Agro-dairy waste valorization for postbiotic production by Lactiplantibacillus plantarum

The increasing cost of commercial culture media and the demand for sustainable bioprocesses have encouraged the use of agro-industrial by-products as alternative fermentation substrates. This study evaluated combined agro-dairy by-products for the growth of Lactiplantibacillus plantarum and postbiotic production. Rice bran and sugar beet pulp extracts were combined with whey powder and corn steep liquor (CSL) to formulate three waste-based media (WBM): WBM5, WBM8, and WBM11, containing the solid-derived components at 5, 8, and 11 g/L and CSL at 15, 20, and 25 mL/L, respectively. The formulations were compared with Base and de Man, Rogosa and Sharpe (MRS) media. Among the waste-based formulations, WBM8 showed the best overall performance, reaching an OD 600 of 5.48 and 3.91 × 10 9 CFU/mL, compared with 6.36 and 8.10 × 10 9 CFU/mL in MRS. WBM8 produced 2.65 g/L lactic acid, 0.79 g/L acetic acid, 165.67 mg GAE/L total phenolic content, and 265 mg/L soluble protein. MRS showed higher lactic acid (3.11 g/L) and soluble protein (281.67 mg/L), while TPC was statistically comparable between MRS (168.67 mg GAE/L) and WBM8. WBM8 yielded a DPPH IC 50 of 450 µg/mL and FRAP of 200 µmol Fe 2+ /g DW versus 478 µg/mL and 190 µmol Fe 2+ /g DW for MRS; these antioxidant indices did not differ significantly between WBM8 and MRS ( p > 0.05). Approximately 87% of initial soluble sugars were consumed in WBM8. Multivariate analyses supported a distinct and favorable WBM8 profile, while their exploratory nature was retained because of the limited number of treatment-level observations. Overall, WBM8 provided the most favorable balance among the waste-based formulations and generated a postbiotic profile that was competitive with MRS for several functional attributes.