Cooking away the vitamins or baking in the goodness? How nutrients can survive food preparation

Plant breeders have strived for years to put nutrients, especially pro-vitamin A, into cassava and sweetpotato. Now the challenge is to follow the new varieties into the kitchen, to make sure that cooking and other processing methods retain the valuable nutrients, and that the prepared food is safe and nutritious.

New varieties of RTB crops, especially cassava and sweetpotato, have been bred to be richer in pro-vitamin A. The RTB Program is now working to improve the foods made from these varieties, to make sure that they retain the nutrients that have been painstakingly bred into them. CIRAD, Natural Resource Institute (NRI), IITA and CIP have teamed up to address the challenge in collaboration with the CGIAR Research Program on Agriculture for Nutrition and Health (which includes the HarvestPlus project).

New varieties of yellow, pro-vitamin A- rich cassava are now being bred and disseminated in sub-Saharan Africa. However, several studies published in 2018 conclude that yellow cassava often loses most of its carotenoids during processing.

Making sweetpotato puree at Organi Ltd in Kenya. J. Low/CIP

Victor Taleon with other colleagues at HarvestPlus and Tawanda Muzhingi, FP4 leader, found that when yellow cassava is boiled, it retains almost all its pro-vitamin A: 93–97%. On the other hand, food processing removes most of the vitamin A. Fufu (a thick, fermented paste eaten as a staple) loses all but 1–3%. Chikwangue, a steamed cassava bread, keeps just 4–18% of the vitamin.

Toluwalope Eyinla and colleagues from IITA and the University of Ibadan studied the retention of beta- carotene (pro-vitamin A) in yellow cassava after sun drying, oven drying and flash drying. When making cassava chips and milled flour, over 80% of the beta- carotene is lost in sun drying, over 90% in oven drying and 95% and more in flash drying. Likewise when the cassava is made into flour and then into cooked dough, it retains only 1–2% of the beta-carotene.

Different cassava varieties react to cooking in unique ways. At CIAT, food scientist Ingrid Aragón and colleagues measured the pro-vitamin A in unfermented flour, fermented flour and gari (a dried cassava grit). The fermented flour and gari retained the most provitamin A (4–15%); however, cooking and fermenting change the pro-vitamin A content of each cassava variety in different degrees. Keeping vitamins depends on the processing method and the variety.

On the bright side, cassava has other properties that make it suitable for food manufacturing. A literature review by Oluwatoyin Ayetigbo of the University of Hohenheim, and colleagues at IITA found that yellow varieties tend to be lower in starch content and dry matter. However, the starch from white and yellow cassava varieties is similar in morphology, thermal, crystallinity and flow properties, so yellow and white cassava are equally suitable for making starch, flour and the products derived from them (like bread).

In another encouraging development at CIAT in Colombia, Luis Londoño found that up to 81% of the pro-vitamin A was retained when cassava was made into casabe, a flat bread that has been made from cassava since pre-Colombian times in the Amazon and Caribbean basins. Recall that boiled cassava, another traditional recipe from the Americas, also retains the vitamins.

As biofortified crop varieties are taken up by food processors, food safety is becoming an important issue. This is the case with sweetpotato, as RTB researchers are examining it critically, to create awareness and to support our partners as they adopt best practices.

Informal and formal food processors are now processing OFSP into puree used to make breads and fried products in Kenya, Malawi and Uganda. CIP scientists and colleagues at the University of Nairobi found that OFSP food processors in Kenya were not complying with good manufacturing practices. Microbial counts on food equipment as well as on the hands of personnel and in packaged OFSP puree were above legal limits. Steaming kills germs in cooked roots, but then the puree is recontaminated in the bakeries. Food handlers need training to produce safe, healthy OFSP puree. A regional workshop on managing food safety by small- scale root, tuber, and banana processors in Africa was conducted by CIP in collaboration with NRI, University of Illinois, UNICEF, FAO and Biosciences eastern and central Africa (BecA) ILRI. “As Africa is urbanizing rapidly, every year more people buy their food at the store. It is up to food researchers and manufacturers to make sure that the food stays healthy and wholesome at every step from the field to the plate,” says Muzhingi.

In the future, it will not be enough to simply breed new cassava varieties that are rich in pro- vitamin A, but to empower small and medium– scale processors to produce food products that are safe to eat and retain their nutrients, while pleasing local palates.