Sweetpotato (Ipomoea batatas) is the seventh most consumed staple food in the world and is considered a food security staple in developing countries due to its adaptability to climate change and productivity under drought conditions (Bonvell-Benjamin, 2007). The main component of sweetpotato is complex starch, yielding one of the densest caloric root vegetables, 86 kcal/100 g [U.S. Department of Agriculture (USDA), 2018]. Sweetpotato has a lower glycemic index (GI) than simple carbohydrate sources, and the abundance of fiber prevents the absorption of glucose in the small intestine, thereby reducing the rate of insulin secretion (Jenkins et al., 1988). For this reason, sweetpotato is considered a good substitute in diabetic and weight control diets for simple, starchy foods such as white bread and potatoes (Solanum tuberosum) (Jenkins et al., 1988). The crop also has a variety of nutritional benefits with respect to both macro- and micronutrients, is abundant in antioxidants, and orange-fleshed cultivars are prominent in carotenoids (Burri, 2011). United States sweetpotato production has greatly increased during the past 15 years, reaching 3.1 billion pounds in 2015 [USDA-National Agriculture Statistics Service (NASS), 2018]. Per capita consumption of sweetpotato increased from 4.2 to 7.6 lb from 2000 to 2015 due in part to awareness of its nutritive value and its increased use in value-added food products.
Mississippi is the third largest producer of sweetpotatoes after North Carolina and California (USDA-NASS, 2018). Sweetpotato is the fourth most valuable crop in Mississippi after soybeans (Glycine max), cotton (Gossypium hirsutum), and corn (Zea mays) (USDA-NASS, 2018). Between 2000 and 2015, Mississippi sweetpotato production increased by 155% (Johnson et al., 2015). In 2017, 29,000 acres were harvested (USDA-NASS, 2018). During an evaluation of the 2011 season, Morgan et al. (2012) reported that the Mississippi sweetpotato industry employed 1059 full-time equivalents. With the steady growth in recent years, the direct output has doubled from $66.4 million to $123 million in 2017 (USDA-NASS, 2018), with nearly an equivalent indirect impact (Morgan et al., 2012).
In addition to the increased production and consumption of sweetpotatoes, there is also increasing scrutiny of produce buyers and consumers of aesthetically pleasing sweetpotatoes meeting stringent guidelines for qualities, including size and shape. For example, Collart et al. (2019) reported that consumer willingness-to-pay for sweetpotatoes decreased as the portion of the sweetpotato skin affected by skinning injury increased. For the 2018 crop year, Meyers (2019) reported that many Mississippi producers did not harvest processing grade sweetpotatoes because of their low value and lack of value-added outlets. As a result, there is a need to develop additional value-added uses for processing grade sweetpotatoes that do not meet stringent standards required to be sold as a fresh market USDA no. 1 grade. One sector of value-added foods that has the potential for using processing grade sweetpotatoes is ice creams and nondairy frozen desserts.
Ice cream is a semi-solid foam or custard made from dairy products such as milk, cream, and nonfat milk powder. This complex and sweet-tasting colloid is frozen below its freezing point so that it is smooth and creamy (Goff, 1997). Commercially produced ice cream incorporates air for a desirable texture and increased volume. Ice cream is a standardized food in the United States that is defined as a dairy frozen dessert when there is a minimum of 10% fat and less than 50% overrun (U.S. Food and Drug Administration, 2018). Ice cream is categorized as economy, premium, and super premium based on its fat content, total solids, and overrun. The greater the amount of fat added and the less air incorporated will result in a smoother ice cream. However, dairy-based products, including ice cream, should not be consumed by those requiring a dairy-free diet because of lactose intolerance, dairy allergies, and/or veganism (Mäkinen et al., 2016).
The global nondairy frozen dessert market reached $400 million in 2017 (Ahuja and Rawat, 2018). Plant-based milk alternatives used in frozen desserts are typically opaque liquid extracted from legumes or tree nuts, most commonly almond (Prunus dulcis) and soybean. Compared with milk, plant-based milk alternatives are lower in calories and comparable in calcium content (Mäkinen et al., 2016). In nondairy frozen desserts, cream is replaced by vegetable oil to maintain a smooth texture; however, coconut (Cocos nucifera) oil can also be used to improve the texture of frozen desserts by functioning as an emulsifier (Santana et al., 2011). Coconut oil is a highly saturated oil with a sweet aroma. It is a natural source of medium-chain fatty acids (MCFAs), with more than 50% MCFAs. MCFAs consist of 6 to 10 carbons; therefore, the hydrolysis and absorption of MCFAs is more efficient than that of long-chain fatty acids because the mechanism of its digestion is similar to glucose (Marten et al., 2006). Coconut oil has a high melting point (24.4 °C), which enables the possibility of its use in frozen desserts. Additionally, coconut oil is used in many commercial products to improve health benefits (Choo et al., 2010) and shelf stability.
In nondairy frozen desserts, milk is replaced with fortified plant-based milk alternatives. Whole milk contains 3.3% protein and almond milk contains 0.5% protein, which is the lowest concentration of the 14 different milk alternatives on the market. The protein content of soy milk varies according to manufacturers. Almond milk and soy milk contain more fiber and less saturated fat than milk (Mäkinen et al., 2016). Although the market for nondairy frozen desserts is rapidly growing, they are not as acceptable as ice cream. Bisla et al. (2012) reported that ice cream made from 100% milk was preferred over that made from 100% soy and other plant-based milk alternative “ice creams.” In a sensory evaluation study of milk (whole, reduced fat, and fat-free) and soy milk (vanilla, fortified, and organic), milk was preferred (Palacios et al., 2009). The objective of this study was to develop sweetpotato-based ice creams and nondairy frozen desserts to add value to underused processing grade sweetpotatoes.
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