Effect of fermentation periods on the nutrient quality and sensory acceptability of Africa Yam Beans ( Sphenostylis sternocarpa ) porridge

(Sphenostylis sternocarpa) is a nutritious food source, not only is it high in protein, but also high in mineral, fiber, lipid, carbohydrate and other nutrients (Uche et al., 2014). Its protein contents compares with some major and commonly consumed legumes. Its amino acid profile is reported to be comparable to those of cowpea, soybean and pigeon pea (Obizoba and Nnam, African yam bean (AYB) is an underutilized trailing legume that grows as intercrop with yam and cassava usually for the edible seeds. The seed can serve as security crop with potential to boost human and animal protein requirement if grown on a large scale in recognition of its high protein content that range from 21 to 28% (Uguru et al., 2001). AYB is important food substitute of cowpea in many parts of Southeastern Nigeria where it is largely grown. For example, it was explored as a source of dietary protein in Southeastern Nigeria during the Biafran-Nigeria Civil war of 1967 – 1970 to feed the malnourished children and refugees (Nwokolo, 1987; Uguru et al, 2001). Introduction Available online at http://www.ajol.info/index.php/njb/index and www.biotechsocietynigeria.org ISSN: 0189 1731 Nig. J. Biotech. Vol. 36 (1): 9-16 (June 2019)

1992). AYB is believed to have strong potential for the management of malnutrition, some degenerative and chronic non-communicable diseases because of its dietary fibre content (Abioye et al., 2015). Proximate analysis of AYB seed by Abioye et al. (2015) showed that it contains 8.73-9.37% moisture, 28.63-30.43%protein, 2.40-3.33% fat, 3.23-3.70% ash, 2.40-3.05% crude fiber, and 50.80-53.57% carbohydrates. However, AYB contains some anti-nutritional factors (trypsin inhibitors, haemagglutins, phytate, tannin, oxalate and alkaloids) that hinder the availability of the nutrients and cause reduced growth (Nwokolo, 1987;Ajibade et al.,2005;Fasoyiro et al, 2006). One other limitation of AYB meal is the flatulence factor due to high content of oligosaccharide (stachyose and raffinose) (Nwinuka et al., 1997;Oboh et al., 1998), which freedom can be achieved through fermentation and other processing methods. AYB is also hard to cook but can be substantially reduced by pre-cooking treatment.
In Southeast region, AYB is processed and eaten by roasting in pan, the seed coat dehulled by bruising with hands or bottle on a flat surface and then winnowed to obtain clean and roasted seeds. The roasted seeds are packaged and retailed in cellophane or corked bottles. It is also sorted and washed in water and then cooked over-night, and made into porridge. As porridge, it can be mixed with yam, cocoyam or trifoliate yam in addition with such ingredients like crayfish, salt, pepper, onion, oil and vegetables. This is regarded as a family delicacy in some Communities of Southeastern Nigeria, especially Abia State. AYB seed are used for different food preparations in Nigeria and other West African Countries. Ogbonna and Sokari (1996) had reported on the fermentation of AYB seed for Owoh production. Jeff-Agboola (2007) also reported on the production of Otiru from AYB seeds through natural fermentation. The nutritional and anti-nutritional composition of AYB seed have been reported by several authors (Ajibade et al., 2005;Ajayi, 2011;Adelekan et al., 2012;Onuoha et al., 2017), unlike the fermented and cooked porridge made from AYB seeds. Studies on fermented and cooked AYB seed is important because the bioavailabilty of nutrients should best be considered based on processed conditions in which the food is consumed.
Fermentation is an important food processing method. It is a less expensive traditional processing method used to improve digestibility, nutritional quality of foods and at the same time, reduce the anti -nutritional factors and toxic substances like phytic acid, polyphenols, oxalic acid, hydrogen cyanide, r a f f i n o s e a n d s t a c h y o s e ( A b u r i m e , 2012).Fermentation modifies natural products and makes it a more acceptable nutrition with characteristic taste and aroma. Odunfa (1988) isolated some microorganisms like Lactobacillus and Bacillus spp in the fermentation of AYB. Ajayi (2011) also reported on the isolation of Aerococcus viridians and Pediococcus cerevisiae from AYB during fermentation. It is reported that undesirable anti-nutrient compounds are degraded by fermenting micro flora (Adanne et al., 2013), resulting in the enhancement of sensory and nutritional values of fermented products when compared to unfermented foods and substrates. Bearing in mind the importance of fermentation in food processing, this study was designed to understand the effect of fermentation periods on quality characteristics of Africa yam bean (Sphenostlis sternocarpa) porridge. The effect of fermentation periods (24, 48 and 72 h) at ambient temperature on the nutrient quality of Africa yam bean (Sphenostylis sternocarpa) porridge, the sensory acceptability and the microbial population involved in the natural fermentation were the major aims of this study.

Materials and Methods
African yam bean (AYB) (Sphenostylis Stenocarpa) was purchased from Ubani market in Umuahia metropolis of Abia State, Nigeria. The chemicals and equipment were from Central Laboratory Service Unit of National Roots Crops Research Institute (NRCRI) Umudike, Umuahia, Nigeria.

Sample preparations and natural fermentation
Five (5) kg of cream colored AYB seeds were sorted, weighed and divided into three portions of 1.5kg each. These portions were labeled 24h fermentation, 48h fermentation and 72 h fermentation. Each portion was washed and soaked in tap water in the ratio of 1:3 for 24h 0 natural fermentation at room temperature (30 C ± 2). The same procedure was used for 48 h and 72 h fermentation.

Preparation of African yam bean porridge
The AYB porridge was prepared according to the method in Figure I. After the fermentation process (24, 48 and 72 h), the beans was rinsed thoroughly with clean water. Each of the 1.5kilograms of the fermented and unfermented beans (control) was boiled with 2.5 liters of water for 90 minutes. The same amount and types of ingredients were added, mixed with wooden spatula and boiled further for 15 minutes and the porridge was made ready for analysis.

Proximate composition of Africa yam bean porridge
The proximate composition of the fermented and unfermented AYB porridge is shown in Table 1. There were significant (p<0.05) variations in the results obtained. The moisture content of the fermented porridge was higher than the unfermented one. The same trend was observed in the protein content of the fermented porridge which were not statistically (p>0.05) different, but showed slight progressive increase from unfermented < 24 h < 48 h < 72 h fermented porridge (26.35 -30.80%). The results shows the protein increased as the fermentation time increased. The fibre content shows that the values of the unfermented, 24 and 48 h AYB porridge were significantly (p<0.05) higher (4.0 -4.31%) than that of 78 h value which showed the least value The method described by Ezeama (2007) was adopted. One (1) mL of the sample dilution from 24h, 48h and 72h fermented liquor was inoculated by spread plates in Nutrient Agar, Potato Dextrose Agar, MRS and MacConkey Agar 0 and were incubated at 37 C while the PDA plates 0 were incubated at room temperature (28 C). At the end of incubation, colonies were counted with a colony counter.

Determination of microbial population of AYB fermented liquor
Flame photometry was used to determine the concentration of potassium and magnesium as described by James (2005).

Determination of Mineral contents
Calcium was determined using the method described by Pearson (1976).

Determination of Anti-nutrients content
Tannin was determined by the method of Harbone (1993), phytate was determined using the Biphyrimidine colorimeter method described by Onwuka (2005), while oxalate content was determined by the titration method described by Day and Underwood (1986).
Mean and standard deviation were calculated for duplicate determinations using the Statistical Package for Social Sciences (SPSS) version 10 Statistic Software Package. Data were expressed as mean ± standard deviation (SD). Comparisons between groups were performed with analysis of non-parametric test. A value of P< 0.05 was considered statistically significant.
Moisture, crude protein, crude fat, crude fibre, ash contents were determined according to the standard methods of Association of Official Analytical Chemists (AOAC), (2010). Carbohydrate was determined by difference as follows: %Carbohydrates = 100 -(%moisture + %fat +%ash + %protein + %crude fibre). The fat content of unfermented porridge (7.78%) was higher than their fermented counterpart. The result shows that the fat content progressively decreased as fermentation time increased from 24 h (4.86%), 48 h (2.91%) and 72h (2.69%), respectively. The same trend was observed in the ash content of the porridge. There was a progressive decrease in the ash content from unfermented porridge > 24 h > 48 h > 72h, respectively. Fat (7.78%), fibre (4.31%) and ash (2.94%) contents of unfermented AYB porridge were higher than those of the 24 h, 48 h and 72 h fermented porridge. The reverse was the case in the moisture and protein contents of the porridge which indicated significant increases in the fermented porridge than the unfermented porridge. The carbohydrate values were not statistically different irrespective of the fermentation time.

Data analysis
Protein content increased with increase in the fermentation time. Fat, ash and fibre contents decreased as fermentation progressed from 24 to 72 h. This may be due to microbial metabolism of these nutrients or their lixiviation in the soaked/fermenting water. The level of this decrease were as follows for fibre (4.31 to 2.98%), fat (7.78 to 2.69%) and ash (2.94 to 1.68%), respectively. Unfermented AYB porridge protein (26.35%) was higher than the values in AYB seed protein previously reported by Emiola (2011) (24.7%), much higher than 4.14 -8.48% protein content reported by Adelekan et al.
(2012) on AYB-shrimp-maize based cereal blends, but maintained the same range with those reported by Onuoha et al. (2017) (27.80%) on AYB flour and Ajayi (2011) (33.03%) on 24 h fermented AYB seed with Pediococcus cerevisiae culture. High protein content is major requirement in food formulation for infants and adults alike.
Fermentation of AYB seeds showed active microbial involvement that resulted in higher proteins content than the unfermented AYB porridge. This shows the impact of fermentation on protein availability which corroborates with the work of Ajayi (2011). Values are means+ standard deviation of duplicate determinations. Means with the same superscripts within the same rows are not significant differences at 0.05 confidence level (p<0.05).

Mineral composition of Africa Yam Bean porridge
Significant (p<0.05) variation was observed in the mineral content of AYB porridge ( The anti-nutrient composition of AYB porridge is shown in Table 3. The result shows progressive reduction of the anti-nutrient phytate from unfermented (0.15 mg/100g) > 24 h (0.11 mg/100g) > 48 h (0.05 mg/100g) > 72 h (0.02 mg/100g) fermented porridge. It shows that the phytate content at 72 h fermentation had the lowest value (0.02 mg/100g), while the unfermented porridge had the highest value (0.15mg/100g). This result indicates the effect of fermentation time on phytate metabolism by fermenting microorganism. Phytate is mainly found in tubers and roots, cereals, vegetables, most legumes such as soya bean, palm kernel seed and cotton seed meal. It forms insoluble salts with divalent metal ions (calcium, magnesium, iron and zinc), and hence interferes with mineral availability since it renders the minerals unavailable for absorption into the body. Phytate also affects protein digestibility by binding with proteolytic enzyme (Onyeike, 2012).

Anti-nutrient compositions of Africa yam bean porridge.
For oxalate content, the unfermented AYB porridge had the highest value (4.82 mg/100g), followed by 24 h fermentation (3.01 mg/100g), and 48 h fermentation (2.66 mg/100g), while the 72 h fermented AYB porridge had the least value (0.25/mg/100g). The result shows that oxalate content reduced considerably during fermentation. Ingestion of foods containing oxalates has been reported to cause caustic effects and irritation to the throat and intestinal tract (Adane et al., 2013). Soaking, fermentation and boiling were found to reduce the oxalate content of the fermented AYB possibly due to the effect of leaching and enzyme hydrolysis of starch during fermentation that resulted in oxalate reduction from 4.71 to 0.25 mg/100g in fermented AYB porridge.
Likewise, the tannin content of 72 h fermented AYB porridge had the lowest value (0.93/mg/100g), while the unfermented had the highest value (8.46mg/100g) This indicates high significant (p<0.05) decrease from 8.46 mg/100g to 0.93 mg/100g during 24 to 72 h fermentation period. The browning of AYB porridge (not shown) can be attributed to the high tannin content, which resulted into mild astringency. Fermentation of AYB seed for 24 h by Pediococcus cerevisiae (Ajayi, 2011) showed considerable reduction of phytic acid from 17.4 to 10.92 mg/100g, while tannic acid and oxalic acid increased from 0.24 to 1.49 mg/100g and from 0.04 to 1.22 mg/100g during fermentation process. These values are in disagreement with the results in this study (Table 3), probably on the basis of their variety, geographical location and fermentation time.

Sensory Acceptability of AYB porridge
The results of the sensory acceptability score is presented in Table 4. The results show significant (p<0.05) differences. Sensory scores were carried out by 45 panelists on a 9 scale hedonic scale for attributes of aroma, texture, taste, appearance, and general acceptability. Result shows that 24 and 48h fermented porridge had higher values in all the parameters tested and were preferred to other samples, showing higher general acceptability.
Fermentation degrades anti-nutrients, extends shelf life, enhance nutritional value and sensory properties of some food products including AYB porridge. With this result, AYB porridge can serve as food substitute for the vulnerable people and diabetics. Unfermented AYB porridge was the least accepted followed by the 72h fermented porridge. The general acceptability of 24 and 48 h fermented porridge was due to its moderate taste and texture. The results suggest that fermentation for at least 24h, but not exceeding 48h, will greatly enhance the sensory acceptability of AYB porridge.

Microbial population of AYB fermented liquor
-6 evaluated at 10 dilution factor Isolation of microorganisms involved in AYB seed fermentation was reported by Ajayi (2011) to include Pediococcus cerevisiae and Aerococcus viridians. Jeff-Agboola (2007) also isolated the following bacteria, Lactobacillus jensenii, Bacillus coagulans, Aerococcus viridians, Pediococcus cerevisiae and yeast, Saccharomyces cerevisiae and Candida mycorderm from natural 0 fermented AYB at 30 C for 72, 96 and 120 h, respectively. We did not attempt to isolate the microorganisms involved in the sample fermentation periods because earlier researchers have identified some which constituted the fermenting micro flora of AYB seeds for porridge production.  The effect of fermentation periods (24, 48 and 72 h) on the quality characteristics of Africa yam bean (Sphenostylis sternocarpa) porridge showed that protein increased as fermentation time increased, while fibre, fat, ash, minerals and anti-nutritional contents showed varying levels of reduction as fermentation time increased probably as a result their microbial utilization and lixiviation. The results also showed that AYB porridge produced at 24 h fermentation, but not exceeding 48 h fermentation will have better sensory acceptability. The microbial population for Total viable and Lactobacillus counts showed increases as fermentation time increased from 24 to 72 h, while Fungal growth reduced as fermentation time increased from 24 to 72 h. Coliform (pathogenic) organism was not noticed throughout the duration of fermentation. From this study, the production of porridge from AYB seed and its nutritional qualities at different fermentation periods have been highlighted. The high nutritional value and reduced antinutritional factors in AYB porridge makes it a valuable nutrient dense food source for all groups of people.  Coliform Count, <10 = growth of microbes insignificantly far less than 10 CFU/g and CFU = Colony forming units of microorganisms.