The aim of this study is to optimize the production of optically pure d (-) lactic acid (DLA) employing a cost-effective production medium. Based on the designed biomass approach, Sporolactobacillus inulinus NBRC 13595 was found to exhibit high DLA titer (19.0 g L ) and optical purity (99.6%). A cost-effective medium was constituted using Palmyra palm jaggery (PJ) from Borassus flabellifer and whey protein hydrolysate (WPH) as carbon and nitrogen sources, respectively. Plackett-Burman design indicated that PJ, WPH, and MnSO as significant variables influence DLA production. A rotatable central composite design and response surface methodology were used to optimize the PJ and WPH concentrations. A maximum DLA titer (170.14 g L ) was predicted for 222.24 g L of PJ and 11.99 g L of WPH, respectively. Fermentation experimental results exhibited a maximum DLA titer (189.0 ± 8.53 g L ) and productivity (5.25 ± 0.24 g L H ), which is the highest ever reported for DLA production from a renewable feedstock in the batch process. The present investigation substantiates that the potential application of economically viable raw feedstocks (PJ and WPH) for enhanced DLA production, which is attributed to 2.5-fold reduction in DLA production cost compared with conventional medium.