# Influence of physicochemical properties of yam starch and flour on extensibility of pounded yam in Côte d'Ivoire

Oluwatoyin Ayetigbo, Adou Emmanuel Ehounou, Romain Domingo, Eric Yapi Yapi, Hermann Dekpaho Gnahe, Hermann Antonin Kouassi, N'Nan Affoué Sylvie Diby, Didier Mbeguie-Mbeguie, Konan Evrard Brice Dibi, Prudence Kahndo Deffan, et al.

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Oluwatoyin Ayetigbo, Adou Emmanuel Ehounou, Romain Domingo, Eric Yapi Yapi, Hermann Dekpaho Gnahe, et al. Influence of physicochemical properties of yam starch and flour on extensibility of pounded yam in Côte d'Ivoire. LWT - Food Science and Technology, 2025, 223, pp.117769. 10.1016/j.lwt.2025.117769. hal-05183048

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Influence of physicochemical properties of yam starch and flour on
extensibility of pounded yam in Côte d'Ivoire

Oluwatoyin Ayetigbo<sup>a,b,*</sup>, Emmanuel Adou Ehounou<sup>c</sup>, Romain Domingo<sup>a,b</sup>, Eric Yapi Yapi<sup>d</sup>, Hermann Dekpaho Gnahe<sup>e</sup>, Hermann Antonin Kouassi<sup>e</sup>, N'nan Sylvie Diby<sup>d,f</sup>, Didier Mbeguie-Mbeguie<sup>b,e,g</sup>, Konan Evrard Brice Dibi<sup>c</sup>, Kahndo Prudence Deffan<sup>c</sup>, Patricia N'goran Haddad<sup>d</sup>, Christian Mestres<sup>a,b</sup>, Santiago Arufe<sup>a,b</sup>, Dominique Dufour<sup>a,b</sup>

ARTICLE INFO

Keywords:

Extensibility

Pounded yam

Physicochemical properties

Bi-extensional viscosity

A B S T R A C T

In this study, we determined pounded yam (PY) extensibility of 19 yam genotypes from Cote d'Ivoire by two procedures: uniaxial extensibility (UAE) and bi-extensional viscosity (BEV); while the physicochemical proper- ties of yam flour and starch such as the swelling power, solubility, pasting properties, amylose and pectin were analysed. We hypothesized that the extensibility of PY significantly depended on inherent physicochemical properties of the yam. Results showed that extensibility of PY ranged between 3.8 and 20 mm and BEV ranged between 2.7·10⁴ - 15.7·10⁴ Pa s, and were significantly different among the yam genotypes (P < 0.0001). Sol- ubility of yam flour and starch ranged between 11.2 - 24.5 % and 7.5–13.9 %, respectively. The peak viscosity of yam flour ranged between 1895 and 3036 cP, varying significantly with genotype and specie. Correlations and multilinear regressions revealed PY extensibility was significantly estimated by solubility and peak viscosity of yam flour (P = 0.005, R² = 0.83). The results are important for breeders in screening and selecting phenotypic traits to breed improved yam varieties with excellent PY quality.

# 1. Introduction

Yams play a significant role in the nutrition and livelihoods of the populations in the West and Central parts of Africa, the Caribbean, and certain parts of Asia and Latin America. The largest producers and consumers of yams are West African countries like Nigeria, Ghana, Benin and Cote d'Ivoire, accounting for about 84 million tons, which repre- sents about 95 % of global production in 2022 (FAOSTAT, 2024).

Pounded yam (PY) is one of the common traditional food products in W. Africa produced by boiling yam and pounding in mortar until a smooth, cohesive, extensible dough is formed. The diversity of yams consist of various types of species, but the most cultivated for the pur- pose of production of PY are the *Dioscorea rotundata* (D. rotundata) and

*Dioscorea alata* (D. alata) species (B. Otegbayo et al., 2006). Yams of *D. rotundata* origin are generally preferred for PY because of their better texture coveted by consumers and higher dry matter yield and stor- ability, but there are *D. alata* yams that possess good textural quality for PY production (Akissoe et al., 2009; Dansi et al., 2024; B. Otegbayo et al., 2006).

The acceptability of PY by consumers depend on the perception of key textural parameters such as smoothness (no lumps), mouldability (ability to easily roll into a ball mass within the palm), cohesiveness (ability of not fracturing), firmness (hardness), extensibility (degree of elongation) and low stickiness (degree of adhesion within the palm) (Bolanle Otegbayo et al., 2011; 2021; Jeannette et al., 2020). Since consumer perception is key for adoption of yam varieties, it is necessary

<footnote><sup>a</sup> CIRAD, UMR Qualisud, F-34398, Montpellier, France</footnote>

<footnote><sup>b</sup> Qualisud, Avignon Université, CIRAD, Institut Agro, IRD, Université de Montpellier, Université La Réunion, Montpellier, France</footnote>

<footnote><sup>c</sup> Centre National de Recherche Agronomique (CNRA), Bouaké, the Republic of Côte d'Ivoire</footnote>

<footnote><sup>d</sup> Centre National de Recherche Agronomique (CNRA), Abidjan, the Republic of Côte d'Ivoire</footnote>

<footnote><sup>e</sup> Université Nangui Abrogoua (UNA), Abidjan, the Republic of Côte d'Ivoire</footnote>

<footnote><sup>f</sup> Université Peleforo Gon Coulibaly, Korhogo, the Republic of Côte d'Ivoire</footnote>

<footnote><sup>g</sup> CIRAD, UMR Qualisud, Abidjan, the Republic of Côte d'Ivoire</footnote>

<footnote>* Corresponding author. UMR-Qualisud, French Agricultural Research Centre for International Development (CIRAD), 73 Rue Jean-Francois Breton, 34398 Montpellier Cedex 5, France.</footnote>

<footnote>E-mail address: oluwatoyin.ayetigbo@cirad.fr (O. Ayetigbo).</footnote>
to characterise the texture of PY in order to screen for varieties that are preferred for advanced breeding. Indeed, the importance of consumer preference as key for adoption of roots, tubers and banana (RTB) varieties cannot be overemphasized in breeding programs in sub-Saharan Africa, which have not, hitherto, been prioritised (Thiele et al., 2021). Extensibility is one of the key textural parameters of PY which describes the perception of how long the PY dough can be extended between the fingers before breaking (Bolanle Otegbayo et al., 2011). Extensibility, the length to which a dough may be pulled under deformation by tension or compression before structural failure (tearing), may be regarded as the instrumental texture parameter used to describe elongation or elasticity of dough food products (Stable micro systems, 2022). Extensibility of PY has been linked to consumer likeability of the food product (Arufe et al., 2023).

Among the characteristics of yam responsible for the sensorial and/or instrumental textural behaviour of PY, a number of physicochemical properties that may play a role have been hypothesized (Bolanle Otegbayo et al., 2011), where it was demonstrated that amylose content, water binding capacity, swelling power and solubility can be associated with sensory stickiness, cohesiveness and stretchability of PY. A correlation has also been found between dry matter of PY and its sensorial elasticity (Akissoe et al., 2009). Pectin's role has been hypothesized and higher significant level was found in *D. rotundata* varieties than *D. alata*, but no significant correlation could be evidenced with instrumental textural parameters of PY (Effah-Manu et al., 2022).

There is little information in literature on the influence of the physicochemical properties of yam starch or flour on the extensibility of PY. In previous works, the effect of physicochemical properties of yam such as amylose, dry matter, starch contents, water absorption, pasting properties, solubility, swelling, and cell microstructure on the textural property of PY such as cohesiveness, smoothness, firmness and adhesiveness has been explored (Akissoe et al., 2011; B. Otegbayo et al., 2006; Bolanle Otegbayo et al., 2011). Other publications have reviewed textural procedures for assessing extensibility of PY without focus on the influence of physicochemical properties of yam starch or flour on extensibility (Arufe et al., 2023; Ayetigbo et al., 2024). Also, no regression models have been proposed to estimate the extensibility of PY by the physicochemical properties of yam starch and flour.

In this work, we explored how the texture (extensibility) of PY may be influenced by the physicochemical properties of the extracted starch and flour obtained from yams such as solubility, swelling power, paste viscosity, amylose and pectin content. Textural evaluation of the yams was conducted by employing recent standard procedures by uniaxial extension (Ayetigbo et al., 2023) and lubricated squeeze flow (Arufe-Vilas et al., 2022). The relationship between the physicochemical properties and texture was analysed, and simple multi-linear regression models were developed to estimate the extensibility of PY. The results provide a basis for breeders to consider screening several yam genotypes and selection for development of improved varieties for PY production based on estimation of extensibility of PY by the physicochemical properties of the yams.

## 2. Materials and methods

### 2.1. Acquisition of yam genotypes

Nineteen genotypes of yams (Table 1) from Ivorian germplasm in the National Agricultural Research Centre (CNRA) were produced under conventional practice and harvested around December 2022/January 2023 at yam fields situated in Bouake town (7° 41' 00" N, 5° 01' 59" E) in Cote d'Ivoire, W. Africa. The genotypes consisted of about 15 hybrids and 4 landraces of which eight were *D. rotundata* and eleven were *D. alata* species. The textural experiments were conducted in March 2023, while the physicochemical and functional properties of yam flour and starch were determined between April and June 2023.

<caption>**Table 1**</caption>

Selected yam genotypes, ease of dough formation, amenability to textural procedures and experts' quality rating.

<table><thead><tr><th rowspan="2"></th><th rowspan="2">Genotype</th><th rowspan="2">Specie</th><th rowspan="2">Landrace/ Hybrid</th><th colspan="2">Ease or difficulty of using method</th></tr><tr><th>UAE</th><th>LSF</th></tr></thead><tbody><tr><td>1</td><td>C20</td><td>D. rotundata</td><td>hybrid</td><td>Easy</td><td>Easy</td></tr><tr><td>2</td><td>CIVCDr 233</td><td>D. rotundata</td><td>landrace</td><td>Easy</td><td>Easy</td></tr><tr><td>3</td><td>CNRAigr1700965</td><td>D. rotundata</td><td>hybrid</td><td>Easy</td><td>Easy</td></tr><tr><td>4</td><td>Krenglè</td><td>D. rotundata</td><td>landrace</td><td>Slight difficulty to form dough sheet due to stickiness</td><td>Easy</td></tr><tr><td>5</td><td>TDr1414005</td><td>D. rotundata</td><td>hybrid</td><td>Easy</td><td>Easy</td></tr><tr><td>6</td><td>TDr1437005</td><td>D. rotundata</td><td>hybrid</td><td>Slight difficulty to form dough sheet due to stickiness</td><td>Easy</td></tr><tr><td>7</td><td>TDr1439027</td><td>D. rotundata</td><td>hybrid</td><td>Easy</td><td>Easy</td></tr><tr><td>8</td><td>TDr1443002</td><td>D. rotundata</td><td>hybrid</td><td>Easy</td><td>Easy</td></tr><tr><td>9</td><td>C18</td><td>D. alata</td><td>hybrid</td><td>Not forming dough sheet</td><td>Easy</td></tr><tr><td>10</td><td>CNRAiga1500020</td><td>D. alata</td><td>hybrid</td><td>Not forming dough sheet</td><td>Easy</td></tr><tr><td>11</td><td>CNRAiga1500021</td><td>D. alata</td><td>hybrid</td><td>Not forming dough sheet</td><td>Easy</td></tr><tr><td>12</td><td>CNRAiga1500121</td><td>D. alata</td><td>hybrid</td><td>Not forming dough sheet</td><td>Easy</td></tr><tr><td>13</td><td>Nza Djidjinou</td><td>D. alata</td><td>landrace</td><td>Slight difficulty to form dough sheet due to fracture</td><td>Easy</td></tr><tr><td>14</td><td>TDa1510080</td><td>D. alata</td><td>hybrid</td><td>Not forming dough sheet</td><td>Easy</td></tr><tr><td>15</td><td>TDa1511008</td><td>D. alata</td><td>hybrid</td><td>Slight difficulty to form dough sheet due to fracture</td><td>Easy</td></tr><tr><td>16</td><td>TDa1515032</td><td>D. alata</td><td>hybrid</td><td>Slight difficulty to form dough sheet due to fracture</td><td>Easy</td></tr><tr><td>17</td><td>TDa1520008</td><td>D. alata</td><td>hybrid</td><td>Not forming dough sheet</td><td>Easy</td></tr><tr><td>18</td><td>TDa1520050</td><td>D. alata</td><td>hybrid</td><td>Slight difficulty to form dough sheet due to fracture</td><td>Easy</td></tr><tr><td>19</td><td>Toulekangbo</td><td>D. alata</td><td>landrace</td><td>Not forming dough sheet</td><td>Easy</td></tr></tbody></table>

UAE- Uniaxial extensibility, LSF- lubricated squeeze flow.

### 2.2. Starch extraction and flour production

For yam starch extraction, a procedure (Pérez et al., 2011) was used with some modifications. Sixteen out of the nineteen yam genotypes were used. About 115–250 g of freshly peeled yam was pulverised three times with twice its mass of distilled water for 10 min. Afterwards, the suspension was sieved in sequence through 425 µm sieve and 200 µm sieve. The residues were washed repeatedly in excess distilled water to recover residual starch. The pooled filtrate was settled and decanted, and the settled starch washed several times. The resulting clear suspension was centrifuged at 6000 g for 5 min at 10 °C. The starch cake was collected, dried in a tunnel dryer (Union Technique, Aquitaine, France) at 40 °C for 48 h, and finely milled (below 60 mesh size). The starch powder was sealed hermetically in plastic film bags (PA/PE 150 × 250 mm, 90 µm) and kept refrigerated in Styrofoam box at 4 °C.

To produce the yam flour, about 300 g of fresh yam flesh was diced into 1 cm³ cubes, freeze dried and milled for 1 min using Dangoumill 300 ball mill (Prolabo, Paris, France), hermetically sealed in plastic film bags and kept refrigerated at 4 °C.
## 2.3. Swelling power and solubility of yam flour and starch

The swelling power and solubility of the flour and starch from the 16 genotypes of yams were determined by a method described by Ceballos et al. (2007) with slight modifications. Briefly, a suspension of 2.5 % w/w starch or flour (dry basis) was heated to 90 °C on a RVA 4500 rapid visco analyzer (Perten Instruments, New South Wales, Australia). The resulting paste was separated into supernatant and sediment in a centrifuge (Eppendorf AG, Hamburg, Germany) at 6000 g for 10 min at 25 °C. The supernatant and sediment were collected in pre-weighed moisture cans and the masses of supernatant (W<sub>su</sub>) and sediment (W<sub>se</sub>) were recorded. The supernatant and sediment were dried at 105 °C for 24 h and 48 h, respectively, and the mass of dried residue of supernatant (D<sub>su</sub>) and sediment (D<sub>se</sub>) were noted. The swelling power (SP) and solubility (SOL) were calculated as shown below:

$$SP (g/g) = \frac{W_{se} - D_{se}}{D_{se}}$$

$$SOL (\%) = \frac{D_{su}}{\text{mass of sample adjusted for dry matter}} \cdot 100$$

## 2.4. Paste characteristics of yam flour and starch

Paste properties of the starch and flour obtained from the 16 genotypes of yams were determined following a standard procedure (Pérez et al., 2011). An 8 %w/w suspension of the starch or flour (on dry basis) in 2 mM silver nitrate solution was prepared in a canister. The suspension was dispersed using T18 basic Ultra-Turrax homogenizer (IKA-Werke GmbH & Co. KG, Staufen, Germany) and analysed on a RVA 4500 rapid visco analyzer (Perten Instruments, New South Wales, Australia). The temperature-time regime applied was as follow: stirring at 960 rpm for 10 s, holding temperature at 50 °C for 50 s at 160 rpm, increment of temperature from 50 °C to 90 °C for 6 min 40 s at 160 rpm, holding temperature at 90 °C for 5 min at 160 rpm, reducing temperature from 90 °C to 50 °C in 6 min 40s, and maintaining the temperature at 50 °C for 2 min. A dedicated software Thermocline for Windows v. 3 was used to analyse the various paste properties including peak viscosity, trough viscosity, breakdown viscosity, final viscosity, setback viscosity, peak time, and pasting temperature.

## 2.5. Pectin content of yam flour

Total pectin content of yam flour obtained after freeze drying was determined according to a standard method (Mestres et al., 2022). Pectins were first extracted at pH 10 with ethylene-diamine-tetra-acetic acid (EDTA) at 55 °C to facilitate extraction without degradation, and to prevent starch extraction. Extracted pectins were then hydrolyzed by hot sulphuric acid to obtain sugar residues and their furfural derivatives. Neutral sugars gave brown derivatives whereas free galacturonic acid was quantified by colorimetry after reaction with m-hydroxydiphenyl (MHDP). This produced a specific fuschia pink complex with a maximum absorption at 520 nm. Galacturonic acid content was calculated after subtracting the brown colour (at 520 nm) generated by neutral sugar hydrolysis using a control curve previously obtained with D-(+)-galacturonic acid monohydrate (>97 %). Total pectin was assayed as Galacturonic acid content in mg Gal. acid/100 g.

## 2.6. Amylose content of yam starch

The amylose content of the starch obtained from the 16 yam genotypes was determined by using a DSC 7 differential scanning calorimeter (PerkinElmer Instruments, Quebec, Canada) with thermal analysis controller (TAC7/DX), according to a standard method (Mestres et al., 2019). The amylose content was calculated as:

$$Amylose (\%) = \frac{\Delta H_{\text{amylose in starch sample}}}{\Delta H_{\text{amylose standard}}} \cdot 100$$

where ΔH is the enthalpy change due to heat flow.

## 2.7. Preparation of pounded yam

Pounded yam was produced following a standard procedure with minor modification (Bolanle Otegbayo et al., 2022). Briefly, after peeling, about 450 g of 2 cm yam cubes was steamed in a QZP/6000 model yam pounding machine (Cheerfengly Ind. Co. Ltd, Taipei, Taiwan) for about 22 min and pounded for 1–3 min depending on the ease of pounding. Typically, *D. rotundata* genotypes required shorter pounding time than *D. alata* genotypes. The PY prepared was rapidly wrapped in aluminium foil to reduce heat and moisture loss, and to retard stiffening, and then kept in a styrofoam box.

## 2.8. Determination of extensibility texture of pounded yam

The uniaxial extensibility (UAE) of PY was determined by a standard procedure (Ayetigbo et al., 2023) using a TA-XT Plus texture analyser (Stable Micro Systems Ltd., Surrey, UK) with HDP/TPB rig. The texture parameters measured included the extensogram peak force, EPF (firmness/hardness, N), extensibility, EXT (length of extension, mm), and extension area, EA (extension work done, N·mm). Exponent software was used to capture texture profiles and calculate the texture parameters. Out of the 19 genotypes considered, only 12 genotypes could be analysed by UAE due to the excessive stickiness and mealiness of the other genotypes, particularly some *D. alata* genotypes. UAE data was collected in duplicates with each replicate of 2–8 measurements depending on the difficulty of dough handling.

The bi-extensional viscosity (BEV) of PY was determined following the lubricated squeezing flow (LSF) standard procedure (Arufe-Vilas et al., 2022) using a texture analyser with a lubricated HDP rig. BEV data was conducted in duplicates, each replicate consisting of 7–8 measurements.

## 2.9. Statistics

The differences among genotypes (*P* < 0.05) and between replicates (*P* > 0.05) was evaluated by one way ANOVA, and variable means were separated by Fisher's multiple comparison and student t-test, respectively. Bivariate correlations between textural and physicochemical variables were conducted at significant levels *P* < 0.05 and *P* < 0.10. Clustering of the variables was performed by canonical and constellation plots while principal components analysis (PCA) was performed by considering the textural parameters as primary variables and the physicochemical parameters as secondary variables. Multi-linear regression models (*P* < 0.05) were derived to estimate the textural parameters of PY by optimizing the standard least square using the independent variables. All statistics were done using JMP Pro v. 17.2.0 (JMP statistical Discovery LLC, NC, USA).

# 3. Results and discussion

## 3.1. Ease of use of textural methods

In Table 1, the genotypes analysed are classified into *D. rotundata* and *D. alata* species. The ease of conducting UAE and LSF tests was included to depict how each genotype was adaptable to the procedures. All the genotypes (Fig. 1) were not equally available for each test, so we mention beforehand which genotypes were analysed. After pounding, some genotypes which predominantly belonged to *D. alata* yams were mealy (friable) and posed some challenges as they fractured during UAE tests, while the *D. rotundata* yams that were very extensible also had
<figure><img src="image_2.png" /><figcaption>(1). C20</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>(2). CIVCDr233</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>(3). CNRAigr1700965</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>(4). Krengle</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>(5). TDr1414005</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>(6). TDr1437005</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>(7). TDr1439027</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>(8). TDr1443002</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>(9). C18</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>(10). CNRAiga1500020</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>(11). CNRAiga1500021</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>(12). CNRAiga1500121</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>(13). Nza Djidjinou</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>(14). TDa1510080</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>(15). TDa1511008</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>(16). TDr1515032</figcaption></figure>

<figure><img src="image_18.png" /><figcaption>(17). TDa1520008</figcaption></figure>

<figure><img src="image_19.png" /><figcaption>(18). TDa1520050</figcaption></figure>

<figure><img src="image_20.png" /><figcaption>(19). Toulekangbo</figcaption></figure>

<caption>Fig. 1. Yams used in the evaluation of extensibility of pounded yam and physicochemical properties of yam flour and starch.</caption>
elements of stickiness. These challenges were not presented for LSF test. Therefore, the specie of yam largely determines the application of the procedure that could be used to determine extensibility.

## 3.2. Uniaxial extensibility texture of pounded yam

As described in the introduction, the extensibility of PY is one of the textural quality traits that is considered key in consumer acceptance. Of the 19 genotypes, only 12 genotypes could be analysed by UAE procedure because the other genotypes were either too sticky or mealy to handle (Table 2).

The doughs produced from the *D. rotundata* genotypes were significantly firmer (0.52–0.80 N, *P* = 5.10⁻²³), had more extensibility (9.5–20.0 mm, *P* = 4.10⁻¹⁹) and required more work to extend (2.9–8.4 N mm, *P* = 1.10⁻¹⁶) than the *D. alata* genotypes which had lower firmness (0.18–0.39 N), extensibility (3.8–7.8 mm) and work done to extend (0.48–1.79 N mm). These values were similar to those obtained by other authors (Arufe et al., 2023), albeit with higher values of firmness and work done to extend. The genotypes were discriminant among one another, and there were two distinct clusters consisting of *D. rotundata* and *D. alata* genotypes based on the texture parameters (Fig. 2).

This kind of distinct clusters has been reported for texture of PY by texture profile analysis (TPA) (Bolanle Otegbayo, Tran, et al., 2024), although TPA was not adapted to direct evaluation of extensibility. The *D. rotundata* genotypes easily formed dough sheet, although, TDr1437005 and Krenglè which clustered together were slightly mealy and sticky, respectively, but produced the most extensible doughs as

generally observed during the experiments (Table 1). The *D. alata* genotypes had half as much extensibility as *D. rotundata* genotypes, and were generally mealy, but some formed dough sheets with little difficulty, such as the clustered genotypes Nzadjidjinou, TDa1515032, TDa1511008 and TDa1520050. It could be observed that the extension parameters of PY were all discriminant among the genotypes (*P* < 0.05), replicable (*P* > 0.05) and accurate (CV<sub>mean</sub> of 2–18 %). The extensibility was the most discriminant parameter (Table 2).

The higher UAE values of PY of *D. rotundata* indicated that its texture may be preferred by consumers than that of *D. alata* as verified in a detail review (Goddard et al., 2015), and overall liking has been reported to be highly positively correlated with UAE values (Arufe et al., 2023).

Consequently, these parameters may be considered for mid-throughput screening of yam genotypes by breeding programs aimed at selecting champion varieties as parents for breeding new ascensions that will be preferred by PY consumers in Cote d'Ivoire.

## 3.3. Bi-extensional viscosity (BEV) of pounded yam

Due to the considerably sticky or mealy nature of some of the PY doughs, the UAE procedure was not applicable for such doughs as observed during the experiments (Table 1), therefore, the LSF procedure was explored to estimate the bi-axial extensional texture. Results (Table 2) showed that all the PY doughs made from the nineteen genotypes could be evaluated by the LSF procedure in spite of the sticky and mealy nature of some of the genotypes.

The BEV of the doughs was discriminant (*P* < 0.001) among the genotypes (Fig. 3a), ranging from 2.7·10⁻⁴ to 15.7·10⁻⁴ Pa s, and the effect

<table><caption>**Table 2**
Uniaxial extensibility (UAE) and Bi-extensional viscosity (BEV) of pounded yam made from the yam genotypes.</caption><thead><tr><th rowspan="2">Genotype</th><th colspan="3">Extensogram peak force (N)</th><th colspan="3">Extensibility (mm)</th><th colspan="3">Extension area (N.mm)</th><th colspan="3">Bi-extensional viscosity (Pa.s)</th></tr><tr><th>Mean</th><th>SDmean</th><th>CVmean (%)</th><th>Mean</th><th>SDmean</th><th>CVmean (%)</th><th>Mean</th><th>SDmean</th><th>CVmean (%)</th><th>Mean (x 104)</th><th>SDmean (x 104)</th><th>CVmean (%)</th></tr></thead><tbody><tr><td><strong>D. rotundata</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>C20</td><td>0.56<sup>c</sup></td><td>0.09</td><td>4</td><td>13.1<sup>b</sup></td><td>1.6</td><td>3</td><td>3.9<sup>c</sup></td><td>0.9</td><td>6</td><td>8.8<sup>d</sup></td><td>1.8</td><td>5.2</td></tr><tr><td>CIVCDr 233</td><td>0.53<sup>c</sup></td><td>0.08</td><td>4</td><td>12.3<sup>bc</sup></td><td>1.3</td><td>3</td><td>3.6<sup>cd</sup></td><td>0.7</td><td>5</td><td>6.7<sup>fgh</sup></td><td>0.9</td><td>3.7</td></tr><tr><td>CNRAigr1700965</td><td>0.64<sup>b</sup></td><td>0.17</td><td>7</td><td>9.5<sup>e</sup></td><td>1.4</td><td>4</td><td>3.1<sup>de</sup></td><td>1.1</td><td>10</td><td>11.6<sup>bc</sup></td><td>1.5</td><td>3.1</td></tr><tr><td>Krenglè</td><td>0.78<sup>a</sup></td><td>0.08</td><td>3</td><td>20.0<sup>a</sup></td><td>1.7</td><td>3</td><td>8.4<sup>a</sup></td><td>1.4</td><td>5</td><td>11.8<sup>bc</sup></td><td>2.2</td><td>4.7</td></tr><tr><td>TDr1414005</td><td>0.52<sup>c</sup></td><td>0.10</td><td>7</td><td>9.9<sup>e</sup></td><td>1.9</td><td>7</td><td>2.9<sup>e</sup></td><td>0.9</td><td>12</td><td>8.2<sup>de</sup></td><td>1.3</td><td>4.1</td></tr><tr><td>TDr1437005</td><td>0.59<sup>bc</sup></td><td>0.05</td><td>4</td><td>19.5<sup>a</sup></td><td>2.7</td><td>7</td><td>6.9<sup>b</sup></td><td>1.6</td><td>12</td><td>5.8<sup>h</sup></td><td>1.0</td><td>4.3</td></tr><tr><td>TDr1439027</td><td>0.53<sup>c</sup></td><td>0.09</td><td>5</td><td>11.7<sup>cd</sup></td><td>0.6</td><td>2</td><td>3.5<sup>ede</sup></td><td>0.5</td><td>4</td><td>6.5<sup>gh</sup></td><td>0.7</td><td>2.6</td></tr><tr><td>TDr1443002</td><td>0.80<sup>a</sup></td><td>0.09</td><td>4</td><td>10.6<sup>de</sup></td><td>0.8</td><td>3</td><td>4.1<sup>c</sup></td><td>0.7</td><td>6</td><td>12.4<sup>b</sup></td><td>2.6</td><td>5.2</td></tr><tr><td><strong>mean</strong></td><td><strong>0.62</strong></td><td></td><td></td><td><strong>13.3</strong></td><td></td><td></td><td><strong>4.6</strong></td><td></td><td></td><td><strong>8.98</strong></td><td></td><td></td></tr><tr><td><strong>sd</strong></td><td><strong>0.11</strong></td><td></td><td></td><td><strong>4.1</strong></td><td></td><td></td><td><strong>2.02</strong></td><td></td><td></td><td><strong>2.63</strong></td><td></td><td></td></tr><tr><td>0.5</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td><strong>D. alata</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Nzadjidjinou</td><td>0.37<sup>d</sup></td><td>0.09</td><td>8</td><td>5.3<sup>g</sup></td><td>1.22</td><td>8</td><td>1.1<sup>fg</sup></td><td>0.5</td><td>15</td><td>15.7<sup>a</sup></td><td>2.4</td><td>3.9</td></tr><tr><td>TDa1511008</td><td>0.22<sup>e</sup></td><td>0.03</td><td>4</td><td>6.9<sup>f</sup></td><td>0.91</td><td>4</td><td>0.9<sup>fg</sup></td><td>0.3</td><td>8</td><td>5.9<sup>gh</sup></td><td>0.9</td><td>3.7</td></tr><tr><td>TDa1515032</td><td>0.39<sup>d</sup></td><td>0.09</td><td>8</td><td>7.8<sup>f</sup></td><td>1.10</td><td>5</td><td>1.8<sup>f</sup></td><td>0.5</td><td>9</td><td>8.2<sup>de</sup></td><td>1.0</td><td>3.2</td></tr><tr><td>TDa1520050</td><td>0.18<sup>e</sup></td><td>0.05</td><td>9</td><td>3.8<sup>h</sup></td><td>1.23</td><td>11</td><td>0.5<sup>g</sup></td><td>0.3</td><td>18</td><td>11.3<sup>c</sup></td><td>1.0</td><td>2.3</td></tr><tr><td>C18</td><td>ND</td><td></td><td></td><td>ND</td><td></td><td></td><td>ND</td><td></td><td></td><td>2.7<sup>j</sup></td><td>0.3</td><td>3.0</td></tr><tr><td>CNAiga1500020</td><td>ND</td><td></td><td></td><td>ND</td><td></td><td></td><td>ND</td><td></td><td></td><td>4.8<sup>i</sup></td><td>0.5</td><td>2.8</td></tr><tr><td>CNRAiga1500021</td><td>ND</td><td></td><td></td><td>ND</td><td></td><td></td><td>ND</td><td></td><td></td><td>6.1<sup>gh</sup></td><td>1.6</td><td>6.5</td></tr><tr><td>CNRAiga1500121</td><td>ND</td><td></td><td></td><td>ND</td><td></td><td></td><td>ND</td><td></td><td></td><td>7.5<sup>ef</sup></td><td>0.9</td><td>2.9</td></tr><tr><td>TDa1510080</td><td>ND</td><td></td><td></td><td>ND</td><td></td><td></td><td>ND</td><td></td><td></td><td>5.7<sup>hi</sup></td><td>1.2</td><td>5.1</td></tr><tr><td>TDa1520008</td><td>ND</td><td></td><td></td><td>ND</td><td></td><td></td><td>ND</td><td></td><td></td><td>5.8<sup>h</sup></td><td>0.9</td><td>3.8</td></tr><tr><td>Toulekangbo</td><td>ND</td><td></td><td></td><td>ND</td><td></td><td></td><td>ND</td><td></td><td></td><td>6.8<sup>fg</sup></td><td>1.3</td><td>4.7</td></tr><tr><td><strong>mean</strong></td><td><strong>0.29</strong></td><td></td><td></td><td><strong>5.9</strong></td><td></td><td></td><td><strong>1.1</strong></td><td></td><td></td><td><strong>7.34</strong></td><td></td><td></td></tr><tr><td><strong>sd</strong></td><td><strong>0.10</strong></td><td></td><td></td><td><strong>1.8</strong></td><td></td><td></td><td><strong>0.5</strong></td><td></td><td></td><td><strong>3.50</strong></td><td></td><td></td></tr><tr><td>Genotype (P value)</td><td colspan="3">7.10<sup>-33</sup></td><td colspan="3">6.10<sup>-54</sup></td><td colspan="3">2.10<sup>-42</sup></td><td colspan="3">3.9·10<sup>-101</sup></td></tr><tr><td>Replicate (P value)</td><td colspan="3">0.32</td><td colspan="3">0.27</td><td colspan="3">0.29</td><td colspan="3">0.40</td></tr></tbody></table>

<footnote><sup>a</sup> Data are presented as mean, standard deviation of the mean (SD<sub>mean</sub>) and coefficient of variation of the mean (CV<sub>mean</sub>). Values in a column with different superscript letters are significantly different at the *P* < 0.05 level. The UAE data are for the 12 genotypes that produced pounded yam that can be rolled into a dough sheet. sd–standard deviation, ND–not determined due to sticky or mealy nature.</footnote>
<figure><img src="image_21.png" /><figcaption>**Fig. 2.** Canonical (a) and constellation (b) plots based on uniaxial extensibility (UAE) texture parameters of pounded yam made from 12 genotypes of yam, showing good discrimination among the genotypes and clustering between *D. alata* and *D. rotundata*.</figcaption></figure>

of replicates was not significant (*P* = 0.404). There was also significant difference in BEV between species (*P* < 0.001), however, no distinction between the clustering of the species, as *D. rotundata* and *D. alata* clustered together (Fig. 3b). Similar outcome of indistinct species clustering pattern has been reported for PY in Benin (Arufe et al., 2023). The difference in clustering outcome between UAE and LSF procedure may be due to the differences in measured parameters (extensibility versus bi-extensional viscosity) test configuration (dough sheet versus cylindrical sample), and deformation axis (uniaxial compression versus biaxial extension).

Classifying the 19 genotypes based on BEV, it was shown that

TDr1443002, CNRAigr1700965, TDa1520050, Krenglè and Nzadjidjinou may be regarded as genotypes with dough of high BEV above 11·10⁴ Pa s, and thus PY with poor flowing ability.

On the other hand, the genotypes CNRAiga1500021, CNRAiga1500020, Toulekangbo, CIVCDr233, TDr1439027, TDa1511008, TDr1437005, TDa1520008, TDa1510080 and C18 with BEV below 7·10⁴ Pa s may be regarded as genotypes with PY dough characterised by low viscosity and high flowing ability.

The relationship between the UAE parameters and BEV was explored to determine if the textural parameters were related. Results showed that no significant correlations were found between the BEV and UAE
<figure><img src="image_22.png" /><figcaption>**Fig. 3.** Canonical (a) and constellation (b) plots of bi-extensional viscosity (BEV) of pounded yam made from 19 genotypes of yam, showing good discrimination among the genotypes but no distinct clustering between *D. alata* and *D. rotundata*.</figcaption></figure>

parameters (correlation between extensibility and BEV was insignificant, R = -0.29, P = 0.35) (Supplementary Table 1). Similar results have been observed in our laboratory experiments on PY of other yam genotypes from other locations (unpublished data). However, it contrasted the significant correlations found between BEV and extensogram peak force and extension area parameters reported for PY from only five *D. rotundata* genotypes (Arufe et al., 2023), albeit with no correlation between BEV and extensibility of PY.

### 3.4. Solubility and swelling power of yam flour and starch

The solubility of yam starch and flour is the amount of water-soluble components that dissolve after pasting at 90 °C. Swelling of the yam starch and flour occur after pasting at 90 °C resulting from water imbibition and increased viscosity (Jia et al., 2023). They are both linked to starch gelatinization resulting in disruption of starch crystal-line order and intermolecular bonds. The results are presented in Supplementary Table 2.

The solubility of yam flour ranged from 11.2 to 24.5 % and 14.6–20.8 % for *D. rotundata* and *D. alata* genotypes, respectively, while solubility of yam starch ranged from 7.5 to 10.9 % and 10.1–13.9 % for *D. rotundata* and *D. alata* genotypes, respectively. Swelling power of yam flour ranged from 10.5 to 17.2 g/g and 11.1–19.0 g/g for *D. rotundata* and *D. alata* genotypes, respectively, while swelling power of yam starch

ranged from 13.5 to 19.6 g/g and 16.1–23.2 g/g for *D. rotundata* and *D. alata* genotypes, respectively. These values were close to those in other publication (Amani et al., 2004). There were no significant differences in the solubility (P = 0.297) and swelling power (P = 0.162) between *D. rotundata* and *D. alata* of yam flour, but *D. rotundata* yam starches had significantly lower solubility (P = 0.0002) and swelling power (P = 0.025) than *D. alata* starches. Same outcome has been reported for Ivorian yams (Amani et al., 2004), although another report claimed no significant difference was found between swelling of both species (Bolanle Otegbayo et al., 2011). This may be associated with the higher UAE values of the PY of *D. rotundata* origins, since intermolecular forces between *D. rotundata* starch molecules and hydrogen bonding with water may have been limited compared to *D. alata* starches. Excess solubility and swelling of starch gel reduce textural strength in starch based foods (Jia et al., 2023). Generally, the flours have higher solubility than starches due to the presence of non-starch soluble components like sugars, some fibers, pectins, alkaloids, proteins and saponins which may contribute significantly to solubility, but these non-starch components may restrict swelling of yam flour. The flour of landrace Krenglè had lower solubility than most *D. rotundata* hybrids but swell more. An interesting case is the hybrid TDr1443002 which has both high solubility and swelling power.
### 3.5. Pasting properties of yam flour and starch

The peak viscosity (PV) of yam flour (Supplementary Table 3) from the *D. rotundata* genotypes were higher than for *D. alata* genotypes (*P* = 0.00006), and the PV was similarly higher for yam starch of *D. rotundata* origin than *D. alata* (*P* = 0.004) (Supplementary Table 4), although other researchers have reported no difference in PV of yam starch among the species (B. O. Otegbayo, Tran, et al., 2024). The PV is reached when the yam flour or starch imbibe water, swell and undergo pasting at elevated temperatures until maximum viscosity is attained (Balet et al., 2019). Krenglè and TDa1515032 with high extensibility particularly have high PV among the flours of *D. rotundata* and *D. alata* genotypes, respectively. This signifies that the extensibility of PY may be related to the PV, as discussed later in the correlations.

The trough viscosity (TV) is the lowest viscosity registered during hot pasting stage when starch granules have lost all birefringence and the starch structure is completely disintegrated after continuous heating in excess water (Jia et al., 2023). TV ranged between 1622 and 2538 cP, and is significantly different among the genotypes. The TV of yam flour was not significantly different between the *D. rotundata* and *D. alata* species (*P* = 0.707), and the TV of yam starch was equally not discriminant between the *D. rotundata* and *D. alata* species (*P* = 0.083). The TV when considered alone, cannot completely define paste stability without considering the PV. The breakdown viscosity (BV), which is the difference between the PV and TV, represents the ability of the yam flour or starch to be stable or disintegrate in viscosity during hot pasting. High BV may signify high extent of loss of integrity of starch components during pasting (Balet et al., 2019). The flour of the *D. rotundata* genotypes were generally less stable than the *D. alata* genotypes (*P* = 0.003), but the starch of *D. rotundata* and *D. alata* were not significantly different in BV (*P* = 0.65). The BV was discriminant among *D. rotundata* genotypes but not discriminant among *D. alata* genotypes. Among the *D. rotundata* genotypes, the flour of hybrid CNRAigr1700965 was uniquely stable, but landrace Krenglè was less stable, while among the *D. alata* genotypes, the flour of landraces C18 and Toulekangbo were unstable but the flour of hybrid CNRAiga1500121 was very stable.

The final viscosity (FV), which is the viscosity at the end of the cold pasting stage of the pasting process, was generally indifferent between flour (*P* = 0.32) of the *D. rotundata* and *D. alata* genotypes, as well as for starch (*P* = 0.29). Insignificant differences in FV of *D. rotundata* and *D. alata* has been reported (B. O. Otegbayo, Tran, et al., 2024). Some yam flour and starch of *D. rotundata* origin with low FV such as landrace Krenglè had higher BEV and those with high FV such as hybrid TDr1439027 had lower BEV. Similar situation was observed for yam flour of *D. alata* origin such as TDa1511008 and TDa1520008.

Setback viscosity (SV) of the yam flour or starch is a measure of susceptibility of the paste to retrogradation resulting from realignment of amylose (Balet et al., 2019). The flour of the *D. rotundata* genotypes had similar SV as the *D. alata* genotypes (*P* = 0.27), with similar situation for the starch (*P* = 0.95). The flour of *D. rotundata* genotypes CNRAigr1700965 and TDr1443002 had the least and highest SV, respectively.

Pasting temperature (PasT) estimates the temperature at which a first sudden rise in viscosity is observed during pasting and indicates the resistance of starch or flour to pasting and its cooking ability. The pasT was slightly but significantly lower (*P* < 0.0001) for flour of *D. rotundata* genotypes (75.9–79.2 °C) than for *D. alata* genotypes (77.6–81.1 °C), but both species were indifferent in starch PasT (*P* = 0.119). There was no clear indication if pasT of the flour influenced PY extensibility but most of the genotypes with particularly high PasT had low PY hardness. Peak time (Pkt) was similar for flour of *D. rotundata* and *D. alata* genotypes (*P* = 0.587), likewise for the starch, no difference was found in Pkt for both species (*P* = 0.743). These observations are in agreement with another report (Wireko-Manu et al., 2011).

Good textural quality of PY has been associated with yams with higher PV, BV, FV, SV and lower PasT (B. Otegbayo et al., 2006), such as

was found for *D. rotundata* genotypes in this work.

### 3.6. Pectin and amylose content

Total pectins content of yam flour sample assayed as galacturonic acid ranged from 771 to 1147 mg Gal. acid/100 g for *D. rotundata* genotypes and 608–894 mg Gal. acid/100 g for *D. alata* genotypes (Table 3). In general, the pectin content was discriminant among the genotypes, with the *D. rotundata* genotypes having significantly higher (*P* < 0.0001) pectin content than *D. alata* genotypes. Among the *D. rotundata* genotypes, CIVCDr233 presented the highest pectin content (1147 mg Gal. acid/100 g) and the *D. alata* genotype C18 had the lowest (608 mg Gal. acid/100 g) pectin content. Pectins are mostly soluble parietal compounds that act as biological glue which enhance extension of cellular components (Bidhendi & Geitmann, 2016).

Similarly, the relatively lower total pectin content in most *D. alata* genotypes has already been reported (Effah-Manu et al., 2022), where *D. rotundata* varieties had similar or slightly higher yield of pectin than *D. alata* varieties depending on the hybrid or landrace designation.

Amylose content of yam starch ranged between 19.0 and 30.6 % for the *D. rotundata* and 20.0–25.5 % for the *D. alata* genotypes, and was not discriminant between both species (*P* = 0.41). The amylose content was in the range observed by other researchers (Akissoe et al., 2006, 2009; Amani et al., 2004) that did not provide evidence of any significant differences in amylose between *D. rotundata* and *D. alata* genotypes. On the other hand, amylose has been reported to be lower in yam starch from *D. rotundata* than *D. alata* species (Bolanle Otegbayo et al., 2011). Among the *D. rotundata* genotypes, CNRAigr1700965 presented the highest amylose content and the lowest extensibility and TDr1437005 had the lowest amylose but one of the higest extensibility. Similar outcome was observed among the *D. alata* genotypes, where TDa1520050 had one of the highest amylose content but the lowest extension texture parameters, while TDa1515032 had the lowest amylose content but highest extension texture parameters.

### 3.7. Correlations between textural and physicochemical properties

Bivariate correlation can provide some insight into determining which physicochemical properties are significantly associated with the texture of PY. The correlations between the textural properties of PY and physicochemical properties of yam flour and starch are shown in Supplementary Table 5. The physicochemical properties found to be significantly (at *P* < 0.1) associated with the texture of PY included solubility of the yam flour and starch, and pasting properties such as PV, TV, BV, FV and PasT of the flour. Similar relationships has been reported for other stretchy yam product like *amala* (Akissoe et al., 2006; Awoyale et al., 2020). Swelling power of yam starch or flour had no relationship with PY extensibility (*P* = 0.77). Most of the starch pasting characteristics of the yams did not significantly contribute to the texture of PY probably because starch extraction involved destruction of the structure of yam matrices and elimination of non-starch components that may play roles in PY extensibility. There was no relationship between pectin content of yam flour or amylose content of yam starch and texture of PY partly due to destruction of the yam matrix during PY production. During the cooking process of steaming and pounding yam to dough, water absorption, solute leaching and starch gelatinization occurred and the structural matrix may be largely destroyed. In a report (Akissoe et al., 2011), dry matter was the only component that was directly correlated to firmness of pounded yam but a combination of dry matter, starch and amylose content was used to predict firmness. It hitherto remains only hypothetical that pectin or amylose may have a role to play in PY texture (Akissoe et al., 2011), but no proof of this is available. Another work (Effah-Manu et al., 2022) observed no significant correlations (*P* < 0.05) were found between pectin content and textural properties of PY. In our case, the direct effect of pectin and amylose on the texture of PY may be masked as methoxy pectins present in cell wall
<caption>**Table 3**</caption>

Pectin content of yam flour and amylose content of yam starch obtained from 16 genotypes of yama.

<table><thead><tr><th rowspan="2">Genotype</th><th colspan="3">Pectin (mg Gal. acid/100 g wet flour)</th><th colspan="3">Amylose (%, starch)</th></tr><tr><th>Mean</th><th>SD<sub>mean</sub></th><th>CV<sub>mean</sub> (%)</th><th>Mean</th><th>SD<sub>mean</sub></th><th>CV<sub>mean</sub> (%)</th></tr></thead><tbody><tr><td><strong><em>D. rotundata</em></strong></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>CIVCDr233</td><td>1147<sup>a</sup></td><td>62</td><td>2.7</td><td>25.4<sup>b</sup></td><td>3.2</td><td>9.0</td></tr><tr><td>CNRAigr1700965</td><td>925<sup>b</sup></td><td>12</td><td>0.6</td><td>30.6<sup>a</sup></td><td>0.3</td><td>0.7</td></tr><tr><td>Krenglè</td><td>805<sup>f</sup></td><td>23</td><td>1.4</td><td>23.9<sup>bc</sup></td><td>0.7</td><td>1.9</td></tr><tr><td>TDr1437005</td><td>771<sup>fg</sup></td><td>21</td><td>1.4</td><td>19.0<sup>e</sup></td><td>0.8</td><td>2.9</td></tr><tr><td>TDr1439027</td><td>848<sup>de</sup></td><td>19</td><td>1.1</td><td>23.3<sup>bcd</sup></td><td>2.7</td><td>8.2</td></tr><tr><td>TDr1443002</td><td>809<sup>ef</sup></td><td>27</td><td>1.6</td><td>21.4<sup>cde</sup></td><td>0.0</td><td>0.0</td></tr><tr><td><strong>Mean</strong></td><td><strong>884</strong></td><td></td><td></td><td><strong>23.9</strong></td><td></td><td></td></tr><tr><td><strong>sd</strong></td><td><strong>139</strong></td><td></td><td></td><td><strong>3.9</strong></td><td></td><td></td></tr><tr><td><strong><em>D. alata</em></strong></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>C18</td><td>608<sup>k</sup></td><td>6</td><td>0.5</td><td>24.1<sup>bc</sup></td><td>0.2</td><td>0.7</td></tr><tr><td>CNRAiga1500020</td><td>706<sup>hi</sup></td><td>19</td><td>1.4</td><td>20.0<sup>de</sup></td><td>0.1</td><td>0.3</td></tr><tr><td>CNRAiga1500021</td><td>894<sup>bc</sup></td><td>28</td><td>1.5</td><td>25.5<sup>b</sup></td><td>0.6</td><td>1.6</td></tr><tr><td>CNRAiga1500121</td><td>868<sup>cd</sup></td><td>50</td><td>2.9</td><td>23.0<sup>bcd</sup></td><td>1.6</td><td>5</td></tr><tr><td>TDa1510080</td><td>nd</td><td>nd</td><td>nd</td><td>23.2<sup>bcd</sup></td><td>0.2</td><td>0.5</td></tr><tr><td>TDa1511008</td><td>701<sup>i</sup></td><td>23</td><td>1.2</td><td>22.8<sup>bcd</sup></td><td>1.2</td><td>3.7</td></tr><tr><td>TDa1515032</td><td>743<sup>gh</sup></td><td>31</td><td>2.1</td><td>20.3<sup>de</sup></td><td>0.4</td><td>1.3</td></tr><tr><td>TDa1520008</td><td>722<sup>hi</sup></td><td>5</td><td>0.4</td><td>22.1<sup>bde</sup></td><td>0.5</td><td>1.5</td></tr><tr><td>TDa1520050</td><td>655<sup>j</sup></td><td>14</td><td>1.1</td><td>24.3<sup>bc</sup></td><td>1.9</td><td>5.5</td></tr><tr><td>Toulekangbo</td><td>634<sup>lk</sup></td><td>42</td><td>3.3</td><td>25.2<sup>b</sup></td><td>4.0</td><td>11.2</td></tr><tr><td><strong>Mean</strong></td><td><strong>725</strong></td><td></td><td></td><td><strong>23.1</strong></td><td></td><td></td></tr><tr><td><strong>sd</strong></td><td><strong>98</strong></td><td></td><td></td><td><strong>1.9</strong></td><td></td><td></td></tr><tr><td>Genotype (P value)</td><td colspan="3">3.9·10<sup>-30</sup></td><td colspan="3">7.7·10<sup>-4</sup></td></tr><tr><td>Replicate (P value)</td><td colspan="3">0.875</td><td colspan="3">nd</td></tr></tbody></table>

materials of yams may have undergone changes during cooking.

## 3.8. Principal components analysis of textural and physicochemical properties

The principal component analysis (PCA) was performed with the four textural properties of PY as the main variables and the physicochemical properties of yam starch and flour that correlated with texture as supplementary variables to unravel the relationships between the parameters and genotypes. The first two components of the PCA (Fig. 4) revealed that 95.6 % of the variation of data was accounted for. The first axis was mainly linked with all the uniaxial extensibility variables; EPF, EA and EXT on the right of the axis. The *D. rotundata* landrace, Krenglè appears particularly positively associated with this axis with its high UAE values, and high peak and breakdown viscosities of the flour on the right of the first axis. At the opposite, the *D. alata* genotypes were mainly situated on the left side of the first axis, and were associated with poor extensibility. The second axis was mainly linked to BEV and *D. rotundata* hybrids TDr1443002 and CNRAigr1700965 clearly situated at positive axis of the component 2. The UAE and BEV variables were not on the same axis of the PCA, implying the unrelated association between both variables. Genotype TDa1511008 in the negative axis of both components was particularly associated with higher flour pasting temperature, final viscosity, and starch solubility, while TDa1520050 was associated with higher flour solubility and starch paste peak time among the *D. alata* genotypes. The *D. rotundata* genotype TDr1439027 was closely associated with the *D. alata* genotypes.

The PCA clearly showed the main variables (mainly flour properties) that were positively (BVflour and PVflour) or negatively (SOLflour and Pkstarch) linked with first axis (uniaxial extensibility variables). Alternatively other, mainly flour, variables appear linked with the second axis.

## 3.9. Regression models to estimate texture of pounded yam

Regression models were developed to estimate the textural parameters of PY based on the physicochemical properties of yam flour and starch (Table 4). Several iterations of regression models were assessed to estimate the textural parameters. Only models which were significant and have significant terms and the highest R² and adjusted R² were considered. In addition, the model residual plots had no defined pattern.

The Extensogram peak force (firmness) of PY could be significantly predicted from the peak viscosity and solubility of the yam flour as well as the interaction between both as shown by the model (*P* = 0.0035). Also, the extensibility and extension area (extension work done) of PY could be significantly predicted from the peak viscosity and solubility of the yam flour. This showed that the solubilisation of yam components and the development of high viscosity by swelling and pasting during cooking and pounding may have contributed significantly to the extensibility of PY. Generally, the extensible texture of PY relied on the physicochemical properties of the yam flour than yam starch, implying that other non-starch components in yam seemed to contribute to the extensibility of PY. Indeed, researchers (Akissoe et al., 2009) reported that the total dry matter components of yams influenced elasticity of PY determined by uniaxial extrusion. There has also been report of associations between solubility and sensory perception of extensibility of PY (Bolanle Otegbayo et al., 2011).

On the other hand, the solubility of the yam flour and starch components were the most significant parameters to estimate the BEV. The model was significant (*P* = 0.014). We can surmise that the solubilized components present in both yam flour and starch contributed to the bi-extensional viscosity of PY.

Some physicochemical properties such as amylose and pectin contents of analysed samples failed to significantly estimate the texture of PY, although, it has been reported that amylose and starch content can predict sensory stretchability of PY (Bolanle Otegbayo, Tran, et al.,

<footnote><sup>a</sup> Data are presented as mean, standard deviation of the mean (SD<sub>mean</sub>) and coefficient of variation of the mean (CV<sub>mean</sub>). Values in the column with different superscript letters are significantly different at the *P* < 0.05 level. nd-not determined. sd-standard deviation.</footnote>
<figure><img src="image_23.png" /><figcaption>**Fig. 4.** Principal components of texture of pounded yam and physicochemical properties of yam flour and starch from 9 genotypes of yam common to all the tests. Texture parameters are the main variables (red solid lines) and physicochemical properties (blue broken lines) are supplementary variables. EPF: extensogram peak force, EXT: extensibility, EA: extension area, BEV: bi-extensional viscosity. SOLflour: solubility of flour, SOLstarch: solubility of starch, PVflour: peak viscosity of flour, BVflour: breakdown viscosity of flour, TVflour: trough viscosity of flour, FVflour: final viscosity of flour, PasTflour: pasting temperature of flour, Pktstarch: peak time of starch.</figcaption></figure>

<table><caption>**Table 4**
Regression models for estimation of extensibility texture of pounded yam.</caption><thead><tr><th>Textural parameter</th><th>Regression model equation</th><th>Model P value</th><th>R<sup>2</sup></th><th>Adjusted R<sup>2</sup></th><th>RMSE</th></tr></thead><tbody><tr><td>Extensogram peak force</td><td>EPF = -1.032 + (-0.0372·SOL<sub>flour</sub>) + (0.000856·PV<sub>flour</sub>) + (SOL<sub>flour</sub> - 16.696)·(PV<sub>flour</sub> - 2544)·0.000162</td><td>0.0035<sup>a</sup></td><td>0.9204</td><td>0.8726</td><td>0.079</td></tr><tr><td>Extensibility</td><td>EXT = -9.587 + (-0.778·SOL<sub>flour</sub>) + (0.0133·PV<sub>flour</sub>)</td><td>0.0051<sup>a</sup></td><td>0.8282</td><td>0.7709</td><td>2.599</td></tr><tr><td>Extension area</td><td>EA = -8.783 + (-0.335·SOL<sub>flour</sub>) + (0.00709·PV<sub>flour</sub>)</td><td>0.0029<sup>a</sup></td><td>0.8573</td><td>0.8097</td><td>1.142</td></tr><tr><td>Bi-extensional viscosity</td><td>BEV = 224947 + (5230·SOL<sub>flour</sub>) + (-22605·SOL<sub>starch</sub>)</td><td>0.0136<sup>a</sup></td><td>0.7610</td><td>0.6814</td><td>15798</td></tr></tbody></table>

2024).

## 4. Conclusion

The textural procedures used to evaluate extensibility of pounded yam produced good repeatability and discrimination among yam genotypes, but only the uniaxial extensibility procedure discriminated between the *D. rotundata* and *D. alata* species, unlike the lubricated squeeze flow procedure. The physicochemical properties of the starch and flour obtained from the Ivorian yams such as the peak viscosity and solubility of yam flour and solubility of yam starch were found to significantly correlate with extensibility of PY. Further research needs to be conducted on if any specific pectin compounds or leached amylose

and/or starch properties could play roles in extensibility and other textural properties of pounded yam, and how processing yams alter these properties. The application of these procedures may provide a basis for mid-throughput screening in selection of yam accessions preferred for PY production in Côte d'Ivoire, and we recommend that the physicochemical properties of yam flour and starch should be used by food scientists or breeders in the estimation of PY quality preferred by consumers of yam. While this study was conducted with yams from Côte d'Ivoire, more evidence may be needed to validate these findings with yams from other regions of the world, or other yam species, because environmental and varietal differences may significantly influence the textural or physicochemical properties of yams.

<footnote><sup>a</sup> Significant at *P* < 0.05. The bolded model terms and coefficients are significant (*P* < 0.05). EPF: extensogram peak force, EXT: extensibility, EA: extension area, BEV: bi-extensional viscosity. SOL<sub>flour</sub>: solubility of flour, SOL<sub>starch</sub>: solubility of starch, PV<sub>flour</sub>: peak viscosity of flour. RMSE-root mean square error.</footnote>
CRediT authorship contribution statement

**Oluwatoyin Ayetigbo:** Writing – original draft, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Emmanuel Adou Ehounou:** Writing – review & editing, Validation, Methodology, Investigation, Data curation, Conceptualization. **Romain Domingo:** Writing – review & editing, Methodology, Investigation, Formal analysis, Data curation. **Eric Yapi Yapi:** Writing – review & editing, Investigation, Data curation. **Hermann Dekpaho Gnahe:** Investigation, Data curation. **Hermann Antonin Kouassi:** Writing – review & editing, Investigation, Data curation. **N'nan Sylvie Dibi:** Writing – review & editing, Investigation, Data curation. **Didier Mbeguie-Mbeguie:** Writing – review & editing, Validation, Investigation, Data curation. **Konan Evrard Brice Dibi:** Supervision, Resources, Project administration. **Kahndo Prudence Deffan:** Investigation, Data curation. **Patricia N'goran Haddad:** Supervision, Resources, Project administration. **Christian Mestres:** Writing – review & editing, Validation, Supervision, Resources. **Santiago Arufe:** Writing – review & editing, Writing – original draft, Methodology, Investigation, Formal analysis, Data curation. **Dominique Dufour:** Writing – review & editing, Supervision, Resources, Project administration, Funding acquisition, Conceptualization.

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Ayetigbo Oluwatoyin reports financial support was provided by Bill and Melinda Gates Foundation. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was supported by grant INV-008567 (formerly OPP1178942) financed by Bill & Melinda Gates Foundation (BMGF) to the French Agricultural Research Centre for International Development (CIRAD), Montpellier, France. Complementary support financed by BMGF through the International Potato Center (CIP) was obtained by CIRAD Subgrantee Investment ID INV-041105. The authors thank Léa Ollier and Tina Julien for their assistance with pectin measurement in CIRAD, and Fabrice Kouabenan, N'goran Rolande, Kouame Guy-Marc, Odjesika Madeleine, Zamble Tchambi, Gou'e Emmanuel, Kouame Thiegba, Brice Sidoine, and Hala Kinampinan for their assistance in logistics and experiments at CNRA.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.lwt.2025.117769.

Data availability

Data will be made available on request.

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