811 35 Sweetpotato Production, Processing, and Nutritional Quality V. D. Truong1, R. Y. Avula2, K. V. Pecota3, and G. C. Yencho3 1 USDA‐ARS Food Science Research Unit, Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, USA 2 Department of Food Science and Technology, University of Georgia, Athens, USA 3 Department of Horticultural Science, North Carolina State University, Raleigh, USA Introduction dry matter content (18–25%), high β‐carotene level, sweet and moist‐texture after cooking. Sweetpotato, Ipomoea batatas L. (Lam.), is an This sweetpotato type is imprecisely called important economic crop in many countries. In “yam,” which is not the true tropical yam of terms of annual production, sweetpotato ranks Dioscorea species. Historically, African as the fifth most important food crop in the Americans in Louisiana referred this moist‐ tropics and the seventh in the world food pro- sweetpotato as “nyami” because it reminded duction after wheat, rice, maize, potato, barley, them of the starchy tuber of that name in Africa. and cassava (FAO 2016). Sweetpotato fulfills a The Senagalese word “nyami” was eventually number of basic roles in the global food system, shortened to the trademark “yam” popular in all of which have fundamental implications for the United States. Commercial packages with meeting food requirements, reducing poverty, “yam” labels are required by the US Department and increasing food security (El‐Sheikha and of Agriculture to have the word “sweetpotato” in Ray 2017). the label to avoid confusion to the consumers Sweetpotato roots have high nutritional value (Estes 2009). and sensory versatility in terms of taste, texture, Depending on the flesh color, sweetpotatoes and flesh color (white, cream, yellow, orange, contain high levels of β‐carotene, anthocyanins, purple). The varieties with high dry matter phenolics, dietary fiber, vitamins, minerals, and (>25%), white‐cream flesh color, and mealy firm other bioactive compounds. The β‐carotene in texture after cooking are preferred by the con- orange‐fleshed sweetpotatoes can play a signifi- sumers in the tropics. These varieties are known cant role as a viable long‐term food‐based as tropical sweetpotato (e.g., “bianito,” “batiste,” strategy for combating vitamin A deficiency in or “camote”). The purple‐fleshed sweetpotato the world. Studies in Africa demonstrated that varieties with attractive color and high antho- increased consumption of orange‐fleshed cyanin content are the specialty type in Asia. In sweetpotatoes improved the vitamin A status of the United States, the commercially popular children, pregnant women, and lactating type is the orange‐fleshed sweetpotato with low mothers (Low et al. 2007; Hotz et al. 2012; Handbook of Vegetables and Vegetable Processing, Volume II, Second Edition. Edited by Muhammad Siddiq and Mark A. Uebersax. © 2018 John Wiley & Sons Ltd. Published 2018 by John Wiley & Sons Ltd. 812 Sweetpotato Production, Processing, and Nutritional Quality Van Jaarsveld et al. 2005). Further, polyphenolics about 21%, while the Americas (North, Central, from purple‐fleshed sweetpotatoes exhibited and South) account for about 3.6%. China was diverse biological activities, including protec- the leading producer of sweetpotatoes, with tive antioxidant, anti‐inflammatory, anticancer, 71.54 MMT or about 67% of the global produc- antidiabetic and hepatoprotective activity tion, followed by Nigeria (3.78 MMT), Tanzania effects (Hu et al. 2016; Lim et al. 2013). (3.5 MMT), Ethiopia (2.7 MMT), and Sweetpotato has a strong potential to contribute Mozambique (2.4 MMT). The United States to better nutritional quality of our diets around was the tenth largest producer, with 1.34 MMT the world. This chapter provides a contempo- production. Only two countries in Europe, rary review of production, quality, and process- Portugal and Spain, grow sweetpotatoes, with ing aspects of sweetpotatoes. 22,591 and 13,550 metric tons produced in 2014. In comparison to other major staple food crops, sweetpotatoes have good adaptability to Production and Consumption marginal growing conditions, short production cycle, and high yield potential. The average Sweetpotato has wide production geography, world yield of sweetpotatoes is about 14 tons from 40° north to 32° south latitude of the globe, per hectare. Under subsistence conditions in and it is cultivated in 114 countries. The world many areas of the tropics, the average sweetpo- total production of sweetpotatoes was 106.60 tato yield is about 6 metric tons/hectare, far million metric tons (MMT) in 2014. Since the below the 20–26 metric tons/hectare obtained mid‐1990s, global production has ranged from a in China, Japan, and the United States, where low of 101.28 MMT in 2007 to a high of 147.17 improved varieties, fertilizer applications, and MMT in 1999 (Figure 35.1). In 2014, about cultural managements have been introduced. three‐fourth of the global production was from The per capita consumption is highest in Asia and Pacific Islands, followed by Africa with places where sweetpotatoes are consumed as a World China Americas Africa 150 125 106.6 tons 100 71.5 75 Million metric 50 22.6 25 3.8 0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Figure 35.1 World and regional sweetpotato production for 1994–2014. Source: FAO (2016). Btn and Physiolog 813 staple food, e.g., Papua New Guinea at 550 kg analyses conducted by Huang and Sun (2000) per person per year, the Solomon Islands at 160 kg, and Zhang et al. (2000) also places Central Burundi and Rwanda at 130 kg, and Uganda at America as the region with the most genetic 85 kg. The average annual per capita consump- diversity and probable origin (Huang and Sun tion of sweetpotatoes is estimated at 18 kg in 2000; Zhang et al. 2000). Remains of dried Asia, 9 kg in Africa, 5 kg in Latin America. sweetpotato roots found in Peru have been Between 2000 and 2014, sweetpotato consump- radiocarbon dated back to 8,000–10,000 years tion in the United States increased nearly 80%, old, though it is unknown if these were col- from 1.9 kg to 3.4 kg per capita (FAO 2015; lected from the wild or were domesticated Johnson et al. 2015). Sweetpotato consumption (Engel 1970). Regardless of the center of origin, has been greatly enhanced by the wide spread sweetpotato was widely established in tropical commercial availability of frozen “French‐fried” regions of the new world around 2500 b.c. sweetpotatoes. To accommodate this recent (Austin 1988). It was established in Polynesia, growth trend, increased modern processing prior to European arrival (Roullier, et al. 2013b). capacity has been built within the southern US Europeans in the 1500s spread the sweetpotato sweetpotato growing regions. to Africa and India, with it arriving in China prior to 1600. Secondary centers of diversity include New Guinea, the Philippines, and parts Classification and Origin of Africa (Bohac et al. 1995; Roullier, et al. 2013a, b). The sweetpotato (I. batatas L.) is a dicotyledon- ous plant belonging to the morning glory or Convolvulaceae family. It is a new world crop, Botany and Physiology though there is still some confusion that exists regarding its origin, and primary and secondary The sweetpotato is a herbaceous perennial that centers of diversity. Roullier et al. (2013a,b) and is grown as an annual by stem cuttings or plant Grüneberg et al. (2015) have published thor- sprouts from storage roots (Figure 35.2). It has a ough reviews of this topic. In brief, using data predominately prostrate growth habit typically from morphology, ecology, and cytology, Austin with 1–5 m vines that grow horizontally on (1988) has postulated that cultivated sweetpo- the ground. The plant can be grouped into three tatoes originated somewhere in the region parts: between the Yucatan Peninsula of Mexico and 1) The leaves act as the photosynthetic canopy. the mouth of the Orinoco river in northeastern 2) The stems transport energy to the roots and Venezuela. Recent studies conducted by transport water and minerals from the roots. Roullier, et al. (2013 a, b) incorporating chloro- 3) The root system absorbs water and nutrients plast DNA and molecular phylogeny analyses from the soil, anchors the plant, and can act confirm this hypothesis. They also suggest that as a storage site for energy via the develop- I. batatas most likely evolved from at least two ment of fleshy storage roots. distinct autopolyploidization events in wild populations of a single progenitor species most Sweetpotatoes possess three types of roots: likely I. trifida. Secondary contact between storage, fibrous, and pencil (Kays 1985a; Firon sweetpotatoes domesticated in Central America et al. 2009). Young adventitious roots develop and in South America, from differentiated wild out of both the nodal and the internodal regions I. batatas or I. trifida populations, could have of an underground stem portion of a vine led to further introgression. Molecular marker cutting. Roots from the internodal regions 814 Sweetpotato Production, Processing, and Nutritional Quality Sweetpotato plant Sweetpotato harvesting Harvested sweetpotatoes Figure 35.2 Sweetpotato plant, harvesting and harvested tubers in the market. Source (From left): USDA Plants Database, NC State Extension, USDA‐AMS. normally become fibrous roots and have a and 25°C promote storage root formation and tetrarch arrangement of their primary vascular growth, while temperatures above 25°C sup- tissue. Roots from the nodes are pentarch or press storage root formation and favor shoot hexarch and have the potential to develop into growth. Night air temperatures lower than 15°C enlarged storage roots; however, unfavorable suppress storage root formation, growth, and conditions can cause many or all of these to yield. Air temperatures >30°C reduce storage develop into primary fibrous roots or to lignify root formation and growth, and promote shoot and produce pencil roots.