LWT - Food Science and Technology 154 (2022) 112757

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LWT
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Nutritional composition and physicochemical properties of oat flour sieving

fractions with different particle size
Yujuan Gu , Xiaojie Qian , Binghua Sun , Sen Ma **, Xiaoling Tian , Xiaoxi Wang *
College of Food Science and Engineering, Henan University of Technology, 100 Lianhua Rd., Zhengzhou, Henan Province, China

A R T I C L E I N F O A B S T R A C T

Keywords: Nutritional constituents, hydration, pasting, and thermal properties of oat flour sieve fractions (74–180 μm) and
Oat flour the relationship between composition and characteristics were studied. Starch constituents, protein components
Particle size (except for albumins), and saturated fatty acids (SFA) were mostly distributed in small particle fractions, while
Composition
total protein, albumin, dietary fiber (DF), lipids, and unsaturated fatty acids (UFA) were abundant in large
Pasting property
Thermal property
particle fractions. Amino acids (except for Tyr and Gly) of group I, II, and III were significantly lacking in S2
(150–180 μm), and Cys decreased from 2.51% to 1.50% with the decrease in sieving particle sizes. The largest
particles showed the highest water solubility index (WSI, 9.90%), the medium particles (100–132 μm) exhibited
the highest pasting viscosities (final viscosity of 4148 cP), and the smallest particles had the maximum gelati­
nization enthalpy (ΔH, 3.2 J/g). Correlation analysis demonstrated that except for the basic components, Glu,
Cys, Iso, Phe, C16:0, C18:0, and C18:2n6c also significantly affected the WSI and pasting properties of oat flour,
while amylose, Gly, Ala, Val, Met, and C20:1 were highly correlated with thermal properties. The results are
useful for oat processing and the development of oat-based products with specific particle size range to achieve
desirable characteristics.

1. Introduction relatively higher pasting temperature and lower glycemic index. Ste­
venson, Jane, and Inglett (2007) reported that the starch isolated from
Oat (Avena sativa L.) has attracted much attention owing to its higher oat flour sieving fractions with 150–300 μm showed a lower peak vis­
nutritional value and excellent health function (Butt, Tahir-Nadeem, cosity, final viscosity, and setback viscosity than those of fractions with
Khan, Shabir, & Butt, 2008). However, it is difficult to separate its 300–850 μm and <150 μm. The presence of oat bran fractions (250–500
endosperm, germ, and bran during milling due to the soft structure of μm) had great negative effects on the farinograph behavior and exten­
kernels and whole grain distribution of lipids (Evers & Millart, 2002; sibility of oat dough (Londono, Smulders, Visser, Giliseen, & Hamer,
Doehlert & Mcmullen, 2007; Aprodu & Banu, 2017). Oat is usually 2015), while small particle fractions (<75 μm) of high-fiber oat flour
processed in the form of whole grains, either directly rolled into flakes or had better cook quality of pasta (Piwińska, Wyrwisz, & Wierzbicka,
ground into flour, further serving as porridge, flakes, or some cereal 2016). Meanwhile, bread containing oat bran with 30% smaller particles
breakfast. Owing to gluten deficiency, oat flour is a good source of had the potential to reduce cholesterol due to the high extractability and
gluten-free products for celiac patients. However, the quality of oat flour extract viscosity of β-glucan (Johansson, Andersson, Alminger, Land­
used in the food industry varies significantly because of the lack of a berg, & Langton, 2018). Moreover, some studies have evaluated the
standard oat flour milling process. effect of particle size on the quality characteristics of other cereal
Particle size, an important characteristic parameter in milling, powders. Each particle size had its own contribution to their properties.
significantly affects the intrinsic properties of flour and the quality of Thus, each powder product should be given close attention and studied
end-products (Patwa, Malcoim, Wilson, & Ambrose, 2014). These effects in detail.
have been partially reported. Lee, Kim, Kim, Choi, and Kim (2016) Extensive studies have been conducted on the modification of oat
observed that oat flour with larger particles (40 mesh) showed a flour using different technical methods or by adding other ingredients.

* Corresponding author.
** Corresponding author.
E-mail addresses: masen@haut.edu.cn (S. Ma), xxwanghaut@126.com (X. Wang).

https://doi.org/10.1016/j.lwt.2021.112757
Received 5 June 2021; Received in revised form 30 October 2021; Accepted 1 November 2021
Available online 2 November 2021
0023-6438/© 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Y. Gu et al. LWT 154 (2022) 112757

Limited studies focused on the composition and physicochemical prop­ 2.5. Determination of nutritional composition
erties of oat flour with specific granularity range to clarify the contrib­
uting factors to these characteristics. The objective of this study was to The total starch content was analyzed using α-amylase method and a
analyze the differences in nutrient composition, hydration, pasting, and Total Starch Assay Kit (K-TSTA, Megazyme International Ltd., Wicklow,
thermal properties of oat flour sieve fractions with different particle Ireland). The contents of amylose and amylopectin were determined
sizes (74–180 μm), and further to evaluate the relationship between using concanavalin A (Con A) method with Amylose/Amylopectin Assay
composition and characteristics to provide basic guidance for the pro­ Kit (K-AMYL, Megazyme International Ltd., Wicklow, Ireland). The
cessing of oat flour and the development of oat products. damaged starch content was measured using a damaged starch analyzer
(SDmatic, Chopin, France) following the AACC-76-31(2000) method.
2. Materials and methods Total nitrogen (TN) content was determined using automatic Kjel­
dahl apparatus (KjeltecTM8400, Sweden) according to AACC 46-10
2.1. Materials (2000) method, and the protein content was calculated with TN*5.83.
Proteins with different solubilities were extracted with distilled water,
The original oat flour was purchased from Hechuan Green Food Co., 10% sodium chloride, 70% ethanol, and 0.2% sodium hydroxide. Amino
Ltd. (Wuchuan, Inner Mongolia, China), which was obtained by stir- acid content was determined using an automatic amino acid analyzer
frying and grinding of naked oat grain (12.29 g/100 g moisture, 1.69 (LA8080, Japan) with reference to AACC 07-01 and 07–11 (2000).
g/100 g ash, 14.18 g/100 g protein, 63.71 g/100 g starch, 6.38 g/100 g The lipid content was tested using AACC 30-25 (2000) Soxhlet
lipid) from Wuchuan mountain. The original oat flour was numbered S0. extraction method. The fat extraction solvent was petroleum ether with
All chemicals used in the experiments were at least analytical grade. a boiling point of 30–60 ◦ C, and the fat was extracted for 20 h using a
Mixed amino acid standard, mixed fatty acids standard, and enzyme 50 ◦ C water bath. The fatty acid compositions were analyzed by gas
reagents were purchased from Sigma-Aldrich Co., Ltd (St. Louis, MO, chromatography (GC, 7890A, Agilent, USA) after the methylated treat­
USA). Other chemicals were obtained from SinoPharm Chemical Re­ ment of fat extract following the AACC 58-19 (2000) methods with some
agent Co. Ltd. (Shanghai, China). modifications. 2 mL 2 g/100 g sodium hydroxide methanol solution was
added to the fat extract for 30 min using an 85 ◦ C water bath, and then 3
2.2. Preparation of oat flour sieve samples mL of 14% boron trifluoride methanol solution was added for 30 min
using an 85 ◦ C water bath. When the temperature of water bath dropped
The original oat flour was separated using an electric sieve (JJSY 30 to room temperature, 1 mL of n-hexane was added. The mixture was
× 10, Shanghai Jiading Cereals and Oils Instrument Co., Ltd., China). oscillated for 2 min and allowed to stand for 1 h to stratify. Then, 100 μL
The original oat flour S0 (100 g) was weighed and sieved orderly with of supernatant was taken and diluted with n-hexane to 1 mL. The
180, 150, 132, 100, and 74 μm sieves. When the increase of sieve- mixture was filtered through a 0.45 μm filter membrane and tested. The
through material was less than 5%, the sieving finished. Then six oat chromatographic conditions are as follows: chromatographic column,
flour sieve fractions were obtained and numbered S1 (>180 μm), S2 HP-88 (100 m × 0.25 mm × 0.20 μm); heating procedure, initially
(150–180 μm), S3 (132–150 μm), S4 (100–132 μm), S5 (74–100 μm), and 100 ◦ C for 13 min, then increase to 180 ◦ C at 10 ◦ C/min and maintain for
S6 (<74 μm). The mass distribution is shown in Table 1. 6 min, then increase to 192 ◦ C at 1 ◦ C/min and maintain for 9 min, then
increase to 230 ◦ C at 3 ◦ C/min and maintain for 10 min; injector tem­
2.3. Determination of particle size distribution (PSD) perature, 240 ◦ C; carrier gas, nitrogen; flow rate, 1.3 mL/min; split in­
jection, 0.8; detector: FID; detector temperature, 280 ◦ C.
The PSD of seven oat flour samples were measured using a laser The contents of total dietary fiber (TDF), soluble dietary fiber (SDF),
particle size analyzer (NKT2010-L, Shandong Naikete Analytical In­ and insoluble dietary fiber (IDF) were measured using the AACC 32-05
strument Co., Ltd., China) (Qian, Sun, Zhu, Zhang, & Wang, 2020). The and 32-21 (2000) methods.
refractive index was 1.52, and the shading rate was controlled at
10–15%. The results were expressed by D10, D50, and D90 (Table 1 and 2.6. Hydration properties
Fig. 1A).
The hydration properties including water absorption index (WAI),
2.4. Microstructure observation by scanning electron microscope (SEM) swelling power index (SPI), and WSI were determined and calculated
using the method described by Zhang, Gao, Tong, and Li (2018).
The microstructures of oat flour particles were observed by SEM (Co.
S-3400NII, HITACHI, Japan) according to the procedures described by 2.7. Pasting properties
Ren, Ma, Xu, and Hu (2020) with some adjustments. Each sample was
fixed on the load table using a double-sided adhesive tape and then Pasting viscosity was determined by rapid viscosity analyzer (RVA-
coated with gold to provide conductivity, and images were observed at TecMaster, Perten Instruments, Australia) based on a previous study
1000 × magnifications under an acceleration voltage of 3 kV. (Palavecino, Penci, & Ribotta, 2019) with some modification. The test

Table 1
Particle size distribution, mass distribution, and hydration properties of oat flour sieving fractions.
Oat flour samples D10(μm) D50(μm) D90(μm) Mass distribution (%) WAI(g/g) WSI(%) SPI
e d d b c
S0 31.04 ± 0.74 97.04 ± 2.75 179.65 ± 4.59 100 3.55 ± 0.02 5.74 ± 1.13 3.77 ± 0.02b
S1 100.72 ± 0.75a 161.13 ± 0.21a 241.10 ± 0.21a 7.13 ± 0.38d 3.68 ± 0.10ab 9.90 ± 1.36a 4.08 ± 0.10ab
S2 84.50 ± 1.00b 140.77 ± 1.05b 210.99 ± 3.42b 12.18 ± 0.95c 3.67 ± 0.09ab 8.33 ± 0.57b 4.00 ± 0.12ab
S3 70.68 ± 0.87c 121.79 ± 0.64c 190.91 ± 0.29c 8.40 ± 1.44d 3.70 ± 0.29ab 5.84 ± 0.27c 3.93 ± 0.3ab
S4 34.36 ± 0.94d 83.73 ± 1.32e 146.51 ± 1.23e 33.03 ± 2.38a 4.02 ± 0.15a 4.86 ± 0.46cd 4.23 ± 0.17ab
S5 20.17 ± 0.16f 51.92 ± 0.17f 103.54 ± 0.41f 28.05 ± 3.03b 3.69 ± 0.34ab 4.31 ± 0.30d 3.86 ± 0.36ab
S6 15.66 ± 0.11g 33.33 ± 0.20g 70.50 ± 0.07g 11.22 ± 1.79c 3.49 ± 0.13b 4.83 ± 0.45cd 3.66 ± 0.16b

Data are the mean ± standard deviation of at least two replicates. Different lowercase letters within a column indicate statistical differences among samples (p＜0.05,
Duncan test).
WAI: water absorption index; WSI: water solubility index; SPI: swelling power index.

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Fig. 1. Particle size distribution and morphology of oat flour sieving fractions (A) particle size distribution curve, (B) S0, (C) S1, (D) S2, (E) S3, (F) S4, (G) S5, (H) S6.

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Y. Gu et al. LWT 154 (2022) 112757

procedure was subjected to a heat-hold-cool-hold temperature cycle: composed of large fiber fragments, and some small starch particles and
incubating at 50 ◦ C for 60 s, heating to 95 ◦ C within 222 s, holding at protein matrices were attached to them (Fig. 1C and D). With the
95 ◦ C for 150 s, cooling to 50 ◦ C within 228 s, and maintaining at 50 ◦ C decrease in mesh size, large fiber fragments were separated, mainly
for 120 s. The pasting parameters are as follows: peak viscosity (PV), including the endosperm lumps surrounded by irregular starch particles
trough viscosity (TV), final viscosity (FV), breakdown viscosity (BV), and protein fragments (Fig. 1E and F). As the sieve aperture continued to
setback viscosity (SV), pasting temperature (PT), and pasting time (T). decrease, small starch particles and small protein fragments were
separated, and the amount of damaged starch granules increased
2.8. Thermal properties (Fig. 1G and H). This was similar to those of wheat flour sieving fractions
in a previous study (Lin, Gu, & Bian, 2019).
Differential scanning calorimetry (DSC, TA- Q20 Instrument, USA) Microscopic observation showed that the oat flour sieving fractions
was used to evaluate thermal properties according to the method had different chemical compositions (starch, protein, and fiber), prob­
described by Duque, Leong, Agyei, Singh, and Oey (2020) with slight ably leading to the diversity of physicochemical properties.
modifications. Aluminum pans were filled with oat flour (2.5 mg, dry
basis) and deionized water with a ratio of 1:3. The test procedure 3.3. Main nutritional composition analysis
involved in equilibrating at 10.00 ◦ C for 1 min and then heating to
130 ◦ C at a rate of 10 ◦ C/min. The parameters recorded in DSC were as Based on the microstructure results, the main nutritional compo­
follows: onset temperature (To), peak temperature (Tp), conclusion nents were first studied to clearly understand the composition distri­
temperature (Tc), ΔH, and gelatinization temperature range (ΔT, bution of oat flour particles with different sizes, as shown in Fig. 2.
Tc− To).
3.3.1. Starch composition
2.9. Statistical analysis Starch, a major carbohydrate in cereal grains, consists of two
important components amylose and amylopectin, significantly affecting
All the analyses were performed at least in duplicate. The data were the physicochemical and functional properties of starch. Therefore, the
expressed as the mean ± standard deviation. The data were analyzed by changes in starch composition were analyzed first. With the decrease in
one-way analysis of variance and evaluated by Duncan’s multiple range mesh sizes, the total starch, amylose, amylopectin, and damaged starch
test (level of significance, P＜0.05) using SPSS16.0 Statistical Software contents of sieve fractions showed an overall increasing trend, from
Program (SPSS Incorporated, Chicago). The figures were plotted using 34.34% to 69.87%, 6.07%–11.78%, 28.30%–58.26%, and 7.76%–
Origin 8.5 software. 9.76%, respectively (Fig. 2A and B). The variation trend was the same as
in the previous study (Jun, Yoo, Song, & Kim, 2017), even though the
3. Results and discussion particle size range was different (160–250 μm). The results show that
these components were mostly distributed in smaller particles (<132
3.1. Sieve analysis and PSD μm).
The ratio of amylose to amylopectin increased first (highest in S3,
Table 1 clearly shows that the mass distribution was significantly about 0.23), then decreased, and tended to be constant (about 0.2), all of
different, ranging from 7.13% to 33.03%. This result indicates that oat which were lower than that of S0 (0.25). This ratio is the main reason for
flour is a mixture of various sizes of oat flour particles. More than 70% of the changes of oat starch composition, which may further affect the
oat flour particles could pass through the 132 μm sieve, which was starch properties of oat flour sieving fractions (Miles, Morris, Orford, &
supported by the cumulative distribution curve of S0 (Fig. 1A). The Ring, 1985). Moreover, because of the differences in oat variety and
maximum percent (33.03%) was in S4 (100–132 μm), followed by S5 milling technology, the amylopectin content of oat starch in this study
(74–100 μm) of about 28.05%. While the smallest particle S6 (<74 μm) (79.85–83.50%) was higher than that reported in the previous study
accounted for 11.22%, lower than the value (about 34%) in the differ­ (77.33%) of Simsek, Whitney, and Ohm (2013), while the amylose
ential volume distribution of S0 (Fig. 1A). This is because small particles content of oat starch (16.49–20.15%) in this study was lower than that
easily agglomerated due to electrostatic action and van der Waals force in earlier studies (19.40–29.5%) (Hoover & Senanayake, 1996).
(Luo, Wang, & Zhuang, 2019), which made some small particles adhere
to the larger particles and not pass through the sieve. Meanwhile, this 3.3.2. Protein composition
was the reason why the D50 of each sieving sample was relatively lower Protein distribution of oat flour sieve fractions had significant dif­
than the corresponding mesh size. The largest particles (S1, >180 μm) ferences (Fig. 2C and D). The total protein content gradually decreased
had the minimum weight percent (7.13%). This was consistent with the (19.29–9.65%, Fig. 2C) with the reduction of sieve aperture, close to the
PSD of S0 (D90 for 179.65 μm), indicating that the fraction (>180 μm) protein content (9.7–17.3%) of oat grains reported by previous studies
was less than 10%. (Sterna, Zute, & Brunava, 2016). Compared to other cereal grain (such
All oat flour particles showed unimodal curves (Fig. 1A), indicating as wheat and barley), oat had a higher protein content and unique
that the PSD was relatively uniform. Significant differences were protein composition with a lower level of prolamin and a higher level of
observed in the PSD (D10, D50, and D90) of sieving fractions. D50 ranged globulin (Klose, Schehl, & Arendt, 2009).
from 33.33 μm to 161.13 μm, demonstrating the sieving process was To further analyze the distribution of protein components, four sol­
effective. The D50 of S0 was 97.04 μm between 83.73 μm (D50 of S3) and vents were used to separate oat protein into albumin, globulin, prola­
121.79 μm (D50 of S4) in accordance with mass distribution. min, and glutelin according to Osborne protein fractionation. The results
are shown in Fig. 2D (% of total protein). Except for albumin, the other
3.2. Microstructure analysis three protein components were more distributed in the smaller particle
fractions (<132 μm), while albumin was mostly distributed in the larger
The microstructures were observed by SEM (Fig. 1B–H). Oat flour particle fractions (>150 μm). This was because the albumin was mostly
granules (S0) mainly consisted of endosperm blocks, whole starch distributed in the parts close to the superficial bran layer, while the other
granules with an irregular shape, damaged starch granules, irregular three proteins were mainly distributed in the endosperm (Draper, 2010;
protein fragments, and fiber fragments (Fig. 1B), similar to the results of Klose & Arendt, 2012; Lásztity, 1998). The content of globulin, the
untreated oat flour described by Duque et al. (2020). Clearly, the par­ major storage protein in oat, measured in this study was relatively lower
ticle sizes gradually decreased (Fig. 1C–H), validating the observed (17.50–23.88%), far below 50% (Klose & Arendt, 2012). This was
difference in PSD in Table 1. The larger particles (S1 and S2) were mainly probably related to the extraction method, and the globulin may not be

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Fig. 2. Nutrient component distribution of oat flour sieving fractions with different particle sizes (A) total starch and the ratio of amylose to amylopectin, (B)
damaged starch, amylose, and amylopectin (% of flour), (C) total protein and protein extraction rate, (D) four protein components (% of total protein), (E) TDF and
the ratio of SDF to TDF, (F) SDF and IDF (% of flour).

completely extracted. Inversely, the glutelin content was higher 3.3.3. Amino acid composition
(28.98–42.87%), but this was understandable. The glutelin amount was Based on the above analysis of protein components, the amino acid
directly related to the extraction efficiency of albumin, globulin, and composition of oat flour sieve fractions was determined (Table 2). For a
prolamin, and the values reported in earlier studies ranged from 5% to better comparative analysis, the amino acids were divided into six
66%, especially in other fractions where globulins had also been found classifications (I-Ⅵ) according to the changing trend.
(Klose & Arendt, 2012). Amino acids of group I, II, and III were relatively lacking in S2
According to the determination of protein components, the extrac­ (150–180 μm). This is consistent with the results obtained in the study of
tion rate of protein was obtained (Fig. 2C). The protein extraction rate Lee et al. (2016) that these amino acids contents were lower in the oat
ranged from 57.72% to 76.37%, showing an increasing trend with flour of 80 mesh (about 180 μm) and 100 mesh (150 μm). Amino acid
decreasing particle sizes. Though the samples (>132 μm) had a higher contents of group I in larger particle fractions (>150 μm) were lower
protein content, their protein extraction rates were lower. This is than that in medium and small granule fractions, which were mostly
probably because the higher fat content in larger particles hindered distributed in S5 (74–100 μm), close to S0. Glu was the most abundant
protein extraction (Liu et al., 2009). Moreover, no significant differences amino acid accounting for 16.32–20.01%, lower than the results
were observed in the protein extraction rate among the smaller particle (29.66% and 23.9%) obtained by Sterna et al. (2016) and Pomeranz,
fractions (<132 μm). Robbins, and Briggle (1971). While amino acid contents of group II

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Table 2
Amino acid composition of oat flour sieving fractions (% of total protein).
Group Amino acid S0 S1 S2 S3 S4 S5 S6
a d e c abc
I Asp 7.35 ± 0.00 6.71 ± 0.04 6.30 ± 0.05 7.04 ± 0.01 7.20 ± 0.01 7.25 ± 0.18 ab 7.15 ± 0.07bc
Glu 19.97 ± 0.36a 16.96 ± 0.29c 16.32 ± 0.32c 18.65 ± 0.2b 19.78 ± 0.3a 20.01 ± 0.72a 19.85 ± 0.55a
Leu 7.27 ± 0.24a 6.43 ± 0.22bc 6.15 ± 0.18c 7.00 ± 0.15ab 7.16 ± 0.2a 7.40 ± 0.39a 7.31 ± 0.29a
II Thr 3.17 ± 0.12a 3.01 ± 0.07a 2.74 ± 0.09b 3.03 ± 0.05a 3.07 ± 0.04a 3.00 ± 0.19ab 2.95 ± 0.10ab
Val 4.18 ± 0.12a 3.94 ± 0.15ab 3.67 ± 0.12b 4.08 ± 0.16a 4.22 ± 0.16a 4.20 ± 0.08a 4.04 ± 0.11a
Tyr 2.26 ± 0.12a 2.18 ± 0.07a 1.76 ± 0.05b 1.91 ± 0.05b 2.34 ± 0.05a 1.50 ± 0.02c 1.50 ± 0.09c
Phe 4.51 ± 0.12a 3.91 ± 0.11b 3.76 ± 0.09b 4.27 ± 0.10a 4.63 ± 0.16a 4.60 ± 0.21a 4.56 ± 0.19a
Lys 3.17 ± 0.00ab 3.24 ± 0.04a 2.89 ± 0.05c 3.11 ± 0.05ab 3.17 ± 0.04ab 3.10 ± 0.05b 2.95 ± 0.10c
His 2.09 ± 0.12a 1.87 ± 0.07bc 1.64 ± 0.04d 1.91 ± 0.05bc 1.97 ± 0.05ab 1.75 ± 0.1cd 1.76 ± 0.02cd
Arg 5.51 ± 0.12a 5.29 ± 0.07ab 4.80 ± 0.05c 5.20 ± 0.05b 5.51 ± 0.09a 5.25 ± 0.15b 5.13 ± 0.12b
Pro 4.34 ± 0.24a 3.86 ± 0.18bc 3.55 ± 0.21c 4.12 ± 0.21ab 4.18 ± 0.23ab 4.00 ± 0.08abc 3.83 ± 0.11bc
III Ser 4.18 ± 0.12a 3.91 ± 0.11ab 3.61 ± 0.13b 4.04 ± 0.10a 3.99 ± 0.16a 3.95 ± 0.13ab 3.94 ± 0.18ab
Gly 4.14 ± 0.06a 4.17 ± 0.11a 3.88 ± 0.08bc 4.16 ± 0.16a 4.08 ± 0.1ab 4.05 ± 0.01abc 3.83 ± 0.11c
Ⅳ Cys 2.09 ± 0.24ab 2.51 ± 0.26a 2.18 ± 0.21ab 2.13 ± 0.16ab 1.97 ± 0.18bc 1.70 ± 0.17bc 1.50 ± 0.09c
Ⅴ Met 0.19 ± 0.01b 0.46 ± 0.00a 0.17 ± 0.00d 0.18 ± 0.00c 0.19 ± 0.00b 0.12 ± 0.00e 0.18 ± 0.00c
Iso 3.22 ± 0.06b 2.80 ± 0.00c 2.69 ± 0.00d 3.15 ± 0.00b 3.30 ± 0.03a 3.30 ± 0.05a 3.32 ± 0.03a
Ⅵ Ala 4.72 ± 0.18a 4.56 ± 0.15a 4.30 ± 0.18a 4.57 ± 0.10a 4.54 ± 0.16a 4.65 ± 0.28a 4.46 ± 0.19a

Data are the mean ± standard deviation of at least two replicates. Different lowercase letters within a column indicate statistical differences among samples (p＜0.05,
Duncan test).

(except for Lys and Tyr) in medium particles were higher than those of higher than that in other cereal flour (Aprodu & Banu, 2017). This is
large and small particles, which was the richest in the fractions with because the distribution of lipids in oat kernels gradually decreased from
100–132 μm (S4) (except for Lys). Lys was mainly in S1 (>180 μm), the outer layer to the inside the kernel (Hu, Xing, & Ren, 2010), which
indicating the level of Lys in cortical protein was relatively higher than also confirmed that bran had the highest concentration of lipids among
that in endosperm protein as confirmed by Klose and Arendt (2012). The the oat milling fractions (Lásztity, 1998).
distribution of Gly and Ser (group III) in the fractions with particle size To further analyze the distribution of lipids, the fatty acid compo­
less than 150 μm gradually decreased. sitions were determined (Table 3). Oat flour (S0) contained about
Cys (group Ⅳ) showed a decreasing trend with the decrease of 76.89% UFA, 34.69% PUFA (polyunsaturated fatty acids), 23.11% SFA,
sieving particle size. Also, Cys in large particle fractions (>150 μm) was and similar results were obtained by previous studies (Biel, Jacyno, &
obviously higher than that in S0 and other fractions, showing that Cys Kawecka, 2014). With the decrease in sieve fraction particle sizes, the
was mostly present near the oat cortex. No obvious change trend was levels of UFA and PUFA reduced, while the level of SFA increased.
observed in the amino acids of group Ⅴ. However, Met in the largest Among them, the contents of C18:1n9c, C18:2n6c, C16:0 and C18:0
particles (S1, 0.46%) was 2.4–3.8 times higher than other samples, and changed obviously, accounting for about 97% of total fat acids. Other fat
Iso was mostly found in the fractions (<150 μm). No significant differ­ acids (approximately 3%) showed a slight variation, indicating that
ence was observed in the distribution of Ala (group Ⅵ), indicating Ala these fat acids were relatively evenly distributed in sieving fractions.
was evenly distributed in oat grains.
3.3.5. Dietary fiber
3.3.4. Lipids and fatty acid composition The contents of TDF, SDF, and IDF of S0 were 9.40%, 3.44%, and
Lipids content also decreased with the reduction of sieve fraction 5.96%, respectively. The proportion of SDF to TDF was 36.60%, indi­
particle sizes, ranging from 8.31% to 5.92% (Table 3), significantly cating that about one third of the fiber was soluble, consistent with

Table 3
Fatty acid composition of oat flour sieving fractions (% of total fatty acids).
Fatty acid S0 S1 S2 S3 S4 S5 S6

C14:0 0.26 ± 0.00cd 0.26 ± 0.00d 0.26 ± 0.00cd 0.26 ± 0.00cd 0.27 ± 0.00bc 0.27 ± 0.00b 0.28 ± 0.01a
C15:0 0.01 ± 0.00ab 0.01 ± 0.00a 0.01 ± 0.00ab 0.01 ± 0.01ab 0.01 ± 0.00ab 0.00 ± 0.00b 0.01 ± 0.00ab
C16:0 20.51 ± 0.03d 19.47 ± 0.01f 19.61 ± 0.03f 20.18 ± 0.00e 20.79 ± 0.01c 21.14 ± 0.03b 21.49 ± 0.17a
C16:1 0.17 ± 0.00d 0.18 ± 0.00a 0.17 ± 0.00b 0.17 ± 0.00c 0.16 ± 0.00de 0.16 ± 0.00e 0.17 ± 0.00c
C17:0 0.04 ± 0.00a 0.04 ± 0.00ab 0.04 ± 0.00ab 0.04 ± 0.00ab 0.04 ± 0.00ab 0.04 ± 0.00ab 0.04 ± 0.00b
C18:0 1.86 ± 0.00c 1.68 ± 0.00f 1.78 ± 0.00e 1.83 ± 0.00d 1.88 ± 0.00b 1.90 ± 0.00a 1.90 ± 0.01a
C18:1n9c 41.01 ± 0.06c 41.26 ± 0.01b 41.66 ± 0.04a 41.29 ± 0.00b 40.87 ± 0.02d 40.46 ± 0.01e 40.06 ± 0.12f
C18:2n6c 33.71 ± 0.03cd 34.59 ± 0.00a 33.95 ± 0.02b 33.74 ± 0.00c 33.52 ± 0.01f 33.57 ± 0.02ef 33.63 ± 0.1de
C20:0 0.17 ± 0.00a 0.16 ± 0.00b 0.17 ± 0.00a 0.17 ± 0.00a 0.17 ± 0.00a 0.17 ± 0.00a 0.17 ± 0.00a
C18:3n6 0.01 ± 0.00b 0.02 ± 0.00a 0.02 ± 0.00a 0.02 ± 0.00ab 0.02 ± 0.00ab 0.01 ± 0.00b 0.02 ± 0.00a
C18:3n3 0.89 ± 0.01bc 0.95 ± 0.00a 0.86 ± 0.01d 0.91 ± 0.00b 0.89 ± 0.00bc 0.88 ± 0.00c 0.88 ± 0.00c
C20:1 0.83 ± 0.00b 0.82 ± 0.00c 0.90 ± 0.00a 0.83 ± 0.00b 0.82 ± 0.00c 0.81 ± 0.00c 0.79 ± 0.01d
C20:2 0.04 ± 0.00a 0.05 ± 0.01a 0.05 ± 0.00a 0.05 ± 0.00a 0.05 ± 0.00a 0.05 ± 0.01a 0.05 ± 0.01a
C22:0 0.07 ± 0.00c 0.08 ± 0.00a 0.08 ± 0.00ab 0.07 ± 0.00c 0.08 ± 0.00b 0.08 ± 0.00ab 0.08 ± 0.00b
C22:1n9 0.11 ± 0.00a 0.10 ± 0.00c 0.10 ± 0.00bc 0.10 ± 0.00bc 0.11 ± 0.00abc 0.11 ± 0.00a 0.11 ± 0.00ab
C20:5n3 0.04 ± 0.00ab 0.06 ± 0.01a 0.05 ± 0.00ab 0.04 ± 0.00ab 0.04 ± 0.00ab 0.05 ± 0.00ab 0.04 ± 0.00b
C24:0 0.20 ± 0.00c 0.20 ± 0.00bc 0.23 ± 0.00a 0.23 ± 0.00a 0.21 ± 0.01b 0.21 ± 0.00bc 0.21 ± 0.00bc
C24:1 0.07 ± 0.01a 0.06 ± 0.00a 0.06 ± 0.00a 0.06 ± 0.00a 0.06 ± 0.00a 0.07 ± 0.01a 0.07 ± 0.01a
UFA 76.89 ± 0.03d 78.09 ± 0.02a 77.82 ± 0.02b 77.21 ± 0.01c 76.55 ± 0.02e 76.18 ± 0.03f 75.83 ± 0.2g
PUFA 34.69 ± 0.04cd 35.67 ± 0.02a 34.93 ± 0.01b 34.76 ± 0.00c 34.53 ± 0.01e 34.57 ± 0.03e 34.62 ± 0.08de
SFA 23.11 ± 0.03d 21.91 ± 0.02g 22.18 ± 0.02f 22.79 ± 0.01e 23.45 ± 0.02c 23.82 ± 0.03b 24.17 ± 0.20a

Total fatty acids content 5.67 ± 0.13cd 6.11 ± 0.16bc 6.61 ± 0.29a 6.23 ± 0.06ab 5.74 ± 0.10cd 5.46 ± 0.29d 5.68 ± 0.09cd
Lipid content 7.20 ± 0.05c 8.31 ± 0.01a 7.80 ± 0.14b 6.95 ± 0.34c 6.33 ± 0.42d 6.01 ± 0.01d 5.92 ± 0.00d

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Y. Gu et al. LWT 154 (2022) 112757

previous studies (Sterna et al., 2016; Lásztity, 1998). Significant dif­ molecules, and water binding sites, leading to better solubility (Shi et al.,
ferences were observed in the DF content of oat flour sieve fractions, 2016). However, the sieving treatment in this study mainly resulted in
presenting a decreasing trend with the decrease in particle sizes (Fig. 2E the difference of components, which were beneficial or detrimental to
and F). The DF content of large particle fractions (S1) was 5–8 times water solubility verified by correlation analysis (Table A.1). WSI was
more than that of small particles (S6). This is because the fiber fragments positively correlated with the total protein, albumin, total fat, DF, Cys,
gradually separated in sieving processing. The results were supported by C18:2n6c, UFA, and PUFA, and negatively correlated with starch
the observation of SEM. However, the ratio of SDF to TDF did not change composition, globulin, prolamin, and glutelin, Asp, Glu, Iso, Leu, Phe,
regularly with particle sizes, but had significant differences among the C16:0, C18:0, and SFA. Based on the above results, it can be inferred that
samples. The ratio in the fractions (100–132 μm) was the lowest the cellular matrix structure formed by particles of different sizes, the
(27.97%) and the ratio in the smallest particles (<74 μm) was the integrity of particle structure, the solubility of different components, and
highest (56.70%, more than one third). This proportion reflected the the intermolecular interaction may influence the leaching of hydratable
changes in dietary fiber compositions, influencing its physicochemical substances (Anguita, Gasa, Martin-Orue, & Perez, 2006; Kethireddipalli,
and functional properties (Dhingra, Michael, Rajput, & Patil, 2012) and Hung, Phillips, & McWatters, 2002; Shi et al., 2016).
characteristics of oat flour sieving fractions.

3.5. Pasting properties

3.4. Hydration properties
The pasting properties of oat flour sieve fractions are shown in
The results of hydration properties are shown in Table 1. No signif­ Table 4. Significant differences were observed in pasting properties
icant differences were observed in values of WAI and SPI among larger among samples. The values of PV, TV, FV, and SV of sieve fractions first
particle fractions (>132 μm), while WAI and SPI decreased with the increased and then decreased with the decrease in particle sizes,
decrease in particle sizes of smaller particle fractions (<132 μm). A reaching the highest at S4 (100–132 μm). The values of BV showed a
better swelling power was observed in S4 (100–132 μm), which was significantly increasing trend, while the PT had no significant differ­
related to the high ratio of amylopectin (% of total starch). It has been ences except for the coarsest particles. The changes in pasting properties
reported that the swelling power of flour/starch depends on the ratio of oat flour fractions obtained by sieving were probably caused by the
and molecular weight of amylose to amylopectin, as well as on intra­ differences in compositions as well as the decrease in particle sizes.
molecular and intermolecular interactions (Mir & Bosco, 2014). Thus, PV is the maximum viscosity of starch granules at the highest
for larger particle fractions, swelling power could be inhibited by the swelling extent during heating. The highest PV of S4 could be strongly
interaction of lipids and amylose, while for smaller particle fractions, related with its best swelling capacity and highest amylopectin content.
amylopectin played an important role in swelling power that swelling The decreased PV in coarser particles can be attributed to the fact that
was a property of amylopectin (Tester & Morrison, 1990). Moreover, the the presence of high levels of lipids hindered the swelling of oat starch,
slight decrease of WAI in the smallest particle fractions (<74 μm) could and the formation of a starch-lipid complex inhibited the leaching of
be influenced by the reduction of protein and amylose (% of total starch) amylose (Debet & Gidley, 2006; Larsson, 1980), while the further
that possibly hindered the water absorption ability (Ahmed, Al-Jassar, & decrease of PV in smaller particles can be ascribed to the reduction of
Thomas, 2015), consistent with the results obtained by Kerr, Ward, amylopectin content (% of total starch) (Tester & Morrison, 1990),
Mcwatters, and Resurreccion (2000) who also observed poor water ab­ similar to the results of fine rice flour (Ahmed et al., 2015). TV showed
sorption capacity in fine flour. the lowest viscosity recorded at the end of heating phase, showing that
WSI, which showed the leaching index of water-soluble components the starch granules would not swell further, and the fracture of swollen
from flour (Wang et al., 2010), ranged from 4.31% to 9.90%, having starch granules resulted in a sharp decrease in viscosity (Sharma, Singh,
significant differences among samples and presenting a decreasing trend & Subramanian, 2013). Lower TV of the larger particle fractions could
with the changes in sieving particles. The results did not agree with the be due to the lower starch content and higher protein and dietary fiber
study described by Shi et al. (2016) who observed an increasing trend of that influenced the swelling and breaking of starch granules (Ragaee &
WSI. This could be attributed to the differences in particle characteristics Abdel-Aal, 2006). However, the decrease of TV in fractions (＜132 μm)
obtained by sieving and regrinding. Regrinding treatment increased the was ascribed to the reduction of particle sizes that enhanced the disin­
surface area of particles, which exposed more polar groups, soluble tegration sensitivity of starch granules (Shi et al., 2016). FV showed the

Table 4
RVA pasting viscosity and thermal properties parameters of oat flour sieving fractions.
Oat flour PV(cP) TV(cP) BV(cP) FV(cP) SV(cP) T(min) PT(◦ C) To (◦ C) Tp (◦ C) Tc (◦ C) ΔH（J/ ΔT (◦ C)
samples g）

S0 2967 ± 2334 ± 633 ± 3940 ± 1606 ± 6.4 ± 84.8 ± 57.98 ± 69.05 ± 79.42 ± 1.27 ± 21.44 ±
31.1c 0.0c 31.1c 48.8bc 48.8ab 0.0b 0.1b 1.68ab 3.14a 2.28a 0.21c 0.60bc
S1 1437 ± 1302 ± 135 ± 2847 ± 1545 ± 6.3 ± 90.5 ± 58.42 ± 69.67 ± 77.35 ± 1.03 ± 18.93 ±
24.7f 25.5f 0.7f 48.8e 23.3b 0.0c 1.1a 2.62ab 8.15a 4.96a 0.44c 2.33cd
S2 2413 ± 1999 ± 414 ± 3599 ± 1600 ± 6.6 ± 86.0 ± 52.60 ± 70.64 ± 81.43 ± 2.11 ± 28.84 ±
21.9e 22.6e 0.7e 30.4d 7.8ab 0.0a 0.6b 4.14b 8.05a 1.26a 0.31bc 2.88a
S3 2884 ± 2355 ± 530 ± 3992 ± 1638 ± 6.6 ± 85.2 ± 58.54 ± 71.24 ± 80.05 ± 1.11 ± 21.51 ±
58.0d 17.7bc 40.3d 110.3bc 92.6ab 0.0a 0.7b 2.38ab 1.34a 1.93a 0.13c 0.45bc
S4 3202 ± 2489 ± 713 ± 4148 ± 1659 ± 6.4 ± 84.8 ± 57.94 ± 71.00 ± 80.64 ± 2.40 ± 22.70 ±
4.9a 17.0a 21.9b 10.6a 6.4a 0.0b 0.0b 2.57ab 0.31a 0.71a 0.74ab 3.28bc
S5 3199 ± 2382 ± 817 ± 4012 ± 1630 ± 6.3 ± 84.8 ± 62.36 ± 70.69 ± 78.55 ± 1.63 ± 16.19 ±
0.7a 11.3b 12.0a 33.2b 44.5ab 0.0bc 0.0b 0.98a 0.83a 1.05a 0.19bc 0.08d
S6 3103 ± 2292 ± 811 ± 3867 ± 1575 ± 6.3 ± 85.0 ± 56.63 ± 70.87 ± 80.67 ± 3.20 ± 24.04 ±
7.1b 5.7d 1.4a 7.8c 13.4ab 0.0bc 1.3b 0.98ab 0.23a 1.20a 0.63a 0.23b

Data are the mean ± standard deviation of at least two replicates. Different lowercase letters within a column indicate statistical differences among samples (p＜0.05,
Duncan test).
PV: peak viscosity; TV: trough viscosity; FV: final viscosity; BV: breakdown viscosity; SV: setback viscosity; T: pasting time; PT: pasting temperature; To: onset
temperature; Tp: peak temperature; Tc: conclusion temperature; ΔH: gelatinization enthalpy; ΔT: gelatinization temperature range.

7
Y. Gu et al. LWT 154 (2022) 112757

highest viscosity values recorded at the end of cooling phase, which Tp and Tc were barely influenced by the sieving particle sizes, which
showed the association of starch molecules in the disintegrated swollen were around 70 ± 1 ◦ C and 79 ± 2 ◦ C, respectively. Besides, it was
starch granules (Miles et al., 1985). The increase in FV from 2847 cP to observed that the thermal transition temperature of oat flour in this
4148 cP with the reduction of particle sizes may depend on the degree of study was slightly higher than that of native oat starch reported by
amylose leaching and the volume and stiffness of the remaining particles Berski et al. (2011) and Ziegler et al. (2018), which can be ascribed to
(Palavecino et al., 2019). However, the decrease in FV from 4148 cP to the effect of other components on starch gelatinization. A correlation
3867 cP in smaller sieve fractions was mainly related to the increase in analysis (Table A.1) showed that Tp had significant correlation with
damaged starch content, i.e., FV was negatively correlated with the amylose (r = 0.847*), Met (r = − 0.850*), and C20:1(r = − 0.885*). Jane
damaged degree of starch particles reported in a previous study (Has­ et al. (1999) reported that high transition temperatures were found in
jima, Li, & Dhitala, 2013). high amylose starch with a longer average chain length. Furthermore,
BV resulted from the fracture of swollen starch particles and the Torres, Moreira, Chenlo, and Morel (2013) showed that the
weakening of bonding forces, reflecting the stability of starch paste order-disorder process of starch-lipid complexes affected these thermal
(Pinto et al., 2012). A higher BV in smaller particle fractions showed the transition temperatures. Overall, the ΔH of fractions (<132 μm) was
swollen starch granules were more likely to break down, presenting poor higher than that of fractions (>132 μm). However, the values were
paste stability and weak shear resistance. This is consistent with the significantly lower than those of oat starch reported by Stevenson et al.
results of sieving lentil flour (Ahmed, Taher, Mulla, Al-Hazza, & (2007) and Berski et al. (2011), which was caused by the partial gela­
Luciano, 2016). SV is the differentials between FV and TV, indicating the tinization of starch in the stir-frying of oat grains. The ΔH of the smallest
recrystallization of starch granules and retrogradation tendency of particles (3.20 J/g) was 3.1 times that of the largest particles (1.03 J/g).
starch gel system during the cooling phase (Ahmed et al., 2016; Shi The lower ΔH was probably connected with the lower crystallinity (Kerr
et al., 2016). The higher values of SV in medium particles showed that et al., 2000; Moorthy, 2002), while an increasing ΔH of the smallest
the gelatinized starch in these sieved fractions had more recrystalliza­ particles might be mainly attributed to the increase of starch content
tion during cooling processing, and these starches were more likely (Ahmed et al., 2016). In addition, the ΔH of granular flour was also
subjected to retrogradation. The decrease of SV in fine particles was due related to the melting of overall amylopectin crystals (Lopez-Rubio,
to lower swelling power and small amount of amylose leaching (Qian Flanagan, Gilbert, & Gidley, 2008), requiring more energy to gelatinize
et al., 2020). The PT (90.5 ◦ C) of the largest particle fractions (S1) was the long-chain crystallites. Correlation analysis showed ΔH had signif­
significantly higher than that of other oat flour particles, which can be icant negative correlation with Gly (r = − 0.839*) (Table A.1). Obvi­
ascribed to the presence of high amounts of lipids that made starch ously, the thermal properties of oat flour sieve fractions had a complex
require a higher temperature to gelatinize (Hoover, Smith, Zhou, & relationship with particle size, components, and structure.
Ratnayake, 2003).
A correlation analysis showed a significant correlation between 4. Conclusions
pasting viscosities and composition (Table A.1). Starch composition,
globulin, prolamin, glutelin, Glu, Iso, Phe, C16:0, C18:0, and SFA had Oat flour sieve fractions had different nutritional composition and
positive correlation with PV, TV, BV, and FV, while total protein, al­ physicochemical properties. Starch constituents, protein components
bumin, total fat, DF, Cys, Met, C18:2n6c, UFA, and PUFA had negative (except for albumins), and SFA were mostly distributed in small parti­
correlation with PV, TV, BV, and FV. This indicates that the differences cles, while the total protein, albumins, DF, fat, and UFA were abundant
in components after sieving modified the pasting behaviors of starch in large particles. Amino acids (except for Tyr and Gly) of group I, II, and
granules. III were significantly lacking in S2 (150–180 μm). Owing to the differ­
ences in compositions, the largest particle fractions showed the highest
3.6. Thermal properties WSI, the medium particles (100–132 μm) exhibited the highest pasting
viscosities, and the smallest particle fractions had the maximum ΔH.
The thermal properties are shown in Table 4. No systematic changes Meanwhile, this study also demonstrated that the compositions had
were observed in these parameters with the change in particle sizes. significant correlation with these properties, but this relationship needs
However, significant differences were found in To, ΔT, and ΔH among to be deeply explained by further fine structural analysis of these
the samples. The sieve fractions (74–100 μm) showed the highest To at components.
62.36 ◦ C and the lowest ΔT for 16.19 ◦ C, while the fractions (150–180
μm) had the lowest To at 52.60 ◦ C and the highest ΔT of 28.84 ◦ C. To CRediT authorship contribution statement
showed the threshold at which the molecules began to acquire fluidity,
which would allow them to crystallize over time. This indicated the Yujuan Gu: Conceptualization, Software, Validation, Investigation,
molecules of the fractions (74–100 μm) required a higher temperature to Data curation, Methodology, Writing – original draft, Writing – review &
gain mobility to crystallize. The differences in observed To of sieving editing. Xiaojie Qian: Software, Visualization, Writing – review &
fractions originated from the components of the particles itself, but it editing. Binghua Sun: Conceptualization, Writing – review & editing,
was difficult to assert the actual contribution of each component to as Supervision. Sen Ma: Methodology, Project administration, Writing –
the fractions were not separated and concentrated (Ahmed, Al-Foudari, review & editing, Supervision, Funding acquisition. Xiaoling Tian: Data
Al-Salman, & Almusallam, 2014). Meanwhile, except for Ala (r = curation, Formal analysis, Software. Xiaoxi Wang: Resources, Super­
0.976**) and Val (r = 0.824*), no significant correlation was observed vision, Funding acquisition.
between To and compositions (Table A.1). ΔT, which expressed the
gelatinization temperature range, indicated the integrity and stability of Declaration of competing interest
crystalline structure (Tester & Morrison, 1990). The difference in ΔT
among the samples reached about 12.7 ◦ C, showing significant differ­ The authors declare that they have no known competing financial
ences in the integrity and stability of the crystalline structure of starch in interests or personal relationships that could have appeared to influence
the sieve fractions. The lower the ΔT, the higher the crystalline the work reported in this paper.
perfection degree (Maaran, Hoover, Donner, & Liu, 2014). The vari­
ability in ΔT values were due to the differences in the amylose content, Acknowledgments
the ratio of amylose to amylopectin, the amount of starch-lipid complex,
starch structure, and the heterogeneity of crystallites (Kang, Hwang, This work was supported by National Key Research and Develop­
Kim, & Choi, 2006). ment Program of China (No. 2018YFD0401001), Innovation Fund

8
Y. Gu et al. LWT 154 (2022) 112757

Supported Project from Henan University of Technology (No. Jun, H. I., Yoo, S. H., Song, G. H., & Kim, I. S. (2017). Effect of particle size of naked oat
flours on physicochemical and antioxidant property. Korean Journal of Food
2020ZKCJ11), the Key Scientific and Technological Project of Henan
Preservation, 24(7), 965–974.
Province (No. 202102110143). Kang, H. J., Hwang, I. K., Kim, K. S., & Choi, H. C. (2006). Comparison of the
physicochemical properties and ultrastructure of japonica and indica rice grains.
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Supplementary data to this article can be found online at https://doi. particle size on functionality and physicochemical properties of cowpea flour. Cereal
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Kethireddipalli, P., Hung, Y. C., Phillips, R. D., & McWatters, K. H. (2002). Evaluating the
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