**1.1 African yam bean**

African yam bean which, is commonly referred to as AYB, is one among the underutilized grain legumes of tropical Africa. The crop is grown for its edible seeds and tuberous roots. **Figure 1** presents AYB seeds harvested from a field evaluation in 2020. AYB seeds are enclosed in pods measuring about 3–15 cm long, such that a single pod can accommodate up to 30 seeds. The crop is a climber usually grown in mixed cropping with major crops [10–12]. AYB is locally adopted and has wide adaptability across diverse environmental conditions [13, 14]. Even though the crop is usually cultivated as an annual crop [15–17], some schools of thought consider it as perennial [18–20]. The cultivation of AYB majors among smallholder farmers across sub-Saharan Africa, of which Nigeria is one country prominent on the list [21]. The consumption of AYB is known to contribute to daily nutrition, food availability, and diet diversification to communities utilizing it; this date back to the Nigerian civil war of 1967–1970, where the crop's food and nutritional potentials were efficiently utilized in fighting malnutrition and hunger [15, 22–24].

The seeds of AYB provide an affordable source of protein when compared with other plant sources and animal extract. Aside from its rich protein content, its high carbohydrate content [25, 26] is comparable to the amount reported in grain cereals.

**Figure 1.** *Dried AYB seeds. (A) Non variegated seeds (B) Variegated seeds. Source: field evaluation (Shitta et al. [9]).*

#### *A Review on the Cooking Attributes of African Yam Bean (*Sphenostylis stenocarpa*) DOI: http://dx.doi.org/10.5772/intechopen.99674*

AYB's amino acid (histidine, isoleucine, lysine, methionine) profile is more in quantity than the amount observed in soybean [27–29]. Likewise, several authors have reported the presence of essential nutrients in AYB's seeds [25, 26, 30–36]. AYB tubers (**Figure 2**) contain considerable amount of magnesium (167 mg/100 g), potassium (1010 mg/100 g), protein (15–16%), and carbohydrate (67–68%) [34]. In addition to the crop's nutritional qualities, the crop is flexible for use in various diets; it can be utilized as a condiment, or as a whole meal, or as a snack. The contribution of AYB in feeds enrichment is an added advantage of the crop's food and nutrition attributes [37, 38].

Considering the enormous potential of AYB and its role in some African traditions [39–41]; the efficient utilization of AYB can reduce hunger and nutritional challenges in sub-Saharan Africa. Nevertheless, the food potential of the crop remains widely untapped, which can be attributed to several constraints such as long cooking hours of up to 24 hours [41–44], a long-maturity cycle of 9–10 months [16, 17, 45], and the abundance of anti-nutrition factors [35, 46–49]. However, the genetic variability reported in the crop [9, 50–53] provides a foundation for breeders to develop improved cultivars. In particular, the availability of AYB cultivars with reduced cooking time could boost the cultivation and consumption of the crop. Up-to-date information on cooking-related attributes is a prerequisite for improving cooking time trait. Keeping the above in view, the present review brings to knowledge cooking variables reported in AYB. Also, the review proposes the application of standard procedures and molecular technology for advanced studies. Furthermore, the present document is intended to stimulate more research interest towards improving cooking time in the crop.

**Figure 2.** *AYB tubers. Source: field evaluation (Shitta et al. [9]).*


**Table 1.**

*Means of some physical properties reported in AYB seeds.*

#### **1.2 Structure of African yam bean seeds**

Past research investigations have explained the relationship between seed properties, variety type, seed storage conditions, and cooking time [54, 55]. **Table 1** presents the physical properties reported in AYB seeds. AYB seeds are, dicot in nature and they can measure up to 10 mm in length and 7 mm in width and thickness[9, 50–53, 56]. The seeds of AYB differ in texture across germplasm; they could be rough, wrinkled, or smooth. The electron microstructure study of seeds revealed the presence of smooth starch granules exhibiting different sizes and shapes [57]. The cells were bounded by cell walls same as observed in other legumes [58, 59]. Likewise, the round undulating surface observed in the cotyledon is similar in structure to that of cowpea [59, 60]. For seeds subjected to milling, the cotyledon and cell components showed structural change. Equally, cell wall materials and protein matrix were reduced to flakes and particles; however, the structure of starch granules remained unchanged. The micrographs of cotyledon, flour, and starch showed the size of starch granules within the range of 4–40 μm for lengths and 4–25 μm for diameter [57].

#### **2. Cooking quality in African yam bean**

Preparing and cooking food is an integral part of daily living [61, 62]. For example most grain legumes are subjected to cooking before consumed; the cooking process converts raw food into a ready-to-eat product. Also, cooking facilitates the destruction of foodborne pathogens, thereby eliminating microbial hazards and achieving quality [63]. Moreover, the physical and chemical changes that occur during cooking increases the digestibility and availability of nutrient for use and storage in the body [64]; through processes including inactivation of antinutrient, starch gelatinization, proteins denaturation, leaching of polyphenols and solubilization of polysaccharides among other factors [59, 65, 66]. Despite the importance of cooking in food and nutrition the cooking culture is dwindling, especially in industrialized societies where individuals are exposed to a busy lifestyle with little time at their deposal. To cope with busy schedules, consumptions are choosing convenience food that requires less cooking time. Also, reports have shown that consumers are ready to pay more in exchange for long cooking hours [67, 68].

Cooking time, an attribute of cooking quality is defined as the time from the beginning of cooking up to when the food becomes tender and suitable to eat [66, 69]. AYB, the same as most legumes is characterized by seed hardness, requiring long


*A Review on the Cooking Attributes of African Yam Bean (*Sphenostylis stenocarpa*) DOI: http://dx.doi.org/10.5772/intechopen.99674*

**Table 2.**

*Source, cooking method, cooking time, end product, and references reported in AYB cooking experiments.*

cooking hours of up to 24 hours (**Table 2**) in some scenarios [80]. Seed hardness has been identified as a heritable trait but also affected by seed composition, production, and, storage environment [54, 81, 82]. The mechanism by which seeds become hard-to-cook is categorized as a very complex phenomenon; it includes processes such as changes in the intracellular cell wall, middle lamella, polysaccharides, and other components. The hard-to-cook mechanism in seeds has been extensively reviewed by authors [83–85]. According to a particular study, an increase in calcium ion concentration led to a subsequent increase in seed hardness and a decrease in phytate concentration. It was also reported that a higher rate of leaching in phytate and peptic acid occurred in cooked and soaked hard-to-cook seeds than in fast-to-cook seeds [85].

Generally, grains with short cooking time are more preferred by consumers; because less time is invested in their preparation, and importantly less energy is spent when compared to energy requirements for grains with long cooking time. In addition, several studies have shown that nutrients such as minerals and proteins are conserved when grains are cooked over a short period. In contrast grains requiring long cooking hours usually lose a significant amount of nutrients [55, 86]. Cooking methods reported in AYB include boiling, steaming, roasting, and frying. However, advanced procedures including, sensory analysis: involving sensory panel [87, 88]; tactile method: [89] a method of compressing seeds within the thumb; texture analysis: [87] a method that measures the resistance of seed compression using a texture analyzer [90] have been investigated in major legumes.

#### **2.1 Cooking method reported in AYB**

#### *2.1.1 Boiling*

Boiling cooking method is a moist approach whereby the target food is submerged into a liquid. Cooking is achieved through the transfer of heat from the cooking equipment to the liquid in contact with the food. The food surface absorbs the heat and through conduction, the heat passes through to cook the food. The boiling method was experimented with selected AYB grains. The steps included boiling the grains in water for 480 minutes (**Table 2**) and thereafter oven drying for 24 hours before milling into flour [70]. In another report, AYB grains were boiled for 228 minutes. The analysis of the boiled seeds showed a reduction in phytate content and an increase in moisture content [47]. In addition, the boiling cooking method was reportedly used in preparing porridge. The procedure included presoaking seeds overnight and boiling them for 60 minutes. The porridge analysis showed an increase in carbohydrate, gross energy, fiber, lipid, water absorption capacity, oil absorption, bulk density, and gelation capacity however a decrease in protein and moisture content was observed [71].
