Dioscorea Rotundata Research Articles

Effect of Steam Blanching and Storage Durations on the Physicochemical Properties of White Yam (Dioscorea rotundata) Slices

White yam (Dioscorea rotundata) is a vital crop in many tropical regions, and its preservation and quality retention are of paramount importance for ensuring food security. This study investigated the impact of steam blanching and different storage durations on the physicochemical properties of white yam slices. White yam slices were subjected to varying steam blanching durations of 1 min, 3 min and 5 min, followed by oven drying at 60℃ for 72 hours and storage at room conditions for 7 days. Physicochemical properties such as proximate composition, total soluble solids, titrable acidity, moisture content, color and pH were measured before and after blanching. The results showed that the steam blanching durations significantly (p ˂ 0.05) affected all the physicochemical properties measured. The proximate results showed the non-blanched (control) samples had higher moisture (65.04±0.35), crude protein (4.55±0.04), fat (0.53±0.01), fibre (1.42±0.02) and ash contents (2.25±0.02) than the blanched samples with exception of the carbohydrate content (26.22±0.29) where the control samples had lower values. Proximate components decreased with blanching duration, except for carbohydrate content, while storage duration did not significantly affect the measured attributes, despite slight changes in moisture content, color, and pH. However, the duration of blanching and storage significantly impacted the physicochemical attributes. These findings have significant implications in the food processing industry, promoting the development of improved storage and preservation strategies for white yam and also ensure food security and reduced post-harvest losses.

Effect of Planting and Mulching Materials on Growth and Yield of White Yam (Dioscorea rotundata) in Ikorodu, Lagos State, Nigeria

The effect of planting and mulching materials on growth and yield of white yam was evaluated in Ikorodu. White yam head, bottom and seed yam were used as planting materials while cooking banana pseudostem, banana leaves and guinea grass (Panicum maximum) were used as mulching materials and control plot was left unmulched.. Planting and mulching materials had significant effect on days to sprouting, vine length and yield of white yam. Seed yam performed relatively better than head and bottom setts in growth and yield. Grass mulch significantly (P < 0.05) gave higher rate of emergence and had tuber yield greater than the banana pseudostem, leave mulch and the unmulched plots. Irrespective of mulching materials, it was found that mulching significantly (P< 0.05) increased tuber yield than the unmulched yam. Interaction between planting and mulching materials also had a significant effect on days to sprouting, vine length and yield of yam. The control (unmulched) plots performed least amongst the treatments. It could be suggested that banana pseudostem and leaves be chopped, fermented, dried and milled to serve better as mulching material and to improve the physical quality of the soil. It is therefore suggested that more work be conducted on the use of banana pseudostem as mulching material to determine the nutrient composition of the material and the appropriate level for its use.

Effect of tillage, fertilizers and storage structures on quality shelf life of white yam (Dioscorea rotundata Poir) in south west Nigeria

This study examined the effect of tillage, fertilizers and storage structures on quality shelf life of white yam in South West Nigeria. The study was a factorial experiment consisting of Tillage, Fertilizers and Storage Structure. The tillage system involved Heap Tillage (HT) and Ridge Tillage (RT), while Fertilizers involved Poultry Manure (PM), N15P15K15 (NPK) and Control (CLT) and two types of Storage Structures namely; Traditional Barn (TB) and Open Sided Storage Structure (OSSS) were combined to form the treatments. The experiment was a 2x3x2 factorial combination arranged in a Randomised Complete Block Design (RCBD). The treatments were replicated three times for each location respectively. A total of 72 ridges and 144 heaps were used to make a population of 288 plants per location. The tubers were weighed to ensure uniformity before planting. The plot size was 18mx18m square with a pathway of 1.0m between blocks making a total of 324 square metres. At harvest, the tubers were weighed immediately. They were then kept separately in the two storage structures namely: Traditional Barn (TB) and the Open Side Storage Structure (OSSS) for a period of 3 months. After the 3rd months of storage, the tubers were examined and data collected. The weight of each tuber from each storage structure was taken periodically to evaluate the weight loss and assess the keeping quality periodically. The findings of this study demonstrated the significant influence of tillage, fertilizers, and storage structures on the quality, shelf life, nutrient use efficiency, and nutrient composition of white yam. Excessive fertilizer application was found to increase rotting and deterioration levels. Hence, farmers and stakeholders should carefully consider fertilizer application rates to minimize post-harvest losses and enhance food security. Further investigations are needed to explore the underlying mechanisms responsible for the observed effects and to optimize fertilizer management practices for yam storage. Organic fertilization enhances the nutrient use efficiency and nutritional quality of yam, while appropriate storage structures, play a crucial role in preserving the quality and extending the shelf life of the harvested tubers. Based on the result of the study, open sided storage should be considered by producers of yams for storing their harvested tubers due to the facts that, it performed well in minimizing nutrient lost, weight loss and decay to considerable level and prevented pests/rodents attack on yam tubers.

Molecular Profiling Ecofriendly Trichoderma Biological Control Agent of Yam Tuber Microbial Rot in Northern Nigeria

This research on isolation and identification of yam rot pathogen fungi from North central Nigeria was carried out to investigate some fungal species associated with yam rot using white yams (Dioscorea rotundata) obtained from Adamawa State, Benue State and Plateau State (Jos) Nigeria. Seven fungi species which cause yam rot were isolated during this study, namely: Aspergillus flavus, Aspergillus niger, Penicillium citrinum, Penicillium echinulatum, Penicilum purpurogenum, Trichoderma spp and Trichophyton spp. Trichoderma yunnanense strain RCBBR_GA1 OP8008361 was identified molecularly. Pathogenicity test carried out confirmed these organisms as the pathological agent of the rot. A. niger statistically has the highest frequency of occurrence (100%). The least encountered fungal species were the P. citrinum (16.6%), P. purpurogenum (33.3%) and Trichophyton spp (33.3). Percentage growth inihibition of A. flavus, A. niger, P. citrinum, P. echinulatum, P. purpurogenum, Trichoderma spp and Trichophyton spp was carried out and they showed varying degree of inhibition. However, Trichopyton spp shows the highest growth of inhibition at 96 hours (41.4%) and 120 hours (73.7%). Trichoderma exhibited the highest control of the isolates (80 mm). Trichoderma inhibited mycelia extension growth of A. flavus (25 mm), A. niger (25 mm), P. citrinum (23 mm), P. echinulatum (23 mm), P. purpurogenum (24 mm) and Trichopyton spp (22 mm) at 96 hours. The result shows that Trichoderma was able to inhibit the growth of the pathogenic fungi, which are associated with yam rot. Fungal isolates from yam rot were examined morphologically and microscopically and the nature of rot was varied. It is recommended that enzymes from Trichoderma should be extracted and applied for reduction of microbial rot of yam tubers.

Genome-wide development of intra- and inter-specific transferable SSR markers and construction of a dynamic web resource for yam molecular breeding: Y2MD.

Microsatellite markers are widely used in population genetics and breeding. Despite the economic significance of yams in developing countries, there is a paucity of microsatellite markers, and as of now, no comprehensive microsatellite marker database exists. In this study, we conducted genome-wide microsatellite marker development across four yam species, identified cross-species transferable markers, and designed an easy-to-use web portal for the yam researchers. The screening of Dioscorea alata, Dioscorea rotundata, Dioscorea dumetorum, and Dioscorea zingiberensis genomes resulted in 318,713, 322,501, 307,040, and 253,856 microsatellites, respectively. Mono-, di-, and tri-nucleotides were the most important types of repeats in the different species, and a total of 864,128 primer pairs were designed. Furthermore, we identified 1170 cross-species transferable microsatellite markers. Among them, 17 out of 18 randomly selected were experimentally validated with good discriminatory power, regardless of the species and ploidy levels. Ultimately, we created and deployed a dynamic Yam Microsatellite Markers Database (Y2MD) available at https://y2md.ucad.sn/. Y2MD is embedded with various useful tools such as JBrowse, Blast, insilicoPCR, and SSR Finder to facilitate the exploitation of microsatellite markers in yams. This study represents the first comprehensive microsatellite marker mining across several yam species and will contribute to advancing yam genetic research and marker-assisted breeding. The released user-friendly database constitutes a valuable platform for yam researchers.

Phenotypic and Pathogenic Characterization of Leaf Fungi of Yam (Dioscorea spp) Varieties Grown In Côte D’Ivoire

Yam (Dioscorea spp) occupies an important place in the diet of the populations of Côte d’Ivoire. It is a real source of starch and therefore generates enormous commercial potential. However, the decrease in production due to pest attacks represents a real threat to this crop. This study was conducted with the aim of improving yam production in Côte d’Ivoire. To do so, isolations carried out on yam leaves showing symptoms of foliar diseases have allowed us to identify 9 fungal genera. These were Colletotrichum sp., Fusarium sp., Pestalotiopsis sp., Pestalotia sp., Botryodiplodia sp., Aspergillus sp., Mucor sp., Curvularia sp. and Phytophtora sp. Among these fungi, the genus Colletotrichum sp. was the most isolated with a rate of 56% followed by the Fusarium and Pestalotia genera (8%). Pathogenicity tests performed on healthy leaves of two yam varieties revealed that the Dioscorea alata is more susceptible to fungi compared to Dioscorea rotundata. The largest average diameter of necrosis was caused by Pestalotiopsis sp. (5.97 cm) on the Dioscorea alata variety while the smallest was caused by Colletotrichum sp.9 on Dioscorea rotundata (0.5 cm). Combatting these fungi need to be developed for effective management of leaf diseases of yam in Côte d’Ivoire.

Dietary Exposure to Polycyclic Aromatic Hydrocarbons and the Probabilistic Health Risk Assessment of Eating Roasted Yams (Dioscorea Species) by African Population

The roasting of food is one of the oldest food preparation and preservation technologies. Although roasted foods have been associated with potential health hazards, this processing method is still used in many foods. This study was carried out to ascertain the health risks of ingesting white (Dioscorea rotundata), and bitter yam (Dioscorea dumetorum) roasted with firewood, charcoal, and charcoal augmented with PET bottles. The PAH content in all the roasted yam samples was identified and analyzed using gas chromatography-mass spectroscopy (GC-MS). A total of 8 PAHs were identified in both yam species; however, bitter yam roasted with augmented charcoal contained 9 PAHs. The total EDI showed that bitter yam roasted with augmented charcoal (6.59E-1) had the highest PAH content while white yam roasted with only charcoal contained the lowest (1.27E-1). The hazard quotients and indexes revealed that bitter yam had the highest HQ in all the roasting methods except for napathalene, fluoranthene and benzo (a) pyrene in samples roasted with charcoal.  The HI for both species in all the roasting methods was above 1 (>1), while firewood produced the highest HI. Benzo (a) anthracene was the most potent PAH identified across the yam species and the roasting techniques. The evaluated ILCR showed that dibenzo (a, h) anthracene identified in white yam smoked with charcoal had the highest tendency to cause cancer (6.38E-1) while the least PAH was acenaphthylene (3.35E-6) which was seen in bitter yam roasted with charcoal. Therefore, it is necessary to inform the consumers of the possible health implications associated with consuming roasted yams and especially yam roasted with augmented charcoal

Identification of diagnostic KASP‐SNP markers for routine breeding activities in yam (Dioscorea spp.)

AbstractMaintaining genetic purity and true‐to‐type clone identification are important action steps in breeding programs. This study aimed to develop a universal set of kompetitive allele‐specific polymerase chain reaction (KASP)‐based single nucleotide polymorphism (SNP) markers for routine breeding activities. Ultra‐low‐density SNP markers were created using an initial set of 173,675 SNPs that were obtained from whole‐genome resequencing of 333 diverse white Guinea yam (Dioscorea rotundata Poir) genotypes. From whole‐genome resequencing data, 99 putative SNP markers were found and successfully converted to high‐throughput KASP genotyping assays. The markers set was validated on 374 genotypes representing six yam species. Out of the 99 markers, 50 were highly polymorphic across the species and could distinguish different yam species and pedigree origins. The selected SNP markers classified the validation population based on the different yam species and identified potential duplicates within yam species. Through penalized analysis, the male parent of progenies involved in polycrosses was successfully predicted and validated. Our research was a trailblazer in validating KASP‐based SNP assays for species identification, parental fingerprinting, and quality control (QC) and quality assurance (QA) in yam breeding programs.

Effect of Mineral Fertilisation on Tuber Yield and Quality in Yams (Dioscorea alata and Dioscorea rotundata)

This study assessed mineral fertilisation impact on tuber yield and food quality in yam genotypes—Dioscorea alata and Dioscorea rotundata. Four genotypes, each from D. alata and D. rotundata, were used in field experiments conducted in Ibadan, Nigeria, during the 2017 and 2018 cropping seasons. Experiments were conducted under low soil NPK fertility conditions with and without Fertiliser treatments. Plots subjected to fertiliser treatment received recommended NPK rate for the area. Tuber yield, functional and pasting properties of yam flour, and sensory attributes of pounded yams were collected. The results revealed varying responses of the genotypes to tuber yield and food quality following fertiliser application. Fertiliser application has generally increased fresh tuber yield. However, it had an impact on the flour quality and textural attributes of pounded yams for some genotypes. In genotypes Danacha and TDa0200012, Fertiliser application increased fresh tuber weight by 29.6% and 28.3%, and dry tuber weight by 19.7% and 24.9%, respectively, without compromising tuber quality. This implies that both genotypes exhibited a greater capacity for nutrient uptake and nutrient use efficiency. However, for genotype Ojuiyawo, Fertiliser application effectively increased tuber yield but negatively affected tuber quality. Our results emphasize the importance of assessing the impact of fertilization on tuber yield and quality for each genotype and selecting the appropriate genotype to improve productivity through mineral fertilization. The outcomes of this study have broader applicability in improving yam productivity across sub-Saharan Africa and are useful for sustainable agriculture in yam-growing regions.

Organogenesis versus somatic embryogenesis pathway efficiencies in in vitro propagation of white and water yams

AbstractThe primary goal of this study was to compare the multiplication rates of yam varieties propagated through organogenesis and somatic embryogenesis (SE). Callus was induced from axillary bud explants of three genotypes of Dioscorea rotundata (Asiedu, Ekiti2a, and Kpamyo) and two genotypes of Dioscorea alata (Swaswa and TDa2014) cultured in Murashige and Skoog (MS) medium containing 9.1 µM 2,4-dichlorophenoxylacetic acid and 5.4 µM naphthaleneacetic acid. Plantlets were regenerated in MS containing 4.4 µM benzylaminopurine and 34 µM uniconazole-P through SE. Single-node cuttings of the five genotypes were grown in MS for 8 wk via organogenesis. The SE and organogenesis regenerants were acclimatized and potted in a 2 (propagation techniques (PTs)) × 5 (genotypes) factorial arranged in a completely randomized design (r = 10). The multiplication ratios (MR), number of tubers (NoT) of the SE, and organogenesis regenerants were collected and analyzed using ANOVA, and means were separated using DMRT (P ≤ 0.05). The SE and organogenesis MR ranged from 1:2 (TDa2014) to 1:8 (Asiedu) and 1:4 (Asiedu) to 1:5 (Ekiti2a and TDa2014), respectively. The NoT differed among genotypes, ranging from 1.15 ± 0.49 (Swaswa) to 2.45 ± 1.39 (Asiedu), and between PTs, ranging from 1.42 ± 0.70 (SE) to 1.86 ± 1.11 (organogenesis). The optimum propagation pathway was genotype-specific.

Molecular and phenotypic profiling of white Guinea yam (Dioscorea rotundata) breeding lines

Phenotypic and genotypic profiling helps identify genotypes with suitable and complementary traits for genetic improvement in crops. A total of 32 traits were assessed in 36 genotypes of white Guinea yam established in a 6 × 6 triple lattice design. The objective was to evaluate an array of plant traits that define the genetic merits of breeding lines for yam improvement. Different analytical tools were used to identify and prioritize relevant traits defining the genetic merits of breeding lines in the yam improvement program. Out of the 32 traits measured, the linear combination of 14 traits that minimize within-group variance and maximize between-group variance for discriminating the genetic values of yam breeding lines were identified. When best linear unbiased prediction with genomic relationship matrix (GBLUP) was used, the accuracies of genomic breeding values were higher (r=0.87 to 0.97) for the seven traits (dry matter content, intensity of flesh oxidization of shredded tuber, pasting temperature, pasting time, tuber flesh colour, yam mosaic virus and fresh tuber yield) with high broad-sense heritability values (H2m>0.6). While, for the remaining seven traits with low (H2m<0.3) to medium (H2m=0.3 to 0.54) broad-sense heritability values, the accuracies of genomic estimated breeding values (GEBV) were low (r<0.4) to medium (r=0.4-0.8). The genotype–trait (GT) biplot display revealed superior clones with desirable genetic values for the key traits. These results are relevant for parental selection aimed at improving key agronomic traits in white Guinea yam.

Optimization of treatments for the germination and establishment of botanical yam (Dioscorea rotundata) seeds

Botanical yam (Dioscorea rotundata) seeds are currently used by yam breeders to generate and conserve new varieties of yam instead of seed yams (vegetative propagule). Yam seed treatment through scarification is one of the most effective methods of improving seed germination and seedling establishment. This study was carried out under greenhouse condition to determine the best seed treatment for the germination and establishment of botanical yam seeds. The set up involved a soil mixed with carbonized rice husk using five different seed treatments; dry heating (DHS) at 60 0C, mechanical scarification + gibberellic acid (MSS + GA), mechanical scarification (MSS), acid scarification with sulphuric acid (ASS) and soaking in hot water at 80 0C (SOS). The findings showed that the treatment, MSS + GA and MSS only, had significant (P<0.05) positive effect on the seed emergence and seedling establishment compared to the untreated control (COS) and other treatments. ASS caused seed damage resulting to no emergence. The findings showed that carbonized grain waste (rice husk) enhanced soil fertility and seed treatment (MSS + GA) was the best to improve yam seed germination and seedling establishment. These treatments can be efficiently applied to reduce the long gestation periods and increase yield in yam breeding programmes.

Expected yield and economic improvements of a yam seed system in West Africa using agro‐physiological modelling

Societal Impact StatementYam is a major tropical root crop and a staple food for millions of people in West Africa. The model used in this study shows that promoting the use of improved seed tubers would help increase yields and profitability for farmers. This could lead to improved food security, increased income and higher standards of living. Additionally, the model serves as a useful decision‐support tool for farmers and technicians to choose, depending on the species, the optimum seed‐tuber weight and planting date. This study provides agronomic arguments to justify investments in the improvement of yam planting materials in West Africa.Summary Yam (Dioscorea spp.) is a major tropical root crop, grown mainly in West Africa using traditional extensive techniques. Farmers typically reuse seed tubers by setting aside up to 30% of their production for the next season, leading to high planting material variability that affects yields. Several initiatives aim to promote the use of improved seed tubers. However, to help their adoption, it is necessary to quantify the agronomic and economic advantages. To address this, a model for individual plant growth and development was developed based on six experiments in Benin from 2007 to 2009. This model simulates the combined effect of emergence (through photoperiod and temperature) and seed‐tuber weight on yam plant growth and development. Its predictions were highly correlated with observed plant tuber yield (R2 > 0.83). Results highlight the crucial role of key processes such as seed‐tuber physiological age and photoperiod sensitivity. The study shows that for the traditional planting dates, the use of improved planting material could lead to a yield increase of 22%–27% and a gain in profitability of 30% and 40% for Dioscorea alata and Dioscorea rotundata, respectively. The model proved to be a useful decision‐support tool for choosing an optimum seed‐tuber weight, depending on the species and the planting date. This study validates investments in yam seed systems in West Africa. However, beyond seed size and health, other factors such as dormancy, storage time and their management need to be considered to address emergence heterogeneity and its impact on yield.

Agronomic and hormonal approaches for enhancing flowering intensity in white Guinea yam (Dioscorea rotundata Poir.).

Developing novel white Guinea yam (Dioscorea rotundata) varieties is constrained by the sparse, erratic, and irregular flowering behavior of most genotypes. We tested the effectiveness of nine agronomic and hormonal treatments to enhance flowering on D. rotundata under field conditions. Genotypes responded differently to flower-inducing treatments (p<0.001). Of the test treatments, pruning and silver thiosulfate (STS) were effective in increasing the number of spikes per plant and the flowering intensity on both sparse flowering and monoecious cultivars. STS and tuber removal treatments promoted female flowers on the monoecious variety while pruning and most treatments involving pruning favored male flowers. None of the treatments induced flowering on Danacha, a non-flowering yam landrace. Flower-enhancing treatments had no significant effect on flower fertility translated by the fruit set, since most treatments recorded fruit sets above the species' average crossability rate. Flower-enhancing techniques significantly influenced number of tubers per plant (p = 0.024) and tuber dry matter content (DMC, p = 0.0018) but did not significantly affect plant tuber yield. Nevertheless, treatments that could enhance substantially flowering intensity, such as pruning and STS, reduced tuber yield. DMC had negative associations with all flowering-related traits. This study provided insights into white yam flower induction and suggests promising treatments that can be optimized and used routinely to increase flowering in yam crop, without significantly affecting flower fertility and tuber yield.

Physicochemical and sensory attributes of some selected varieties of white yam (&lt;i&gt;Dioscorea rotundata&lt;/i&gt;)

The physicochemical and sensory properties of five varieties of Dioscorea rotundata were investigated for their potential end uses. The water absorption capacity, water binding capacity, swelling power, solubility index, pH, and pasting properties of flour processed from the yam tubers were determined. Also, the sensory attributes of pounded yam produced from the tubers were evaluated. In terms of colour, Gbongi had the highest whiteness value (82.27). Lasinrin had the highest moisture content (39.47 %) and swelling capacity (6.11g/g), Efuru had the highest water absorption capacity (132.50%) and pH (6.75). Gbongi had the highest solubility index (13.82%). Awana had the highest peak viscosity (293.70RVU) holding strength viscosity (279.20RVU) and peak time (7.00min). Lasinrin had the highest breakdown viscosity (140.25RVU) setback viscosity (295.00RVU) and pasting temperature (82.55oC) while Efuru had the highest final viscosity (437.83RVU). All the varieties had good ratings for the pounded yam sensory attributes (stretchability, stickiness, mouldability, smoothness, colour, hardness). All the varieties were acceptable regarding the general acceptability of the pounded yam. The qualities of yam cultivars suggested their appropriateness as an alternative for other flour-based pastestypically consumed by Nigerians.

Mathematical Modelling and the Effect of Blanching on the Drying Kinetics of White Yam (Dioscorea rotundata)

Mathematical Modelling and the Effect of Blanching on the Drying Kinetics of White Yam (Dioscorea rotundata)

Genome-wide dissection of the genetic factors underlying food quality in boiled and pounded white Guinea yam.

Food quality traits related to the genetics of yam influence the acceptability for its consumption. This study aimed at identifying genetic factors underlying sensory and textural quality attributes of boiled and pounded yam, the two dominant food products from white Guinea yam. A genome-wide association study (GWAS) of a panel of 184 genotypes derived from five multi-parent crosses population was conducted. The panel was phenotyped for the qualities of boiled and pounded yam using sensory quality and instrument-based textural profile assays. The genotypes displayed significant variation for most of the attributes. Population differentiation and structure analysis using principal component analysis (PCA) and population structure-based Bayesian information criteria revealed the presence of four well-defined clusters. The GWAS results from a multi-random mixed linear model with kinship and PCA used as covariate identified 13 single-nucleotide polymorphic (SNP) markers significantly associated with the boiled and pounded yam food qualities. The associated SNP markers explained 7.51-13.04% of the total phenotypic variance with a limit of detection exceeding 4. Regions on chromosomes 7 and 15 were found to be associated with boiled and pounded yam quality attributes from sensory and instrument-based assays. Gene annotation analysis for the regions of associated SNPs revealed co-localization of several known putative genes involved in glucose export, hydrolysis and glycerol metabolism. Our study is one of the first reports of genetic factors underlying the boiled and pounded yam food quality to pave the way for marker-assisted selection in white Guinea yam. © 2023 Society of Chemical Industry.

ANNUAL EFFECTIVE DOSE ESTIMATION DUE TO THE NATURAL RADIOACTIVITY IN YAM TUBERS (Dioscorea rotundata) CULTIVATED IN NORTHCENTRAL NIGERIA

Yam tubers (Dioscorea rotundata) and soil from commercially cultivated farmland in northcentral Nigeria were collected and investigated for their natural radioactivity content using a 3” × 3” NaI(Tl) gamma detector. Average activities of 238U, 232Th and 40K in the investigated farm soil were 38.13±3.76 Bq kg-1, 15.06±0.99 Bq kg-1 and 381.80±15.50 Bq kg-1, respectively. The results agree with the world’s acceptable levels of safety. Activities measured in the yam tubers were in the range from BDL -76.68±9.73 Bq kg-1 for 238U, BDL - 19.77±1.30 Bq kg-1 for 232Th and 312.50±20.73 - 627.94±38.37 Bq kg-1 for 40K, with average values of 29.23±4.0, 13.10±0.72 and 445.10±27.20 Bq kg-1, respectively. The total effective dose from radionuclide intake from yam ingestion fluctuated between 272.12 μSv y-1 and 935.97 μSv y-1. Correlation analysis identified 238U and 232Th as the leading contributors to the total effective dose from ingesting yam tubers cultivated in northcentral Nigeria.

English

Starch fillers were extracted from three plant sources namely amora tuber, Tacca lentopeteloides; sweet potato, Ipomoea batatas; yam starch, Dioscorea rotundata and their particle size, pH, amylose, and amylopectin percentage decomposition determined accordingly. The starch was introduced into natural rubber in liquid phase (through gelatinization) by the latex compounding method and compounded according to standard method. The prepared starch/natural rubber composites was characterized by Instron Universal testing machine (UTM) for tensile mechanical properties. The composites was further characterized by x-ray diffraction and crosslink density analysis. The particle size determination showed that amora starch granules has the smallest particle size (156 &times; 47 &mu;m) followed by yam starch (155 &times; 40 &mu;m) and then sweet potato starch (153 &times; 46 &mu;m) with the biggest particle size. The pH test also revealed that amora starch has a near neutral pH of 6.9, yam 6.8, and sweet potato 5.2 respectively. Amylose and amylopectin determination showed that yam starch has a higher percentage of amylose (29.68), followed by potato (22.34) and then amora starch with the lowest value (14.86) respectively. The tensile mechanical properties testing revealed that yam starch produced the best tensile mechanical properties followed by amora starch and then sweet potato starch. The structure, crystallinity/amorphous nature of the product composite was confirmed by x-ray diffraction, while the nature of crosslinking was confirmed by swelling test in toluene solvent using the Flory-Rehner approach. The increasing values of crosslink density in the starch/rubber composite is a clear evidence of good interfacial adhesion between the starch fillers and the rubber, hence good dispersion of starch fillers in the rubber. This research has rendered a workable strategy for enhancing interfacial interaction between a hydrophilic filler (Starch) and hydrophobic polymeric matrix (natural rubber) yielding moderately good tensile mechanical properties with prospects for the rubber processing industry. The studied fillers can partially replace carbon black as natural rubber fillers with reduced cost, no risk to human health and also an environment friendly approach. Key words: Natural rubber, fillers, starch, amylose, amylopectin, crosslink density, mechanical properties.

In situ dynamic rheological analysis of raw yam tubers: a potential phenotyping tool for quality evaluation.

Most rheological analyses in yam have been done on starch gels, which requires starch extraction from the tubers. In situ rheology bypasses the need of starch extraction and relies on the original cell structure and complex matrix organization under stress or strain. Dynamic rheological properties of tuber from 16 accessions belonging to four yam species (Dioscorea rotundata, D. alata. D. bulbifera and D. dumetorum) were investigated for potential use as a medium throughput phenotyping screening tool that can indicate the quality of yam food products or their industrial potentials. Rheographs of the tubers illustrated differences in the structure of D. bulbifera compared to other yam species. High initial storage modulus (G') of yam parenchyma indicated tubers with strong and rigid structure which do not lose their structural integrity easily on heating. Dioscorea rotundata and D. alata varieties exhibited a lower temperature at which gelatinization took place (Tgel ) equivalent to the irreversible transition during starch gelatinization (75.3 and 79.8 °C) and took shorter time (867 and 958 s, respectively) to reach the G' maximum, compared to other species. The stress relaxation test showed that the higher the dry matter of the tubers, the higher the work to rupture the structure. Rheological characteristics G', loss modulus (G″), swelling capacity and Tgel showed potential as suitable quality indicators for yam products. In situ rheological characterization of yam tubers could be used as an instrumental screening tool to phenotype for quality in yam products. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.