Abstract
The aim of this study was to determine the most suitable time for harvesting marama (Tylosema esculentum) root as an alternative source of novel starch by evaluating the quality of marama root and its starch during growth periods of 12 months. The effects of time on the proximate analysis of marama roots as well as the thermal properties, size and physicochemical properties of the starch were also investigated. Marama was planted in September and total starch of marama roots on both as is and dry bases increased significantly (p<0.05) from 24 g/kg to 115 g/kg and 259 g/kg to 601 g/kg, respectively, from 2 to 12 months after planting. Amylose content significantly (p<0.05) decreased from about 50.7% to 21.4% of the starch for the same time period. The size of marama root starch granules significantly (p<0.05) increased from 8.6 μm to 15.1 μm. The marama root harvested after 2 months had the highest crude protein content (33.6%). In terms of thermal properties, the peak temperature decreased significantly with time (ranging from 93.0 °C to 73.4 °C), while the ΔH increased significantly with time. The findings indicate that marama should be planted early in summer and harvested between 4 and 8 months for optimal starch before winter.
 Significance:
 
 Proximate and starch characteristics of marama storage roots differ significantly with time of harvest. This suggests that desired functional properties can be achieved by controlling growth time. The marama root harvested at 4 months is highly nutritious, it has high protein content, starch that is high in amylose and is suitable for consumption as a fresh root vegetable in arid to semi-arid regions where few conventional crops are able to survive. Marama root is a climate smart crop and it could potentially contribute to food security in arid regions. The results obtained in this study suggest that the optimum time for harvesting marama as a root vegetable is at 4 months while the optimum time for harvesting marama for its starch is at 8 months. Younger roots have higher amylose, and hence higher gelatinisation temperatures, and therefore may be more suitable to be used as a coating during frying.
Highlights
Starch is the most common carbon reserve stored in plants; it is of great significance for both food and non-food industrial uses.[1]
Our findings suggest that the amylose content decreases as the total starch content increases during storage root development, which is an indication of a delay in amylopectin synthesis as compared to amylose
The chemical composition of marama storage root was affected by the age of the root
Summary
Starch is the most common carbon reserve stored in plants; it is of great significance for both food and non-food industrial uses.[1]. Starch is a major source of energy in the human diet. It accounts for approximately 50% of calorie intake in developed countries and 90% of calorie intake in developing countries.[4] Current sources of commercially available starch are a restricted range of crops, the most important being maize, potato, wheat and cassava with smaller amounts from rice, sorghum, sweet potato, arrowroot, sago and mung beans.[5] The main crops in sub-Saharan Africa are maize, rice, pearl millet, sorghum, cassava, yam and sweet potatoes.[6] there is no commercialised starch from indigenous staple crops in Namibia and they are underutilised. The underutilised crops may provide starches or flours with novel physicochemical properties
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