Sweet potato: origin and production

CHAPTER 2

Sweet potato: origin and production Tai-Hua Mu1 and Peng-Gao Li1,2,3 1

Institute of Food Science and Technology, Chinese Academy of Agricultural Sciences; Key Laboratory of Agro-Products Processing, Ministry of Agriculture and Rural Affairs, Beijing, People’s Republic of China 2 School of Public Health, Capital Medical University, Beijing, People’s Republic of China 3 Beijing Key Laboratory of Environmental Toxicology, Capital Medical University, Beijing, People’s Republic of China

Origin Botanical characteristics of sweet potatoes The sweet potato (Ipomoea batatas [L.] Lam) is a dicotyledonous plant that belongs to the family Convolvulaceae. It is an herbaceous perennial vine that has white and purple sympetalous flowers, large nutritious storage roots, and alternate heart-shaped or palmately lobed leaves. The large, starchy, sweet-tasting tuberous roots are by far the most important part of the plant. It is a storage root, not a tuber or thickened stem like the potato (Solanum tuberosum). It is also different from yams. They are not related to each other despite a physical and compositional similarity. The roots of sweet potatoes are long and tapered, with a smooth skin whose color ranges between yellow, orange, red, brown, purple, and beige. Its flesh ranges from beige to white, red, pink, violet, yellow, orange, and purple (Fig. 2.1). The storage root contains a large amount of starch that can be turned into energy in the human body so the root can be consumed as a staple food instead of other staple food crops such as rice, wheat, and corn. The roots, leaves, and stems of sweet potatoes are all edible and nutritious, and thus the cultivation of the sweet potato can play a vital role in ensuring the food security of many developing countries. Meanwhile the nutritional needs of the people in these countries can also be met by proper consumption of the whole plant. Each 100 g of the fresh root provides an energetic value of 85 kcal, which is greater than that for potatoes but less than for cereals. The root also provides a small amount of protein and relatively higher amounts of vitamins and minerals than cereals. Some varieties of sweet potatoes contain a very high amount Sweet Potato DOI: https://doi.org/10.1016/B978-0-12-813637-9.00002-8

© 2019 Elsevier Inc. All rights reserved.

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Figure 2.1 Sweet potato with different flesh color.

of β-carotene that can be converted into vitamin A in the human body, thus the cultivation and consumption of these varieties have been recommended as an applicable approach to prevent the epidemic of vitamin A deficiency that is widespread in many developing countries. The young leaves, shoots, and vine of the plant are a good source of dietary fiber, as well as of many vitamins, minerals, and antioxidant molecules, which makes the sweet potato an excellent vegetable. Nowadays, to fully utilize the value of the plant, the young leaves have been made into teas and powder drinks for human consumption.

The origin and the dissemination of sweet potatoes around the world As to the origin of sweet potatoes, it is now widely accepted that the plant originated from the tropical regions in the South and Central America. Although it is now mainly produced in China, the plant is not native to China. In fact the plant was introduced to China only about 631 years ago. According to most of the sources, the origin and domestication of sweet potatoes are thought to be in either Central America or South America (Austin, 1988). In Central America, sweet potatoes were domesticated at least 5000 years ago (Bovell-Benjamin, 2014; Nishiyama, 2006). The plant was then brought to other tropical and subtropical regions around the world and became popular in the islands of the Pacific Ocean (Bovell-Benjamin, 2014; Nishiyama, 2006). Archeologists have found prehistoric remnants of sweet potatoes in Polynesia from about CE 1000 1100 according to radiocarbon dating. They have hypothesized that ancient Polynesians may have interacted with people on the west coast of South America and brought sweet potatoes to the islands of the Pacific Ocean long before the Europeans set foot on the continent.

Sweet potato: origin and production

7

By analyzing the DNA of 1245 sweet potato varieties from Asia and the Americas, researchers have proven that the root vegetable had made it all the way from the Andes to Polynesia nearly 400 years before Christopher Columbus landed in the New World in 1492 (Roullier et al., 2013). Polynesian and European voyagers then spread sweet potatoes rapidly to other parts of the world. It was first diffused throughout Polynesia, in already populated islands such as Hawaii, Easter Island, and some other islands of eastern Polynesia, and then into New Zealand around CE 1150 1250. During the 16th century, Spanish and Portuguese traders and travelers introduced it into the Philippines and Indonesia. From these points, local traders, European travelers, or both, may have distributed sweet potatoes into the rest of the Asia. It was introduced from the Philippines as a food crop to Fujian Province of China in about 1387, to Japan in about 1735 (Takegoshi, 2003) and to Korea in about 1764 (Kim, 2012). Because its planting material can be multiplied greatly from a very few roots and due to its high adaptability, sweet potatoes spread quickly throughout Asia, Latin America, and Africa during the 17th and 18th centuries. Now the sweet potato is widely cultivated throughout tropical and warm temperate regions, wherever there is sufficient water to support its growth (O’Hair et al., 1990). Notably the introduction and cultivation of sweet potatoes in China in the late Ming dynasty greatly alleviated the food shortage at that time and prompted the central government of the following Qing dynasty to enlarge the sweet potato cultivation area in China and spread it to other farther north regions in Asia. Nowadays, sweet potatoes are planted in almost every province of China, even in the coldest Heilongjiang Province in the far north of China.

Production Sweet potatoes are now widely cultivated all over the world wherever the plant can survive and the sweet potato has become one of the most important food crops in terms of human consumption. As a high-yield tuberous crop, the plant can be cultivated in poor soil and water conditions, such as in sub-Saharan Africa, parts of Asia, and the Pacific Islands. With the advancement of agronomic technology, more and more varieties of sweet potatoes have been bred to meet the needs of either the consumer or the food processing industry.

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Sweet Potato

Worldwide production According to the statistics from the Food and Agriculture Organization of the United Nations (FAO), the world’s total production of sweet potatoes in 2016 was 105 million tons. In comparison to other crops that can be consumed as a staple food, sweet potatoes are the sixth largest crop, ranking just behind corn (1060 million tons), wheat (749 million tons), rice (741 million tons), potato (376 million tons), and cassava (277 million tons). Although the cultivation of sweet potatoes is widespread around the world, production is not evenly distributed around the world. China is the biggest producer of sweet potatoes in the world. In 2016 China alone produced 71 million tons of sweet potatoes, accounting for 68% of the world’s total production. Meanwhile a large number of the varieties of the plant have been cultivated in China. Main cultivation regions and countries Nowadays, more than 100 million tons of sweet potatoes are produced globally each year, approximately 95% of which are grown in developing countries. Asia is today the largest sweet potato-producing region in the world. More than 78 million tons were produced in Asia in 2016. Africa is the second largest producer, producing 21 million tons in 2016. The Americas, the original home of sweet potatoes, grows less than 5% of the world’s supply. Europe has only a very small sweet potato production, mainly in Portugal. To date the ranking of the regions and continents in terms of their production of sweet potatoes is very stable. Asia is far ahead of other continents, followed by Africa and South America. As shown in Table 2.1 Table 2.1 Annual production of sweet potatoes in different continents, 2014 16 (million tons). Continent

2014

2015

2016

Asia Africa South America and Caribbean North and Central America Oceania Europe Total

79.14 (75.67%) 20.67 (19.77%) 2.44 (2.33%)

78.96 (76.01%) 20.01 (19.26%) 2.49 (2.40%)

78.60 (74.72%) 21.32 (20.27%) 2.81 (2.67%)

1.39 (1.33%)

1.48 (1.42%)

1.51 (1.43%)

0.88 (0.84%) 0.05 (0.05%) 104.57 (100%)

0.90 (0.86%) 0.05 (0.05%) 103.88 (100%)

0.91 (0.86%) 0.05 (0.05%) 105.19 (100%)

Source: Data from FAOSTAT Database (http://www.fao.org).

Sweet potato: origin and production

9

the world’s total production of sweet potatoes was 105.19, 103.88, and 104.57 million tons in the years 2014 16, respectively. Asia accounts for 74.72% of global production in 2016, followed by Africa (20.27%), South America and the Caribbean (2.67%), and North and Central America (1.43%). Europe and Oceania have only a very small sweet potato production, contributing only 0.86% and 0.05% of the world’s total in 2016, respectively. Thus it is obvious that the cultivation of sweet potatoes is not widespread in developed countries in spite of the fact that they have far more advanced agricultural technologies than most of the countries in Asia and Africa. In 2016 the total output of sweet potatoes in Asia was 78.60 million tons. Table 2.2 shows that 67.30% of the world’s total production was contributed by China, which produced 70.79 million tons in 2016. It means that practically 90.07% of the annual production in Asia was contributed by China. The second largest producer is Nigeria, which accounts for 3.72% of the global output in 2016. The output from the United Republic of Tanzania is near to that of Nigeria, contributing 3.63% of the world’s total output in 2016. The shares from other countries were all lower than 3%. In Asia there are 24 countries that plant sweet potatoes. Indonesia is behind China but head of India in the ranking, with the production of 2.27 million tons (2.16% of the worldwide output) in 2016. The output from India (1.47 million tons) is close to that of the United States, which is the only American country that ranks among the top 10 sweet potato producers in the world. The United States produced 1.43 million tons in 2016, accounting for 1.36% of the world total output. In Europe, there are only four countries that produce sweet potatoes. The leading European country in sweet potato production is Portugal, which produced 22,901 tons in 2016, followed by Spain (13,523 tons), Italy (12,456 tons), and Greece (3305 tons). Reasons for the imbalance in sweet potato production among different regions and countries The differences in the amounts of sweet potato produced in different regions and countries are caused by many factors. First, in China’s history the central government has played an important role in propagating and encouraging the cultivation of sweet potatoes in the vast land of this big country. As a result it soon became the world’s largest grower. Second, the demand for the production of sweet potatoes is closely related to its

Table 2.2 Top 20 countries in terms of the annual production (million tons) of sweet potatoes, 2014 16. 2014

2015

2016

Country

Value

%

Country

Value

%

Country

Value

%

China Nigeria The United Republic of Tanzania Ethiopia Indonesia Angola Uganda Vietnam The United States Madagascar India Rwanda Japan Kenya Papua New Guinea Burundi Brazil Philippines Cuba Haiti World total

71.54 3.75 3.50

68.41 3.59 3.35

71.36 3.83 3.45

68.69 3.69 3.33

67.3 3.72 3.63

2.58 2.28 1.84 1.74 1.34 1.28 1.09 1.04 0.9 0.85 0.73 0.64 0.64 0.5 0.5 0.49 0.49 100

2.30 2.05 1.93 1.51 1.41 1.34 1.23 1.23 1.06 0.93 0.81 0.69 0.60 0.58 0.54 0.51 0.49 103.88

2.21 1.97 1.86 1.46 1.35 1.29 1.19 1.18 1.02 0.9 0.78 0.66 0.57 0.56 0.52 0.49 0.48 100

China Nigeria The United Republic of Tanzania Indonesia Uganda Ethiopia Angola India The United States Vietnam Madagascar Rwanda Japan Mozambique Burundi Papua New Guinea Kenya Brazil Haiti Cuba

70.79 3.92 3.82

2.70 2.38 1.93 1.82 1.40 1.34 1.14 1.09 0.94 0.89 0.76 0.67 0.66 0.53 0.52 0.51 0.51 104.57

China Nigeria The United Republic of Tanzania Indonesia Uganda Angola Ethiopia The United States Vietnam Kenya India Madagascar Rwanda Japan Papua New Guinea Brazil Burundi Philippines Cuba Haiti

2.27 2.13 1.94 1.83 1.47 1.43 1.27 1.11 0.92 0.86 0.73 0.73 0.70 0.70 0.67 0.65 0.59 105.19

2.16 2.02 1.84 1.74 1.4 1.36 1.21 1.06 0.87 0.82 0.69 0.69 0.67 0.66 0.64 0.62 0.57 100

Source: Data from FAOSTAT Database (http://www.fao.org).

Sweet potato: origin and production

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uses. In many countries where the annual production is small, sweet potatoes are mainly consumed as a vegetable, but in other regions, such as in some tropical areas, especially in Africa, almost all sweet potatoes are consumed as a staple food. As a result, Africa soon became the second largest grower and consumer of sweet potatoes. Third, the cultivation of sweet potatoes is closely related to the final uses. Chinese has developed a great number of uses for this starchy food crop. In particular, the invention of the starch vermicelli (“fentiao” in Chinese) has greatly increased the demand for this crop. Vermicelli made from sweet potatoes is widely welcomed in many kinds of Chinese cuisines, such as hot pots, stewed vegetables, and convenience fast food. The unique flavor, taste, and physicochemical properties make sweet potatoes irreplaceable by other starch materials such as corn, potato, and cassava starch. As a result, although sweet potatoes are no longer used as a staple food in China, there is still a huge market. Nowadays, about half of the total production of sweet potatoes is used for starch extraction, the remainder is used for fresh consumption, animal feed, or the manufacturing of other products. These factors keep the demand for the crop at a stable high level. There are several cultural factors that also influence the cultivation and production of sweet potatoes. It is not only in poor countries or regions that sweet potatoes are considered as a staple food. This also holds true for many other regions around the world in hard times when there is a crop failure of other staple foods, because sweet potatoes are productive and can be grown in poor soils with little fertilizer. Thus since they are a reliable crop even in cases of crop failures of other staple foods, sweet potatoes are often associated with hard times in the minds of some people. When these people became affluent enough to change their diet, they tend to abandon sweet potatoes and turn to other foods. As a result the cultivation area of the plant may diminish in these areas. The good news is that sweet potatoes are so delicious that they soon gain the favor of the young generation and sweet potatoes become popular again after a period of time. In the meantime, with the advancement of the food processing technology, more and more industrial uses of sweet potatoes have been found, ushering in a new era of development and planting of this highyield crop. Importation and exportation of sweet potatoes In 2016, there were 117 countries that imported a total amount of 306,056 tons of sweet potatoes from other countries. As shown in

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Table 2.3, the leading countries in the importation of sweet potatoes are the United Kingdom (66,128 tons), followed by Canada (50,619 tons), the Netherlands (32,096 tons), and Japan (21,710 tons), clearly demonstrating that sweet potatoes are loved by people in developed countries too. Many of the countries in the importing countries’ list, including the United Kingdom, Canada, the Netherlands, France, and Germany, do not plant sweet potatoes themselves at all, so all of their needs are met by importation. Japan is an exception as it produced 942,300 tons of sweet potatoes itself. However, production could not meet its own demands and as a result it imported 21,710 tons from other countries. In 2013 the worldwide sweet potatoes imports amounted to US$ 252.11 million. As shown in Fig. 2.2, in the past 10 years before 2013, the amount was increasing continuously from US$ 85.13 million in 2004. After 2012 the growth rate seems to have increased (from US$ 210.15 million to US$ 252.11 million) and the figure may progressively increase in the future. According to the data from the FAOSTAT database, in 2013 the worldwide exports of sweet potatoes totaled 256,988 tons. Interestingly, as shown in Table 2.4, China is not the largest exporter. The leading country in the exportation of sweet potatoes is the United States (128,231 tons), followed by China (19,870 tons) and Egypt (15,651 tons). The reason may be due to that China does not export much of sweet potato, and some other countries do not have much to export. This also demonstrates that in countries that have a relatively large annual production, such as China and Nigeria, sweet potatoes are mainly for domestic consumption and the domestic needs in these countries are very stable. This also implies that the planting of sweet potatoes is very important for these countries. Whereas for many other countries, such as the countries in Europe, the cultivation of the sweet potato is barely significant compared with that of the potato, which is considered an integral part of the daily diet. In Europe, sweet potatoes are mainly consumed as a vegetable or confectionery. Sporadic importation in small amounts alone can meet their needs. In the last few years importation has undergone a gradual increase thanks to the demand in the industrial sector (confectionery). Trend in worldwide production of sweet potatoes The annual production of sweet potatoes is determined by the yield of the crop and the areas used to plant it. As shown in Fig. 2.3, in the last

Table 2.3 The amount (tons) of the imported sweet potatoes from other countries for the top 60 countries in 2013. Country

Value

Ranking

Country

Value

Ranking

Country

Value

Ranking

The United Kingdom Canada The Netherlands Japan Thailand

66,128

1

Lebanon

2032

21

400

41

50,619 32,096 21,710 15,301

2 3 4 5

1687 1485 1350 1320

22 23 24 25

381 360 291 289

42 43 44 45

The United States Italy France

15,220 14,274 14,208

6 7 8

Uruguay Sweden Kuwait Hong Kong SAR, P.R. China Republic of Korea Switzerland Poland

Macau SAR, P.R. China Oman Rwanda Hungary El Salvador

1253 1235 1232

26 27 28

276 252 249

46 47 48

Malaysia Germany Singapore

9809 7469 7428

9 10 11

1134 1105 1011

29 30 31

Bahamas Romania The Czech Republic Nepal Slovakia South Africa

237 233 217

49 50 51

Saudi Arabia Haiti Niger

4559 3682 2835

12 13 14

1000 906 600

32 33 34

Brunei Darussalam Mainland China New Zealand

212 187 183

52 53 54

Belgium Finland China Ireland Mexico The United Arab Emirates

2755 2572 2507 2404 2261 2217

15 16 17 18 19 20

505 477 443 429 425 403

35 36 37 38 39 40

Russian Federation Lithuania Bahrain Somalia Maldives Argentina

167 142 106 106 104 100

55 56 57 58 59 60

Chile Norway Plurinational State of Bolivia Spain Namibia Taiwan, Province of China Botswana Austria Greece Iceland Denmark Portugal

Source: Data from FAOSTAT Database (2013) (http://www.fao.org).

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Figure 2.2 The import value (US$1000) of sweet potatoes around the world from 2004 to 2013. Source: Data from FAOSTAT Database (http://www.fao.org).

decade, the worldwide area of sweet potato cultivation has increased from 8,141,292 ha in 2007 to 8,623,973 ha in 2016. Figs. 2.4 and 2.5 show that the increase in the worldwide cultivation area is mainly contributed by Africa, which has increased steadily from 2.86 million ha in 2008 to 4.19 million ha in 2016, an increase of 46.5%. The increase in the cultivation area in Africa has successfully counteracted the decrease in Asia, which has been progressively decreasing since 2008, from 4.51 million ha in 2008 to 3.91 million ha in 2016, a decrease of 13.3%. The year 2015 is a historic moment that marks a turning point. That was the year that Africa surpassed Asia in terms of the area used to plant sweet potatoes and became the world’s leading continent in terms of the area under sweet potato cultivation. Fig. 2.5 also shows that the cultivation area in the Americas has increased in recent years, increasing from 273,726 ha in 2013 to 362,126 ha in 2016, an increase of 32.3%. Considering that the Americas are the origin of sweet potatoes, the climate and soil conditions are most suitable for their growth, and there are huge areas of fertile, arable lands in the Americas, the prospects are very attractive for a greatly increased production of sweet potatoes in the Americas. In comparison the areas under cultivation in Europe and Oceania have been very steady over this same period, with no big changes, implying that the people in these

Table 2.4 The amount (tons) of the exported sweet potatoes from the top 60 countries in 2013. Country

Value

Ranking

Country

Value

Ranking

Country

Value

Ranking

The United States

128,231

1

Ecuador

1488

21

92

41

China

19,870

2

Japan

1029

22

87

42

Egypt The Netherlands Indonesia Spain Dominican Republic Honduras The United Kingdom

15,651 15,348 9797 9246 8556 7181 6345

3 4 5 6 7 8 9

611 589 552 552 483 436 311

23 24 25 26 27 28 29

62 59 57 53 53 39 38

43 44 45 46 47 48 49

Denmark Italy Peru Brazil

4994 4566 3575 2784

10 11 12 13

India Germany Australia Canada Portugal Albania Taiwan, Province of China Singapore Argentina Senegal Oman

The United Arab Emirates Islamic Republic of Iran Tonga Hungary Cameroon Mali Republic of Korea Slovenia Mexico

283 280 274 273

30 31 32 33

34 30 27 22

50 51 52 53

South Africa

1979

14

Madagascar

202

34

20

54

Turkey France Malaysia Belgium

1946 1894 1834 1583

15 16 17 18

159 136 119 116

35 36 37 38

19 18 17 16

55 56 57 58

Saint Vincent and the Grenadines Jamaica

1550

19

Costa Rica Guatemala Lithuania Hong Kong SAR, P.R. China Kenya

Austria Lebanon Colombia The Czech Republic Bosnia and Herzegovina Uganda Benin Yemen Philippines

112

39

Greece

13

59

1503

20

Rwanda

93

40

Swaziland

13

60

Source: Data from FAOSTAT Database (2013) (http://www.fao.org).

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Figure 2.3 Worldwide cultivation area (ha) of sweet potatoes, 2007 2016. Source: Data from FAOSTAT Database (http://www.fao.org).

Figure 2.4 Cultivation area (hectare) of sweet potatoes in Asia and Africa, 2007 2016. Source: Data from FAOSTAT Database (http://www.fao.org).

continents still have not formed the habit of eating food that contains sweet potatoes. As we have mentioned earlier, Africa is now the largest sweet potato cultivation region in the world. However, the yield of sweet potatoes in Africa is far lower than that of other continents. As shown in Fig. 2.6 the

Sweet potato: origin and production

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Figure 2.5 Cultivation area (hectare) of sweet potatoes in the Americas, Europe, and Oceania, 2007 2016. Source: Data from FAOSTAT Database (http://www.fao.org).

Figure 2.6 Comparison of the yield of sweet potatoes on different continents, 2007 2016. Source: Data from FAOSTAT Database (http://www.fao.org).

yield of the crop in Asia is relatively higher than that of other continents. In 2016 the yield in Asia was as high as 200,823 hg/ha. The yield in Europe was 198,252 hg/ha, which is also very high. But the yields in other continents were much lower than Asia and Europe. For instance, the yield in Africa was only 50,903 hg/ha, which is only about one fourth

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of that in Asia. However, this also means that there is a great potential for Africa to increase its production level of sweet potatoes in the future.

The production of sweet potatoes in China Cultivation area and yield As we have mentioned earlier, the cultivation of sweet potatoes in Asia has been progressively decreasing in the last decade. It is mainly caused by the decline of the area under cultivation in China. As shown in Fig. 2.7, during this period the cultivation area in China has declined from 3.76 million ha in 2008 to 3.28 million ha in 2016, a decline of 12.8%. The decline of the area under cultivation for sweet potatoes in China is caused by many factors. First, China has a long history of massive cultivation of sweet potatoes and the land used to plant the crop is widespread all over the country, especially in the hard times before the country’s reform and opening up to the world. However, with the rapid development of the economy in China after the 1980s, the food choices of Chinese people have changed greatly. People in most parts of China now have access to a huge variety of vegetables, fruits, and almost every kind of food all year round. As a result the demands for staple foods such as rice, wheat, and corn have all declined proportionally. The people no longer need to grow so many sweet potatoes to keep them alive as they were forced to do during the previous hard times. According to the China

Figure 2.7 Cultivation area of sweet potatoes in China, 2007 2016. Source: Data from FAOSTAT Database (http://www.fao.org).

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Table 2.5 The uses of sweet potatoes in China. Usages

Percentage in 2013

Predicted percentage, 2016 20

Quantity (million tons)

Extracting starch Consuming as fresh vegetable Animal feed Inevitable losses Reserved as seeds for the coming year Aggregate

50 25

55 30

44 55 24 30

10 10 5

5 5 5

4 5 4 5 4 5

100

100

80 100

Source: Data from Dai, Q.W., Niu, F.X., Sun, J., Cao, J., 2016. Changes analysis of sweet potato production and consumption structure in china. J. Agric. Sci. Technol. 18, 201 209.

Rural Statistical Yearbook (2014), the proportion of the land used to grow sweet potatoes has decreased from above 4% in 1995 to less than 2% in 2016. Second, as shown in Table 2.5, approximately 50% of sweet potatoes in China are used as a raw material for the extraction of the starch. However, during the extracting process, a huge volume of wastewater and fibrous residues are produced simultaneously. Both of the by-products still contain a significant amount of the starch and other nutrients, such as proteins, sugars, and a myriad of micronutrients. They are very prone to spoilage and unavoidably pollute the environment around the factory. In the past 20 years or so, many rivers and much arable land have been contaminated. As a consequence, the government has closed these factories to save the environment. This has also hit the farmers’ willingness to plant the crop and has led to the reduction in the area under cultivation for sweet potatoes in China. Third, with the advancement of agricultural technology, the annual yield of sweet potatoes per hectare has been increased significantly. Farmers can maintain sufficient production with less and less land. According to the data from the FAOSTAT database, in China’s history the area planted with sweet potatoes reached as high as 10.61 million ha in 1961, with an annual production of 74.02 million tons and a yield of 69,738 hg/ha. In contrast, the cultivation area in 2016 (3.28 million ha) had declined to only one-third of that in 1961 but the total production was almost the same (70.57 vs 74.02 million tons) because the yield has been increased tremendously (215,056 vs 69,738 hg/ha).

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Main cultivation regions in China With data obtained from the China Rural Statistical Yearbook (2014), the major provinces growing sweet potatoes in China and the areas planted from 1982 to 2013 are displayed in Table 2.6. It can be found that, in 2013, Sichuan Province and Chongqing municipality together accounted for 25.2% of the total planting area of sweet potatoes in China. Guangdong and Hainan Provinces in combination contributed 3.62 million ha, accounting for 10.8% of the total area. Henan Province is the third largest region in the list, harvesting 3.02 million ha in 2013, corresponding to 9.0% of the total planted area in China. It is also obvious that the planting areas in all of the regions have been decreasing since 1982. Main uses of sweet potatoes in China Sweet potatoes are a versatile crop that can be used for a wide range of purposes. It is estimated that sweet potatoes can be converted to more than 2000 chemical products through various processes. Not only can sweet potatoes be used directly as foodstuffs or feedstuffs, but they also can be used as a raw material in order to extract other products with a higher added value, such as starch, pectin, β-amylase, β-carotene, anthocyanin, and dietary fibers, to name only a few. As shown in Table 2.7, it is predicted that during the 13th “Five-Year Plan” period (2016 20) of China, the total value of the sweet potato industry in China will reach 900 to 1080 billion Chinese Yuan, of which the value of sweet potatoes consumed as fresh vegetables will reach 750 900 billion Yuan. The second major use of sweet potatoes is the extraction of the edible starch that is widely used in Chinese cuisine. The third major use is the use of the extracted starch to further produce various types of the starch vermicelli that is widely welcomed in East Asian countries such as China, South Korea, and Japan. Various snacks made from sweet potatoes, such as dried or fried sweet potato chips, are also welcomed by Chinese people. They are predicted to contribute 20 25 billion Chinese Yuan during this period. The whole powder made from sweet potatoes has been gaining recognition in China in recent years. The powder can be stored for a much longer time than many other forms of the product and thus can be used all year round. In addition, the whole powder has the merit of maintaining most of the nutrients of the fresh sweet potatoes. This is very important from a modern nutritional point of view. Thus it is possible that this processing route will have a rapid development in the future. Other promising uses of sweet potatoes include producing convenient

Table 2.6 The areas (ha) planted in the major sweet potato growing provinces in Mainland China, 1982 2013. Regions

1982

1992

2002

2012

2013

Share in 2013 (%)

Sichuan 1 Chongqing Guangdong 1 Hainan Henan Shandong Guizhou Guangxi Hunan Fujian Anhui Jiangxi Yunnan Hebei Hubei Jiangsu Zhejiang Shaanxi Liaoning Shanxi Jilin Beijing Neimenggu Shanghai Tianjing Ningxia Aggregate

13,970,000 6,149,000 8,993,000 10,809,000 917,000 2,297,000 2,965,000 2,376,000 6,829,000 1,086,000 561,000 3,362,000 1,950,000 3,260,000 1,360,000 979,000 300,000 372,000 38,000 61,000 2000 1000 90,000 419,000 69,146,000

13,420,000 5,727,000 7,246,000 6,697,000 1,251,000 2,526,000 3,059,000 2,588,000 5,700,000 1,419,000 874,000 2,976,000 1,956,000 1,925,000 1,130,000 1,025,000 448,000 481,000 48,000 66,000 8000 5000 43,000

12,521,000 4,805,000 5,523,000 2,802,000 2,322,000 2,890,000 2,915,000 2,597,000 3,806,000 1,454,000 1,650,000 2,220,000 1,988,000 1,438,000 1,022,000 897,000 605,000 529,000 22,000 62,000 26,000 8000 19,000

8,485,000 3,595,000 3,119,000 2,450,000 2,431,000 2,111,000 1,553,000 1,618,000 1,478,000 1,254,000 1,425,000 1,006,000 786,000 602,000 533,000 500,000 271,000 214,000 55,000 21,000 400 10,000 11,000

8,418,000 3,623,000 3,019,000 2,485,000 2,484,000 2,004,000 1,863,000 1,664,000 1,443,000 1,320,000 1,297,000 962,000 658,000 585,000 545,000 542,000 242,000 219,000 55,000 14,000 11,000 10,000 7000

25.2 10.8 9.0 7.4 7.4 6.0 5.6 5.0 4.3 3.9 3.9 2.9 2.0 1.7 1.6 1.6 0.7 0.7 0.2 0.0 0.0 0.0 0.0

60,618,000

52,121,000

33,528,400

33,470,000

100

Source: Data from China Rural Statistical Yearbook 2014.

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Table 2.7 Prediction of sweet potato processing industry in China, 2016 20.

Fresh consumption Edible starch Starch vermicelli Snacks Whole powder Industrial starch Total

Raw material consumption (million tons)

Products (million tons)

Value (billion Yuan)

24 30

25 30

750 900

40 50 25 30 4 5 5 10 15 68 85

8 5 1 1 2

150 200 100 120 20 25 20 10 15 900 1080

10 6 1.2 3

Source: Data from Dai, Q.W., Niu, F.X., Sun, J., Cao, J., 2016. Changes analysis of sweet potato production and consumption structure in china. J. Agric. Sci. Technol. 18, 201 209.

snack foods as well as more sophisticated industrial products such as alcohol, citric acid, food pigments, and modified starches. For example, sweet potatoes can be converted into ethanol through fermentation and dehydration and then used as the fuel for automobiles. It is estimated that each hectare of sweet potatoes can produce 4500 6000 kg of 95% ethanol. From 2018 traditional gasoline will gradually be replaced by ethanol gasoline to be used as the fuel for vehicles in China. By 2020 the whole country will achieve the goal of the full coverage of the use of the ethanol gasoline in all cars. This also provides an opportunity for the sweet potato processing industry. Output of the sweet potatoes processing industry in China Postharvest processing of sweet potatoes in China has several characteristics. First, in East, Central, and Southwest China, sweet potatoes are mainly used for starch extraction. The downstream utilization of the starch in these regions is mainly focused on the production of various types of starch vermicelli. However, in North and Southeast China, starch extraction is not widespread. Fresh sweet potatoes are usually directly dried by various means to produce the dried slice and strip products. These products go directly to the snack food market. In recent years many companies have been also exploring new processing and utilization methods to enrich their product lines as well as to prolong their production season. New product forms, such as sweet potato powder, frozen mashed sweet potato chips, steamed bread, and noodles, are also appearing

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in the market. The second characteristic of the Chinese sweet potato processing industry is that it is dominated by small workshops. Most of the small workshops employ only dozens of or even just a few employees. Large-scale processing plants are still too few and their production capacity is limited. Moreover, these large-scale enterprises are mainly located in the relatively rich provinces in East and Central China. According to the statistics from the China Sweet Potato StarchSpecialized Committee, China Starch Industry Association (CSPSSCCSIA, www.zgganshu.com), there are only 38 relatively large sweet potato processing companies in China. In 2016 these companies in combination produced 294,800 tons of sweet potato starch, 395,100 tons of dried sweet potatoes, 6000 tons of whole sweet potato powder, and 29,900 tons of other sweet potato products. In terms of the starch production, there were only six companies with an output of 10,000 tons or more in 2016, including four in Shandong Province, one in Henan Province, and one in Jiangsu Province. The output of these six companies (218,300 tons) accounted for 74.05% of the total output. There were only eight enterprises with an annual output exceeding 5000 tons, of which five were from Shandong Province, and one each from Henan, Hubei, and Jiangsu Province, respectively. Their combined output (230,300 tons) accounted for 78.12% of the total output. In 2016 the member companies of the CSPSSC-CSIA in combination produced 162,800 tons of the vermicelli from sweet potato starch. There were only three companies with an output exceeding 10,000 tons, including one each in Shandong, Henan, and Sichuan Province. The output of these three companies (131,300 tons) accounted for 80.65% of the total output. There were only five companies with an annual output of more than 5000 tons, including two companies in Shandong, and one each in Henan, Sichuan, and Hubei Province. The output of these five companies (145,300 tons) accounted for 89.25% of the total output of sweet potato vermicelli. In comparison to the huge amount of fresh sweet potatoes harvested in China, it is obvious that the limited total output of the processed products from these relatively large-scale companies from the CSPSSC-CSIA cannot represent the total output of the country. It is known that there are numerous small- and microscale processing workshops that are widespread all over the country, and these have also produced an innumerable amount of starch, vermicelli, and snack food products from sweet

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Sweet Potato

potatoes. However, it is too hard to record and/or calculate the total outputs of these small- and microscale companies. Prospects for the future As we have mentioned earlier, there are still many obstacles that hinder the development of the sweet potato processing industry. First, fresh sweet potatoes are perishable and it is very hard for ordinary peasants to preserve them for a long period of time. As a consequence most of the harvested sweet potatoes must be processed into other products as soon as possible; otherwise there will be serious economic loss. Second, the environmental pollution caused by the by-products of the starch-extracting factories must be solved properly; otherwise these factories will be shut down by the government. It means that a revolutionary processing roadmap must be conceived to completely utilize the whole value of the tuberous root without producing any by-products and pollutants. In 2018 a company in Henan Province took the initiative to change its mindset and adopted Peng-Gao Li’s innovative invention of a novel concentrated sweet potato extract production method to carry out the deep processing of sweet potatoes. Using this patented method, the factory can fully utilize the entire sweet potato root without producing any waste, and without any environmental pollution. During the process, three kinds of final products, namely starch, concentrated sweet potato extract, and high dietary fiber powder, can be simultaneously obtained. As a result the added value of the final products is tremendously augmented. With the promotion of this novel processing technology, China’s sweet potato processing industry is expected to usher in a new period of development. Of course, there are still many other problems that need to be solved. In this aspect the most imperative task is the comprehensive study of the physicochemical, functional, and nutritional properties of the whole plant. This is the prerequisite for the R&D of most of the food products. In early 2015 China launched a national project of producing potatobased staple foods, such as steamed bun, bread, and noodles. This government project is considered beneficial for ensuring the food security of the country and augmenting the nutritional status of the people. This policy is also beneficial for the development of the sweet potato industry. The fibrous residue produced during the starch extraction process still contains approximately 40% 50% of the starch and 20% 30% of the dietary fiber on a dry basis, so it can to be processed into a high fiber staple food powder. The powder can be used to produce steamed buns (mantou in

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Chinese), pancakes (shaobing in Chinese), and biscuits as well as a myriad of local specialty staple foods that are enthusiastically welcomed by the local people in different parts of China. All in all, it is obvious that deep processing is vital for the growth of the sweet potato industry in the leading countries. New forms of the product must be developed from this crop to meet the upgraded demands of the modern market. Otherwise a decline in the production of sweet potatoes is predicted.

References Austin, D., 1988. Exploration, maintenance, and utilization of sweet potato genetic resources. International Potato Center, the Taxonomy, Evolution and Genetic Diversity of Sweet Potatoes and Related Wild Species. Lima, Peru. Bovell-Benjamin, A.C., 2014. Sweet Potato: Origins and Development. Springer, New York. Dai, Q.W., Niu, F.X., Sun, J., Cao, J., 2016. Changes analysis of sweet potato production and consumption structure in china. J. Agric. Sci. Technol. 18, 201 209. Kim, J., 2012. A history of korea: from “land of the morning calm” to states in conflict. Indiana University Press, Bloomington. Nishiyama, I., 2006. Evolution and domestication of sweet potato. Bot. Mag. Tokyo 84, 377 387. O’Hair, S.K., Janick, J., Simon, J.E., 1990. Tropical root and tuber crops. Advances in new crops. In: Proceedings of the First National Symposium ‘New Crops: Research, Development, Economics’, Indianapolis, IN, USA. Roullier, C., Benoit, L., Mckey, D.B., Lebot, V., 2013. Historical collections reveal patterns of diffusion of sweet potato in Oceania obscured by modern plant movements and recombination. Proc. Natl Acad. Sci. U.S.A. 110, 2205 2210. Takegoshi, Y., 2003. The Economic Aspects of the History of the Civilization of Japan. Taylor & Francis, London.

Further reading Van Tilburg, J.A., 1995. Easter Island: Archaeology, Ecology and Culture. British Museum Press and Smithsonian Institution Press, London and Washington, DC. Bassett, K.N., Gordon, H.W., Nobes, D.C., Jacomb, C., 2004. Gardening at the edge: documenting the limits of tropical Polynesian kumara horticulture in southern New Zealand. Geoarchaeol. Int. J. 19, 185 218.