Yam Storage Research Articles

Storage of West African yam (Dioscorea spp.) seeds: modelling seed survival under controlled storage environments

Survival data was collected from seeds of two yam species, D. dumetorum and D. togoensis stored at moisture contents ranging from 3% to 25% under temperatures ranging from 5°C to 55°C for 400 days (13 months). The data was subjected to probit analysis to estimate seed longevity under each of the seed storage treatment combinations. The relationship between seed longevity and storage environment was evaluated by a seed viability equation whose constants were determined by linear regression modelling. Seed viability constants estimated for D. dumetorum were K E = 5.859, C W = -3.060, C H = -0.0007, C Q = -0.0007 and for D. togoensis were K E = 4.505, C W = -1.646, C H = -0.020, C Q = -0.00011. R-values of the data fit to the equation were approximately 0.92 for D. dumetorum seeds and 0.87 for D. togoensis seeds. The estimated constants are recommended for monitoring the viability of seed lots of the species in gene banks operating controlled storage facilities within the range of the experimental storage conditions.

Biochemical and textural changes in trifoliate yam Dioscorea dumetorum tubers after harvest

Biochemical and textural changes were investigated in trifoliate yam Dioscorea dumetorum tubers, after harvest, in an attempt to study the chemical and physical changes associated with the raw and cooked tubers and how these relate to the hardening phenomenon of the tubers after harvest. A 2×2×3×4 factorial experiment, with cultivar, storage condition, treatment and storage time as their respective variables, was done. Samples were analysed for moisture, starch, reducing sugars, alcohol-soluble sugars, acid and neutral detergent fibre, cellulose, hemicellulose and lignin. The Warner–Bratzler test cell was used in a TA.XT2 Texture Analyser to measure the hardness of cooked tubers. The moisture and starch contents of the tubers decreased from 77.8 to 70.4% and 70.5 to 66.5 g/100g, respectively in a period of 72 h of storage, suggesting rapid dehydration after harvest and breakdown of starch. All the other chemical indices increased with storage time. These changes were influenced by the storage temperature and the treatment given to the tubers prior to storage. In general, samples stored at 4 °C showed smaller changes in the chemical indices than those at 28 °C, suggesting a temperature-dependence of the changes. Both cultivars of yam showed increase in hardness with storage time. A high correlation ( r=0.9503–0.9913) was noted between the texture and the chemical indices of the white cultivars. Storage of the trifoliate yam, Dioscorea dumetorum, immediately after harvest, leads to reduction in moisture and starch contents and increase in sugars and structural polysaccharides. Low temperature storage may reduce the hardening phenomenon. A mechanism for the hardening phenomenon has been proposed.

Comparison of Storage Stability of three Yam Species in a Humid Environment

The chemical composition of three yam species (Dioscorea rotundata Poir, D. esculenta (Lour) Burk and D. bulbiferaL.) was estimated as a measure of storage stability and susceptibility/tolerance to Penicillium oxilicum. Free fatty acid (FFA) and peroxide value (PV) were highest in Dioscorea bulbiferafollowed by D. rotundata and least in D. esculenta indicating a better storage stability in D. esculenta. The biochemical functions of the tubers, estimated as the quantity of Krebs Cycle acids, indicated the highest quantity in D. bulbiferafollowed by D. rotundata and least in D. esculenta. The biochemical functions were lower 3 months after harvesting indicating the initiation of tuber dormancy and higher 6 months after harvesting which coincided with the initiation of tuber sprouting, thus, showing the increased metabolic activities during sprouting. However, the quantity of ascorbic acid was highest in D. esculenta followed by D. rotundataand least in D. bulbifera. The extent of tuber rot by Penicillium oxilicum confirmed that D. esculentawas the most tolerant of the species and therefore most stable in storage, followed by D. rotundataand least is D. bulbifera. The differential amounts of the chemicals could be an indicator for screening yam species for tolerance/susceptibility to rot organisms and thus for estimating their storage stability. Keywords: Yam species, rot organism, storage stability and yam storage [IJARD Vol.3 2002: 127-130]

Yam Storability and Economic Benefits of Storage Under the Modern (underground) and Traditional (Yam barn) Technologies in southeastern Nigeria

This paper examines yam storability and the economic benefits of storage under the modern (underground) and the traditional (yam barn) storage technologies in Southeastern Nigeria. Data were collected mainly from 55 respondents who were interviewed, as well as from measurement of storage parameters on yam tubers stored in 55 traditional yam barns and 11 modern underground yam storage structures. The results show that on the average about 55 percent of the tubers stored under the modern technology and less than 20 percent of the tubers stored under the traditional system remained in a fairly good condition after the fifth month of storage; and the value of storage loss was about N46,231 for the traditional yam barn and N23,951 for the modern storage system per 1000kg of tubers stored under both systems. Hence the value of storage losses under the traditional system was about 55 percent higher than that under the modern system. On the average about 400kg yams valued at N22,280 was saved from 1000kg of yams stored under the modern storage technology for a period of five months. The net benefits would be significantly higher if the full potentials of the modern storage technology are exploited especially in terms of prolong storage which attracts higher revenue from stored tubers. Key words: Yam; storability; modern; ttraditional; technology.

Incidence of yam (Discorea rotundata Poir) rots, inoculation-induced quality changes, and control by chemical fungicides and modified atmospheres

Abstract Five genera of moulds (Aspergillus, Botryodiplodia, Fusarium, Penicillium and Rhizopus) were isolated from yam (Discorea rotundata) and used for inoculation of tuber samples at two wound depths of 10 and 15 mm with either single or paired cultures. The three prevalent isolates (Aspergillus, Fusarium and Penicillium) were each used to inoculate other yam samples before dipping in various fungicides to monitor the magnitude of lesion/rot development. Storage of samples in modified atmospheres and the effects of inoculation (using Aspergillus) on physico-chemical changes were also evaluated. Lesions/rots induced at 10 mm depth were significantly larger than those induced at 15 mm depth. Pair-inoculation of Aspergillus and Rhizopus induced the most extensive rots, and minimum rot size occurred when Fusarium was co-inoculated with either Botryodiplodia or Penicillium. Dithane M-45 (manganese ethylenebis-dithiocarbamate or Mancozeb) significantly reduced these rots while sodium benzoate was least effective. Equilibrium modified atmospheres created by packing the samples inside a polyethylene bag of 18 μm thickness significantly maintained the quality of the samples. Inoculation of samples with Aspergillus sp. resulted in a significant decrease in carbohydrate and moisture content but enhanced crude protein content. Application of combined control methods (hurdle technology) is therefore recommended for control of yam storage lesions/rots and enhancement of storage life.

Effect of storage system and sprout removal on post-harvest yam (Dioscorea spp.) fresh weight losses

Two aspects of yam storage practice were tested from 1994 to 1995 in central Côte d'Ivoire. The first experiment compared the storage environment in pits or sheds with that of the traditional yam open barn method. The pits allowed the daily range of variation in temperature to be reduced while maintaining a high relative humidity (RH), whereas the temperature and RH in the sheds were similar to those of the yam barns. Differences in temperature and RH between the storage systems had little effect on the fresh weight losses of the tubers. The more effective protection against solar radiation and rain afforded by the sheds and pits reduced fresh weight losses in D. cayenensis rotundata by 12% over 6·5 months in comparison with the barns. The second experiment tested the regular removal of the sprouts. Sprout removal reduced fresh weight losses equally over 5 and 6 months' storage. The reduction in fresh weight loss was 12% for cv. Gnan (D. cayenensis rotundata) during 6 months' storage. Monthly sprout removal gave an equal benefit in pits, in sheds and on yam barns. The monthly cutting of sprouts at the base should be encouraged in places where this is not already done. The total loss is mainly determined by the growth of the sprouts and the reduction in weight after onset of sprouting, which are highly dependent on species and cultivar. Bètè bètè yams had better keeping qualities than all the other cultivars tested.

Respiratory changes in yam storage tissue (Dioscorea spp.) infested with Meloidogyne incognita using a novel technique for measuring oxygen uptake

SummaryA simple, novel application is described which measures the oxygen uptake in respiring tissues using an electrochemical gas sensor to monitor volume concentration changes in ambient oxygen with output to a chart recorder. Oxygen uptake by white yam, Dioscorea rotundata cvs Nwopoko and Obioturugo; and yellow yam, D. cayenensis (cv. Ukom Manu) which were heavily infected with root‐knot nematode, was significantly higher than in the non‐infected tissue. However, the rate of oxygen uptake in D. rotundata was significantly higher than in D. cayenensis.

Título en español

La naturaleza de la dominancia en la brotación de los tubérculos del ñame (Dioscorea rotundata Poir) se estudió en condiciones ambientales en un tinglado corriente para almacenar ñames. Los tubérculos enteros brotaron en el extrema proximal, o sea en la base morfológica o extrema en que el tubérculo esta adherido al tallo. El único vástago que brota en un ñame entero inhibe la brotación de otros vástagos a lo largo del eje del tubérculo. Si el tubérculo se corta en tres secciones: "cabeza" (región basal or proximal), "media" y "rabo" (región apical o distal) se estimula la brotadura de vástagos laterales en la superficie debajo de la región basal. Al separar la región basal desaparece la tensión que impedía que los vástagos laterales brotaran en el tubérculo entero. Esto indica una fuerte dominancia basal sobre los brotes basales en el tubérculo entero. La fisiología de la dominancia en tubérculos enteros podría describirse como "dominancia basal" en vez de "dominancia apical", ya que en la brotadura de un tubérculo entero, es el brote basal (el de la base morfológica o extrema proximal) el que inhibe el desarrollo de brotes laterales a lo largo del eje del tubérculo.

Some biochemical changes associated with post‐harvest storage of white yam (Dioscorea rotundata) tubers

AbstractHealthy Dioscorea rotundata tubers were kept for 8 months under local storage conditions and periodically analysed for the activity of some enzymes of carbohydrate metabolism as well as for the concentrations of key tuber metabolites. Except for polyphenol oxidase, all the other enzymes monitored showed low and maximum activities before and at onset of sprouting, respectively. The activities of these enzymes after sprouting remained higher than those in the pre‐sprouting period. Hexokinase, alcohol dehydrogenase and phosphorylase showed an approximately 2‐fold increase in activity at sprouting while glucose‐6‐phosphate dehydrogenase showed a more than 3‐fold increase in activity. Polyphenol oxidase (PPO) activity and starch content decreased steadily with storage with PPO activity decreasing to one‐half by the end of storage. L‐ascorbate, total polyphenols, carotenoids and lipids increased with storage and peaked at sprouting.