EFFECT OF POSTHARVEST WAXING TREATMENTS, YAM VARIETY AND TUBER SIZE ON SHELF LIFE OF WHITE YAM

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

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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.