Flour power: UP researchers boost nutritive benefits of sweet potato with novel drying technology

Researchers at the University of Pretoria (UP) have found a way to make orange-fleshed sweet potato last longer in an effort to benefit from this smart crop and address micronutrient deficiencies among young children and pregnant women.

As part of InnoFoodAfrica, a multinational, cross-continental project that aims to enhance food and nutrition security in Africa, UP researchers have discovered that they can leverage the health benefits of the vegetable by making it into flour.

Identified by their orange pulp, orange sweet potatoes contain beta-carotene, which is converted into vitamin A in the body. However, these potatoes have a short shelf life of only two to three weeks – but by making flour out of them, the UP team has found a way to expand the number of ways orange-fleshed sweet potatoes can be used.

PhD Food Sciences candidate Daddy Kgonothi has been central to the development of this flour, and has been working under the guidance of Professor Naushad Emmambux and Dr Nwabisa Mehlomakulu of the Department of Consumer and Food Sciences at UP.

“We dried the sweet potatoes and made it into flour by way of various drying methods, which we compared with the freeze-drying method,” Kgonothi explains. “Since it is a very perishable product, drying and milling the potatoes into flour is one of the best methods one can apply – flours can have a shelf life of at least a year.”

The process began with the team sourcing sweet potatoes from a commercial farm in North West, following a four- to six-month growth period, from planting to harvesting.

“It is a seasonal crop and, in South Africa, it is planted around November or December,” Kgonothi says. “The harvest takes place between March and June or July.”

The team then set about testing different drying methods.

“The whole process took about three weeks, which included testing the drying process and doing the actual drying and milling,” Kgonothi says. “We used microwaves, infrared applications and convection ovens to dry the potatoes, and discovered that when we combined microwave drying with infrared drying, the process was much faster. There was also a higher retention of beta-carotene.”

With vitamin A deficiency being one of the leading causes of micronutrient deficiencies in children up to the age of six and among pregnant women, flour made from orange-fleshed sweet potato could offer a helpful solution. Also, because the novel drying technology (of combining microwave and infrared applications) results in a higher retention of beta-carotene, the orange-fleshed sweet potato flour that is produced will be a particularly strong source of vitamin A.

“The flour is also a good source of dietary fibre, and of minerals such as iron, zinc and phosphorus,” Kgonothi says.

“Orange-fleshed sweet potatoes can be used in several ways,” he adds. “One way is to boil it as a root and consume it, or to make fried chips from it. As flour, the application of orange-fleshed sweet potatoes is more diverse: the flour can be used in baked products like fortified bread or biscuits; as stabilisers in soups; as a thickening agent, due to its rich dietary fibre; and because of its low viscosity, it can be used to make baby food – it is easy for infants to swallow.”

Click on the gallery in the sidebar to see how the flour is milled

To learn more about the Innofood Africa project, please visit: https://innofoodafrica.eu/

Prof Mohammad Naushad Emmambux

September 20, 2022

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  • Professor Mohammad Naushad Emmambux

    Professor Mohammad Naushad Emmambux completed his undergraduate studies at the University of Mauritius and his postgraduate studies at the University of Pretoria (UP). He has been with UP for 22 years, and has been doing research for 16 years.

    “UP is a globally recognised, research-intensive university that provides a platform for growth, independent thinking and for making a difference to society,” he says.

    Prof Emmambux’s research is centred on the following:

    • Chemistry, nutrition and technology of plant food biopolymers (starch, protein and non-starch polysaccharides) in food and non-food systems;
    • Green/energy-efficient technologies such as extrusion, microwave and infrared for quick cooking, instant and convenient nutrient-dense plant-based foods
    • Food structure (micro, meso, nano and molecular) and rheology interface in food systems and processing

    His research contributes to the betterment of the world because it falls within the area of food and nutrition security. It addresses several Sustainable Development Goals (sDGs) including SDG 2: Zero Hunger and SDG 3: Good Health and Well-being.

    Prof Emmambux leads the food biopolymer research group in the Department of Consumer and Food Sciences; co-leads the technological innovation programme at the Department of Science and Innovation (DSF)/National Research Foundation (NRF) Centre of Excellence in Food Security; and leads the EU-funded InnoFoodAfrica project at UP. The two latter projects are cross-faculty initiatives that involve UP’s Faculties of Humanities, Health Sciences and Engineering.

    Over the past 18 months, Prof Emmambux and his research team have been working on reducing the glycaemic index (GI) of maize meal.  

    “We have found that complexation of starch with lipids as well as heat-moisture treatment increased the resistant starch content in maize meal porridge,” he explains. “The latter had a lower GI and the resistant starch comprising of amylose lipid complexes showed good prebiotic effects as it promoted the growth of good microbes and produced beneficial free fatty acids. We have a patent for manufacturing starch microspheres that are stable under mechanical stress. The starch microsphere can be used to mimic fat globules in food systems. Thus, we can reduce food calories by replacing fat.”

    The team has also shown that household-level technologies such as a microwave can change the oral processing properties of food to accommodate babies from the age of six to 24 months when complementary foods are introduced. “This will help to increase the nutrient density of complementary foods,” Prof Emmambux says.

    A recent highlight for the professor was presenting the EU-sponsored project InnoFoodAfrica at the New European Bauhaus Festival in June 2022.

    The research team has started two new projects: making protein nanofibers, which will be used as human tissue scaffolding, and making use of green chemistry to modify proteins from indigenous African plants; these proteins can be used in gluten-free alternatives.

    Prof Emmambux says his research matters because he and his research team are pushing scientific boundaries in the field of food science and technology. “We are making a difference by solving African and global problems related to food and nutrition security.”

    While no specific person has inspired him in his research effort, he says, “all my teachers, lecturers and supervisors are my role models and they have inspired me to become a good scientist”.

    He hopes to mentor the next generation of scientists who will help to create a better world for the future. His advice to school learners or undergraduates who are interested in his field is this: “If you have a curious mind and want to make a difference in the world, join the field of food science.”

    In his spare time, he meditates, spends time in nature and travels.

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  • Daddy Kgonothi

    Daddy Kgonothi is a PhD candidate at the University of Pretoria in Food Science. His master’s research study focused on the use of dehydrating processing technologies such as microwave, infrared and ovens and specifically the effects of these novel drying technologies on the physicochemical and nutritional properties of orange-fleshed sweet potato, and particularly the the β-carotene content. His PhD research is focused on exploring other novel processing technologies and looking at their effect on the biopolymer properties such as protein. His interest is to use these processing technologies to modify the properties of biopolymers and diversify their application in the food industry. He is also interested in exploring environmentally friendly, cost effective and faster processing technologies.

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