Acta agriculturae Slovenica, 120/2, 1–17, Ljubljana 2024
doi:10.14720/aas.2024.120.2.15297 Original research article / izvirni znanstveni članek
Comparative assessment for nutritional and antinutritional qualities 
revealed better performance of traditional white-fleshed sweet potatoes 
than orange-fleshed sweet potatoes 
Onwuchekwa OGAH 1, 2, Chikezie Onuora ENE 2, 3, 4, Lilian Nwanneka EBENYI 1, Orinya Onyebuchi 
FREDERICK 5, Ifeanyi Godwin OKPURU 1, 2, Stephen Elem NWANKWO 2, 6
Received July 31, 2023; accepted June 03, 2024.
Delo je prispelo 31. julija 2023, sprejeto 3. junija 2024.
1 Department of Biotechnology, Ebonyi State University, Abakaliki, Nigeria
2 Department of Horticulture and Plant Sciences, Jimma University, Jimma, Ethiopia
3 Department of Agriculture, Alex Ekwueme Federal University Ndufu-Alike, Abakaliki, Nigeria
4 Corresponding author, e-mail: enechike17@gmail.com
5 Department of Medical Biochemistry, Ebonyi State University, Abakaliki, Nigeria
6 Department of Applied Biology, Ebonyi State University, Abakaliki, Nigeria
Comparative assessment for nutritional and antinutritional 
qualities revealed better performance of traditional white-
fleshed sweet potatoes than orange-fleshed sweet potatoes
Abstract: Recent introduction of beta-carotene rich or-
ange-fleshed sweet potatoes (OFSP) has resulted to consum-
ers’ low demands for traditional white-fleshed sweet potatoes 
(TWFSP), without due consideration of their nutritional quali-
ties. This study appraised the nutritional compositions of OFSP 
and TWFSP. They were analyzed for mineral content, antinu-
trients, and phytochemicals at National Root Crops Research 
Institute, Umudike. The field experiment was conducted using 
randomized complete block design with three replicates. TWF-
SP showed higher concentrations of minerals, anti-nutrients 
and phytochemicals than OFSP. In TWFSP, potassium ranged 
from 1879.20 ± 0.01 mg kg-1 (‘B3V3’) to 1960.30 ± 0.01 mg kg
-1 
(‘B2V2’) while in OFSP it varied from 1162.60 ± 0.02 mg kg
-1 
(‘B26T26’) to 1800.20  ±  0.01  mg  kg
-1 (‘B10T10’). The antinu-
trients and phytochemicals results showed that flavonoids 
in TWFSP ranged from 0.30  ±  0.01  mg  TAE kg-1 (‘B1V1’) 
to 970.50  ±  0.02  mg  TAE  kg-1 (B3V3) while it varied from 
0.20 ± 0.01 mg TAE kg-1 (‘B4T4’) to 670.30 ± 0.01 mg TAE kg
-1 
(‘B8T8’) in OFSP. Heritability estimates were high for all antinu-
trients and minerals while genetic advance was high only for 
potassium (42.206) and phosphorus (10.288) traits. Variation 
between phenotypic coefficient of variation and genotypic co-
efficient of variation was negligible, with the former higher for 
most minerals and antinutrients. TWFSP were found richer 
than OFSP, and suggests improvement by selection.
Key words: antinutrient, cultivars, phytochemicals, min-
erals, nutrition, sweet potatoes
Primerjalna ocena hranilne in nehranilne kakovosti je od-
krila, da ima sladki krompir z belim založnim parenhimom 
boljše lastnosti kot tisti z oranžnim
Izvleček: Nedavna uvedba sladkega krompirja z oran-
žnim mesom (OFSP) bogatega z beta-karotenom, je povzročila 
slabše povpraševanje potrošnikov po tradicionalnem sladkem 
krompirju z belim mesom (TWFSP), ne da bi ustrezno upošte-
vali njegove prehranske lastnosti. Ta študija preučuje prehran-
sko sestavo sladkega krompirja z belim in oranžnim mesom 
(založnim parenhimom). Vzorci so bili analizirani na vsebnost 
elementov, bioaktivnih sestavin in antinutrientov na National 
Root Crops Research Institute, Umudike. Nigerija. Terenski 
poskus je bil izveden z uporabo naključne blokovne zasnove s 
tremi ponovitvami. Krompir z belim mesom je pokazal večje 
vsebnosti mineralov, antihranil in bioaktivnih sestavin v pri-
merjavi z oranžnim sladkim krompirjem. V krompirju z belim 
mesom se je kalij gibal od 1879,20 ± 0,01 mg kg-1 (‘B3V3’) do 
1960,30 ± 0,01 mg kg-1 (‘B2V2’), medtem, ko se je v krompirju 
z oranžnim mesom gibal od 1162,60 ± 0,02 mg kg-1 (‘B26T26’) 
do 1800,20 ± 0,01 mg kg-1 (‘B10T10’). Rezultati antinutrientov in 
bioaktivnih sestavin so pokazali, da je bila vsebnost flavonoidov 
v krompirju z belim mesom od 0,30 ± 0,01 mg TAE kg-1 (‘B1V1’) 
do 970,50 ± 0,02 mg TAE kg-1 (B3V3), v krompirju z oranžnim 
mesom pa od 0,20 ± 0,01 mg TAE kg-1 ( ‘B4T4’) do 670,30 ± 0,01 
mg TAE kg-1 (‘B8T8’). Določitve dednih znakov so bile velike za 
vse antinutriente in vsebnosti elementov, genetska prednost je 
bila večja samo za kalij (42,206) in fosfor (10,288). Razlike med 
fenotipičnim in genotipičnim koeficientom spremenljivosti so 
bile zanemarljive, pri čemer so bile razlike v genotipičnem ko-
eficientu večje za vsebnosti večine elementov in antinutrientov. 
Sorte z belim založnim parenhimom so se izkazale po večji 
vsebnosti koristnih snovi, kar nakazuje, da jih je potrebno upo-
rabiti v žlahtniteljskih programih. 
Ključne besede: antihranilo, sorte, fitokemikalije, mine-
rali, prehrana, sladki krompir
Acta agriculturae Slovenica, 120/2 – 20242
O. OGAH et al.
1 INTRODUCTION
Most traditional white-fleshed sweet potato (TWF-
SP) especially cultivars from Abakaliki, Nigeria, seem 
to have gone into extinction as a result of introduction 
of the orange-fleshed sweet potatoes (OFSP) (Mazuze, 
2004). Beta-carotene, a known vitamin A precursor and 
carotenoids are plentiful in OFSP and their regular con-
sumption can prevent blindness especially night blind-
ness (Ndirigue, 2004; Park et al., 2016). TWFSP cultivars 
have been grown among local farmers for several years 
due to their high yielding capability, and consumer’s ac-
ceptability despite its low beta-carotene contents. How-
ever, the high adoption rate of the recently introduced 
OFSP cultivars seemed to have caused a total replace-
ment of TWFSP cultivars among farmers and consumers 
(Mazuze, 2004). 
Although OFSP cultivars have been recognized for 
better beta-carotene contents than TWFSP cultivars, 
there is no elaborate record that compared other nu-
tritional and antinutritional properties between them. 
Generally, sweet potatoes have been a vital food supply 
for the poorest farmers and food-insecure people around 
the world (Sugri et al., 2017). Studies reported that after 
maize, rice, and wheat, sweet potato is the fifth most im-
portant food crop in the developing world, with over 110 
million metric tonnes produced per annum (Kanu et al., 
2018). Sweet potatoes are abundant in protein, dietary 
fiber, polyphenols, vitamins and minerals but low in fat, 
which perhaps made it an ideal food for a greater per-
centage of the world’s populace (Kanu et al., 2018; Tunio 
et al., 2019).
In many countries, including countries of sub-Sa-
haran Africa, sweet potatoes especially white flesh sweet 
potatoes are the most utilized traditional root crops when 
compared to other root crops. In most Nigerian localities, 
TWFSP cultivars appear to be the most prevalent choice 
among local farmers probably among other benefits, be-
cause of their enormous volatile organic compounds (fla-
vor) content (Mazuze, 2004; Kanu et al., 2018).
Previous studies have examined the nutritional 
properties of sweet potato cultivars grown in different 
countries of the world and have found considerable vari-
ation in nutrients among different sweet potato cultivars 
(Sanoussi et al., 2016; Kanu et al., 2018). The differences 
observed could be attributed to soil, climate, growing 
conditions, varying genetic make-up of cultivars and 
other factors (Mwanri et al., 2011; Sanoussi et al., 2016). 
However, none of these studies investigated the nutri-
tional potentials of a given white fleshed sweet potato 
cultivar(s) in comparison with the OFSP cultivars, which 
recently have seemingly dominated greater parts of sub-
Saharan African countries since development and intro-
duction. 
We hypothesize that the nutritional potentials of 
different OFSP and TWFSP cultivars will vary but to 
what extent and which would be better we cannot ascer-
tain. Hence, the present study was undertaken to make 
a comparative assessment or appraisal of the nutrition-
al, antinutritional and phytochemical properties of the 
available traditional white-fleshed sweet potatoes and the 
orange-fleshed sweet potato cultivars in the region and 
check for variability and trait association for better future 
sweet potato breeding. 
2 MATERIALS AND METHODS 
2.1 MATERIALS, EXPERIMENTAL SITE, DESIGN 
AND AGRONOMIC PRACTICE
Twenty-two cultivars of orange-fleshed sweet po-
tato genotypes were collected from the National Root 
Crops Research Institute (NRCRI) Umudike, Abia State, 
Nigeria and three traditional white fleshed cultivars of 
sweet potato were collected from farmers in Abakaliki, 
Ebonyi State, Nigeria. The summary and description of 
each sweet potato cultivar are presented in Table 1.
The stems cuttings were collected and planted at the 
research and teaching farm of the Department of Crop 
Production and Landscape Management, Ebonyi State 
University, Abakaliki, Nigeria during raining season pre-
cisely June, 2019 which lasted till September the same 
year. The experimental design utilized was a randomized 
complete block design with three replicates. Standard 
agronomic management practices included; weeding, 
fertilizer (NPK 20:10:10), fungicide (mancozeb/chloro-
thalonil) and insecticide (malathion1/cypermethrin) ap-
plications at the rates provided on the labels, respectively. 
Tuber weighing 10  kg was harvested from each culti-
var for nutritional analysis. All tubers were harvested, 
washed, and sliced before freeze-drying. 
The dried potato slices were then pulverized, sieved 
through a 100-mesh sieve, and stored at –20  °C for all 
analysis. The laboratory analysis was carried out at the 
NRCRI central molecular biology laboratory, Umudike. 
2.2 MINERAL ANALYSIS
The method of the Association of Official Agricul-
tural Chemists (AOAC) in 2010 was used for the determi-
nation of mineral content; 1 g of the pulverized samples 
was placed in a crucible and ignited in a muffle furnace 
at 550 °C for 6 hours. The resulting ash was dissolved in 
Acta agriculturae Slovenica, 120/2 – 2024 3
Comparative assessment ... of traditional white-fleshed sweet potatoes than orange-fleshed sweet potatoes
10 ml of 10 % HNO3 and heated slowly for 20 minutes. 
After heating, it was filtered and the filtrate was used for 
the determination of mineral content. Atomic Absorp-
tion Spectrophotometer (AAS) was used in all analyses.
2.3 EXTRACTION OF PHENOLICS AND FLAVO-
NOIDS
Total phenolics and flavonoids in freeze-dried OFSP 
and TWFSP roots were determined through colorimetric 
assay using the method of Abidemi (2013). Briefly, 1  g 
of the freeze-dried root powdered sample was weighed 
into clean propylene tubes before the addition of 10 ml of 
80 % methanol, vortexed, shaken on a mechanical shaker, 
and incubated at a temperature of 25 °C for 12 hours. The 
mixture was then centrifuged at 3226 × g for 10 min, and 
the supernatant aliquot was collected to determine the 
total phenolics and total flavonoid contents.
2.4 DETERMINATION OF THE TOTAL POLYPHE-
NOL CONTENT
The method of Baba and Malik (2015) was used to 
quantify the total phenolic content using the Folin-Cio-
calteu technique. Exactly 20 ml of the sample blank solu-
tion (80 % methanol), gallic acid standards (0.001–0.1 kg 
ml-1), and 5 ml of samples were pipetted into their corre-
sponding test tubes, followed by the addition of 100 ml of 
10 % Folin–Ciocalteu reagent and the mixtures are then 
shaken thoroughly. After 5 minutes, 80 ml of 7 % sodium 
carbonate was added and gently mixed before the plate 
was covered with aluminum foil and the reaction was al-
lowed to incubate for 90 minutes at room temperature. 
Table 1: Description of 25 sweet potato cultivars
S/N Genotypes Sources Sowing/Harvesting date Skin and flesh color
1 ‘B6T6’ NRCRI June. 28, 2019/September. 28, 2019 purple/yellow
2 ‘B1T1’ NRCRI June. 28, 2019/September. 28, 2019 purple/yellow
3 ‘B3V3’ ABAKALIKI June. 28, 2019/September. 28, 2019 White/white
4 ‘B17T17’ NRCRI June. 28, 2019/September. 28, 2019 purple/yellow
5 ‘B8T8’ NRCRI June. 28, 2019/September. 28, 2019 purple/yellow
6 ‘B28T28’ NRCRI June. 28, 2019/September. 28, 2019 purple/yellow
7 ‘B13T13’ NRCRI June. 28, 2019/September. 28, 2019 purple/yellow
8 ‘B26T26’ NRCRI June. 28, 2019/September. 28, 2019 purple/yellow
9 ‘B10T10’ NRCRI June. 28, 2019/September. 28, 2019 purple/yellow
10 ‘B16T16’ NRCRI June. 28, 2019/September. 28, 2019 purple/yellow
11 ‘B29T29’ NRCRI June. 28, 2019/September. 28, 2019 Brown/Yellow
12 ‘B19T19’ NRCRI June. 28, 2019/September. 28, 2019 Brown/yellow
13 ‘B2V2’ ABAKALIKI June. 28, 2019/September. 28, 2019 Light purple/white
14 ‘B11T11’ NRCRI June. 28, 2019/September. 28, 2019 Brown/yellow
15 ‘B5T5’ NRCRI June. 28, 2019/September. 28, 2019 Brown/yellow
16 ‘B18T18’ NRCRI June. 28, 2019/September. 28, 2019 Brown/yellow
17 ‘B7T7’ NRCRI June. 28, 2019/September. 28, 2019 Brown/yellow
18 ‘B15T15’ NRCRI June. 28, 2019/September. 28, 2019 Brown/yellow
19 ‘B14T14’ NRCRI June. 28, 2019/September. 28, 2019 Brown/yellow
20 ‘B20T20’ NRCRI June. 28, 2019/September. 28, 2019 Brown/yellow
21 ‘B3T3’ NRCRI June. 28, 2019/September. 28, 2019 Red/yellow
22 ‘B1V1’ ABAKALIKI June. 28, 2019/September. 28, 2019 Red/White
23 ‘B2T2’ NRCRI June. 28, 2019/September. 28, 2019 Red/yellow
24 ‘B4T4’ NRCRI June. 28, 2019/September. 28, 2019 Red/yellow
25 ‘B9T9’ NRCRI June. 28, 2019/September. 28, 2019 Red/yellow
NRCRI: National Root Crops Research Institute, Umudike, Abia State, Nigeria
Acta agriculturae Slovenica, 120/2 – 20244
O. OGAH et al.
The absorbance value was then taken at 725  nm in a 
spectrophotometer. The concentration of total phenolic 
compounds in mg  kg-1 of the dry sample as gallic acid 
equivalent was determined using an external standard 
calibration procedure (mg GAE).
2.5 ANALYSIS OF FLAVONOIDS
Exactly 250 ml titration flask, 0.005 kg of each plant 
sample was weighed, and 100 ml of 80 percent aqueous 
methanol was added at room temperature and agitated in 
an electric shaker for 4 hours. This process was repeated 
with the entire solution filtered through Whatman filter 
paper no. 42. The filtrate was then placed in a crucible 
and evaporated to dryness over a water bath before being 
weighed (Abidemi, 2013).
2.6 ANALYSIS OF TANNIN
Tannin was analyzed using the method of Ejikeme 
et al. (2014). Exactly 0.001 kg of the samples was weighed 
into a plastic bottle followed by the addition of 1000 ml 
of water and shaken for 1 hour in a shaker. It was then 
filtered, and 10 ml of the extract was measured into a test 
tube, along with 3 ml of 0.1 N HCl and three drops of fer-
rocyanide. It was let to stand for 10 minutes before being 
measured in a UV-Spectrophotometer at a wavelength of 
605 nm.
Tannic acid (mg kg-1) = C × extract volume × 0.1
Aliquot volume × mass of the sample
Where, 𝐶 is the concentration of tannic acid read.
2.7 EXTRACTION AND DETERMINATION OF 
OXALATE
Extraction of total oxalate was done as reported by 
Liu et al. (2009) and Nguyễn and Savage (2013). 1 g of 
each powdered sample was added to 0.5 mol  l-1 of HCl 
before being diluted in 1 ml distilled water. The homoge-
nate was put in 10  ml graduated tubes and cooked for 
20 minutes in a boiling water bath. After the homogen-
ate had cooled, distilled water was added to each tube to 
bring the total volume to 10 ml. About 1 ml of the ho-
mogenate was clarified the next day at 4 8C by centrifu-
gation (12,000 g, 10 min). After that, 0.016 ml NaOH (2 
mol l-1) was carefully added to 0.5 ml supernatant.
Initially, a 2 ml test tube was added 20 mg of oxalate 
oxidase and then filled with other ingredients, including 
0.06 ml of distilled water, 0.08 ml of colorant (10 mg of 
4-aminoantipyrine), 25 ml of N, N-dimethylaniline, 0.04 
ml of horseradish peroxide and 0.05 ml oxalate extract. 
The reaction mixture’s absorbance at 555 nm was meas-
ured in a spectrophotometer after 90 minutes of incuba-
tion at room temperature. The oxalate content was cal-
culated using a standard curve made by mixing 0, 2, 4, 6, 
8, and 10 mg oxalic acid into a 1 ml reaction system, re-
spectively. The results are given as mean mg oxalate kg-1 
(Liu et al., 2009).
2.8 SAPONINS ANALYSIS
Saponin was analyzed according to the methods of 
Akpe et al. (2021). In a beaker, 0.005 kg of sample was 
added in 50 ml of 20 % ethanol. The suspension was heat-
ed for four hours in a hot water bath with constant stir-
ring at a temperature of 60 oC. The mixture was filtered 
after 4 hours, and the residue was extracted again with 
another 25  ml of 20  % ethanol. The combined extract 
was concentrated and reduced to 40 ml in a water bath at 
90 oC. The sample was placed in a separator-funnel and 
20  ml diethyl ether was added and thoroughly shaken. 
The extracts’ aqueous layer was recovered, while the oth-
er layers were discarded. Exactly 60 ml of n-butanol was 
then added and the extract was washed twice with 10 ml 
of 5 % aqueous sodium chloride. The remaining extracts 
were evaporated in a water bath and dried in an oven to a 
constant mass and weighed.
2.9 ALKALOIDS ANALYSIS
5  g of sample was weighed into a beaker; 100  ml 
of 100 % acetic acid in ethanol (1:1) was measured into 
the sample container and covered for 4 hours. After four 
hours, the extracted sample was filtered. It was then con-
centrated to a fraction of its original volume using a wa-
ter bath. Drop-by-drop, ammonia solution was added to 
the concentrated extract, allowing the precipitate to settle 
before being filtered and washed with dilute ammonium 
hydroxide. The crude alkaloid was extracted from the 
residue and dried in an oven before being weighed.
2.10 ANTHOCYANINS ANALYSIS 
The total anthocyanin content was calculated using 
Giusti and Wrolstad’s method (2001) and Wegdan et al. 
(2020). In summary, two dilutions of the sample extract 
were made as follows 1  ml of the extracted sample so-
Acta agriculturae Slovenica, 120/2 – 2024 5
Comparative assessment ... of traditional white-fleshed sweet potatoes than orange-fleshed sweet potatoes
lution was added to a 10 ml volumetric flask each. One 
dilution volume was adjusted using potassium chloride 
buffer (pH 1.0), while the other was adjusted with so-
dium acetate buffer (pH 4.5). For equilibration, the di-
lution was allowed to sit for 15 minutes. Each dilution’s 
absorbance was measured against water at 510 and 700 
nm. The diluted sample’s absorbance (A) was determined 
as follows:
A = (A510 – A700) pH 1.0 – (A510 – A700) pH 4.5
The concentration of monomeric anthocyanin pig-
ment was determined using the following formula: Mon-
omeric anthocyanin pigment
(mg 100 g-1) = (A x MW x DF x 1000) / (ε x 1)
Where MW is the molecular weight, DF is the dilu-
tion factor, and ε is the molar absorptivity, calculate pig-
ment content as cyanidin-3-glucoside.
Where MW = 449.2 and ε = 26,900
2.11 STATISTICAL ANALYSIS 
All analyses such as ANOVA, genetic variability 
including phenotypic coefficient of variation percentage 
(% PCV) and genotypic coefficient of variation percent-
age (%  GCV), Pearson correlation, Clusters and PCA 
were performed using the R statistical package (R-4.2.1) 
version (R Core Team, 2022).
3 RESULTS AND DISCUSSION
The results of the mineral contents of orange-fleshed 
sweet potatoes and indigenous or traditional white-
fleshed sweet potatoes are presented in Table 2, Table 3, 
and Figure 1 while those of the antinutrients and phyto-
chemicals are presented in Table 4, Table 5, and Figure 2. 
3.1 COMPARATIVE ANALYSIS OF VARIATION 
AMONG OFSP AND TWFSP 
3.1.1 Minerals 
The results showed significant variation for the 
variables, and that both OFSP and TWFSP cultivars con-
tained all the eight minerals including calcium, iron, po-
tassium, phosphorus, sodium, magnesium, manganese, 
and zinc (Table 2). The studies of Mwanri et al. (2011) 
and Sanoussi et al. (2016) reported the presence of these 
minerals in orange-flesh sweet potatoes. Their concen-
trations as observed in the present study showed evi-
dence that sweet potatoes possess high nutritional value. 
Minerals are needed in the body to keep the heart beat-
ing, blood clotting, nerve responses and reactions, and 
most importantly keep the body fluid balance in check 
(Mwanri et al., 2011; Sanoussi et al., 2016). The proper 
consumption of minerals is essential for human health. 
For instance, potassium is highly needed for proper neu-
ronal transmission, and protein synthesis (Sebeo et al., 
2009). Of the eight minerals studied, the concentrations 
of six minerals including zinc, calcium, iron, potassium, 
phosphorus, and sodium were found to be higher in 
TWFSP compared to the OFSP. The higher concentra-
tions of these minerals in traditional white-fleshed culti-
vars suggested the presence of variation in their genetic 
make-up, and showed that this group may possess more 
nutrient and health benefits than orange-fleshed sweet 
potatoes (Table 3). Zinc and iron contents were higher in 
TWFSP cultivar ‘B3V3’ with values of 8.30 ± 0.01 mg kg
-1 
and 12.60  ±  0.01  mg  kg-1, respectively. Comparatively, 
OFSP cultivars, B8T8 and ‘B26T26’ expressed the values 
7.60 ± 0.02 mg kg-1 and 12.40 ± 0.02 mg kg-1 for zinc and 
iron, respectively. Although there is no literature on the 
TWFSP cultivars used in this study, the values we had 
for OFSP cultivars were close to those of Sanoussi et al. 
(2016). Zinc has been reported as a catalyst in a variety of 
activities in our bodies including involvement in macro-
molecules metabolism and required for cell division, tis-
sue repair and normal reproductive development (Sebeo 
et al., 2009). Furthermore, iron has been implicated in the 
formation of hemoglobin in red blood cells, hence TWF-
SP cultivars, especially ‘B3V3’ will be of health impor-
tance for people with a metabolism health related prob-
lems and those suffering from iron deficiency compared 
to OFSP cultivars with lower mean concentrations. Phos-
phorus and sodium were also higher in TWFSP cultivar 
‘B1V1’ with mean concentrations of 486.40 ± 0.03 mg kg
-1 
and 374.20 ± 0.02 mg kg-1, respectively compared to the 
values of phosphorus (295.80  ±  0.01  mg  kg-1) and so-
dium (216.60 ± 0.01 mg kg-1) in OFSP cultivars ‘B17T17’ 
and ‘B6T6’, respectively. Magnesium and manganese with 
values 301.20 ± 0.03 mg kg-1 and 3.30 ± 0.03 mg kg-1 were 
the only minerals that had higher mean concentrations 
found in OFSP cultivars ‘B18T18’ and ‘B26T26’, respectively. 
These values were against the lowest mean concentra-
tions of 260.50 ± 0.02 mg kg-1 and 1.70 ± 0.01 mg kg-1 for 
magnesium and manganese observed in TWFSP culti-
vars ‘B1V1’ and ‘B3V3’, respectively. These mean concen-
trations varied compared to 235.00 mg kg-1 reported for 
magnesium in an OFSP cultivar (Sanoussi et al., 2016). 
The reason for this variation may be attributed to dif-
ferences in edaphic factors of the locations they were 
Acta agriculturae Slovenica, 120/2 – 20246
O. OGAH et al.
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1i
22
1.
60
 ±
 0
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2d
29
5.
80
 ±
 0
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32
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0 
± 
0.
02
d
5.
40
 ±
 0
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2b
6.
10
 ±
 0
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1.
80
 ±
 0
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‘B
8T
8’
29
3.
70
 ±
 0
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35
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70
 ±
 0
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27
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40
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 0
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g
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60
 ±
 0
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40
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h
1.
50
 ±
 0
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ef
g
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26
T 2
6’
21
6.
60
 ±
 0
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25
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50
 ±
 0
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20
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50
 ±
 0
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38
5.
50
 ±
 0
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62
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a
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50
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10
 ±
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31
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50
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43
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20
 ±
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2g
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20
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16
T 1
6’
28
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80
 ±
 0
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31
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30
 ±
 0
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26
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90
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 0
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30
 ±
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08
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l
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1d
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29
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9’
25
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20
 ±
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 ±
 0
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80
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30
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20
 ±
 0
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01
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27
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50
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70
 ±
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 ±
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30
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20
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70
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32
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36
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50
 ±
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80
 ±
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70
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‘B
18
T 1
8’
32
5.
30
 ±
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29
6.
50
 ±
 0
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39
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 ±
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52
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50
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‘B
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50
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70
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25
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20
 ±
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31
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50
 ±
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23
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42
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30
 ±
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20
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9.
30
 ±
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6.
30
 ±
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h
2.
30
 ±
 0
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1h
‘B
14
T 1
4’
20
6.
40
 ±
 0
.0
3a
30
1.
60
 ±
 0
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3i
25
4.
40
 ±
 0
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2l
39
8.
40
 ±
 0
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2i
14
87
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j
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80
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7.
60
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‘B
20
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26
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70
 ±
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2g
25
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50
 ±
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22
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80
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40
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50
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31
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50
 ±
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36
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60
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24
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37
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37
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20
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41
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40
 ±
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Th
e r
es
ul
ts
 ar
e t
he
 st
an
da
rd
 d
ev
ia
tio
ns
 o
f t
hr
ee
 d
up
lic
at
e s
am
pl
es
; v
al
ue
s i
n 
th
e s
am
e c
ol
um
n 
w
ith
 si
m
ila
r l
et
te
rs
 ar
e n
ot
 si
gn
ifi
ca
nt
ly
 d
iff
er
en
t a
t 0
.0
5,
 K
ey
s: 
C
a 
= 
ca
lc
iu
m
, N
a 
= 
so
di
um
, P
 =
 p
ho
sp
ho
ru
s, 
K
 =
 p
ot
as
siu
m
, Z
n 
= 
zi
nc
, F
e 
= 
iro
n,
 M
g 
= 
m
ag
ne
siu
m
, M
n 
= 
m
an
ga
ne
se
Acta agriculturae Slovenica, 120/2 – 2024 7
Comparative assessment ... of traditional white-fleshed sweet potatoes than orange-fleshed sweet potatoes
planted and fertilizer application as has been suggested 
in potato (Solanum tuberosum L.) (Liang et al., 2019). 
Manganese is very important component of glucose tol-
erance factor (GTF), which regulates blood glucose levels 
while magnesium is an essential component in many en-
zyme reactions and has an important role in the immune 
system regulation (Siddiqui et al., 2014; Konieczynski et 
al., 2022).
3.1.2 ANTINUTRIENTS AND PHYTOCHEMI-
CALS
The antinutrients (oxalate, tannins, saponins and 
alkaloids) and phytochemicals (total polyphenols, an-
thocyanins and flavonoids) quantified in this study were 
all present in all the 25 cultivars at varying concentra-
tions (Table 4). TWFSP cultivars had higher concentra-
tions of all the antinutrients when also compared with 
OFSP (Table 5). The alkaloids and anthocyanin were 
the two compounds higher in OFSP than TWFSP. The 
highest mean value of alkaloids concentrations in OFSP 
was 1.30  ±  0.01  mg  kg-1 for cultivar ‘B6T6’ contrary to 
1.20 ± 0.01 mg kg-1 for TWFSP cultivar ‘B1V1’. The val-
ues we obtained for alkaloids in this study deferred from 
the 6.20 ± 0.01 mg kg-1 reported in different cultivars of 
OFSP (Ogah et al., 2014; Akpe et al., 2021). This may be 
due to differences in plant maturity date, post-harvest 
storage and processing, location, growth season, soil type 
and nutrients (Li et al., 2012). Alkaloids have been impli-
cated in a wide range of pharmacological effects, includ-
ing anti-malarial, anti-cancer (Kittakoop et al., 2014), 
anti-bacterial (Cushnie et al., 2014) and anti-hypergly-
cemic (Qiu et al., 2014). Other compounds quantify in 
this study including oxalate, flavonoids, tannin, poly-
phenols and saponin were higher in TWFSP than OFSP. 
The concentrations of total polyphenols, flavonoids, tan-
nins and oxalate in TWFSP were 123.80 ± 0.01 mg kg-
1, 970.50  ±  0.02  mg  kg-1, 4.70  ±  0.01  mg  kg-1, and 
382.20  ±  0.02  mg  kg-1, respectively for cultivars ‘B3V3’ 
compared to the maximum mean concentration val-
ues of 89.20  ±  0.02 mg  kg-1, 673.80  ±  0.0102  mg  kg-1, 
3.90 ± 0.01 mg kg-1 and 330.30 ± 0.0 mg kg-1 respectively 
in OFSP cultivars ‘B1T1’, ‘B8T8’, ‘B4T4’ and ‘B13T13’ respec-
tively. The concentrations obtained for tannin, flavonoids, 
and total polyphenols varied compared to the studies 
by Akpe et al. (2021) that reported 2.80 ± 0.01 mg kg-1, 
9.70 ± 0.01 mg kg-1, and 7.20 ± 0.01 mg kg-1 for tannins, 
flavonoids, and total polyphenols, respectively. Flavo-
noids have antioxidant effects and have been shown to 
inhibit the initiation, promotion, and progression of 
tumors and can equally reduce coronary heart disease 
(Ezeonu & Ejikeme, 2016). Tannins have also been im-
plicated in antiviral, antibacterial, and antitumor activ-
ity (Ezeonu & Ejikeme, 2016) while saponins are help-
ful in treating yeast and fungal infections. TWFSP also 
has higher content of oxalate with mean concentrations 
of 7.20 ± 0.01 mg kg-1 compare to 6.20 mg kg-1 in OFSP. 
Oxalate can prevent calcium absorption and utilization 
in the body. This eventually could lead to disorders like 
osteomalacia and rickets in the human body (Reddy & 
Pierson, 1994).
Table 3: The basic statistics description of mineral content of TWFSP and OFSP
TWFSP (Traditional white-fleshed sweet potatoes)
Parameter Ca Na Mg P K Fe Zn Mn
Mean 374.60 391.40 272.20 467.30 1913.70 11.70 7.40 1.90
Median 374.20 391.40 274.70 473.40 1901.50 11.60 7.50 1.90
Minimum 363.10 372.40 260.30 442.10 1879.10 10.70 6.20 1.40
Maximum 386.60 410.60 281.60 486.60 1960.40 12.70 8.40 2.30
Range 235.00 38.20 21.30 44.50 81.30 2.00 2.20 0.90
OFSP (Orange-fleshed sweet potatoes)
Parameter Ca Na Mg P K Fe Zn Mn
Mean 281.80 305.10 248.10 392.30 1513.00 8.80 5.70 1.50
Median 291.20 307.10 251.40 402.50 1500.50 8.80 5.90 1.60
Minimum 206.20 218.70 200.30 295.70 1162.40 2.50 3.30 0.30
Maximum 340.90 382.60 333.40 452.70 1800.20 12.50 7.80 3.50
Range 134.70 163.90 133.10 157.00 637.80 10.00 4.50 3.20
Ca = calcium, Na = sodium, P = phosphorus, K = potassium, Zn = zinc, Fe = iron, Mg = magnesium, Mn = manganese
Acta agriculturae Slovenica, 120/2 – 20248
O. OGAH et al.
Ta
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d
Th
e 
re
su
lts
 a
re
 th
e 
st
an
da
rd
 d
ev
ia
tio
ns
 o
f t
hr
ee
 d
up
lic
at
e 
sa
m
pl
es
; v
al
ue
s i
n 
th
e 
sa
m
e 
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lu
m
n 
w
ith
 si
m
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et
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 a
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ot
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nt
ly
 d
iff
er
en
t a
t 0
.0
5
Acta agriculturae Slovenica, 120/2 – 2024 9
Comparative assessment ... of traditional white-fleshed sweet potatoes than orange-fleshed sweet potatoes
3.2 TRAIT ASSOCIATION, GENETIC VARIABILI-
TY AND PRINCIPAL COMPONENT ANALYSIS 
The comprehensive correlations between the levels 
of all the minerals, antinutrients and phytochemicals in 
OFSP and TWFSP were investigated using Pearson’s cor-
relation analysis. 
Among the minerals, positive significant correla-
tions across the minerals were observed except for zinc 
and manganese, which had either negative or positive 
insignificant correlation with other minerals. Potassium 
showed substantial positive correlation with phosphorus 
(r = 0.776) and calcium (r = 0.707) (Figure 1). The re-
sult of this study is in congruence with that of Sanoussi 
et al. (2016) who reported high significant correlation 
between calcium and magnesium in sweet potatoes. 
Among the phytochemicals, total polyphenols showed 
the highest significant positive correlation with antho-
cyanins and flavonoids with correlation values of 0.980 
and 0.980 respectively. Oxalate, which is an antinutrient, 
showed significant association with tannins and saponins 
with values of 0.477 and 0.593, respectively (Figure 2). 
The strong positive correlation observed among traits 
suggested high relatedness among them and that any trait 
can influence the other in the same direction. 
Considering minerals, antinutrients and phyto-
chemicals, the percentage value of PCV were higher than 
the percentage values of GCV showing how little the en-
vironment affected each trait. PCV values for minerals 
ranged from 39.981 to 10.581, while GCV values ranged 
from 37.875 % to 8.9714 %. PCV values for antinutrients 
and phytochemicals ranged from 159.890 % to 20.302 % 
while GCV values ranged from 149.450 % to 19.824 % 
(Table 6). The difference between GCV and PCV was very 
small and ranged from 2.1058 to 0.000 for minerals, while 
the difference between PCV and GCV for antinutrients 
and phytochemicals ranged from 10.4906 % to 0.0942 %. 
The PCV and GCV reported in our study are higher than 
the values of 14.41 % and 15.98 % reported for Iron by 
Amoros et al. (2020) and lower than the 254.75 % and 
253.96 % respectively, reported for anthocyanin by Dutta 
et al. (2022). The higher percentage values of PCV than 
GCV showed that environment influences the expression 
of minerals and antinutrients in sweet potatoes, while the 
extremely small (less than 10 %) difference between PCV 
and GCV confirmed that environment indeed interacts 
in the expression of all traits studied (Uyeda et al., 2015). 
This equally implies that selection and hybridization may 
not be suitable for improving the content of sweet pota-
toes (Uyeda et al., 2015).
Heritability (H2b) in the broader sense was gener-
ally high for antinutrients, phytochemicals and minerals, 
ranging from 0.7189 to 1.0 for minerals and from 0.8731 
to 0.9934 for antinutrients and phytochemicals (Table 6). 
This result varied slightly higher than the 0.81 reported 
for iron and zinc by Uyeda et al. (2015) and the same 
with the studies of Dutta et al. (2022) who reported 0.99 
for anthocyanin. The genetic advance (GA) was relatively 
low for all traits except potassium (42.206) and phos-
phorus (10.288) among the other traits for minerals. 
The genetic advance for phytochemicals was higher for 
flavonoids and anthocyanin with values of 35.699 and 
57.526, respectively. The low genetic advance with high 
heritability observed in all minerals, antinutrients and 
Table 5: The basic statistics description of antinutrient and phytochemical contents of TWFSP and OFSP
TWFSP (Traditional white-fleshed sweet potatoes)
Parameters OXA TAN SAP ALK POL FLA ANT
Mean 6.10 4.10 1.40 0.60 42.00 323.80 259.70
Maximum 7.20 4.70 1.80 1.30 123.90 970.60 690.60
Range 2.20 1.40 0.70 1.20 122.80 970.40 653.60
Minimum 5.00 3.30 1.10 0.10 1.10 0.20 37.00
Median 6.10 4.30 1.50 0.40 1.20 0.70 51.70
OFSP (Orange-fleshed sweet potatoes)
Parameters OXA TAN SAP ALK POL FLA ANT
Mean 4.10 3.10 0.80 0.60 25.70 183.20 154.10
Median 4.10 3.10 0.80 0.60 1.10 0.70 59.10
Minimum 1.40 2.10 0.30 0.20 0.30 0.10 37.20
Maximum 6.20 4.20 1.50 1.30 98.30 806.50 495.30
Range 4.80 2.10 1.20 1.10 98.00 806.40 458.10
OXA = Oxalate, TAN = Tannins, SAP = Saponins, ALK = Alkaloids, POL = Polyphenol, FLA = Flavonoids, ANT = Anthocyanins 
Acta agriculturae Slovenica, 120/2 – 202410
O. OGAH et al.
Figure 1: Pearson correlation plot for minerals. Ca = calcium, Na= sodium, P= phosphorus, K= potassium, Zn = zinc, Fe = iron, 
Mg = magnesium, Mn= manganese, Red color = Orange-fleshed sweet potatoes, Green = Traditional white-fleshed sweet potatoes
Figure 2: Pearson correlation plot for antinutrients. OXA = Oxalate, TAN = Tannins, SAP = Saponins, ALK = Alkaloids, POL 
=Total polyphenols, FLA = Flavonoids, ANT = Anthocyanins, Red color = Orange-fleshed sweet potatoes, Green = Traditional 
white-fleshed sweet potatoes
Acta agriculturae Slovenica, 120/2 – 2024 11
Comparative assessment ... of traditional white-fleshed sweet potatoes than orange-fleshed sweet potatoes
Ta
bl
e 
6:
 E
st
im
at
es
 o
f g
en
et
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ar
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nd
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hy
to
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s f
ro
m
 d
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t c
ul
tiv
ar
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f o
ra
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fle
sh
ed
 a
nd
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t p
ot
at
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s
Tr
ai
ts
G
ra
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M
in
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PV
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G
C
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C
a 
= 
ca
lc
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m
, N
a 
= 
so
di
um
, P
 =
 p
ho
sp
ho
ru
s, 
K
 =
 p
ot
as
siu
m
, Z
n 
= 
zi
nc
, F
e =
 ir
on
, M
g 
= 
m
ag
ne
siu
m
, M
n 
= 
m
an
ga
ne
se
, O
X
A
 =
 O
xa
la
te
, T
A
N
 =
 T
an
ni
ns
, S
A
P 
= 
Sa
po
ni
ns
, A
LK
 =
 A
lk
al
oi
ds
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O
L 
= 
Po
ly
-
ph
en
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FL
A
 =
 F
la
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A
N
T 
= 
A
nt
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cy
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s, 
V
E 
= 
En
vi
ro
nm
en
ta
l v
ar
ia
nc
e, 
V
G
 =
 G
en
ot
yp
ic
 v
ar
ia
nc
e, 
PV
 =
 P
he
no
ty
pi
c v
ar
ia
nc
e, 
EC
V
 =
 E
nv
iro
nm
en
ta
l c
oe
ffi
ci
en
t o
f v
ar
ia
tio
n,
 G
C
V
 =
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en
ot
yp
ic
 
co
effi
ci
en
t o
f v
ar
ia
tio
n,
 P
C
V
 =
 P
he
no
ty
pi
cc
oe
ffi
ci
en
t o
f v
ar
ia
tio
n,
 H
2b
 =
 B
ro
ad
 se
ns
e 
he
rit
ab
ili
ty
, G
A
 =
 G
en
et
ic
 a
dv
an
ce
, G
A
M
 =
 G
en
et
ic
 a
dv
an
ce
 a
s a
 p
er
ce
nt
ag
e 
of
 m
ea
n,
 M
in
 =
 M
in
im
um
, M
ax
 =
 
M
ax
im
um
, G
ra
. M
 =
 G
ra
nd
 m
ea
n
Acta agriculturae Slovenica, 120/2 – 202412
O. OGAH et al.
phytochemicals studied indicates that these traits are sig-
nificantly influenced by environmental factors and phe-
notypic selection may not be possible for enhancement 
(Uyeda et al., 2015). 
The PCA biplot loading for the minerals revealed an 
overall variance of 68.3  % for dimensions 1 and 2. Di-
mension (PC1) explained the highest variation at 48.9 % 
(Figure 3). The plot of different dimensions for the min-
erals showed that dimension 2 had the highest concen-
trations or magnitude of zinc and manganese while iron 
and sodium were higher in dimensions 4 and 5, respec-
tively (Figure 4). Magnesium had higher concentration 
Figure 3: Principal component analysis for minerials. Ca = calcium, Na= sodium, P = phosphorus, K = potassium, Zn = zinc, Fe = 
iron, Mg = magnesium, Mn = manganese
Figure 4: Dimension plots analysis for minerals. Ca = calcium, Na = sodium, P = phosphorus, K = potassium, Zn = zinc, Fe = 
iron, Mg = magnesium, Mn = manganese
Acta agriculturae Slovenica, 120/2 – 2024 13
Comparative assessment ... of traditional white-fleshed sweet potatoes than orange-fleshed sweet potatoes
in dimension 3 compared to other dimensions whereas 
potassium was higher in dimension 5, comparatively. A 
PCA biplot demonstrates how each trait affects a princi-
pal component and how they are related to one another. 
Based on the factor loading, manganese, phosphorus, po-
tassium, zinc, and sodium contributed most to the varia-
tion observed in PC1 suggesting a positive and high cor-
relation with some of the cultivars such as ‘B28T28’, ‘B10T10’, 
‘B2V2’, ‘B8T8’, ‘B3V3’, and ‘B1V1’ since the smaller angle (less 
than 90 degree) between the two vectors indicates posi-
tive and greater correlation (Olanrewaju et al., 2021). It 
is clear from the PCA biplot that accessions loading in 
PC1 had a larger content of minerals (Mn, P, K, Zn, and 
Na) than accessions loading in PC2. The present result is 
similar to the studies of Laurie et al. (2022) which found 
sweet potatoes major nutrient in PC1.
The biplot of the principal component analysis for 
antinutrients revealed an overall variance of 78.7 % for 
dimension 1 and 2. Dimension (PC1) explained the 
highest variation at 48.8 % (Figure 5). The plot of differ-
ent dimensions for antinutrients showed that dimensions 
3 and 5 had the highest concentrations of alkaloid and 
oxalate, respectively (Figure 6). Among the 5 dimensions 
considered, saponin was higher in dimension 4. Based 
on the factor loading, saponin, oxalate, tannin, and alka-
loids contributed most to the variation observed in PC1 
indicating a positive and high correlation with some of 
the cultivars such as ‘BIV1’, ‘B13T13’, and ‘B3V3’. The PCA 
biplot clearly showed that the accessions loading in PC1 
had a higher content of antinutrients than the accessions 
loading in PC2. The analysis also revealed that out of the 
three cultivars that showed strong and positive associa-
tion with these antinutrients (saponin, oxalate, alkaloid, 
and tannin), two (‘B1V1’ and ‘B3V3’) were of traditional 
white flesh sweet potato cultivars. Although, studies are 
limited based on the samples used in the present study, 
however, our findings are similar to those of Ellong et al. 
(2014) which also reported strong relationship between 
polyphenols or phenoics and sweet potatoes.
Figure 5: Principal component analysis for anti-nutrient. OXA = Oxalate, TAN = Tannins, SAP = Saponins, ALK = Alkaloids, 
POL = Total Polyphenols, FLA = Flavonoids, ANT = Anthocyanins
Acta agriculturae Slovenica, 120/2 – 202414
O. OGAH et al.
3.3 CLUSTER ANALYSIS
The hierarchical clustering analysis constructed 
using pvclust cluster method with AU/BP Pvalues in 
percentages and the bootstrapping of 10,000 are shown 
below in figures 7 and 8 for mineral and antinutrients, 
Figure 6: Dimension plot analysis for antinutrient. OXA = Oxalate, TAN = Tannins, SAP = Saponins, ALK = Alkaloids, POL = 
Total Polyphenols, FLA = Flavonoids, ANT = Anthocyanins
Figure 7: Cluster dendrogram with au/bp values (%) based mineral. The values at the edges of the cluster are P-values (%) 
calculated over a multiscale bootstrap with 1000 resamples. Values on the left in red = au (approximate unbiased) P-values, and 
values on the right in green = bp (bootstrap probability) values. Clusters with au above 95 % are highlighted in blocks suggest high 
relatedness.
Acta agriculturae Slovenica, 120/2 – 2024 15
Comparative assessment ... of traditional white-fleshed sweet potatoes than orange-fleshed sweet potatoes
respectively. This method offers two types of p-values: 
AU (Approximately Unbiased) p-value and BP (Boot-
strap Probability) value. The AU p-value calculated by 
multiscale bootstrap resampling is a better approxima-
tion of the unbiased p-value than the BP value calculated 
by normal bootstrap resampling. Therefore, AU p-values 
above 95  % indicate significant clusters (Suzuki & Shi-
modaira, 2009; de Croos & Pálsson, 2012). The cluster 
dendrogram for the minerals grouped the genotypes 
into two groups (A and B) according to the related-
ness of their mineral composition. Cluster A contains 
only six cultivars, including all traditional white-fleshed 
sweet potatoes (‘B1V1’, ‘B2V2’ and ‘B3V3’) and a few OFSP 
(‘B10T10’, ‘B8T8’ and ‘B28T28’). Cluster B consists of 19 geno-
types and included all OFSPs.
The cluster dendrogram for antinutritional analy-
sis (Figure 8) was also divided into two clusters A and 
B. Cluster B was further divided into B1 and B2. Cluster 
A had eight genotypes, including ‘B13T13’, ‘B6T6’, ‘B17T17’, 
‘B26T26’, ‘B1T1’, ‘B8T8’, ‘B28T28’ and ‘B3V3’. ‘B3V3’ was the only 
TWFSP in cluster A. However, cluster B had two TWF-
SPs, B2V2 in cluster B1 and ‘B1V1’ in cluster B2. Cluster B 
had a total of 17 genotypes. The appearance of ‘B3V3’ of 
TWFSP among the cultivars of OFSP in cluster A showed 
that the grouping pattern of the genotypes did not com-
pletely follow their source or geographical distribution. 
This suggests that ‘B3V3’ which fell into cluster A despite 
its origin or geographical distribution showed a sign of 
broad genetic base of the genotype. Lee et al. (2019) re-
ported that breeding has enhanced the diversity of culti-
vated potatoes, especially with its related wild relatives at 
both phenotypic and genotypic levels. This type of clus-
tering was also reported by Lee et al. (2015) where OFSP 
cultivars fell into the same cluster compared to TWFSP.
4 CONCLUSIONS 
The study revealed significant variation for the traits 
in both TWFSP and OFSP cultivars. Of the eight miner-
als studied, the concentrations of six minerals including 
zinc, calcium, iron, potassium, phosphorus, and sodium 
were found to be higher in TWFSP compared to the 
OFSP which suggest that the former may possess more 
nutrient and health benefits than the latter.
Except for alkaloids and anthocyanin, TWFSP cul-
tivars had higher concentrations for all the antinutrients 
compared to OFSP cultivars.
Figure 8: Cluster dendrogram with au/bp values (%) for antinutrient analysis. The values at the edges of the cluster are P-values 
(%) calculated over a multiscale bootstrap with 1000 resamples. Values on the left in red = au (approximate unbiased) P-values, 
and values on the right in green = bp (bootstrap probability) values. Clusters with au above 95 % are highlighted in block suggest 
high relatedness 
Acta agriculturae Slovenica, 120/2 – 202416
O. OGAH et al.
The positive significant correlations across the min-
erals and phytochemicals suggested high relatedness 
among traits and this can encourage the selection of few-
er traits in future trials, which would reduce cost in traits 
measurement and management without undermining 
experiment precision. 
The high genetic advance with high heritability ob-
served for potassium and phosphorus (minerals), flavo-
noids and anthocyanin (phytochemicals) indicates that 
these traits would respond to selection as the best im-
provement approach.
Despite the lack of carotene, the traditional white-
fleshed sweet potatoes proved to possess higher con-
centrations of these minerals and phytochemicals than 
orange-fleshed sweet potatoes of which the three varie-
ties of TWFSP involved in the study stood out the best, 
comparatively.
4.1 ACKNOWLEDGEMENTS
We are grateful to the National Root Crops Research 
Institute, Umudike, Nigeria, for providing us with the fa-
cility and genetic materials.
4.2 DATA AVAILABILITY STATEMENT
All data set generated during and/or analyzed to 
support the findings of this study are phenotypic data 
and can be made available from the corresponding au-
thor on request.
4.3 COMPETING INTERESTS 
The authors declare that there are no conflicts of 
interest, financial or nonfinancial, directly or indirectly.
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