Effect of Postharvest Waxing Treatments, Yam Variety and Tuber Size on Shelf Life of White Yam (Dioscorea rotundata Poir)

Abstract

A significant quantity of yam tubers gets deteriorated in storage due to sprouting, weight loss, and rotting. There was, therefore, the need to identify cost effective ways of extending postharvest life of yam tubers without compromising with the health of consumers. Therefore, field research was conducted to explore the effect of shea butter & palm kernel oil waxing, yam variety, and tuber size on postharvest shelf life of Puna, Asana, and Punjo varieties of white yam (Dioscorea rotundata). Laboratory experiment was also carried out to find out the possible sensory quality changes that might have occurred as a result of shea butter and palm kernel oil waxing. The field experiment was conducted using the farmers’ own storage facilities at Apiakura located along the Jasikan-Abotoase trunk road in the Volta Region of Ghana. The variable factors used in the field experiment were waxing, yam variety and tuber size while the fixed factors were similar storage facilities, and constant ambient conditions (temperature, relative humidity, and wind speed in and around the storage facilities). The waxing comprised shea butter, palm kernel oil waxing and unwaxed tubers (control). Yam varieties used were Puna, Asana, and Punjo, whilst tuber sizes used were smaller tuber size (with surface factor 1.1 ±1), medium tuber size (with surface factor (1.4 ±1) and bigger tuber size (with surface factor 1.7 ±1). The experimental design used was a 3 x 3 x 3 factorial in randomized complete block design. Four storage facilities were used. Each storage facility was used as an experimental block, and they were located at different farms. Each block contained 27 treatment combinations. Data collected were weight loss (%), sprouting (%), and rotting (%) at 2 weeks intervals. The sensory evaluation was conducted in the Home Economics Food Laboratory at Bueman Senior High School at Jasikan using 20 trained sensory panellists. Sensory qualities evaluated were; taste, flavour, texture, attractiveness (appearance) of the cooked, and acceptability to consumers. Food tests were carried out at the Nuguchi Memorial Research Institute to monitor the moisture contents and the levels of reducing sugars in the stored yam to verify the occurrence of sprouting and weight loss. The results from the study indicated that shea butter and palm kernel oil waxing reduced weight loss, sprouting, and rotting significantly (p< 0.05) for up to three months. Yam variety and tuber size were also found to affect weight loss significantly (p < 0.05). There were interaction effects among the three factors (waxing materials, tuber size, and yam variety) used. In addition, waxing, yam variety, and tuber size were also found to affect taste, texture, and flavour of the yam tubers. However, these treatments did not affect attractiveness and acceptability. Shea butter and palm kernel oil waxing reduced weight loss, sprouting, and rotting. Generally, the result showed great potential for yam farmers and exporters whose income is being affected by high tuber weight loss (desiccation), sprouting, and rotting. This discovery, will also boast food security situation in Ghana.