Antibacterial and Antioxidant Activities of Red Rice/Brown Rice, Si Boo Gan Tang Rice and its Rice Bran Extracts

This study aimed to assess the biological properties of Si Boo Gan Tang Rice and bran extract. Antibacterial activity was evaluated using the agar well diffusion method, revealing inhibitory effects exclusively on gram-positive bacteria by both ethanolic Si Boo Gan Tang Rice (RE) and bran (RBE) extract. The inhibition zone of RE to methicillin-resistant Staphylococcus aureus (MRSA142), Staphylococcus aureus TISTR517, Bacillus cereus ATCC 11778, and Micrococcus luteus TISTR 884 was 2.07 ± 0.06, 1.94 ± 0.07, 1.95 ± 0.03, and 2.04 ± 0.03 cm, respectively. For RBE, the inhibition zones to methicillin-resistant S. aureus (MRSA142), Staphylococcus aureus TISTR517, B. cereus ATCC 11778, and M. luteus TISTR 884 were 2.07 ± 0.06, 2.00 ± 0.04, 1.67 ± 0.04, and 2.42 ± 0.56 cm, respectively. Scanning electron microscope (SEM) analysis indicated changes in the morphology of Staphylococcus aureus TISTR517 and Methicillin-resistant Staphylococcus aureus (MRSA142) cells treated with the RE and RBE, characterized by cell swelling and the formation of a fibrous network around them, contrasting with the control group. Antioxidant activity was assessed via DPPH, ABTS, and FRAP assay. The RBE displayed significant antioxidant potential, with IC50 values of 0.78 and 0.69 mg/mL in the DPPH and ABTS assays, respectively. Conversely, the aqueous rice bran (RBW) extract had IC50 values of 3.83 and 0.90 mg/mL in the same assays. For the RE, IC50 values were 1.11 mg/mL (DPPH) and 0.78 mg/mL (ABTS), while the aqueous rice (RW) extract had IC50 values of 4.45 mg/mL (DPPH) and 1.75 mg/mL (ABTS). In the FRAP assay, all the extracts RW, RBW, RE and RBE demonstrated ferric level reductions of 37.82, 36.85, 56.24, and 81.45 µmol/g extract, respectively. Phenolic content in the extracts ranged from 34.82 to 154.31 mg GAE/g extract, while flavonoid concentrations varied between 2.17 and 8.78 mg QE/g extract. HIGHLIGHTS All extracts showed inhibitory effects exclusively on gram-positive bacteria, particularly effective against Staphylococcus aureus and Methicillin-Resistant Staphylococcus aureus (MRSA142). The ethanolic rice bran extract (RBE) demonstrated the highest antioxidant activity, with lowest IC50 values in DPPH (8.11 mg/mL) and ABTS (3.67 mg/mL) assays, and a highest FRAP value (81.45 µmol/g). All extracts exhibited significant phenolic content, ranging from 34.82 to 154.31 mg GAE/g extract, contributing to their potent antioxidant properties. GRAPHICAL ABSTRACT