COMPARATIVE STUDY OF THE STORABILITY OF WHITE YAM (Dioscorea rotundata) WITH DIFFERENT STORAGE TECHNIQUES

Abstract

Four storage structures were constructed and used to study the storability of white yam (Discorea rotundata). The barn was constructed under a cashew tree to provide shade: the yam tubers were attached to the barn with the aid of local twig (rope), two at time in a vertical position, to allow proper aeration of the yam tubers; wooden platform (1m x 1m) was constructed with a flat surface raised up to a height of 17cm to allow for air circulation underneath and placed in the laboratory where yam tubers were arranged on it. A rectangular shaped ground pit with a depth of 1meter was dug under a cashew tree beside the barn, straw of dried grasses and dried wood were laid at the base of the pit, followed by the yam and another set of straw to cover the yams before a thin layer of the soil was finally used to cover it up. Wooden shelf (1.5m x 1m) which was raised to a height of 35.8cm was used in the laboratory to store the yams at ambient temperature 28oC ± 2oC and 75% ± 5% relative humidity. Samples were collected at four weeks interval from each storage structure for laboratory analysis of proximate composition (moisture content, crude ash, crude protein, crude fibre and crude fat content). Mineral analysis (Phosphorous, Potassium, Calcium, Magnesium and Nitrogen) was also carried out using atomic absorption spectrophotometer (AAS). The sensory evaluation was carried out on the fresh yam tubers before storage and subsequently for six months to examine changes in organoleptic properties (taste, colour, texture and flavour) of the stored yam tubers. Observable changes in physiological properties of stored yam tubers (dormancy and sprouting) were monitored monthly for six months. Loss in weight ranged for platform storage 5.98 to 44.88; pit storage 4.57 to 47.37; barn storage 4.35 to 35.45 and shelf storage 4.76 to 37.09. The moisture ranged, for platform storage 10.73 to 48.88; pit storage 6.53 to 41.83; barn storage 6.42 to 30.16 and shelf storage 6.44 to 34.83. the barn recorded the least moisture loss after six months of storage. The percentage crude fibre, increased but was not significantly different from others. The ash content increased in barn and shelf storage but was not significantly different from others. The crude protein decrease in all storage structures evaluated but differs from each other significantly. The mineral composition across all storage structure was not significantly different except potassium content that was significantly different from others. The data collected were subjected to analysis of variance (ANOVA) using SPSS and the means were separated using New Duncan’s Multiple Range Test. Results showed that in all the storage methods, there were rapid drop in weights, moisture contents, dry matters and in all the mineral components of the stored yams. In addition, sensory evaluation rated the stored tubers higher than the fresh tubers. Moreover, the results of the study of physiological properties of the yam tubers under various storage conditions showed that, there was no sprouting at the first two months of storage as a result of dormancy. However, sprouting begins to occur from the third month of storage and it was very predominant in yam barn and shelf storage