Optimization of Lactic Acid Production from Dairy Whey Using Indigenous Lactic Acid Bacteria

Abstract

Kamana Emmanuel and Niyonagize Theophile

Sweet whey from cheese production is an environmentally challenging but nutrient-rich, underutilized resource. This study converted sweet whey from three dairy processors in Northern Rwanda into lactic acid using indigenous lactic acid bacteria (LAB). LAB-4 (Lactobacillus sp.) was selected for its superior acidification performance, and fermentation conditions were optimized using Response Surface Methodology. Optimal conditions of 37 °C, initial pH 6.0, and 10% (v/v) inoculum produced 43.2 ± 1.2 g/L lactic acid after 48 h, with a yield of 0.873 g/g and fermentation efficiency of 75.4%. The process reduced COD by 67.3%, while calcium lactate precipitation achieved 75.0% extraction yield and 82.5% purity. Production cost was estimated at USD 2.10/kg at 500 L/day. These findings demonstrate a practical and sustainable strategy for reducing whey-related pollution while generating valuable lactic acid for food and industrial applications and supporting dairy-waste valorization in Rwanda.

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