ABSTRACT

The phenotypic and molecular characterization of lactic acid bacteria (LAB) species associated with ugba (fermented African oil bean seeds) and evaluation of their fermentation capabilities and biopreservative potentials were studied. A total of seven LAB isolates from ugba were presumptively identified using phenotypic method while confirmations of their full identities were obtained using randomly amplified polymorphic DNA (RAPD) and PCR-16S rDNA gene nucleotide sequencing. Among the LAB isolates, three including Lactobacillus plantarum, Lactobacillus brevis and Lactobacillus fermentum were selected as potential candidates of starter cultures as a result of their technological properties for use in the production of ugba. The ugba produced using LAB starter cultures and uninoculated samples were subjected to chemical and microbiological analysis during storage. Results show that the LAB inoculated and uninoculated ugba samples were significantly different (p<0.05) in hydrogen ion concentration (pH) and total titratable acidity (TTA) during storage. The temperature range recorded (28-36^oC) favoured the growth of lactic acid bacteria. The pH of the inoculated ugba samples decreased towards acidity and the uninoculated counterpart increased slightly towards alkalinity, ranging within 3.42 – 7.32, while the total titratable acidity decreased, falling within the range of 0.033 – 0.085 as the storage days progressed. Result of organic acid content showed that; formic, acetic, lactic and butyric acids significantly (p<0.05) increased as storage period progressed. The proximate composition of the ugba indicated that ugba sample inoculated with Lactobacillus plantarum and Lactobacillus brevis had the highest values in protein, fat, ash and carbohydrate contents during storage. The antinutritional factors of ugba samples inoculated with LAB starter culture were lower than their uninoculated counterparts at the end of the fermentation process and storage period. Ugba inoculated with L. plantarum and L. brevis had the lowest values in all the antinutrients investigated during storage. Ugba inoculated with L. plantarum and L. brevis recorded the highest values in potassium, phosphorous and sodium, followed by ugba inoculated with L. brevis and L. fermentum in calcium and magnesium contents in the mineral contents. The water-soluble vitamins; vitamin C (ascorbic acid), vitamins B₁ (thiamine), B₂ (riboflavin), and B₃ (niacin) screened showed that they decreased as storage period progressed. The fatty acids identified in the samples include four (4) saturated fatty acid (lauric, palmitic, myristic and stearic), one (1) monounsaturated fatty acid (oleic) and two (2) polyunsaturated fatty acids (linolenic and linoleic) respectively. Both linolenic and linoleic acids showed a significant (p<0.05) increase throughout the storage period followed by oleic acid. The presence of essential amino acids such as threonine, lysine, valine, leucine, phenylalanine, methionine, and isoleucine were indicated in the ugba samples with significant differences (p<0.05) during storage. GC-MS analyses of the ugba samples revealed twenty eight (28) flavour volatile compounds during storage, consisting of nine compounds of hydrocarbons (32%), one aldehyde (4%), six alcohols (21%) and three carbonyls (11%). Others include seven esters (25%) and two unidentified compounds (7%) which could not be grouped into any of the classes. The microbial quality of ugba samples inoculated with LAB starter cultures showed less microbial load with improved keeping qualities than their uninoculated counterparts during storage. Results from this study have demonstrated the usefulness of a polyphasic taxonomy approach for characterization of LAB strains being proposed as potential candidates of starter cultures for food biopreservation thereby improving process control, and increase storage stability of the ugba products in Nigeria.