This chapter will draw the conclusion of this research, make recommendations, and identify future research opportunities.
6.1 Conclusion
The literature review in Chapter 2 revealed that amadumbe remains an underutilised crop in South Africa, and very little research is available on the post-harvest storage of the tuber. The tuber has health-related benefits due to its high resistant starch and fibre content. The high resistance starch reduces glucose absorption in the small intestine, which is ideal for diabetic people. While higher fibre content helps regulate the blood sugar levels of consumers.
Currently, mechanical refrigeration, evaporative cooler, and underground storage pits are used to control or partially regulate temperature and relative humidity. However, there is limited information on how low-temperature storage and other storage technologies impact the quality of fresh amadumbe corms, flours, and starches. The review also determined that no work has reported the effect of CoolBot® and evaporative cooler storage on the quality of amadumbe corms, flours, and starches. It also showed that amadumbe is processed into flour and starch because of its high moisture content. The review also found that amadumbe can be used in various processing industries, such as producing chips, noodles, cookies, and paste. The possibility of using amadumbe in these processing industries is dependent on the quality parameters such as colour, texture, dry matter content, swelling power, water and oil holding capacities, solubility, and specific gravity. The review showed that the quality of amadumbe varies with the cultivar, geographical location, maturity stage, planting period, storage, and growing conditions. Therefore, the effect of storage conditions on the quality of South African amadumbe cultivars needs to be established.
The main purpose of this study was to determine the optimum storage conditions that result in reduced post-harvest losses of amadumbe. This was achieved by evaluating and analysing the effects of different storage methods such as Ambient (A), Underground pit (U), CoolBot® and evaporative cooler (CBEC), High-Cold (HC), and Low-cold (LC) on the quality properties of
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amadumbe corms, flours, and their starches. This research addresses the challenge of amadumbe being stored in environments that promote post-harvest losses. It also provides the environmental conditions that can be used to design innovative storage facilities that will have reduced post-harvest losses and low capital and operating costs.
The results showed that High-cold storage conditions (9.26 – 11.54℃, 97.57 – 100.00 %) followed by CoolBot® and evaporative cooler storage conditions (12.32 – 15.72℃, 64.75 – 92.76 %) are best storage methods and resulted in a minimal loss in the quality attributes of amadumbe corms, flours, and starches. While Ambient storage conditions (17.30 – 23.59℃, 75.02 – 75.15 %) resulted in a short shelf life and massive loss in quality attributes.
Chapter 3 focused on evaluating the effect of storage conditions on the physiological and mechanical properties of amadumbe corms. Storage conditions, storage period, and the interaction of these factors influenced the physiological and mechanical properties of amadumbe corms. The results revealed that Ambient storage conditions had a short shelf-life and massive quality changes. While High-cold storage followed by CoolBot® and evaporative cooler storage had slow quality changes. Ambient storage had the highest increase in physiological weight loss, hardness, toughness, specific gravity, and dry matter content. It also had the lowest decrease in shear force and cutting energy. While High-cold storage followed by CoolBot® and evaporative cooler storage (12.32 – 15.72℃, 64.75 – 92.76 %) seemed to have a slow quality change
Chapter 4 focused on determining the effect of storage conditions on the quality attributes of flour derived from stored amadumbe corms. The results showed that the physicochemical properties of amadumbe flour are influenced by storage conditions, storage period, and the interaction of these factors. Flour derived from corms stored in High-cold storage followed by CoolBot® and evaporative storage conditions were of better quality than all storage conditions.
In contrast, Ambient storage was the worst storage and showed a massive loss in quality attributes. Flour derived from corms stored in High-cold storage were of better quality. It had minimal reductions in (moisture content, swelling power, solubility, and protein content), minimal increase in (a* and b*), and the highest increase in the (oil holding and water holding capacities). While Ambient storage conditions showed a massive loss in quality attributes. The
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microscopic morphologies of amadumbe flour were irregular and polygonal in shape. The flours exhibited larger densely packed granular particles connected by fibrous materials on day 0. After 70 days of storage, there was a reduction in the size and compactness of the granular particles. The change in flour morphology was less profound in High-cold storage.
Chapter 5 focused on determining the effect of different storage conditions on the quality attributes of starch derived from stored amadumbe corms. The results revealed that storage conditions, storage period, and the interaction of storage conditions and storage period influenced the quality attributes of amadumbe starch. Starch derived from corms stored in Ambient storage conditions showed a massive loss in quality attributes while corms stored in High-cold storage followed by CoolBot® and evaporative storage conditions had minimal losses in quality attributes. High-cold storage resulted in the lowest reduction in starch yield, granular starch size, swelling power, solubility, and L*. It also resulted in the highest increase in water holding capacity and oil holding capacity. While Ambient storage resulted in the highest decrease in starch yield, granular starch size, swelling power, solubility, and L*. The starch morphology study revealed that the granules of amadumbe starch are predominantly irregular and polygonal-shaped. The granules of starch were densely packed and large on day 0. However, after 70 days of storage, the granules become loosely packed and reduced in size.
The loss in granular morphology was less profound in High-cold storage than in all storage conditions due to less degradation.
6.2 Recommendations
Based on the findings of this study, the following recommendations can be made:
1. CoolBot® and evaporative cooler is the second-best storage condition with high relative humidity. The storage chamber can be improved by lowering the temperature below 10℃ and increasing the ventilation.
2. Packaging may be added as a treatment to reduce post-harvest losses.
3. Pre-treatment with chemicals such as sodium chloride, ethanol, and sodium hypochlorite may be added as a treatment to reduce microbial spoilage.
4. The tubers that are stored must not only be of similar weight but also similar sizes.