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Sweet Potato Granules
CHAPTER
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Sweet Potato Granules
SECTION 1: BACKGROUND FOR DEVELOPING SWEET POTATO GRANULES SECTION 2: TECHNOLOGIES AND KEY POINTS IN MANUFACTURING SWEET POTATO GRANULES 2.1 Manufacturing Technologies 2.2 Key Points 2.2.1 Selection of Special Cultivars 2.2.2 Storage of Raw Sweet Potatoes 2.2.3 Selection of Materials 2.2.4 Cleaning 2.2.5 Peeling 2.2.6 Slicing 2.2.7 Color Preservation 2.2.8 Calcium Soaking 2.2.9 Steaming 2.2.10 Mashing 2.2.11 Addition of Emulsifier 2.2.12 Drying SECTION 3: APPLICATIONS OF SWEET POTATO GRANULES 3.1 Applications of Sweet Potato Granules in Bread 3.1.1 Procedure of Making Bread with Sweet Potato Granules 3.1.2 Skills for Making Bread with Sweet Potato Granules 3.1.3 Effects of Sweet Potato Granules on Bread Production 3.2 Applications of Sweet Potato Granules in Biscuits 3.2.1 Procedure of Making Biscuits with Sweet Potato Granules
Sweet Potato Processing Technology. DOI: http://dx.doi.org/10.1016/B978-0-12-812871-8.00005-2 Copyright © 2017 China Science Publishing & Media Ltd. Published by Elsevier Inc. All rights reserved.
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3.2.2 Key Points in the Procedure for Making Biscuits with Sweet Potato Granules 3.2.3 Effects of Sweet Potato Granules on Biscuit Production 3.3 Applications of Sweet Potato Granules in Noodles 3.3.1 Manufacturing Technologies 3.3.2 Key Points in the Procedure for Making Noodles with Sweet Potato Granules 3.3.3 Effects of Sweet Potato Granules on Noodle Production 3.4 Applications of Sweet Potato Granules in Thick Slurries References
Abstract As a new product, sweet potato granules have been concerned by more and more people because of the characteristics, such as high cell integrity, wide reprocessing prospects, excellent storage properties, and so on. In this chapter, the background for developing, technologies and key points in manufacturing, methods of preparing bread, biscuits, noodles, and thick slurries with sweet potato granules were described.
SECTION 1: BACKGROUND FOR DEVELOPING SWEET POTATO GRANULES China is a top sweet potato production country in terms of the planting area and annual output. However, the sweet potato processing industry in China has developed slowly because of various problems, such as a low processing rate, limited finished products, and few processing components. Sweet potatoes in China are utilized as follows: 50% for feed, 14% for human consumption, 6% for cultivars, and only 15% for industrial processing. The other 15% decay due to improper storage (Lei et al., 2001). The sweet potato processing rate in China is significantly lower than those in the developed countries, such as South Korea and Japan. At present, Chinese sweet potatoes are mainly made into elementary commodities, such as starch, noodles, vermicelli, and chips, and a further expansion of the product range is required. In addition, the main component of sweet potatoes involved in processing is starch, and other nutritious components, including dietary fibers, proteins, and pectin, are rarely used during sweet potato processing.
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The preceding issues make it necessary to study and develop new products and to increase the comprehensive sweet potato processing rate. This is also expected by the Chinese government to promote key agricultural products that will improve regional agricultural economies. Sweet potato granules are produced from raw sweet potatoes. After a series procedures, including the selection, washing, peeling, slicing, color preservation, and boiling, the sweet potato cells are decomposed into several whole cells under certain conditions. After that, granules are obtained by drying with a low shear strength and a low extrusion pressure. Unlike simple dehydrated sweet potato products, sweet potato granules are a type of powder having a relatively high cell integrity, which contributes to a large number of processing advantages, including a high nutrition retention rate, wide reprocessing prospects, and excellent storage properties. Thus, sweet potato granules gradually became an ideal new sweet potato product in China. This chapter provides new perspectives on the research and development of sweet potato granules, and is aimed at exchanging information regarding, and promoting the development of, the sweet potato granule industry in China.
SECTION 2: TECHNOLOGIES AND KEY POINTS IN MANUFACTURING SWEET POTATO GRANULES 2.1 MANUFACTURING TECHNOLOGIES After years of painstaking research, our laboratory proposed an entire high-quality sweet potato granule manufacturing process involving several important technologies. Compared with the manufacturing technologies in other reports, those presented in our study were simple, conserved energy, and required only a low-cost equipment investment. The process is as follows:
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2.2 KEY POINTS 2.2.1 Selection of Special Cultivars The deviation in the quality of sweet potato granules (including free starch contents) produced from different sweet potato cultivars can reach 26.41%. Therefore, appropriate sweet potato cultivars need to be selected before the manufacturing of sweet potato granules. In a series of experiments, we found that the cultivars “Xu 25-2,” “Shang 0110-3,” “Suyu 303,” were suitable for making sweet potato granules.
2.2.2 Storage of Raw Sweet Potatoes Similar to other agro-products, sweet potatoes can be stored before granule production to prolong their lifecycle and increase the comprehensive use of equipment. In addition, sweet potatoes have thin skins and high water concentrations, making them prone to decay not stored correctly. The decay of raw materials causes nutritional losses, which further damages the economic benefits of sweet potato granule manufacturing. Thus, appropriate storage methods for raw sweet potatoes must be used to optimize the manufacturing of sweet potato granules. The process of storing raw sweet potatoes is as follows:
Raw sweet potatoes that are not damaged, without scabs, and with intact skins should be selected for storage. To sterilize raw sweet potatoes, hot steam and disinfectant can be used. The steam sterilization conditions are: Application mode: Spraying; spraying pressure: 1.2 times the standard atmospheric pressure; spray time: 3 s; steam temperature at the potato surface: 90 C. Disinfectants are used as follows: Application mode: Soaking; disinfectant type: Iprodione or carbendazim; disinfectant concentration: 0.1%; soaking time: 5 s (Afek and Orenstein, 2003). For wound healing of raw sweet potatoes, the following parameters are used: Temperature: 30 C; humidity: 92%; duration: 4 7 days (Van Oirschot et al., 2006). The appropriate sweet potato storage temperature ranges from 13 to 16 C. Because of changes in the color, flavor, and taste during sweet potato storage, the recommended storage temperature is 16 C.
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2.2.3 Selection of Materials The first food priority is safety. As a new type of sweet potato product, considerable attention to safety during their production is required. When sweet potatoes encounter the black spot pathogen, a toxin is produced, which consists of ipomeamarone and sweet potato ketoalcohol. The two toxins cause nausea, or even vomiting, dizziness, fatigue, and numbness in serious scenarios, with a fatality rate of 16%. After sweet potatoes are infected by black spot pathogen, its threats to human bodies cannot be eliminated or destroyed by boiling, steaming, or roasting. Therefore, it is important to filter out raw sweet potatoes impacted by the black spot pathogen during the manufacturing of sweet potato granules. After being infected by black spot pathogen, sweet potatoes have black spots, became hardened, and have a bitter taste. Thus, before manufacturing of sweet potato granules, sweet potatoes damaged by worms, with black spots, and showing decay need to be manually removed.
2.2.4 Cleaning Sweet potatoes are a rhizomatous crop, which grow underground and have impurities, like mud, on their surfaces when they are harvested. To keep the impurity concentration at a relatively low level in sweet potato granules, raw sweet potatoes need to be washed before manufacturing. A traditional potato cleaning method is based on a blowing cleaner. After potatoes are immersed and washed, they are sent to a blowing machine. By air-stirring and the rubbing of the roller, as well as the spray of high-pressure water, the potatoes are cleaned (Liu et al., 1999). Alternatively, the vibration of a rotating screen is employed to remove large-sized mud particles and sand, and then high-pressure water is used to rinse the potatoes (Kang et al., 2002). In addition, a cleaning method with both vertical and horizontal washing machines has been used for potato cleaning (He et al., 2005a,b).
2.2.5 Peeling Differences in the skin and flesh of sweet potato varieties generally exist. The taste of sweet potato skin is unpleasant; therefore, unpeeled
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sweet potatoes have a negative influence on the appearance and taste of sweet potato granules. At present, the main peeling methods include alkaline, steam, and abrasive peeling. Alkaline peeling treats materials with an alkaline solution at a certain concentration, and then washes them to remove their skins (Liu et al., 1999). Steam peeling places potatoes into a steam tank, ripens the potato skins with high-pressure steam, and abruptly reduces the pressure to peel their skins (Fang et al., 2002). Abrasive peeling uses a device with multiple rotation shafts. When potatoes and brushes on the rotation shafts rotate in different directions, abrasive force is produced to peel potato skins. Sweet potatoes have deep eyes, and therefore, most manufacturers use the abrasive or manual method to remove sweet potato skins.
2.2.6 Slicing During the production of sweet potato granules, the cell tissues of sweet potatoes are generally softened and loosened by heat. Sweet potatoes usually have irregular shapes, and thus, the direct heating of sweet potatoes results in excessive or insufficient softening and loosening of some parts, while other parts are appropriately softened and loosened. In this case, sweet potatoes need to be sliced to pieces of the same thickness to achieve even heating during the softening and loosening of the materials. The most appropriate slice thickness ranges from 8 to 15 mm for the manufacturing of sweet potato granules.
2.2.7 Color Preservation Color is an important factor influencing food quality. In food processing, enzyme-triggered and nonenzymatic browning introduce inevitable changes in the finished products’ color. Therefore, protective coloration is a crucial procedure in the manufacturing of sweet potato granules. Our study demonstrates that 0.1% ascorbic acid is an ideal color-retention agent during the production of sweet potato granules.
2.2.8 Calcium Soaking Our study shows that the calcium concentration is a key factor influencing the quality of sweet potato granules. After sweet potatoes are soaked in calcium solutions at different concentrations, the produced granules contain different free starch contents, with a variance of 6%.
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The most appropriate calcium concentration ranges from 56.04 to 63.96 ppm for the calcium soaking of sweet potato granules.
2.2.9 Steaming Steaming is a core procedure during the production of sweet potato granules. The purpose of steaming is to loosen the sweet potato cell tissue to cause it to decompose into whole single-cells in later procedures. Insufficient or excessive steaming is unfavorable for the complete separation of sweet potato cell tissues. The most appropriate steaming duration is 11.21 12.80 min for the manufacturing of sweet potato granules.
2.2.10 Mashing Unlike traditional sweet potato products, sweet potato granules are powdered products that are dried after compacted sweet potato cells are separated. Mashing is the main procedure for breaking the compacted cells. At present, sweet potato mashing is usually performed by squeezing and stirring. The latter is more fitted to the production of sweet potato granules because it retains a higher cell integrity level.
2.2.11 Addition of Emulsifier According to earlier reports, after a certain amount of emulsifier is added to sweet potatoes during mashing, the stickiness of the products is decreased, improving their dispersion (Ooraikul et al., 1978). Thus, the free starch content of sweet potato granules is significantly decreased. During the manufacturing of sweet potato granules, the most suitable emulsifier added to the products is 0.1% glycerin monostearate.
2.2.12 Drying The following methods can be used to dry sweet potato granules: Drying by air flow, freeze drying, spray drying, and drying using a rake dryer (Zhang, 2004). The procedure for drying sweet potato granules varies according to the drying method. If sweet potato granules are dried by air flow, then dried granules must added to mashed sweet potatoes to ensure the smooth loading of materials and to prevent sticking. In this way, the water content in mashed sweet potatoes is decreased to B30%, which satisfies the requirement of the air flow dryer. The freeze drying and spray drying procedures are simpler, requiring only the loading of sample materials.
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SECTION 3: APPLICATIONS OF SWEET POTATO GRANULES In recent years, research in China reported on the methods of utilizing sweet potato granules. According to the reports, sweet potato granules can be applied in bread (Lin, 2009); biscuits (Liang, 2009); noodles (Zhang et al., 2012); and thick slurries (Yuan, 2009). The following sections described the preparations of bread, biscuits, noodles, and thick slurry-associated food with sweet potato granules.
3.1 APPLICATIONS OF SWEET POTATO GRANULES IN BREAD Bread is important in human diets because it is convenient for consumption, easy to carry, and rich in nutrition. However, the dietary fiber content in bread is low due to its raw materials, which do not meet the modern requirements of a balanced human diet. Sweet potato granules represent a special raw material for making bread. Their addition during bread production helps to increase the nutrient value and improve the bread quality because of their thickening, water absorption, and water holding capabilities. They also provide supplemental dietary fiber.
3.1.1 Procedure of Making Bread with Sweet Potato Granules The making of bread with sweet potato granules involves flour mixing and production. Flour mixing skills:
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Production skills:
3.1.2 Skills for Making Bread with Sweet Potato Granules 3.1.2.1 Activation of Dry Yeast Dry yeast was dissolved in 30 C water and then left for 30 min before use. When dry yeast was used, mixing with white sugar was prohibited. 3.1.2.2 Flour Mixing White sugar, margarine, sweet potato granules, and bread improver were adequately stirred before they were mixed with flour. The flour was agitated for 8 min at a low speed and then agitated for 4 min at a high speed. 3.1.2.3 Static Fermentation Fermentation parameters are important to achieve a static fermentation effect. The fermentation temperature was under 27 or 28 C, the relative humidity was kept between 75% and 80%, and the fermentation time was 2 h. 3.1.2.4 Bread Formation Fermented dough was ready for division. Generally, dough was cut into B100 g pieces. The gas in dough must be eliminated by squeezing. Then, the dough can be made into a bread base of the required shape. 3.1.2.5 Proofing The suitable proofing conditions were as follows: Temperature: 35 40 C; relative humidity: 90% 95%; and duration: 45 min. 3.1.2.6 Baking To properly bake bread with sweet potato granules, the suitable temperature was determined to be 210 220 C, and the baking duration was 15 min.
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3.1.2.7 Cooling and Packing Bread with sweet potato granules was naturally cooled. When the central temperature becomes 35 C, the bread should be immediately packaged. Delayed packing will result in a great water loss, accelerated aging, flavor changes, and an increase in the risk of fungal infection. 3.1.2.8 Optimization of the Recipe for Making Bread with Sweet Potato Granules An optimized recipe for bread with sweet potato granules includes the following additives: 8% sweet potato granules; 12% white sugar; 0.8% bread improver; and 1.5% yeast.
3.1.3 Effects of Sweet Potato Granules on Bread Production Bread with sweet potato granules made using the preceding method is soft, tasty, not sticky, and elastic. The bread aroma is concordant with sweet potatoes. In addition, the storage stability of bread containing sweet potato granules is significantly improved when compared with bread without sweet potato granules.
3.2 APPLICATIONS OF SWEET POTATO GRANULES IN BISCUITS People are paying increasing attention to nutrition and health issues, resulting in greater food requirements. Because of the high nutrient content and the protective health-related functions of sweet potatoes and related products, such as sweet potato granules, the applications of sweet potato granules in biscuit manufacturing not only extend the sweet potato industry but also meet the consumers growing requirements. Biscuits containing sweet potato granules have a market great potential. The following section describes the method of producing biscuits using sweet potato granules.
3.2.1 Procedure of Making Biscuits with Sweet Potato Granules Biscuits with sweet potato granules are manufactured as follows:
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3.2.2 Key Points in the Procedure for Making Biscuits with Sweet Potato Granules 3.2.2.1 Supplemental Ingredient Treatment Supplemental ingredients used in biscuits with sweet potato granules included vegetable oil, white sugar, sodium bicarbonate, ammonium bicarbonate, gluconolactone, salt, eggs, vitamin C, water, and flavors. These ingredients required treatment before use. For example, white sugar must be ground to powder, and ammonium bicarbonate (leavening agent), sodium bicarbonate, and salt must be completely dissolved. The leavening agent and salt can be dissolved in eggs. Incompletely dissolved ammonium bicarbonate (leavening agent) and sodium bicarbonate will exist in the biscuit base as granules. When the base is baked, decomposed leavening agents will aggregate, which easily causes a foam on the biscuit, leading to black spots on the surface and blank pockets inside the biscuit. As a result, the biscuit quality is degraded. 3.2.2.2 Recommended Ratio of Granules to Supplemental Ingredients in Biscuits with Sweet Potato Granules The ratio of sweet potato granules to supplemental ingredients affects the quality of biscuits containing sweet potato granules. A low proportion of sweet potato granules indicates a high proportion of supplement ingredients, leading to an inadequate sweet potato flavor. A high proportion of sweet potato granules results in a thick sweet potato flavor, but a deteriorated dough performance, which makes it difficult to form biscuits, which are also hard to chew. The amounts of grease and white sugar added to biscuits containing sweet potato granules greatly influence the biscuit quality. A low
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grease volume makes biscuits hard to chew and causes a dry nonsmooth surface. A high grease volume leads to crisp biscuits, but they have an oily taste and are easy-to-break. A low white sugar content leads to inadequate caramelization during biscuit baking, unsatisfactory colorization, and haad to rd#to#chew biscuits. A high white sugar content leads to crisp biscuits, but they are dark in color and excessively sweet tasting. Our study showed that the proper proportions of sweet potato granules and other ingredients in the biscuit were as follows: 100 g high-gluten flour; 30 g sweet potato granules; 15 g grease; 20 g white sugar; 1 g sodium bicarbonate; 0.8 g ammonium bicarbonate; 1.6 g gluconolactone; 0.5 g salt; 4 g egg; 8 mg vitamin-C; an appropriate volume of flavoring; and water, as determined by the dough mixing conditions. 3.2.2.3 Mixing After sweet potato granules were evenly mixed with flour, the supplemental ingredients were added and mixed evenly. 3.2.2.4 Dough Concoction The temperature of the dough concoction should be kept between 22 and 28 C. 3.2.2.5 Rolling Dough was rolled flat and then dried before biscuits took shape. 3.2.2.6 Baking The most proper parameters for baking biscuits with sweet potato granules included the surface temperature of 220 C, bottom temperature of 190 C, and baking time of 9 min. 3.2.2.7 Cooling The baked biscuits containing sweet potato granules were quickly taken out and cooled to 38 40 C under room temperature, which allowed the water in the biscuits to continue evaporating, preventing biscuit deformation. 3.2.2.8 Arrangement and Packing Broken and irregular biscuits were eliminated, and then, the other biscuits were packed and sealed.
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3.2.3 Effects of Sweet Potato Granules on Biscuit Production Biscuits with sweet potato granules made using the preceding method that have a homogeneous color of gold or light purple. The taste is mildly sweet and crisp, with a loose structure. There is a sweet potato flavor, and high levels of dietary fiber and protein. Its taste and texture are like those of crisp biscuits, but the added grease volume does not meet the requirement of crisp biscuits. It is a new type of biscuit, between semihard and crisp.
3.3 APPLICATIONS OF SWEET POTATO GRANULES IN NOODLES Noodles are an important flour product consumed daily by people. With the elevation of living standards, people have increased their requirements for noodles. A large number of nutritious materials, including oat, buckwheat, mushroom, and egg, have been added to noodles to enhance their healthy properties. Sweet potato granules are nutritious and have many health-related functions and, therefore, can be added to noodles. The following section describes the method of producing noodles containing sweet potato granules.
3.3.1 Manufacturing Technologies The technologies for manufacturing noodles with sweet potato granules are as follows:
3.3.2 Key Points in the Procedure for Making Noodles with Sweet Potato Granules 3.3.2.1 Suitable Sweet Potato Granules for Making Noodles The quality of noodles containing sweet potato granules is significantly affected by the sweet potato granules. The sweet potato granule’s size is negatively correlated to the rate of broken noodles during its cooking. In contrast, the cooking loss rate of noodles increases
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concordantly with the size of sweet potato granules. The bend-to-break rate becomes lower and then higher as the size increases. Taking into account the rate of broken noodles during cooking, the cooking loss rate, and the bend-to-break rate, Zhang et al. (2012) concluded that the proper sweet potato granule size is 100 mesh for making noodles. 3.3.2.2 Proper Amount of Sweet Potato Granules for Noodle Production If excessive sweet potato granules are added, the gluten content of noodles is insufficient, making the noodles less elastic, easy-to-break, and less resistant to cooking. Taking into account the rate of broken noodles during cooking, the cooking loss rate, and the bend-to-break rate, Zhang et al. (2012) found that 10% sweet potato granules was the optimum amount for making noodles. 3.3.2.3 Mixing with Water and Flour and Static Aging With the increase in the dough’s water content, the breaking rate during the cooking of noodles containing sweet potato granules rose, and the cooking loss rate and bend-to-break rate first decreased and then increased. Therefore, the water content in dough is a parameter requiring special attention. During the preparation of noodles with sweet potato granules, the following parameters were recommended: Water content in dough: 24%; dough kneading time: 18 min; dough kneading temperature: 24 28 C; static aging time: 30 min (Zhang et al., 2012). 3.3.2.4 Rolling The thickness requires special attention during the rolling procedure. Thinly rolled noodles have a high cooking loss rate, while thickly rolled noodles have a high bend-to-break rate. The appropriate thickness for rolled noodles with sweet potato granules was 1.3 mm (Zhang et al., 2012).
3.3.3 Effects of Sweet Potato Granules on Noodle Production Noodles with sweet potato granules made in the preceding method have good chewiness, satisfactory hardness, excellent stickiness, and extraordinary performance.
3.4 APPLICATIONS OF SWEET POTATO GRANULES IN THICK SLURRIES Sweet potato granules can be used as materials for producing bread, biscuits, and noodles. They can also be put into concerted applications
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containing milk powder to make nutritionally balanced thick-slurry foods with sweet potato granules. Yuan (2009) conducted measurements on the amino acid content in sweet potato granules and whole milk powder, calculated the amino acid modes of sweet potato granules and whole milk powder, and evaluated the thick-slurry foods made with different proportions of sweet potato granules and milk powder based on the amino acid ratio coefficient and chemical scores. Then, based on approximations among the amino acid mode, standard World Health Organization (WHO)/Food and Agriculture Organization (FAO) mode, and all-egg mode of the prepared products, the best ratio of sweet potato granules to milk powder in thick-slurry foods was found to be 8:2. In addition, when considering stability and stickiness, the best stabilizer amounts of the thick-slurry foods containing sweet potato granules, as determined using the univariate analysis of variance (ANOVA) and orthogonal tests, were as follows: 0.65% sodium carboxymethylcellulose; 0.6% xanthan gum; 0.2% monoglyceride; and 12% saccharose.
REFERENCES Afek, U., Orenstein, J., 2003. Decreased sweet potato decay during storage by steam treatments. Crop Prot. 22, 321 324. Fang, X.F., Wu, G., 2002. A study on the production technologies of potato granules. Grain Oil Process. Food Mach 1, 14 16 (in Chinese). He, X.Y., Yang, S., 2005a. Production control of potato granules. Grain Oil Food Sci. Technol. 2 (13), 39 40 (in Chinese). He, X.Y., Yang, S., 2005b. Quality and production control of potato granules. Grain Oil 2, 15 17 (in Chinese). Kang, W.Y., Zhang, T., 2002. Processing technologies and product quality standards of potato granules. New Technol. New Prod. 2, 16 18 (in Chinese). Lei, M., Lu, X.L., Mao, L.J., 2001. Recent sweet potato food development and trend in China. Grain Oil Process. Food Mach. 11, 12 14 (in Chinese). Liang, M.F., 2009. A Study on the Processing Characteristics of Sweet Potato Granules and the Technologies of Applying Them to Biscuit Production. Changsha: Hunan Agricultural University (in Chinese). Lin, H., 2009. A Study on the Processing Characteristics of Sweet Potato Granules and Their Application in Bread Making. Changsha: Hunan Agricultural University (in Chinese). Liu, J.G., Chen, X.W., 1999. A brief introduction to the technologies for processing potato granules. Potato Mag 13 (1), 58 60 (in Chinese). Ooraikul, B., 1978. Production of Potato Granules. U.S. Patent: 4110478, 1978. Van Oirschot, Q.E.A., Rees, D., Aked, J., et al., 2006. Sweetpotato cultivars differ in efficiency of wound healing. Postharvest Biol. Technol. 42, 65 74.
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Yuan, L.N., 2009 Research on the Anti-breaking of Sweet Potato Granule Cells and Their Thickslurry Food. Wuhan: Central China Agricultural University (in Chinese). Zhang, T., 2004. New Technologies for Producing Whole-cell Sweet Potato Granules. People’s Republic of China: 03100273.0 (in Chinese). Zhang, Y., Xiao, Y.L., Chen, G., et al., 2012. A study on the influence of sweet potato granules on noodle quality. Food Ferment. Technol. 48 (1), 44 48 (in Chinese).
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Sweet Potato Granules
SECTION 1: BACKGROUND FOR DEVELOPING SWEET POTATO GRANULES SECTION 2: TECHNOLOGIES AND KEY POINTS IN MANUFACTURING SWEET POTATO GRANULES 2.1 Manufacturing Technologies 2.2 Key Points 2.2.1 Selection of Special Cultivars 2.2.2 Storage of Raw Sweet Potatoes 2.2.3 Selection of Materials 2.2.4 Cleaning 2.2.5 Peeling 2.2.6 Slicing 2.2.7 Color Preservation 2.2.8 Calcium Soaking 2.2.9 Steaming 2.2.10 Mashing 2.2.11 Addition of Emulsifier 2.2.12 Drying SECTION 3: APPLICATIONS OF SWEET POTATO GRANULES 3.1 Applications of Sweet Potato Granules in Bread 3.1.1 Procedure of Making Bread with Sweet Potato Granules 3.1.2 Skills for Making Bread with Sweet Potato Granules 3.1.3 Effects of Sweet Potato Granules on Bread Production 3.2 Applications of Sweet Potato Granules in Biscuits 3.2.1 Procedure of Making Biscuits with Sweet Potato Granules
Sweet Potato Processing Technology. DOI: http://dx.doi.org/10.1016/B978-0-12-812871-8.00005-2 Copyright © 2017 China Science Publishing & Media Ltd. Published by Elsevier Inc. All rights reserved.
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3.2.2 Key Points in the Procedure for Making Biscuits with Sweet Potato Granules 3.2.3 Effects of Sweet Potato Granules on Biscuit Production 3.3 Applications of Sweet Potato Granules in Noodles 3.3.1 Manufacturing Technologies 3.3.2 Key Points in the Procedure for Making Noodles with Sweet Potato Granules 3.3.3 Effects of Sweet Potato Granules on Noodle Production 3.4 Applications of Sweet Potato Granules in Thick Slurries References
Abstract As a new product, sweet potato granules have been concerned by more and more people because of the characteristics, such as high cell integrity, wide reprocessing prospects, excellent storage properties, and so on. In this chapter, the background for developing, technologies and key points in manufacturing, methods of preparing bread, biscuits, noodles, and thick slurries with sweet potato granules were described.
SECTION 1: BACKGROUND FOR DEVELOPING SWEET POTATO GRANULES China is a top sweet potato production country in terms of the planting area and annual output. However, the sweet potato processing industry in China has developed slowly because of various problems, such as a low processing rate, limited finished products, and few processing components. Sweet potatoes in China are utilized as follows: 50% for feed, 14% for human consumption, 6% for cultivars, and only 15% for industrial processing. The other 15% decay due to improper storage (Lei et al., 2001). The sweet potato processing rate in China is significantly lower than those in the developed countries, such as South Korea and Japan. At present, Chinese sweet potatoes are mainly made into elementary commodities, such as starch, noodles, vermicelli, and chips, and a further expansion of the product range is required. In addition, the main component of sweet potatoes involved in processing is starch, and other nutritious components, including dietary fibers, proteins, and pectin, are rarely used during sweet potato processing.
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The preceding issues make it necessary to study and develop new products and to increase the comprehensive sweet potato processing rate. This is also expected by the Chinese government to promote key agricultural products that will improve regional agricultural economies. Sweet potato granules are produced from raw sweet potatoes. After a series procedures, including the selection, washing, peeling, slicing, color preservation, and boiling, the sweet potato cells are decomposed into several whole cells under certain conditions. After that, granules are obtained by drying with a low shear strength and a low extrusion pressure. Unlike simple dehydrated sweet potato products, sweet potato granules are a type of powder having a relatively high cell integrity, which contributes to a large number of processing advantages, including a high nutrition retention rate, wide reprocessing prospects, and excellent storage properties. Thus, sweet potato granules gradually became an ideal new sweet potato product in China. This chapter provides new perspectives on the research and development of sweet potato granules, and is aimed at exchanging information regarding, and promoting the development of, the sweet potato granule industry in China.
SECTION 2: TECHNOLOGIES AND KEY POINTS IN MANUFACTURING SWEET POTATO GRANULES 2.1 MANUFACTURING TECHNOLOGIES After years of painstaking research, our laboratory proposed an entire high-quality sweet potato granule manufacturing process involving several important technologies. Compared with the manufacturing technologies in other reports, those presented in our study were simple, conserved energy, and required only a low-cost equipment investment. The process is as follows:
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2.2 KEY POINTS 2.2.1 Selection of Special Cultivars The deviation in the quality of sweet potato granules (including free starch contents) produced from different sweet potato cultivars can reach 26.41%. Therefore, appropriate sweet potato cultivars need to be selected before the manufacturing of sweet potato granules. In a series of experiments, we found that the cultivars “Xu 25-2,” “Shang 0110-3,” “Suyu 303,” were suitable for making sweet potato granules.
2.2.2 Storage of Raw Sweet Potatoes Similar to other agro-products, sweet potatoes can be stored before granule production to prolong their lifecycle and increase the comprehensive use of equipment. In addition, sweet potatoes have thin skins and high water concentrations, making them prone to decay not stored correctly. The decay of raw materials causes nutritional losses, which further damages the economic benefits of sweet potato granule manufacturing. Thus, appropriate storage methods for raw sweet potatoes must be used to optimize the manufacturing of sweet potato granules. The process of storing raw sweet potatoes is as follows:
Raw sweet potatoes that are not damaged, without scabs, and with intact skins should be selected for storage. To sterilize raw sweet potatoes, hot steam and disinfectant can be used. The steam sterilization conditions are: Application mode: Spraying; spraying pressure: 1.2 times the standard atmospheric pressure; spray time: 3 s; steam temperature at the potato surface: 90 C. Disinfectants are used as follows: Application mode: Soaking; disinfectant type: Iprodione or carbendazim; disinfectant concentration: 0.1%; soaking time: 5 s (Afek and Orenstein, 2003). For wound healing of raw sweet potatoes, the following parameters are used: Temperature: 30 C; humidity: 92%; duration: 4 7 days (Van Oirschot et al., 2006). The appropriate sweet potato storage temperature ranges from 13 to 16 C. Because of changes in the color, flavor, and taste during sweet potato storage, the recommended storage temperature is 16 C.
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2.2.3 Selection of Materials The first food priority is safety. As a new type of sweet potato product, considerable attention to safety during their production is required. When sweet potatoes encounter the black spot pathogen, a toxin is produced, which consists of ipomeamarone and sweet potato ketoalcohol. The two toxins cause nausea, or even vomiting, dizziness, fatigue, and numbness in serious scenarios, with a fatality rate of 16%. After sweet potatoes are infected by black spot pathogen, its threats to human bodies cannot be eliminated or destroyed by boiling, steaming, or roasting. Therefore, it is important to filter out raw sweet potatoes impacted by the black spot pathogen during the manufacturing of sweet potato granules. After being infected by black spot pathogen, sweet potatoes have black spots, became hardened, and have a bitter taste. Thus, before manufacturing of sweet potato granules, sweet potatoes damaged by worms, with black spots, and showing decay need to be manually removed.
2.2.4 Cleaning Sweet potatoes are a rhizomatous crop, which grow underground and have impurities, like mud, on their surfaces when they are harvested. To keep the impurity concentration at a relatively low level in sweet potato granules, raw sweet potatoes need to be washed before manufacturing. A traditional potato cleaning method is based on a blowing cleaner. After potatoes are immersed and washed, they are sent to a blowing machine. By air-stirring and the rubbing of the roller, as well as the spray of high-pressure water, the potatoes are cleaned (Liu et al., 1999). Alternatively, the vibration of a rotating screen is employed to remove large-sized mud particles and sand, and then high-pressure water is used to rinse the potatoes (Kang et al., 2002). In addition, a cleaning method with both vertical and horizontal washing machines has been used for potato cleaning (He et al., 2005a,b).
2.2.5 Peeling Differences in the skin and flesh of sweet potato varieties generally exist. The taste of sweet potato skin is unpleasant; therefore, unpeeled
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sweet potatoes have a negative influence on the appearance and taste of sweet potato granules. At present, the main peeling methods include alkaline, steam, and abrasive peeling. Alkaline peeling treats materials with an alkaline solution at a certain concentration, and then washes them to remove their skins (Liu et al., 1999). Steam peeling places potatoes into a steam tank, ripens the potato skins with high-pressure steam, and abruptly reduces the pressure to peel their skins (Fang et al., 2002). Abrasive peeling uses a device with multiple rotation shafts. When potatoes and brushes on the rotation shafts rotate in different directions, abrasive force is produced to peel potato skins. Sweet potatoes have deep eyes, and therefore, most manufacturers use the abrasive or manual method to remove sweet potato skins.
2.2.6 Slicing During the production of sweet potato granules, the cell tissues of sweet potatoes are generally softened and loosened by heat. Sweet potatoes usually have irregular shapes, and thus, the direct heating of sweet potatoes results in excessive or insufficient softening and loosening of some parts, while other parts are appropriately softened and loosened. In this case, sweet potatoes need to be sliced to pieces of the same thickness to achieve even heating during the softening and loosening of the materials. The most appropriate slice thickness ranges from 8 to 15 mm for the manufacturing of sweet potato granules.
2.2.7 Color Preservation Color is an important factor influencing food quality. In food processing, enzyme-triggered and nonenzymatic browning introduce inevitable changes in the finished products’ color. Therefore, protective coloration is a crucial procedure in the manufacturing of sweet potato granules. Our study demonstrates that 0.1% ascorbic acid is an ideal color-retention agent during the production of sweet potato granules.
2.2.8 Calcium Soaking Our study shows that the calcium concentration is a key factor influencing the quality of sweet potato granules. After sweet potatoes are soaked in calcium solutions at different concentrations, the produced granules contain different free starch contents, with a variance of 6%.
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The most appropriate calcium concentration ranges from 56.04 to 63.96 ppm for the calcium soaking of sweet potato granules.
2.2.9 Steaming Steaming is a core procedure during the production of sweet potato granules. The purpose of steaming is to loosen the sweet potato cell tissue to cause it to decompose into whole single-cells in later procedures. Insufficient or excessive steaming is unfavorable for the complete separation of sweet potato cell tissues. The most appropriate steaming duration is 11.21 12.80 min for the manufacturing of sweet potato granules.
2.2.10 Mashing Unlike traditional sweet potato products, sweet potato granules are powdered products that are dried after compacted sweet potato cells are separated. Mashing is the main procedure for breaking the compacted cells. At present, sweet potato mashing is usually performed by squeezing and stirring. The latter is more fitted to the production of sweet potato granules because it retains a higher cell integrity level.
2.2.11 Addition of Emulsifier According to earlier reports, after a certain amount of emulsifier is added to sweet potatoes during mashing, the stickiness of the products is decreased, improving their dispersion (Ooraikul et al., 1978). Thus, the free starch content of sweet potato granules is significantly decreased. During the manufacturing of sweet potato granules, the most suitable emulsifier added to the products is 0.1% glycerin monostearate.
2.2.12 Drying The following methods can be used to dry sweet potato granules: Drying by air flow, freeze drying, spray drying, and drying using a rake dryer (Zhang, 2004). The procedure for drying sweet potato granules varies according to the drying method. If sweet potato granules are dried by air flow, then dried granules must added to mashed sweet potatoes to ensure the smooth loading of materials and to prevent sticking. In this way, the water content in mashed sweet potatoes is decreased to B30%, which satisfies the requirement of the air flow dryer. The freeze drying and spray drying procedures are simpler, requiring only the loading of sample materials.
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SECTION 3: APPLICATIONS OF SWEET POTATO GRANULES In recent years, research in China reported on the methods of utilizing sweet potato granules. According to the reports, sweet potato granules can be applied in bread (Lin, 2009); biscuits (Liang, 2009); noodles (Zhang et al., 2012); and thick slurries (Yuan, 2009). The following sections described the preparations of bread, biscuits, noodles, and thick slurry-associated food with sweet potato granules.
3.1 APPLICATIONS OF SWEET POTATO GRANULES IN BREAD Bread is important in human diets because it is convenient for consumption, easy to carry, and rich in nutrition. However, the dietary fiber content in bread is low due to its raw materials, which do not meet the modern requirements of a balanced human diet. Sweet potato granules represent a special raw material for making bread. Their addition during bread production helps to increase the nutrient value and improve the bread quality because of their thickening, water absorption, and water holding capabilities. They also provide supplemental dietary fiber.
3.1.1 Procedure of Making Bread with Sweet Potato Granules The making of bread with sweet potato granules involves flour mixing and production. Flour mixing skills:
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Production skills:
3.1.2 Skills for Making Bread with Sweet Potato Granules 3.1.2.1 Activation of Dry Yeast Dry yeast was dissolved in 30 C water and then left for 30 min before use. When dry yeast was used, mixing with white sugar was prohibited. 3.1.2.2 Flour Mixing White sugar, margarine, sweet potato granules, and bread improver were adequately stirred before they were mixed with flour. The flour was agitated for 8 min at a low speed and then agitated for 4 min at a high speed. 3.1.2.3 Static Fermentation Fermentation parameters are important to achieve a static fermentation effect. The fermentation temperature was under 27 or 28 C, the relative humidity was kept between 75% and 80%, and the fermentation time was 2 h. 3.1.2.4 Bread Formation Fermented dough was ready for division. Generally, dough was cut into B100 g pieces. The gas in dough must be eliminated by squeezing. Then, the dough can be made into a bread base of the required shape. 3.1.2.5 Proofing The suitable proofing conditions were as follows: Temperature: 35 40 C; relative humidity: 90% 95%; and duration: 45 min. 3.1.2.6 Baking To properly bake bread with sweet potato granules, the suitable temperature was determined to be 210 220 C, and the baking duration was 15 min.
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3.1.2.7 Cooling and Packing Bread with sweet potato granules was naturally cooled. When the central temperature becomes 35 C, the bread should be immediately packaged. Delayed packing will result in a great water loss, accelerated aging, flavor changes, and an increase in the risk of fungal infection. 3.1.2.8 Optimization of the Recipe for Making Bread with Sweet Potato Granules An optimized recipe for bread with sweet potato granules includes the following additives: 8% sweet potato granules; 12% white sugar; 0.8% bread improver; and 1.5% yeast.
3.1.3 Effects of Sweet Potato Granules on Bread Production Bread with sweet potato granules made using the preceding method is soft, tasty, not sticky, and elastic. The bread aroma is concordant with sweet potatoes. In addition, the storage stability of bread containing sweet potato granules is significantly improved when compared with bread without sweet potato granules.
3.2 APPLICATIONS OF SWEET POTATO GRANULES IN BISCUITS People are paying increasing attention to nutrition and health issues, resulting in greater food requirements. Because of the high nutrient content and the protective health-related functions of sweet potatoes and related products, such as sweet potato granules, the applications of sweet potato granules in biscuit manufacturing not only extend the sweet potato industry but also meet the consumers growing requirements. Biscuits containing sweet potato granules have a market great potential. The following section describes the method of producing biscuits using sweet potato granules.
3.2.1 Procedure of Making Biscuits with Sweet Potato Granules Biscuits with sweet potato granules are manufactured as follows:
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3.2.2 Key Points in the Procedure for Making Biscuits with Sweet Potato Granules 3.2.2.1 Supplemental Ingredient Treatment Supplemental ingredients used in biscuits with sweet potato granules included vegetable oil, white sugar, sodium bicarbonate, ammonium bicarbonate, gluconolactone, salt, eggs, vitamin C, water, and flavors. These ingredients required treatment before use. For example, white sugar must be ground to powder, and ammonium bicarbonate (leavening agent), sodium bicarbonate, and salt must be completely dissolved. The leavening agent and salt can be dissolved in eggs. Incompletely dissolved ammonium bicarbonate (leavening agent) and sodium bicarbonate will exist in the biscuit base as granules. When the base is baked, decomposed leavening agents will aggregate, which easily causes a foam on the biscuit, leading to black spots on the surface and blank pockets inside the biscuit. As a result, the biscuit quality is degraded. 3.2.2.2 Recommended Ratio of Granules to Supplemental Ingredients in Biscuits with Sweet Potato Granules The ratio of sweet potato granules to supplemental ingredients affects the quality of biscuits containing sweet potato granules. A low proportion of sweet potato granules indicates a high proportion of supplement ingredients, leading to an inadequate sweet potato flavor. A high proportion of sweet potato granules results in a thick sweet potato flavor, but a deteriorated dough performance, which makes it difficult to form biscuits, which are also hard to chew. The amounts of grease and white sugar added to biscuits containing sweet potato granules greatly influence the biscuit quality. A low
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grease volume makes biscuits hard to chew and causes a dry nonsmooth surface. A high grease volume leads to crisp biscuits, but they have an oily taste and are easy-to-break. A low white sugar content leads to inadequate caramelization during biscuit baking, unsatisfactory colorization, and haad to rd#to#chew biscuits. A high white sugar content leads to crisp biscuits, but they are dark in color and excessively sweet tasting. Our study showed that the proper proportions of sweet potato granules and other ingredients in the biscuit were as follows: 100 g high-gluten flour; 30 g sweet potato granules; 15 g grease; 20 g white sugar; 1 g sodium bicarbonate; 0.8 g ammonium bicarbonate; 1.6 g gluconolactone; 0.5 g salt; 4 g egg; 8 mg vitamin-C; an appropriate volume of flavoring; and water, as determined by the dough mixing conditions. 3.2.2.3 Mixing After sweet potato granules were evenly mixed with flour, the supplemental ingredients were added and mixed evenly. 3.2.2.4 Dough Concoction The temperature of the dough concoction should be kept between 22 and 28 C. 3.2.2.5 Rolling Dough was rolled flat and then dried before biscuits took shape. 3.2.2.6 Baking The most proper parameters for baking biscuits with sweet potato granules included the surface temperature of 220 C, bottom temperature of 190 C, and baking time of 9 min. 3.2.2.7 Cooling The baked biscuits containing sweet potato granules were quickly taken out and cooled to 38 40 C under room temperature, which allowed the water in the biscuits to continue evaporating, preventing biscuit deformation. 3.2.2.8 Arrangement and Packing Broken and irregular biscuits were eliminated, and then, the other biscuits were packed and sealed.
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3.2.3 Effects of Sweet Potato Granules on Biscuit Production Biscuits with sweet potato granules made using the preceding method that have a homogeneous color of gold or light purple. The taste is mildly sweet and crisp, with a loose structure. There is a sweet potato flavor, and high levels of dietary fiber and protein. Its taste and texture are like those of crisp biscuits, but the added grease volume does not meet the requirement of crisp biscuits. It is a new type of biscuit, between semihard and crisp.
3.3 APPLICATIONS OF SWEET POTATO GRANULES IN NOODLES Noodles are an important flour product consumed daily by people. With the elevation of living standards, people have increased their requirements for noodles. A large number of nutritious materials, including oat, buckwheat, mushroom, and egg, have been added to noodles to enhance their healthy properties. Sweet potato granules are nutritious and have many health-related functions and, therefore, can be added to noodles. The following section describes the method of producing noodles containing sweet potato granules.
3.3.1 Manufacturing Technologies The technologies for manufacturing noodles with sweet potato granules are as follows:
3.3.2 Key Points in the Procedure for Making Noodles with Sweet Potato Granules 3.3.2.1 Suitable Sweet Potato Granules for Making Noodles The quality of noodles containing sweet potato granules is significantly affected by the sweet potato granules. The sweet potato granule’s size is negatively correlated to the rate of broken noodles during its cooking. In contrast, the cooking loss rate of noodles increases
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concordantly with the size of sweet potato granules. The bend-to-break rate becomes lower and then higher as the size increases. Taking into account the rate of broken noodles during cooking, the cooking loss rate, and the bend-to-break rate, Zhang et al. (2012) concluded that the proper sweet potato granule size is 100 mesh for making noodles. 3.3.2.2 Proper Amount of Sweet Potato Granules for Noodle Production If excessive sweet potato granules are added, the gluten content of noodles is insufficient, making the noodles less elastic, easy-to-break, and less resistant to cooking. Taking into account the rate of broken noodles during cooking, the cooking loss rate, and the bend-to-break rate, Zhang et al. (2012) found that 10% sweet potato granules was the optimum amount for making noodles. 3.3.2.3 Mixing with Water and Flour and Static Aging With the increase in the dough’s water content, the breaking rate during the cooking of noodles containing sweet potato granules rose, and the cooking loss rate and bend-to-break rate first decreased and then increased. Therefore, the water content in dough is a parameter requiring special attention. During the preparation of noodles with sweet potato granules, the following parameters were recommended: Water content in dough: 24%; dough kneading time: 18 min; dough kneading temperature: 24 28 C; static aging time: 30 min (Zhang et al., 2012). 3.3.2.4 Rolling The thickness requires special attention during the rolling procedure. Thinly rolled noodles have a high cooking loss rate, while thickly rolled noodles have a high bend-to-break rate. The appropriate thickness for rolled noodles with sweet potato granules was 1.3 mm (Zhang et al., 2012).
3.3.3 Effects of Sweet Potato Granules on Noodle Production Noodles with sweet potato granules made in the preceding method have good chewiness, satisfactory hardness, excellent stickiness, and extraordinary performance.
3.4 APPLICATIONS OF SWEET POTATO GRANULES IN THICK SLURRIES Sweet potato granules can be used as materials for producing bread, biscuits, and noodles. They can also be put into concerted applications
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containing milk powder to make nutritionally balanced thick-slurry foods with sweet potato granules. Yuan (2009) conducted measurements on the amino acid content in sweet potato granules and whole milk powder, calculated the amino acid modes of sweet potato granules and whole milk powder, and evaluated the thick-slurry foods made with different proportions of sweet potato granules and milk powder based on the amino acid ratio coefficient and chemical scores. Then, based on approximations among the amino acid mode, standard World Health Organization (WHO)/Food and Agriculture Organization (FAO) mode, and all-egg mode of the prepared products, the best ratio of sweet potato granules to milk powder in thick-slurry foods was found to be 8:2. In addition, when considering stability and stickiness, the best stabilizer amounts of the thick-slurry foods containing sweet potato granules, as determined using the univariate analysis of variance (ANOVA) and orthogonal tests, were as follows: 0.65% sodium carboxymethylcellulose; 0.6% xanthan gum; 0.2% monoglyceride; and 12% saccharose.
REFERENCES Afek, U., Orenstein, J., 2003. Decreased sweet potato decay during storage by steam treatments. Crop Prot. 22, 321 324. Fang, X.F., Wu, G., 2002. A study on the production technologies of potato granules. Grain Oil Process. Food Mach 1, 14 16 (in Chinese). He, X.Y., Yang, S., 2005a. Production control of potato granules. Grain Oil Food Sci. Technol. 2 (13), 39 40 (in Chinese). He, X.Y., Yang, S., 2005b. Quality and production control of potato granules. Grain Oil 2, 15 17 (in Chinese). Kang, W.Y., Zhang, T., 2002. Processing technologies and product quality standards of potato granules. New Technol. New Prod. 2, 16 18 (in Chinese). Lei, M., Lu, X.L., Mao, L.J., 2001. Recent sweet potato food development and trend in China. Grain Oil Process. Food Mach. 11, 12 14 (in Chinese). Liang, M.F., 2009. A Study on the Processing Characteristics of Sweet Potato Granules and the Technologies of Applying Them to Biscuit Production. Changsha: Hunan Agricultural University (in Chinese). Lin, H., 2009. A Study on the Processing Characteristics of Sweet Potato Granules and Their Application in Bread Making. Changsha: Hunan Agricultural University (in Chinese). Liu, J.G., Chen, X.W., 1999. A brief introduction to the technologies for processing potato granules. Potato Mag 13 (1), 58 60 (in Chinese). Ooraikul, B., 1978. Production of Potato Granules. U.S. Patent: 4110478, 1978. Van Oirschot, Q.E.A., Rees, D., Aked, J., et al., 2006. Sweetpotato cultivars differ in efficiency of wound healing. Postharvest Biol. Technol. 42, 65 74.
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Yuan, L.N., 2009 Research on the Anti-breaking of Sweet Potato Granule Cells and Their Thickslurry Food. Wuhan: Central China Agricultural University (in Chinese). Zhang, T., 2004. New Technologies for Producing Whole-cell Sweet Potato Granules. People’s Republic of China: 03100273.0 (in Chinese). Zhang, Y., Xiao, Y.L., Chen, G., et al., 2012. A study on the influence of sweet potato granules on noodle quality. Food Ferment. Technol. 48 (1), 44 48 (in Chinese).