi et al. / Food Hydrocolloids 77 (2018) 646e658 655
the values of the modules of complex viscosity (h�) of the starches
(A-D) were higher than those for apparent viscosity (h), showing
that they have deviated from the Cox-Merz rule, which states that
the complex viscosity at a given frequency is equal to the apparent
viscosity at the same shear rate (Moraes, Fasolin, Cunha, &
Menegalli, 2011). This behaviour is attributed to structure rupture
as a result of excessive shear rates during measurements, resulting
in a low apparent viscosity (Schramm, 1998).
This deviation from the Cox-Merz rule could confirm the elastic
structure of the gel, which was not affected by small measurements
of oscillatory amplitude. Commonly, the values of the complex
viscosities of most food dispersions are higher than the apparent
viscosity values (Rao, 2007).
3.5. Total phenolic content and antioxidant capacity
Polyphenols are secondarymetabolites, supporting the essential
functions of the reproduction and growth of plants, acting as a
defence mechanism against pathogens, parasites and predators, as
well as contributing to the pigmentation of plants. Polyphenols,
which are widely distributed in the superior plants, are of much
interest because of their antioxidant activity and their ability to
reduce the risk of diseases caused by oxidative stress such as cancer
(Tokusoglu & Hall, 2011).
The total phenolic content (TPC) present in the LSS was
expressed in mg of GAE per 100 g of the samples, and the antiox-
idant capacity (AC) of the methanolic phenolic extracts determined
by the DPPH, ABTS and FRAP assays was expressed in mmol TE/
100 g. Both of the latter are shown in Table 5.
The TPC content of the starch samples (A-D) ranged from
2.29 mg GAE/100 g to 19.07 mg GAE/100 g. Statistical analysis
showed that the TPC in the analysed starches decreased signifi-
cantly (p77 (2018) 646e658656
phenolic compound content after maturation.
3.6. Phenolic acids and flavonoid profile
Seven bioactive compounds were identified and quantified in
the LSS at the unripe and ripe maturation stages using ultra high-
efficiency liquid chromatography (UHPLC) (Table 1). Of these,
three were hydroxycinnamic acids (chlorogenic, p-coumaric and
trans-cinnamic); three other compounds were flavonoids (kaemp-
ferol, rutin and naringin), and one was hydroxybenzoic acid (3,4-
dihydroxybenzoic).
The most abundant compound in all the raw starch extracts was
the kaempferol, which is a very common antioxidant in fruits and
vegetables, ranging from 99.08 to 330.46 mg/kg of extract. In
addition to its antioxidant properties, kaempferol also has anti-
tumor activity and defends against free radicals, which promote the
Table 5
Total phenolic content and antioxidant activity of phenolic extracts of Loquat seed starch by the DPPH, ABTS and FRAP assays.
Samples Total phenolic content (mg GAE/100 g) DPPH (mmol TE/100 g) ABTS (mmol TE/100 g) FRAP (mmol TE/100 g)
A (UN) 11.17 ± 0.27 c 130.03 ± 1.91 c 174.05 ± 5.26 c 81.87 ± 0.09 d
A (RI) 4.06 ± 0.25 e 60.47 ± 1.36 f 90.79 ± 4.55 f 48.05 ± 0.45 f
B (UN) 19.07 ± 0.23 a 240.94 ± 7.06 a 285.27 ± 5.50 a 155.72 ± 0.62 a
B (RI) 11.14 ± 0.16 c 135.18 ± 4.86 d 158.91 ± 3.98 d 84.64 ± 0.24 c
C (UN) 16.78 ± 0.34 b 192.42 ± 1.40 b 247.50 ± 4.06 b 108.20 ± 0.47 b
C (RI) 6.78 ± 0.38 d 67.66 ± 4.44 e 101.51 ± 3.39 e 57.84 ± 0.33 e
D (RI) 2.29 ± 0.09 f 24.87 ± 1.64 g 49.82 ± 5.29 g 24.43 ± 0.41 g
Different lowercase letters mean significant differences by the Duncan test (pHoover, R. (2001). Composition, molecular structure, and physicochemical proper-
ties of tuber and root starches: A review. Carbohydrate Polymers, 45, 253e267.
Hornung, P. S., �Avila, S., Lazzarotto, M., da Silveira Lazzarotto, S. R., de Andrade de
Siqueira, G. L., Schnitzler, E., et al. (2017). Enhancement of the functional
properties of Dioscoreaceas native starches: Mixture as a green modification
process. Thermochimica Acta, 649, 31e40.
Hornung, P. S., do Prado Cordoba, L., da Silveira Lazzarotto, S. R., Schnitzler, E.,
Lazzarotto, M., & Ribani, R. H. (2016). Brazilian dioscoreaceas starches. Journal of
Thermal Analysis and Calorimetry, 127, 1869e1877.
Hornung, P. S., Oliveira, S. De, & Rosa, S. (2016). Investigation of the photo-oxidation
of cassava starch granules. Journal of Thermal Analysis and Calorimetry, 123,
2129e2137.
Ionashiro, M. (2004). Giolito - fundamentos da Termogravimetria An�alise T�ermica
Diferencial Calorimetria Explorat�oria Diferencial (Giz Editorial).
Jacquier, J. C., Kar, A., Lyng, J. G., Morgan, D. J., & McKenna, B. M. (2006). Influence of
granule size on the flow behaviour of heated rice starch dispersions in excess
water. Carbohydrate Polymers, 66, 425e434.
Juliano, B. O., Onate, L. U., & del Mundo, A. M. (1965). Relation of starch composition,
https://doi.org/10.1016/j.foodhyd.2017.11.006
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	3.6. Phenolic acids and flavonoid profile
	4. Conclusion
	Appendix A. Supplementary data
	References