Effect of fermentation period on the organic acid and amino acid contents of Ogiri from castor oil bean seeds

Abstract

Aims: To monitor the changes in the concentration of organic acid and amino acid contents during the fermentation of castor oil bean seed into ogiri. Methodology and results: In this study, ogiri, a Nigerian fermented food condiment was prepared from castor oil bean using Bacillus subtilis as a monoculture starter for the production of three different fermented castor oil bean condiment samples: B1( 0% NaCl/Lime), B2 (2% NaCl), B3 (3% Lime). Variations in the composition of the castor oil bean with fermentation over 96 h periods were evaluated for organic acid and amino acid contents using High Performance Liquid Chromatography. Organic acids were detected in the fermented castor oil bean samples as fermentation period increased to 96 h. Organic acids identified were oxalic, citric, tartaric, malic, succinic, lactic, formic, acetic, propionic and butyric acids. The lactic acid contents in sample B1 (0% NaCl/Lime) decreased initially and then increased as the fermentation period progressed. The value at 96 h fermentation was 1.336 µg/mL as against 0.775 µg/mL at 0 h fermentation. Sample B3 (3% lime) had lactic acid content that increased as fermentation period increased with lactic acid content of 1.298 µg/mL at 96 h fermentation. The acetic acid content of sample B1 increased as fermentation progressed and at 96 h fermentation, its value was 1.204 µg/mL while those of B2 and B3 were 0.677 µg/mL and 1.401 µg/mL respectively. The three fermented castor oil bean samples also contained sufficient amount of amino acids. Sample B1 had the highest values in isoleucine glycine and histidine with values 1.382 µg/mL, 0.814 µg/mL and 1.022 µg/mL respectively while sample B2 had the highest value in leucine content with 0.915 µg/mL at 96 h fermentation, closely followed by sample B3 and B1 with 0.798 µg/mL and 0.205 µg/mL respectively. The results of amino acid analysis indicated a high concentration of all amino acids at 96 h of fermentation. Conclusion, significance and impact of study: Sufficient organic acids were detected in the three Bacillus fermented castor oil bean samples. The production of organic acids is undoubtedly the determining factor on which the shelf life and the safety of the final product depend while the inhibition of pathogenic and spoilage flora is also dependent on a rapid and adequate formation of these organic acids. The results of amino acid analysis indicated a high concentration of all amino acids especially at 96 h of fermentation. Amino acids are known to play a major role in the taste and flavour development of foods Thus the flavour and aroma of ogiri may be due to the production of amino acids, especially glutamic acid during the fermentation process.