Utilisation of agricultural residues for antioxidant exopolysaccharide production by <i>Bacillus</i> spp.

This study tested the antioxidant activities of exopolysaccharides (EPSs) produced by eight <i>Bacillus</i> spp. from Thai milk kefir utilising four agricultural by-products in Thailand; copra meal, mangosteen peel, sorghum, and para rubber sawdust as carbon sources. Sorghum showed the highest starch and sugar content of 73.33% while copra meal showed the lowest (13.08%). <i>B. tequilensis</i> PS21 produced the highest dry weight EPS, followed by <i>B. amyloliquefaciens</i> KW1 and <i>B. tequilensis</i> PS22 from four substrates. <i>B. tequilensis</i> PS21 generated the most EPS with sorghum (0.75 ± 0.09 g DW/100 mL culture), followed by mangosteen peel (0.61 ± 0.07 g). EPS from <i>B. amyloliquefaciens</i> KW1 using copra meal displayed the highest DPPH radical scavenging activity of 33.39 ± 1.34% and EPS from the same bacteria using sorghum displayed the highest hydroxyl radical scavenging activity of 49.78 ± 0.86%. This approach demonstrated a bio-circular green economy paradigm in converting agricultural biowastes into valuable EPS biomaterials with potential applications.