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1. Introduction
Numerous instant food products continue to emerge in food markets due to the growing demand for convenience foods and the reduced labour involved in food preparation. In some studies, the correlation between convenience and food choice or preference has been discussed (de Boer et al., 2004; Jaeger, 2006). Jaeger (2006) asserts that convenience in product handling, preparation, and consumption has increasingly influenced consumers’ purchasing decisions. According to Aworh (2008), the development of various instant traditional root- and tuber-based food products is particularly attributable to the difficulties associated with processing root and tuber products. Dioscorea alata is one of such tuber crops.
One of the 11 commercially important yam species and a main crop in tropical and subtropical areas is water yam, often referred to as winged yam (Neina, 2021). Due to its favorable agronomic traits and quality properties, such as its high yield, improved tuber storability, and resistance to non-staking conditions, this yam species is widely farmed (Neina, 2021). Because of its low sugar content, water yams have a low glycaemic index, which is beneficial for diabetics (Udensi et al., 2010). Moreover, it contains significant amounts of potent antioxidants such as diosgenin, alkaloids (dioscorine), and polyphenolic chemicals (tannins). In comparison to D. cayensis, D. escunlenta, D. rotundata, and D. trifida, it also has a greater protein content, more vitamin C, and fewer fats (Muzac-Tucker et al., 1993).
Additionally, water yams have anti-cancer, purgative, anti-inflammatory, anti-rheumatism, and anti-leprosy qualities. It has antioxidant properties and seems to reduce diabetes (Zhang et al., 2019). Even though water yam has many agronomic and nutritional benefits, it is still underutilized. This is mainly because consumers have historically believed that water yam is inferior to white yam in terms of food product quality, which has led to the neglect of the many health, nutritional, and economic advantages of this yam species. Traditionally, water yam is processed into boiled yam, yam flour for amala, fried yam, and fried yam balls known as Ojojo (Barde et al., 2021).
Ojojo is a deep-fat fried snack produced from Dioscorea alata tuber (Onwueme, 2006). According to Aminu et al. (2018), the freshly peeled D. alata tuber is traditionally grated into a viscous mass and mixed with other chopped vegetables like pepper and onion. The grating of the tuber takes the most energy and time, making it the most laborious process. To reduce the drudgery associated with traditional Ojojo preparation, a simpler method involving the conversion of Dioscorea alata tuber into flour has been proposed. This method could improve handling, storage, and year-round availability. However, optimizing the frying process remains crucial, as it significantly impacts the textural and sensory qualities of the final product (Ananey-Obiri et al., 2018; Giovanelli et al., 2017; Sobukola et al., 2008). Squeezing the tissue against the abrasive surface of grating utensils also causes hand injuries for processors. As a result, scientific research is required to lessen or eliminate the monotony of traditional Ojojo processing. A form of value addition would be the development of a simpler method for preparing the product (Aminu et al., 2018). This could be done by carefully grinding the Dioscorea alata tuber into flour, which will make it easier to handle, store, and keep for longer and can be used to make Ojojo all year. Nonetheless, the frying process of Ojojo should be controlled.
According to Ananey-Obiri et al. (2018), deep-fat frying is a common method of cooking that uses oil or fat as the medium for the transfer of heat and comes into direct contact with the food at a temperature above the boiling point of water. It is a complicated process that involves the temperature of the heated oil, the amount of time it takes to fry, the method used, the ratios of food weight to frying fat volume and surface area to volume, some characteristics of the food, and the fat source (Sobukola et al., 2008). The food’s physical, chemical, and sensory characteristics are altered. As a result, giving the products a better texture, improved appearance, and enhanced flavor (Giovanelli et al., 2017). According to reports, deep-fat frying increases the fat content of fried food because of the oil’s absorption and retention. This means that the average calorie consumption of French fries and hamburgers is 42% and 53%, respectively, after frying (USDA, 2013). According to reports, interactions between the amino group of lysine and carbonyl compounds caused the available lysine in fish fillets to decrease by approximately 17% and by 25% when the fish oil was used for continuous deep-fat frying for 48 h (Oluwaniyi et al., 2010). Abebe et al. (2024) found that for fried sweet potato chips of different varieties (Kabode, Dilla, and Kulfo, respectively), the optimum frying temperatures were 154.8°C for 3.82 min, 160.1°C for 3.66 min and 162.65°C for 3.04 min. According to Fikry et al. (2021), the optimum frying temperature and time for fried falafel—a typical Egyptian dish made with chickpeas, water, onion, garlic, spices, parsley, paprika, and sesame seeds—are 178.8°C and 11 min. Fried yam chips were shown to have an optimal frying temperature of 175-180°C while utilizing tubers with an initial dry matter of 0.18-0.21 kg/kg and frying for 4-5 min (Sobukola et al., 2008). However, as of the time this article was written, Ojojo’s frying conditions had not been reported.
The Ojojo’s texture and subsequent consumer acceptance are thought to be affected by variations in frying temperature and time. As a result, the purpose of this research is to ascertain the relationship between the textural characteristics and consumer acceptability of Ojojo made from Dioscorea alata flour at various frying temperatures and times. This study aims to explore these variables to establish optimal frying conditions for Ojojo made from Dioscorea alata flour, thereby ensuring consistent quality and broad accessibility throughout the year.
2. Materials and methods
The Dioscorea alata tubers (white-fleshed variety), groundnut oil, fresh pepper, and onions were purchased from the Oja Oba market in Nigeria’s Kwara State Ilorin-west Local Government Area. The Food Science and Technology Laboratory at Kwara State University, Malete provided the knife, grater, trays, cabinet dryer, blender, deep fryer (Crown Star 3.5 L, MC-DF3139, Guangzhou FHT China Technology Co., Ltd., Shenzhen, China), weighing balance, plastic buckets, aluminum foil, and other utensils.
Okoye et al.’s method (2018) was modified to make flour from the tubers of Dioscorea alata. Sorting was used to get rid of the mechanically damaged tubers of Dioscorea alata that had reached maturity. To get rid of dirt and soil, the tubers underwent a thorough washing. Before being blanched at 100°C for 2 min and drained in a basket, the properly washed tuber was hand-peeled and sliced thinly with kitchen knives. Before hammer milling and sieving (500 mm mesh size), the blanched Dioscorea alata slices were spread out in a single layer inside a perforated tray and dried in an oven at 60°C for 12 h. Before any further processing, the flour was packed in a bag made of polyethylene.
According to Okoye et al.’s method (2018), which had been modified, was used to make the Ojojo. About 100 g of flour and 200 mL of water were combined to make the paste for Ojojo preparation. To 200 g of the paste, approximately 5 g of chopped fresh pepper, 4 g of chopped onions, 0.1 g of seasoning, and 0.1 g of salt were added. After thoroughly mixing the ingredients with a handheld food blender, 40 mL of the mixture was scooped into an electric deep fryer (Crown Star 3.5 L, MC-DF3139, Guangzhou FHT China Technology Co., Ltd.) with 3 L of hot vegetable oil to deep fried (Fig. 1) at various temperatures and times determined by the Central Composite Rotatable Design of Design Expert Software version 6.0 (Table 1).
The sensory properties of the Ojojo were evaluated using a well-structured questionnaire with 20 panelists selected among the students of the Kwara State University Malete, Kwara state. Each panelist was presented with nine different coded samples of Ojojo produced from different frying temperatures and times. Sensory evaluation was carried out by scoring each sample on a 9-point hedonic scale (where 9 = extremely liked and 1 = extremely disliked). The sensory attributes evaluated on the Ojojo are taste, texture, color, appearance, aroma, and overall acceptability. The sensory evaluation was done to pick the most liked, slightly liked, and least liked samples which were then used for texture analysis and consumer acceptability. The Kwara State University Ethical Committee in Malete, Kwara State, issued the ethical permission to conduct this study (Ref: KWASU/CR&D/REA/2023/0060) following the Helsinki Declaration of 1975 on human experimentation.
The 170°C for 5 min, best frying condition from the sensory acceptability test, was used to produce the control sample from fresh Dioscorea alata tuber. Before proceeding with subsequent analyses, the Ojojo was drained and allowed to cool. The overall acceptability of the Ojojo showed that 170°C for 5 min (Fig. 2A) was the most liked, 160°C for 3 min (Fig. 2B) was slightly liked, and 180°C for 4 min (Fig. 2C) was the least liked. Then, the Ojojo (4 samples) produced under each of these frying conditions was evaluated for its texture attributes and sensory acceptability.
The Sensorial texture profile analysis (STPA) was done using the method that was reported by Otegbayo et al. (2007). This was done with a well-structured questionnaire using the same panelists (20 persons) who participated in the sensory evaluation following verbal agreement. To score for chewiness, gumminess, and hardness, four distinct coded samples of Ojojo were presented to each panelist. These samples had been fried at various temperatures and times.
A TA-XTPlus-Stable Microsystems, United Kingdom, 50 kg load cell texture analyzer was utilized for the instrumental texture profile analysis of the Ojojo. The Ojojo’s resilience, hardness, chewiness, and gumminess are the texture characteristics derived from the analyzer. During the evaluation, the Ojojo samples were kept in a cooler at 28-30°C (Awoyale et al., 2021).
A well-structured questionnaire with 50 respondents was used to assess Ojojo’s sensory acceptability in three locations within Kwara State—Malete (longitude 8°43′23″N latitude 4°29′2″E), Ilorin (longitude 8°31′7″N latitude 4°28′58″E), and Safari (longitude 8°42′17″N latitude 4°28′1″E).
The Statistical Package for the Social Sciences (SPSS version 21) was utilized for the analysis of the variance of the generated data. Response Surface Central Composite Rotatable Design from Design-Expert (version 6.0) was utilized for the optimization. Using XLSTAT free version 2022, the principal component analysis (PCA) was used to summarize the relationships between Ojojo’s textural attributes and sensory acceptability.
3. Results and discussion
There was a significant difference in all the sensory properties of the Ojojo samples. However, there were no significant differences (p>0.05) in the Ojojo fried at 170°C for 4 min, and 170°C for 3 min in terms in terms of all the sensory properties (Table 2). Ojojo fried at 170°C for 5 min was the most preferred, and Ojojo fried at 180°C for 4 min was the least liked in terms of the overall acceptability. The variations in the overall acceptability of the Ojojo samples may be attributed to the different processing conditions.
Awoyale et al. (2021) reported that texture is an important characteristic that influences consumer acceptability of starchy products. The sensory texture characteristics of Ojojo produced at various frying temperatures and times are shown in Table 3. All the samples were, on average, chewable, moderately hard, and gummy. The hardness and chewiness of the Ojojo samples did not differ significantly (p>0.05), but the gumminess was significantly different from the control sample (Table 3).
Hardness is one of the most important texture parameters in determining whether a product is acceptable to consumers (Akissoe et al., 2009; Otegbayo et al., 2007). The findings indicate that Ojojo consumers may prefer moderately hard products. Even though both samples were fried at 170°C for 5 min, the Ojojo’s hardness from the frying condition of 170°C for 5 min was significantly different from the control sample (p<0.05). This could have something to do with the Ojojo being made before the yam tuber was processed into flour. However, frying at 160°C for 3 min and 180°C for 4 min yielded Ojojo of comparable hardness to the control sample. This is because the hardness of these samples and the control sample did not differ in a statistically significant way (p>0.05).
Gumminess is one of the changes that take place in cell separation during the frying of snacks. It is the degree to which samples stick to the hand, mouth surface, or teeth (Otegbayo et al., 2007). A moderately sticky Ojojo might be liked by buyers. All the Ojojo samples had significantly different gumminess from the control sample (p<0.05). This variation may be attributed to the flouring of the fresh Dioscorea alata tuber before the production of the Ojojo samples. Additionally, the increased frying time of the fresh paste may have reduced the exudation of gelatinized starch, resulting in the control sample’s high gumminess. The release of amylose or gelatinized starch from the ruptured cells of the control sample may also cause the separation of the cells (Abong et al., 2009).
According to Karaolu and Kotancilar (2008), chewiness is the mouthfeel that results from prolonged elastic resistance from the food. It is interesting to note that the chewiness of the Ojojo produced at 170°C for 5 min was not significantly different from that of the control sample (p>0.05). This suggested that the product’s chewiness, in comparison to other sensory texture characteristics like hardness and gumminess, is unaffected by the fresh Dioscorea alata tuber’s transformation into flour prior to the production of Ojojo.
Table 4 displays the instrumental texture characteristics of the Ojojo produced at various frying temperatures and times. The force required to compress the sample is its hardness (Otegbayo et al., 2007). The Ojojo that was produced under each of the frying conditions did not significantly differ in hardness from the control sample (p>0.05). This indicates that the instrumental hardness of the product is unaffected by the fresh Dioscorea alata tuber being turned into flour before the production of Ojojo.
If the surface of the sample is sticky, a negative force will be generated after the sample has been subjected to pressure deformation. It can be interpreted as having a sticky texture in the food industry (Goddard et al., 2015). The degree to which the fried food adheres to the hand, mouth surface, or teeth is known as adhesiveness (Awoyale et al., 2021). The Ojojo’s adhesiveness ranged from -15.40 to -1.84 N/m2, with the control sample having the highest adhesiveness and the Ojojo fried at 180°C for 4 min having the lowest adhesiveness. As a result, the Ojojo prepared from the control sample may not be as tasty for consumers as the Ojojo prepared from the frying condition of 180°C for 4 min.
Gumminess is the amount of energy required to break down a semi-solid food so that it can be taken in. It is calculated by multiplying the cohesiveness by the hardness (Awoyale et al., 2021; Goddard et al., 2015). The gumminess of the Ojojo samples went between 1.40 N/m2 and 2.00 N/m2. Ojojo of comparable gumminess to that of the control sample was produced from the frying condition of 180°C for 4 min, even though there was no significant difference (p>0.05) in the gumminess of the Ojojo samples. However, the texture of fried starchy foods suffers from gumminess (Otegbayo et al., 2007). This suggested that, due to their lack of gumminess, the Ojojo produced under frying conditions of 170°C for 5 min and 160°C for 3 min might be more popular with consumers.
The energy required to masticate solid food to a ready-for-swallow state is chewiness (Chandra et al., 2015). It is essential to note that the chewiness of the Ojojo produced under all frying conditions was not significantly different from that of the control sample (p>0.05). This suggested that the chewiness of Ojojo is unaffected by the fresh Dioscorea alata tuber being ground into flour prior to production.
According to Yusuf et al. (2017), products may not be accepted by consumers if they are perceived to have poor textural quality. The results of sensory acceptability test revealed that the samples, location, and interaction between the samples and locations significantly influenced Ojojo’s consumer acceptability. In all three locations (Malete, Ilorin, and Safari Town), the control sample performed the best (p<0.05) (Table 5). This could be because the Ojojo has a significant (p<0.05) negative correlation with sensory gumminess (r=-0.94) and a positive correlation (r=0.96) with consumer acceptability (Supplementary Table S1).
The principal component analysis biplot also showed that the control sample, a fresh Ojojo from Dioscorea alata tuber, was in the same quadrant as the Ojojo’s sensory gumminess (Fig. 3). Compared to the control sample, the Ojojo produced under the frying conditions of 180°C for 4 min, 160°C for 3 min, and 170°C for 5 min was slightly acceptable (Table 5). The positive correlation that exists between the instrumental adhesiveness (r=0.85), and the consumer acceptability of the Ojojo may be the reason for the slight acceptability of the Ojojo produced from 170°C for 5 min (Fig. 3, Supplementary Table S1). Additionally, as depicted in Fig. 3, the 108°C for 4 min fried Ojojo’s slight acceptability may be attributable to its sensory hardness.
We were able to separate the Ojojo samples based on the textural characteristics and consumer acceptability of the Ojojo using the Principal Component Analysis (PCA) biplot in Fig. 3. Principal Component (PC)1 was responsible for 53.32 percent of the variance in the data, while PC2 was responsible for 28.93 percent. The Ojojo’s instrumental adhesiveness, instrumental hardness, and consumer acceptability were all in the same quadrant with Ojojo produced at 160°C for 3 min and 170°C for 5 min. In a similar vein, the control sample was in the same quadrant as the Ojojo’s sensorial gumminess, while the Ojojo from 180°C for 4 min was in the same quadrant with the sensorial hardness. This indicated that the instrumental hardness and instrumental adhesiveness may have contributed to the consumer preference for the Ojojo prepared from the frying temperatures of 160°C for 3 min and 170°C for 5 min in all locations.
4. Conclusions
The acceptability of the Ojojo prepared at 160°C for 3 min and 170°C for 5 min by the consumer was linked to instrumental adhesiveness and instrumental hardness. Similarly, the primary characteristic of the Ojojo made at 180°C for 4 min is the sensory hardness, while that of the control sample exhibited sensory gumminess. Therefore, fresh Dioscoreaalata tuber can be processed into flour and utilized for Ojojo production at frying temperatures and times of 160°C for 3 min or 170°C for 5 min to reduce the drudgery involved in the use of fresh Dioscoreaalata tuber and obtain preserved Ojojo.
