Evaluation of Quality of White Yam Cultivars (Pona and Dente) in two Improved Traditional Storage Structures

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February, 2017
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Harvested yams are often stored in structures such as barns. The poor conditions of most barns usually lead to storage losses due to rot, weight loss, sprouting etc. To curb this situation, two improved traditional barns were introduced. Despite the efficiency of these new barns, their effect on food quality of stored yams has not been studied. This study therefore aimed to evaluate the temperature and relative humidity in two improved barns (rectangular and circular) and to determine the effect of the barns on the physical, chemical and sensory properties of two yam cultivars; pona and dente stored for six months. A total of 240 tubers of each cultivar were used for the study. Data loggers were used to measure temperature and relative humidity inside and outside the barns. The physical parameters determined were weight loss, rotting, sprouting and rodent damage. Chemical analysis determined included proximate, starch and sugar. Sensory evaluation was carried out on the stored and hidden controlled boiled yam at the end of the storage period to assess their preference by potential consumers using the scale 1-9 with 1 being like extremely, 5- neither like nor dislike and 9 being dislike extremely. Temperature in the barns over the storage period ranged from 25.4-30.8oC in the rectangular barn and 25.4-30.4oC in the circular barn. Relative humidity in the rectangular barn ranged from 37.9-79.3% and from 40.9-80.7% in the circular barn. Weight loss of 23.42% and 21.94% for pona in circular and rectangular barns respectively were recorded at the end of the storage period. Dente recorded comparatively higher weight loss of 28.57% in circular barn and 26.39% in rectangular barn. Rot was seen earlier (after 1st month) and higher in pona cultivar (48.33% for both circular and rectangular barns) than dente (16.67%- circular, 11.67%-rectangular). In each of the cultivars sprouting started right from the first month and peaked at the fourth month. Dente tubers had about 51.19% and 46.96% sprout in circular and rectangular barns respectively, higher than pona tubers (38.85% in circular and 38.38% in rectangular barn); however, rodent damage was very minimal at the end of the storage period. There was no significant difference in the physical properties of samples stored in rectangular and circular barns. Proximate analysis revealed an average decrease in carbohydrate from 32.18g/100g to 23.81g/100g and 37.36g/100g to 23.18g/100g in dente and pona cultivars respectively in circular barn at the end of the storage period. Moisture content decreased significantly (p>0.05) for dente cultivar from 62.3g/100g to 49.9g/100g in circular barn and 48 .1g/100g in rectangular barn. Both ash and fat contents did not change significantly. After three months of storage, protein content of pona stored in circular barn increased significantly from 2.31g/100g to 6.13g/100g and similar observation was made for dente in the rectangular barn. As the starch content decreased over the storage period, the sugar content in both cultivars increased. Sugar content of pona was higher (from 3.91g/100g to 6.20g/100g) than dente (from 3.21g/100g to 4.30g/100g) in rectangular barn. Again, the different barn types did not significantly affect the chemical properties of the tubers. Between the two cultivars, pona was preferred (3-like moderately) based on its sensory properties against dente (4-like slightly). Stored yams showed better sensory properties compared to the control. To keep harvested tubers as fresh as possible, it is therefore recommendable for tubers to be stored up to about four months even in the improved barns.
A thesis submitted to the Department of Food Science and Technology, College of Science, Kwame Nkrumah University of Science and Technology, Kumasi in partial fulfilment of the requirements for the degree of Master of Science in Food Science and Technology.