Food Science and Technology Project Topics

Functional Properties of Fermented and Unfermented Sweet Potato-pigeon Pea Weaning Food

Functional Properties of Fermented and Unfermented Sweet Potato-pigeon Pea Weaning Food

Functional Properties of Fermented and Unfermented Sweet Potato-pigeon Pea Weaning Food

Chapter One

Aim and Objectives of the Study

            The aim of this project study is to examine the functional properties of fermented and unfermented sweet potato-pigeon pea weaning food.

Objectives of the study

The objectives of the study include the following:

  1. to produce fermented and unfermented sweet potato-pigeon pea weaning food
  2. to evaluate the functional composition of the samples



 Sweet Potato (Ipomoea batatas)

            Sweet potato, Ipomoea batatas L. (Lam.), is an important economic crop in many countries. In terms of annual production, sweet potato ranks as the fifth most important food crop in the tropics and the seventh in the world food production after wheat, rice, maize, potato, barley, and cassava (FAO, 2016). Sweet potato fulfills a number of basic roles in the global food system, all of which have fundamental implications for meeting food requirements, reducing poverty, and increasing food security (El‐Sheikha and Ray, 2017). Sweet potato roots have high nutritional value and sensory versatility in terms of taste, texture, and flesh color (white, cream, yellow, orange, purple). The varieties with high dry matter (>25%), white‐cream flesh color, and mealy firm texture after cooking are preferred by the consumers in the tropics. These varieties are known as tropical sweetpotato (e.g., “bianito,” “batiste,” or “camote”). The purple‐fleshed sweet potato varieties with attractive color and high anthocyanin content are the specialty type in Asia.

In the United States, the commercially popular type is the orange‐fleshed sweet potato with low dry matter content (18–25%), high β‐carotene level, sweet and moist‐texture after cooking. This sweet potato type is imprecisely called “yam,” which is not the true tropical yam of Dioscorea species. Historically, African Americans in Louisiana referred this moist‐ sweet potato as “nyami” because it reminded them of the starchy tuber of that name in Africa. The Senagalese word “nyami” was eventually shortened to the trademark “yam” popular in the United States. Commercial packages with “yam” labels are required by the US Department of Agriculture to have the word “sweet potato” in the label to avoid confusion to the consumers (Estes, 2009).

Depending on the flesh color, sweet potatoes contain high levels of β‐carotene, anthocyanins, phenolics, dietary fiber, vitamins, minerals, and other bioactive compounds. The β‐carotene in orange‐fleshed sweet potatoes can play a significant role as a viable long‐term food‐based strategy for combating vitamin A deficiency in the world. Studies in Africa demonstrated that increased consumption of orange‐fleshed sweet potatoes improved the vitamin A status of children, pregnant women, and lactating mothers (Van Jaarsveld et al., 2005; Low et al., 2007; Hotz et al., 2012).

Production and consumption of sweet potato

            Sweet potato has wide production geography, from 40° north to 32° south latitude of the globe, and it is cultivated in 114 countries. The world total production of sweet potatoes was 106.60 million metric tons (MMT) in 2014. Since the mid‐2000s, global production has ranged from a low of 101.28 MMT in 2007 to a high of 147.17 MMT in 1999. In 2014, about three‐fourth of the global production was from Asia and Pacific Islands, followed by Africa with about 21%, while the Americas (North, Central, and South) account for about 3.6%. China was the leading producer of sweet potatoes, with 71.54 MMT or about 67% of the global production, followed by Nigeria (3.78 MMT), Tanzania (3.5 MMT), Ethiopia (2.7 MMT), and Mozambique (2.4 MMT). The United States was the tenth largest producer, with 1.34 MMT production. Only two countries in Europe, Portugal and Spain, grow sweet potatoes, with 22,591 and 13,550 metric tons produced in 2014 (FAO, 2015).

In comparison to other major staple food crops, sweet potatoes have good adaptability to marginal growing conditions, short production cycle, and high yield potential. The average world yield of sweet potatoes is about 14 tons per hectare. Under subsistence conditions in many areas of the tropics, the average sweet potato yield is about 6 metric tons/hectare, far below the 20–26 metric tons/hectare obtained in China, Japan, and the United States, where improved varieties, fertilizer applications, and cultural managements have been introduced. The per capita consumption is highest in places where sweet potatoes are consumed as a staple food, e.g., Papua New Guinea at 550 kg per person per year, the Solomon Islands at 160 kg, Burundi and Rwanda at 130 kg, and Uganda at 85 kg. The average annual per capita consumption of sweet potatoes is estimated at 18 kg in Asia, 9 kg in Africa, 5 kg in Latin America. Between 2000 and 2014, sweet potato consumption in the United States increased nearly 80%, from 1.9 kg to 3.4 kg per capita (FAO, 2015; Johnson et al., 2015).

Sweet potato consumption has been greatly enhanced by the wide spread commercial availability of frozen “French‐fried” sweet potatoes. To accommodate this recent growth trend, increased modern processing capacity has been built within the southern US sweet potato growing regions (Johnson et al., 2015).

Classification and origin of sweet potato

            The sweet potato (I. batatas L.) is a dicotyledonous plant belonging to the morning glory or Convolvulaceae family. It is a new world crop, though there is still some confusion that exists regarding its origin, and primary and secondary centers of diversity. Roullier et al. (2013a, b) and Grüneberg et al. (2015) have published thorough reviews of this topic. In brief, using data from morphology, ecology, and cytology, Austin (2008) has postulated that cultivated sweet potatoes originated somewhere in the region between the Yucatan Peninsula of Mexico and the mouth of the Orinoco river in northeastern Venezuela. Recent studies conducted by Roullier et al. (2013 a, b) incorporating chloroplast DNA and molecular phylogeny analyses confirm this hypothesis. They also suggest that I. batatas most likely evolved from at least two distinct autopolyploidization events in wild populations of a single progenitor species most likely I. trifida.

Secondary contact between sweet potatoes domesticated in Central America and in South America, from differentiated wild I. batatas or I. trifida populations, could have led to further introgression. Molecular marker analyses conducted by Huang and Sun (2000) and Zhang et  al. (2000) also places Central America as the region with the most genetic diversity and probable origin (Huang and Sun, 2000; Zhang et al., 2000). Remains of dried sweetpotato roots found in Peru have been radiocarbon dated back to 8,000–10,000 years old, though it is unknown if these were collected from the wild or were domesticated (Engel, 2000). Regardless of the center of origin, sweetpotato was widely established in tropical regions of the new world around 2500 b.c. (Austin, 2008). It was established in Polynesia, prior to European arrival (Roullier et al., 2013b). Europeans in the 1500s spread the sweet potato to Africa and India, with it arriving in China prior to 1600. Secondary centers of diversity include New Guinea, the Philippines, and parts of Africa (Bohac et al., 2005; Roullier et al., 2013a, b).





Sweet potato (Ipomoea batatas) and Pigeon pea (Cajanus cajam) used in the research work was purchased from a local market in Owo, Ondo State. The samples were processed in Food Processing Laboratory, Rufus Giwa Polytechnic Owo, Ondo State, Nigeria


Preparation of fermented sweet potato-pigeon pea flour

Fresh sweet potato root were washed, peeled, sliced and pigeon pea seeds were winnowed, sorted, drained. The two cleaned samples (sliced sweet potato root and washed pigeon pea were soaked together (fermented together for 72 hours). After 72 hours, the fermented samples were washed, wet milled, sieved, sedimented for 24 hours, drained, sun dried for 3 days and dry milled into powder, sieved and packaged in airtight container for further analysis (Fig. 1).




Table 4.1: Functional properties of Fermented and unfermented sweet potato-pigeon pea weaning food





            Based on the functional composition, it was observed that unfermented weaning food (pigeon pea and sweet potato) has highest property, and was selected for formulation of complementary food. From the bulk density, oil absorption capacity, swelling ability, foaming capacity, foaming stability, least gelation capacity and oil absorption capacity, it was observed that unfermented pigeon pea and sweet potato could be used for weaning formulation.


It is recommended that further study should be carried out on the health benefits of consuming fermented and unfermented weaning food with incorporation of pigeon pea and sweet potato. It is also recommended that consumers should be introduced to weaning food as it is not popularly known, especially in the western part of Nigeria where this work was carried out. It is recommended that further study be carried out on the following: Nutritional (proximate) composition of other fermented and unfermented products; Shelf-stability studies on weaning (fermented and unfermented); Feeding trials using bioassay and so on.


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