Sweet Potato

Chemistry, Processing and Nutrition

Taihua Mu,Jaspreet Singh

• Verlag: Academic Press
• Jahr: 2019
• ISBN:
  9780128136386
• Thema: Technology & Engineering
• Thema: Agriculture

Sweet Potato: Chemistry, Processing, and Nutrition presents foundational information, including identification, analysis, and use of chemical components from sweet potato in a variety of food and nonfood uses.

Sweet potatoes can be easily propagated, are rich source of carbohydrates and functional components, and are highly productive, which makes them most suitable for production of staple and functional foods. With the increasing population and the challenges of providing healthy food to the world, there is an increasing consumer demand for new and better sweet potato products, particularly for those in developing countries.

Providing a brief description of the specific sweet potato components, their role during processing and strategies for quality optimization, this book also explores novel methods of sweet potato starch, protein, and pectin modification providing students, researchers, and technologists working in the area of food science and others with the most recent information and state-of-the-art technology for developing new and beneficial uses of sweet potato.

• Includes identification, analysis, and use of chemical components of sweet potatoes
• Presents case studies including problem, factors, proposed solutions, and pros and cons of each
• Allows readers to identify an appropriate solution efficiently and effectively

Chapter 1

Sweet potato: chemistry, processing, and nutrition—an introduction

Tai-Hua Mu¹ and Jaspreet Singh², ¹Institute 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, ²School of Food and Advanced Technology and Riddet Institute, Massey University, Palmerston North, New Zealand

Abstract

This chapter provides an overall introduction to the sweet potato. It starts with a general description of the sweet potato. It then summarizes the characteristics of the starch, protein, dietary fiber, pectin, lipids, polyphenols, and carotenoids of the sweet potato. At the end of the chapter, information on sweet potato staple products and snack foods is presented.

Keywords

Sweet potato; starch; protein; dietary fiber; pectin; lipids; polyphenols; carotenoids; staple products; snack foods

Sweet potato (Ipomoea batatas [L.] Lam) is a dicotyledonous plant belonging to the family Convolvulaceae. The plant bears white and purple sympetalous flowers and has large nutritious storage roots. Sweet potato roots develop mainly as storage roots, bearing alternate heart-shaped or palmately lobed leaves, which are long and tapered. The sweet potato roots have a smooth skin that is yellow, orange, red, brown, purple, and/or beige, and has flesh that is beige to white, red, pink, violet, yellow, orange, or purple depending upon the cultivar. The roots, leaves, and stems of sweet potatoes are all edible and nutritious, and these play a vital role in ensuring the food security of many developing countries. The world’s annual production of sweet potatoes was 105 million metric tons in 2016, with approximately 95% of sweet potatoes being grown in developing countries, and with China ranked as the biggest producer (FAOSTAT, 2016). The world’s production of sweet potatoes is currently stable, as is the ranking of the regions and continents. Sweet potato production in Asia is considerably ahead of the other continents, followed by Africa, South America, Caribbean, North and Central America, Europe, and lastly Oceania (FAOSTAT, 2016). As a versatile crop, sweet potatoes can be used for a wide range of purposes. Sweet potato roots and leaves are rich in starch, protein, dietary fiber, lipids, polyphenols, carotenoids, vitamins, and mineral elements such as potassium and calcium depending on the different varieties. Sweet potatoes can also be utilized as a raw material to extract different functional components with higher nutritional value.

Starch is the major component of sweet potato dry matter and consists of amylose and amylopectin with values ranging from 13.33% to 26.83% and 73.17% to 86.67%, respectively (Abegunde et al., 2013). Sweet potato starch granules vary from polygonal to round to cupuliform/bell shapes with granule sizes ranging from 2 to 42 µm (Chen et al., 2003). The digestibility, syneresis percentage, swelling power, and solubility of sweet potato starches are in the ranges of 10.35%–15.15%, 32.45%–44.68%, 13.46–26.13 g/g, and 8.56%–19.97%, respectively (Abegunde et al., 2013). Sweet potato starches can be modified by physical and chemical methods to improve their physicochemical characteristics and resistance towards digestive enzymes during starch digestion (Yu et al., 2015, 2016), which can aid in them being able to serve as functional additives in food.

Sweet potato contains approximately 1.73%–9.14% of protein on a dry weight basis. Sweet potato protein (SPP) is mainly composed of sporamins, which are rich in essential amino acids, and SPP is comparable with other superior quality vegetable proteins (Mu et al., 2009). Unfortunately SPP is generally discarded as industrial waste during sweet potato starch processing. SPP possesses good gelation and emulsifying properties and can easily be recovered by isoelectric precipitation or ultrafiltration/diafiltration processed methods (Arogundade and Mu, 2012; Arogundade et al., 2012; Khan et al., 2014). SPP hydrolysates (SPPH) show noteworthy antioxidant activity, and SPPH could be obtained by enzymatic hydrolysis under high hydrostatic pressure (Zhang and Mu, 2017).

Sweet potato dietary fiber could be extracted from sweet potato pulp, which is the dehydrated residue produced during sweet potato starch manufacturing. Sweet potato pulp consists of 49.7% dietary fiber, which is rich in pectin (39.5%), cellulose, hemicellulose, and lignin (Takamine et al., 2000). Sweet potato dietary fiber exhibits good physicochemical and functional properties. In particular, sweet potato pectin obtained by sonication-induced modification showed lower molecular weight, higher galacturonic acid content, and stronger antioxidant capacity when compared to unmodified samples and could induce apoptosis-like cell death in colon cancer (Ogutu and Mu, 2017; Ogutu et al., 2018).

Lipids are present in almost all foods and play an important role in human nutrition and the sensory aspects of food. The total lipids (TLs) content of different cultivars of sweet potato normally ranges from 0.72% to 1.44%, consisting of 36.74%–61.04% of neutral lipids (NLs), 30.29%–49.25% of glycolipids (GLs), and 7.05%–17.07% of phospholipids (PLs). The fatty acids (FAs) in sweet potato TLs, NLs, GLs, and PLs include different percentages of palmitic acid (C_16:0), stearic acid (C_18:0), oleic acid (C_18:1), linoleic acid (C_18:2), linolenic acid (C_18:3), and arachidic acid (C_20:0). Sweet potato lipids have been reported to have certain anticancer effects, especially GLs with the contribution of monogalactosyl diacylglycerol and digalactosyl diglyceride (Zhao, 2014).

Polyphenols are composed of a variety of components, and their ingestion for health reasons is currently widely recommended in most developed countries. Sweet potato polyphenolic compounds are separated into two main categories: flavonoids and phenolic acids. Flavonoids are mainly found in sweet potato tuberous roots, and include anthocyanins, rutin, and quercetin, but are also found in sweet potato tops, for example, quercetin glycosides. Sweet potato phenolic acids consist of a mixture of caffeic acid and caffeoylquinic acid derivatives, which are commonly present in all parts of sweet potato leaves, petioles, stems, and tuberous roots.

Sweet potato carotenoids are mainly distributed in orange- and yellow-fleshed sweet potato roots, as well as sweet potato leaves. Approximately 90% of the carotenoids in orange-fleshed sweet potatoes are β-carotene (Kimura et al., 2007). Lutein is a member of the xanthophyll family of carotenoids, and it has been found in the constituent parts of sweet potato tops. Sweet potato cultivars with a high content of carotenoids and deep orange or yellow flesh have been developed. Sweet potato carotenoids show good antioxidant activities and could be used as a solution to vitamin A deficiency.

Nowadays sweet potatoes have been used as an important supplement for different staple products in the food industry, such as sweet potato steamed breads, baked breads, noodles, and pancakes. Sweet potatoes have also been used to produce snack foods, such as sweet potato chips, roast sweet potatoes, biscuits, dried slices, cakes, doughnuts, and extruded snacks. In addition, sweet potatoes are used to produce fermented foods, for example, sweet potato shochu, which is a distilled alcoholic beverage. Furthermore, to ensure the consumers get high quality products, the quality evaluation of sweet potato products is important. In summary, the sweet potato processing industry has good opportunities but at the same time some difficult challenges. The scientists and researchers working in the area of food processing may need to seek further cooperation with sweet potato breeders and growers to maximize the utilization of sweet potatoes for different food processing applications.

References

1. Abegunde OK, Mu T-H, Chen J-W, Deng F-M. Physicochemical characterization of sweet potato starches popularly used in Chinese starch industry. Food Hydrocol. 2013;33(2):169–177.

2. Arogundade LA, Mu T-H. Influence of oxidative browning inhibitors and isolation techniques on sweet potato protein recovery and composition. Food Chem. 2012;134(3):1374–1384.

3. Arogundade LA, Mu T-H, Añón MC. Heat-induced gelation properties of isoelectric and ultrafiltered sweet potato protein isolate and their gel microstructure. Food Res Int. 2012;49(1):216–225.

4. Chen Z, Schols H, Voragen A. Physicochemical properties of starches obtained from three varieties of Chinese sweet potatoes. J Food Sci. 2003;68(2):431–437.

5. FAOSTAT, 2016. Production of crops. Available from: <http://faostat3.fao.org/browse/Q/QC/Ex>.

6. Khan NM, Mu T-H, Zhang M, Arogundade LA. The effects of pH and high hydrostatic pressure on the physicochemical properties of a sweet potato protein emulsion. Food Hydrocol. 2014;35:209–216.

7. Kimura M, Kobori CN, Rodriguez-Amaya DB, Nestel P. Screening and HPLC methods for carotenoids in sweet potato, cassava and maize for plant breeding trials. Food Chem. 2007;100(4):1734–1746.

8. Mu TH, Tan SS, Xue YL. The amino acid composition, solubility and emulsifying properties of sweet potato protein. Food Chem. 2009;112(4):1002–1005.

9. Ogutu FO, Mu T-H. Ultrasonic degradation of sweet potato pectin and its antioxidant activity. Ultrason Sonochem. 2017;38:726–734.

10. Ogutu FO, Mu T-H, Sun H, Zhang M. Ultrasonic modified sweet potato pectin induces apoptosis like cell death in colon cancer (HT-29) cell line. Nutr Cancer. 2018;70(1):136–145.

11. Takamine K, Abe J-i, Iwaya A, Maseda S, Hizukuri S. A new manufacturing process for dietary fiber from sweet potato residue and its physical characteristics. J Appl Glycosci. 2000;47(1):67–72.

12. Yu SX, Mu TH, Zhang M, Ma MM, Zhao ZK. Effects of retrogradation and further acetylation on the digestibility and physicochemical properties of purple sweet potato flour and starch. Starch-Stärke. 2015;67(9–10):892–902.

13. Yu SX, Mu TH, Zhang M, Zhao ZK. Effects of inorganic salts on the structural and physicochemical properties of high-hydrostatic-pressure-gelatinized sweet potato starch. Starch-Stärke. 2016;68(9–10):980–988.

14. Zhang M, Mu T-H. Identification and characterization of antioxidant peptides from sweet potato protein hydrolysates by Alcalase under high hydrostatic pressure. Innovat Food Sci Emerg Technol. 2017;43:92–101.

15. Zhao S-T. Study on the Lipid Composition and Anti-cancer Activity of Sweet Potato Xinjiang Agricultural University 2014.

Inhaltsverzeichnis

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Preface
• Chapter 1. Sweet potato: chemistry, processing, and nutrition—an introduction
• Chapter 2. Sweet potato: origin and production
• Chapter 3. Sweet potato starch
• Chapter 4. Sweet potato protein and its hydrolysates
• Chapter 5. Sweet potato dietary fiber
• Chapter 6. Sweet potato lipids
• Chapter 7. Sweet potato polyphenols
• Chapter 8. Sweet potato carotenoids
• Chapter 9. Sweet potato microstructure, starch digestion, and glycemic index
• Chapter 10. Sweet potato staple foods
• Chapter 11. Sweet potato snack foods
• Chapter 12. Sweet potato fermentation food (sweet potato shochu)
• Chapter 13. Quality evaluation of sweet potato products
• Chapter 14. Global market trends, challenges, and the future of the sweet potato processing industry
• Index