11.2.11 Sun Dried Sweet Potato Slices
Sun dried sweet potato slices are one kind of novel delicious health food, which are sweet, soft, masticable, with good fragrance and rich in nutrition. The product is favored by consumers and has great market potential.The processing steps include:
1. Materials selection: Select long-term stored long and thin sweet potato with the starch transformed into sugar as the raw material.
2. Boiling: Thoroughly boil sweet potatoes in large pot. When boiling, separate sweet potatoes into large, medium and small size groups, and prevent over boiling. Also, do not cover the pot when boiling; if covering is required, cover with one layer of non-toxic plastic film tied along the pot with string. Peel the boiled sweet potatoes, when cooled down.
3. Slicing: After peeling and thorough cooling, the sweet potatoes can be cut into slices 4 cm wide and 8 cm long.
4. Sun curing: Place sliced sweet potato in a well-ventilated place for sun drying. If placed on a roof, dust prevention needs to be considered (preferably on a sunny day without wind). A dryer could also be used. When 80 % of the slices are dried (can be bended but not broken by hand), then sweet potato slices can be collected and stored. It is required to prevent 100 % drying, because 100 % dried sweet potato slices are unable to secrete white powder on the sweet potato slice surface. The curing of sweet potato slices are presented in Figure 11.2.27.
Figure 11.2.27 Sun curing of the sweet potato slices.
5. Sealing and powdering: Place the dried sweet potato slices with a moisture of about 20 % into tanks that are covered by a wooden lid (without sealing). Place the tank into a well-ventilated and cool place until the surface of sweet potato slices inside of the tank are covered by a layer of white powder, which is sugar crystallized in the natural drying process. At this stage the sweet potato slices can be packaged in non-toxic plastic bags for selling. The surface is thoroughly covered by a layer of white sugar powder, looks like dried persimmon, and tastes like soft dates, which makes it is very saleable and can be stored for a very long time because of the high sugar content. The sweet potato slices covered with sugar icing are presented in Figure 11.2.28.
Figure 11.2.28 Sweet potato slices covered with sugar icing.
11.2.12 Summary and Future Research
Sweet potatoes are a good choice to make into various processed food. This chapter has given processing technologies of the different products. The technology needs to be commercialized globally for better economic returns and growth of nations, especially those producing sweet potatoes in large amounts. It is expected that the existing process can be made simpler and make use of other processed foods other than sweet potatoes. In future studies, products with little use of the sugar and salt and other unhealthy food additives should be considered, because more and more people tend to choose foods that are beneficial for their health.
References
Li, C.H. and Mu, T.H. (2005) Sweet potato extrusion technology and product characteristics. Journal of the Chinese Cereals and Oils Association, 6: 58–61.
Li, Y.L., Liu, L.P. and Zhao, L.H. (2008) The development of sweet potato flavor cookies. Science and Technology of Cereals, Oils and Foods, 2: 55–56.
Peng, C.A., Yu, F. and Ma, Y. (2003) Preparation of health sweet potato bread. Journal of Wuhu Professional Technology College, 4: 74–76.
Sun, X.X., Su, H., Wu, S.S., Wang, G.L. and Xu, H. (2013) Development on the purple sweet potato flour cake. Journal ofBengbu College, 5: 13–16.
Tan, F. (1996) Development of puffed sweet potato foods. Agricultural Products Development, 6: 28–29.
11.3 Other Sweet Potato-based Products
Tai-Hua Mu1, Hong-Nan Sun1, and Peng-Gao Li2
1 Institute of Agro-Products Processing Science and Technology, Chinese Academy of Agricultural Sciences, Key Laboratory of Agro-products Processing, Ministry of Agriculture, Beijing, P.R. China 2Department of Nutrition and Food Hygiene, School of Public Health, Capital Medical University, Beijing, P.R. China
11.3.1 Introduction
The consumption of sweet potatoes as such and in the form of different value-added products is very popular across the world. In developed countries, health food with superior quality have been particularly emphasized. Many developed countries also consume sweet potato stems and leaves as high-grade edible vegetables, which have the reputation of “queen of the vegetables”.
This chapter mainly introduces sweet potato in the form of jellies, instant noodles, quick-frozen products, healthcare teas, shoot-tips, sweet beer beverage, purple sweet potato juice, whole flour, health foods and leaf powder.
11.3.2 Sweet Potato Jelly
Sweet potato jelly (Figure 11.3.1) has a natural sweet taste, and its quality is better than the jelly products sold at market, which only contain food flavorings. Therefore, sweet potato jelly is a novel kind of deep-processed sweet potato product.
Figure 11.3.1 Sweet potato jelly.
The following method (Figure 11.3.2) can be adopted for sweet potato jelly:
The processing mainly includes:
1. Pre-treatment: Peel the sweet potato with a stainless steel peeler, and dig out bugs and any black spots. After cleaning and washing off surface silt, cut into regular small pieces.
2. Soaking, color protection and cleaning: Soak the sliced sweet potatoes in a color protection solution (e.g. ascorbic acid, citric acid, etc.) for 1–2 hours, then wash off the impurities and remaining color protection solution with clean water.
3. Ingredients weighing and preparation: Weigh the cleaned sweet potato after color protection processing, then weigh all the ingredients according to the recipe ready for the following use.
4. Steaming: Put the cleaned sweet potatoes into a steamer, and steam until thoroughly cooked. The steamed sweet potatoes are weighed again to evaluate the changes of moisture content before and after steaming. Then prepare water according to the recipe for the following use.
5. Slurring: Mix the steamed sweet potatoes, ingredients and water, and stir with a high-speed beater into a slurry.
6. Boiling: Place the sweet potato slurry into a stainless steel pot and heat up to 80 °C.
7. Filtration: While the slurry is hot, filter it through a 80-mesh stainless steel sieve.
8. Blending: Continuously heat the filtered slurry until boiling, and keep boiling for 5–8 min, then add appropriate amount of acidic agents (e.g. citric acid, ascorbic acid, L-malic acid, etc.), buffer (e.g. sodium dihydrogen phosphate, potassium phosphate monobasic, etc.), gelling agent (e.g. konjac refine flour, carrageenan, etc.), for blending according to practical requirements.
9. Filling: Immediately fill the blended slurry into sterile jelly cups, and seal immediately.