Curing of freshly harvested yams ( Dioscorea spp.) is a process for wounded yams during harvest to heal. In this work the effectiveness of straw, polypropylene and jute sack on curing of seven key farmers’ yam varieties over a duration of 7, 14 and 21 days was studied. Seven key farmers’ yam varieties identified as Pona , Lariboko , Dente , Mutwumudoo , Serwah belonging to D. rotundata , Matches and Akaba belonging to D. alata were studied under different curing treatments. The percentage weight loss of yam tubers varied among the treatments over curing period. Curing under jute sack showed all yam varieties had weight losses less than 2.0%, within 7 days of curing. Five different varieties had weight loss less than 2.0% except Dente under the straw treatment. Mutwumudoo variety showed the highest water loss (8.4%) for polypropylene sheet and 6.9% for Lariboko in the control treatment. During 7 days curing the control and polypropylene treatment did not support yam curing. After 14 days of curing of tubers, similar tends were observed as in 7 days curing. After 14 days of curing under jute sack, percentage weight loss of the tubers ranges from 2.0% - 3.7%. In the straw treatment, the percentage weight loss ranges between 1.0% - 4.7% in all other varieties except Dente (D. rotundata) (8.2%). Polypropylene sheet treatment showed the highest percentage weight loss in Mutwumudoo variety (18.4%). A similar trend was observed for the yam tubers cured for 21days as percentage weight loss of tubers under jute sacks was 2.5 – 9.8%. Curing temperature and humidity ranged between 27°C - 40°C and 87% - 100% rh for yam tubers under the three different treatments of polypropylene, jute and straw. However, the control treatment recorded lower humidity of 60% - 80% rh. Curing material, duration, climatic conditions and yam varieties influenced curing and Serwah variety, which is a D. rotundata is the best bet yam variety to cure under jute sack for 7, 14 and 21 days of curing.
Yams (Dioscorea spp.) are major stable foods in most tropical countries [
Yams serve as an important source of carbohydrate for many people of the sub-Sahara region, especially in the yam zone of West Africa [
Ghana is the third largest producer of yams in the world, following Nigeria and Cote d’Ivoire [
The increasing demand for yam on the local Ghanaian and international markets requires improvement in its production, storage, transportation and marketing. When yams are being harvested, some tubers are injured in the form of cuts, bruises and abrasions. These openings act as entry points to wound pathogens to attack the yam. According to Booth [
Extensive studies has been done on the physiological processes associated with wound repair in yams during curing but limited information is available pertaining to the effect of different materials on curing of yam tubers. This study investigates the effectiveness of straw, polypropylene and jute sack on curing of the seven key farmers’ yam varieties over a cumulative period of 21 days.
Freshly harvested seven key farmers’ yams (Dioscorea spp.) identified as Pona, Lariboko, Dente, Mutwumudoo, Serwah belonging to Dioscorea rotundata, Matches and Akaba belonging to Dioscorea alata were obtained from farm gates at Atebubu in the Atebubu-Amantin District of the Brong Ahafo region in Ghana through the Ministry of Food and Agriculture. The yams were carefully transported to the Pilot Scale Processing Unit of the CSIR-Food Research Institute, where the study was conducted.
Curing materials used were straw, polypropylene and jute sack. The straw was obtained from farmers’ fields in Atebubu. The polypropylene and jute sack were purchased from shops in Atebubu.
Freshly harvested mature tubers of each of the seven selected varieties consisting of 84 tubers per variety were used in the study. The tubers were artificially wounded (4.0 cm × 5.0 cm) using a sharp stainless knife. The wounded tubers were then weighed and the initial weights were recorded. The wounded tubers were arranged in a circular form with the wounded side facing upwards. A temperature/humidity logger was placed on the arranged yams after which it was covered with jute sack. The samples were weighed after curing for 7, 14 and 21 days. The experiment was repeated using polypropylene, straw and a control, which was not covered (
In order to account for the initial mass differences of yam tubers, water loss of yam tubers during curing was expressed in g per g initial mass (g/g). Percentage water loss (% WLt) is given as:
where Wit, Wct are the initial and final weight of tuber after curing at time t (t = duration in curing treatment).
Curing temperature and humidity within each experiment was determined using a Data Logger (Lascar Electronics UK) obtained from Natural Resources Institute, United Kingdom. The data recorded was then analyzed using Data Logging Software Version 5.51 (EasyLog).
Analyses were carried out in triplicates and data expressed as means ± standard deviation. Analysis of variance was performed and Duncan multiple test range was used to separate means using the Statgraphics Centurion 16.1.11 (StatPoint Technologies Inc, USA, 2010). Comparisons between sample treatments and correlation analysis were done with a probability p = 0.05.
In studies reported by Been et al. [
After 14 days of curing of tubers, similar tends were observed for tubers cured for 7 days. In the jute sack, percentage weight loss of the tubers ranges from 2.0% - 3.7%. Only Lariboko variety was 8.4%. In the straw treatment, the percentage weight loss was between 1.0% - 4.7% for all other varieties except Dente (Dioscorea rotundata) (8.2%). Polypropylene sheet treatment showed the highest percentage weight loss in Mutwumudoo variety (18.4%). Percentage weight loss of the other varieties ranges from 1.5% - 4.9%. In control treatments,
percentage weight loss ranges between 1.3 - 13.9%. It recorded the highest percentage water loss of 13.9% in Lariboko variety (
A similar trend was observed for the yam tubers under curing after 21days of curing as percentage weight loss of tubers under jute sacks was 2.5% - 9.8%. Percentage water loss of tubers curing under straw ranges between 2.2% - 10.7%. The highest percentage was 21.6% observed in Mutwumudoo under polypropylene sheets. The percentage weight loss (17.0%) of Lariboko variety was the highest among the tubers under control treatment. In the remaining varieties the percentage water loss was 2.2% - 5.7% (
the cured yam tubers is an indication that healing of wounds is related to a certain loss in tuber weight as reported by Bautista [
Statistical analysis of the mean weight loss of the tubers at curing for the four treatments is presented in Tables 1-3. After 7 days of curing under the different conditions, mean weight loss of the seven yam varieties differed significantly (p = 0.05). Curing under jute sack, the mean weight loss ranged between 0.009 - 0.12 for Mutwumudoo and Serwah as the lowest and Mutwumudoo as the highest yam varieties. Serwah variety recorded the smallest mean weight loss during 7 days curing period under polypropylene sheet and control. However, other varieties behaved quite differently. While Mutwumudoo cured well under jute sack, it did not perform well under polypropylene. A similar trend was observed under straw, which shows that Matches performed well than the other varieties. Curing under polypropylene and control treatment shows Mutwumudoo losing weight more than the other varieties.
Similar trends were observed under the influence of curing treatment and duration of 14 and 21 days. After curing cumulatively for 14 and 21 days Serwah, Matches and Akaba cured appropriately under jute sack and straw than polypropylene and control treatments (
Yam variety | Jute sack | Polypropylene sheet | Straw | Control |
---|---|---|---|---|
Pona | 0.018 ± 0.012a | 0.008 ± 0.008a | 0.007 ± 0.007a | 0.038 ± 0.038a |
Lariboko | 0.016 ± 0.005a | 0.005 ± 0.005a | 0.018 ± 0.014a | 0.069 ± 0.058a |
Dente | 0.011 ± 0.007a | 0.019 ± 0.059a | 0.027 ± 0.027a | 0.004 ± 0.004a |
Mutwumudoo | 0.012 ± 0.001a | 0.084 ± 0.084a | 0.015 ± 0.015a | 0.021 ± 0.012a |
Serwah | 0.009 ± 0.009a | 0.003 ± 0.003a | 0.005 ± 0.004a | 0.014 ± 0.011a |
Matches | 0.011 ± 0.009a | 0.026 ± 0.006a | 0.002 ± 0.002a | 0.003 ± 0.003a |
Akaba | 0.013 ± 0.010a | 0.007 ± 0.007a | 0.008 ± 0.008a | 0.014 ± 0.014a |
Means in column followed by the same letter are not significantly different (p = 0.05) from each other.
Yam variety | Jute sack | Polypropylene sheet | Straw | Control |
---|---|---|---|---|
Pona | 0.037 ± 0.012a | 0.042 ± 0.028a | 0.021 ± 0.010a | 0.033 ± 0.019a |
Lariboko | 0.084 ± 0.055a | 0.033 ± 0.017a | 0.047 ± 0.016ab | 0.139 ± 0.042b |
Dente | 0.025 ± 0.008a | 0.029 ± 0.007a | 0.082 ± 0.030b | 0.017 ± 0.007a |
Mutwumudoo | 0.032 ± 0.011a | 0.184 ± 0.059b | 0.037 ± 0.013a | 0.030 ± 0.009a |
Serwah | 0.020 ± 0.011a | 0.015 ± 0.006a | 0.016 ± 0.007a | 0.027 ± 0.008a |
Matches | 0.023 ± 0.007a | 0.049 ± 0.017a | 0.010 ± 0.005a | 0.013 ± 0.006a |
Akaba | 0.030 ± 0.009a | 0.017 ± 0.006a | 0.018 ± 0.006a | 0.026 ± 0.008a |
Means in column followed by the same letter are not significantly different (p = 0.05) from each other.
The temperature and humidity over 7, 14 and 21 days of curing is presented in Figures 5-7. Curing of yam tubers under the three different treatments showed temperature and humidity in the range of 27˚C - 40˚C and 87%
Yam variety | Jute sack | Polypropylene sheet | Straw | Control |
---|---|---|---|---|
Pona | 0.054 ± 0.014a | 0.063 ± 0.027a | 0.033 ± 0.011ab | 0.057 ± 0.024a |
Lariboko | 0.098 ± 0.042a | 0.054 ± 0.019a | 0.066 ± 0.018bc | 0.170 ± 0.036b |
Dente | 0.033 ± 0.008a | 0.049 ± 0.016a | 0.107 ± 0.027c | 0.029 ± 0.010a |
Mutwumudoo | 0.044 ± 0.011a | 0.216 ± 0.048b | 0.050 ± 0.013ab | 0.040 ± 0.010a |
Serwah | 0.025 ± 0.006a | 0.028 ± 0.011a | 0.028 ± 0.009ab | 0.035 ± 0.008a |
Matches | 0.033 ± 0.009a | 0.049 ± 0.012a | 0.018 ± 0.006a | 0.022 ± 0.007a |
Akaba | 0.041 ± 0.010a | 0.024 ± 0.006a | 0.025 ± 0.006ab | 0.031 ± 0.007a |
Means in column followed by the same letter are not significantly different (p = 0.05) from each other.
- 100% rh, respectively. However, the control treatment recorded lower humidity of 60% - 80% rh (Figures 5-7). These ranges are similar to 35˚C - 40˚C and 80% - 90% for temperature and humidity as reported by FAO (1990). In other studies the best temperature and humidity was 26˚C and 92%, respectively for duration of 11 to 15 days in pit curing system [
Similar curing studies on sweetpotatoes were reported by Tortoe et al. [
Climatic conditions have influences on curing as increase temperature and humidity stimulate the healing process. The healing process during curing causes migration of starch cells within 5 - 10 hours to the injured surface. Suberized layer forms beneath the cut surface after 2 - 3 days and there is production of periderm (cork) after approximately 5 days during healing. The increased structural changes results in high rate of metabolic activity which is maintained until healing is completed [
The process of curing is affected by the curing material, duration of curing, climatic conditions and the varieties of yams. The varieties of the yams behaved differently under the different treatments. However, yam variety Serwah, which is a D. rotundata, is the best bet yam variety to cure under jute sack for 7, 14 and 21 days of curing. However, 7 days curing was appropriate for yams. Additionally, the second best bet yam variety curing under straw was Matches, which is a D. alata. Curing processing is therefore appropriate for wounded yams to cure for storage.
The authors are grateful for sponsorship from Grains from Losses of Root and Tubers Crops Project (GRA- TITUDE Project).