EVALUATION OF THE NUTRITIONAL PROFILE OF AFRICAN YAM BEAN (Sphenostylis stenocarpa) ex. A. Rich. HYDROLYSED WITH PROTEASE FROM LACTIC ACID BACTERIA

Abstract

African yam bean with complex structural component can be broken into simpler and assimilable form so as to derive its maximum dietary benefits. Hence, this study compares the nutritional profile of African Yam Bean (AYB) fermented and hydrolyzed with partially purified protease from protease-producing Lactic Acid Bacteria. Isolation and identification of LAB from fermented food such as ‘ogi’ from red sorghum, Auki yoghurt, ‘nunu’ and ‘iru’ were carried out using conventional and molecular techniques. Qualitative and quantitative screening of isolated LAB for protease production was performed using standard biochemical methods. Partial purification of protease from the best producer was performed using ammonium sulphate precipitation. African yam beans were hydrolyzed with partially purified protease from Lactobacillus brevis. Submerge fermentation technique was employed using LAB with good protease-production potential. The proximate, vitamins and amino acid compositions of the fermented and hydrolyzed samples were carried out using standard chemical methods while mineral composition was determined using atomic absorption spectrophotometry. The LAB identified from the fermented products were Lactobacillus brevis, L. fermentum, L. pentosus, L. plantarum, Enterococcus faecalis and Pediococcus acidilactici. Among the screened LAB, L. brevis isolated from ‘iru’ had the highest protease activity of 7.4 μmol/min/ml, followed by L. fermentum. Specific protease activity increased from 125.92 μmol/min/mg in crude enzyme to 286.701 μmol/min/mg after partial purification. The AYB hydrolyzed with partially purified protease had the highest percentage crude protein content with a value of 35.92 %. However, all the treated samples had their protein contents increased. Fermentation of the sample with co-culture of L. brevis and. L. fermentum had the highest vitamin composition of 1115.56mg/ml, 0.49 mg/ml, 0.49 mg/ml, 23.61 mg/ml and 0.94 mg/ml for vitamins A, B1, B3, C, D, and E respectively. Similarly, Ca, Fe, and K ions were highest in the sample fermented with L. brevis and L. fermentum. Out of the entire amino acids evaluated,glutamic acid had the highest value of 13.15g/100g in sample hydrolyzed with partially purified enzyme. The group of rats fed with 60% AYB hydrolyzed with protease had the highest percentage average weight gain of approximately 144% with improved haematological indices. Liver and large intestine of rats in all the groups showed normal architecture except in group fed with raw AYB where a slight dilation of the sinusoid and destruction of goblet cell was observed. Comparison between different treatments showed that hydrolyzed AYB had improved nutritional contents and as such could aid the digestibility of its hard testa within the gastrointestinal tract.