Microbiological, Physicochemical and Storage Assessment of African Yam Bean (Sphenostylis stenocarpa) Seed-Enriched Cassava (Manihot esculenta) Product (Pupuru) Developed with Starter Cultures

Abstract

Many underexploited food crops with high nutritional potentials abound, hence, the utilisation of mixtures of tubers and legumes indigenous to the developing countries need should be encouraged to combat malnutrition. One of such is fortification of tuber crops with cereal. This study, therefore, developed a nutritious African Yam Bean (Sphenostylis stenocarpa) seed-enriched cassava (Manihot esculenta) product (Pupuru) using Lactic Acid Bacteria (LAB) as starter cultures, with a view to standardise method of production and obtaining product of consistent quality. The lactic acid bacteria isolated from spontaneous fermentation of fresh cassava tubers for 96 h were identified by molecular techniques, and used singly and in a combination, as starter cultures in fermenting cassava for production of Pupuru flour blends. African Yam Bean (Sphenostylis stenocarpa) seed at 5%, 10% and 15% levels were incorporated into the enriched Pupuru flour blends. Proximate analysis of the Pupuru flour blends were determined using standard methods. The values were calculated from the profile values of the proximate analysis, while pasting profiles were determined using Rapid Visco Analyser. The antioxidative activities, and antinutritional contents were determined using standard methods. Microbiological evaluation of the developed product was determined using standard methods. Sensory evaluation was done with a 30 untrained panelists using 9-hedonic scale. Statistical analyses were done using ANOVA at 5% confidence level. The proximate analysis of commercial, spontaneously and starter-fermented African Yam Bean (AYB) (Sphenostylis stenocarpa) seed-enriched Pupuru flour blends (dry basis) indicated that the moisture contents of all the flour blends were significantly different (p<0.05), ranging from 6.78% (EP15 and S1EP15) to 8.09% (CSP100) and were all significantly (p<0.05) lower than in CP (9.26%). Protein content ranged between 3.48% in P100 and 23.20% in S1EP15, and were significantly (p<0.05) higher than the CP (3.18 %). The Energy Values (EVs) of the flour blends ranged from 374.12 kcal/100g in P100 to 398.64 kcal/100g in S1EP15 and increased significantly (p<0.05) with increased AYB seed enrichment. The peak viscosities ranged from 725.00 RVU in S1P100 to 2900.00 RVU in P100. Breakdown Viscosity (BV) in all for the flour blends varied from 89.00 RVU (P100) to 263.00 RVU (EP15). Final Viscosity ranged between 3102.00 RVU in EP5 and 3689.00 RVU in P100 and were lower than in the starter-fermented samples which ranged from 1640.16 RVU in CSEP15 to 2766.75 RVU in S1P100. The amylose contents ranged from 7.79 (S1EP10) to 30.85 (S1P100). The in-vitro starch digestibility of all the Pupuru flour blends varied from 2.59 (EP15) to 10.59 (S2P100), while the in-vitro protein digestibility ranged from 7.64 in P100 to 9.98 in CSEP15. Free fatty acid values varied from 0.95 in CSEP5 to 1.83 in CP. All the Pupuru flour blends contained cyanide ranging from 0.44 to 2.51 mg/kg in S2EP15 and CP, respectively. Tannin content ranged from 1.06 (CSE15) to 2.87 (mg/g) (CP. Phytate content ranged from 0.57 (SP100) to 1.40 mg/100g (EP15); spontaneously fermented flours had 0.85 (P100) to 1.40 mg/100g (EP15). Oxalate contents of all the Pupuru flour blends ranged from 0.98 (CSP100) to 3.23 mg/g (EP15). The antioxidant capacity showed that ABTS activities ranged from 0.0068 (CP) to 0.0159% (CSEP15); DPPH varied from 27.17% (CP) to 188.47% (CSEP15); Flavonoid from 0.0091 (CP) to 0.0281 (mg/g) (CSEP15); Ferric Reducing Antioxidant Power (FRAP) 0.7814 (CP) to 3.5712 (mg/g) (CSEP15); and total phenolic contents from 3.2346 (CSEP15) to 1.5738 mg/g (CP). The microbial counts were lower than the tolerable limit of 1.0 x 104 CFU/g. Overall acceptability of cooked Pupuru porridge differed significantly (p<0.05) ranging from 6.32 (EP15) to 7.83 (CSEP10) indicating that Pupuru with 15% AYB seed produced with starter cultures was acceptable to consumers. The microbiological storage assessment of the flour blends indicated that they were safe and within tolerable levels. The study concluded that improved quality and acceptable Pupuru could be produced from starter culture-fermented cassava fortified with African Yam Bean (AYB) (Sphenostylis stenocarpa) seed