Aims: Leaf blight disease caused by Pantoea spp. reduces rice yields in numerous nations. However, the exact strategy to combat Pantoea spp. has yet to be determined. Bactronophorus thoracites is a promising source of natural antimicrobial agents due to their potential as a substrate to generate peptides with high antimicrobial activity. This study determined the effects of lactic acid fermentation using Lactobacillus casei ATCC334 as a starter culture on antimicrobial activity against rice pathogens, proximate composition, and amino acid profiles from B. thoracites crude extract. Methodology and results: Bactronophorus thoracites was washed and deshelled to collect the flesh and homogenised at 4 °C before freeze-drying. The freeze-dried samples were fermented with L. casei for 4 to 8 days at 37 °C. The antimicrobial activity, MIC and MBC were determined using a spectrometer. The fermented protein was subjected to proximate and amino acid analyses. The antimicrobial activity of fermented B. thoracites protein (FBTP) was significantly (p<0.05) decreased with the increased fermentation days (from 4 to 8 days). The antimicrobial activity was also increased when the glucose concentration increased from 2% to 3%. However, raising the glucose concentration to 4% decreased the antimicrobial activity. The antimicrobial activity was significantly (p<0.05) increased when the substratewater (S/W) ratio increased from 0.84% to 0.96%. The FBTP (4 days, 3% glucose concentration and 0.96% S/W ratio) showed high antimicrobial activity against Pantoea ananatis and P. stewartii. The MIC and MBC values for FBTP were 500 μg/mL and 250 μg/mL against P. ananatis and P. stewartii. The zones of inhibition value for FBTP were 16.0 ± 0.5 mm (1000 μg/mL) and 9.33 ± 0.57 mm (500 μg/mL) for P. ananatis, and 11.7 ± 0.61 mm (1000 μg/mL), 9.33 ± 0.58 mm (500 μg/mL) and 7.17 ± 0.77 mm (250 μg/mL) for P. stewartii. The proximate composition and amino acid profiles of the freeze-dried protein hydrolysate powder were characterised. FBTP produced a higher value of protein (61.56%) and ash (32.38%) and a lower value of total fat (0.273%) and carbohydrates (6.27%) than the B. thoracites crude extract. Total amino acid content was 39.480 g/100 g in B. thoracites crude extract and 155.442 g/100 g in FBTP. The essential amino acid glutamine was the most abundant in B. thoracites crude extract and methionine in FBTP. Conclusion, significance and impact of study This study showed that lactic acid fermentation could produce FBTP using L. casei with improved functional characteristics and as a source of a natural antimicrobial agent against rice pathogens.
Lactic Acid ; Anti-Infective Agents