Optimization of Skim Milk Fermentation Conditions by Response Surface Methodology to Improve ACE Inhibitory Activity Using Lactiplantibacillus plantarum K79

This study was conducted using response surface methodology (RSM) to elucidate fermentation conditions that will optimize ACE inhibitory activity using Lactiplantibacillus plantarum K79. Four independent variables [skim milk (with 1% added glucose) concentration (6% – 14%), incubation temperature (32℃ – 42℃), incubation time (8 – 24 h), and amount of added starter (0.02% – 0.2%)] were evaluated using five-level central composite design and response surface methodology to determine the optimum fermentation condition. The dependent variables were angiotensin converting enzyme (ACE) inhibitory activity (the value obtained from 10 2 diluted supernatant), and pH. The respective coefficients of determinations (R 2 ) were 0.791 and 0.905 for ACE inhibitory activity and pH. The maximum ACE inhibitory activity was 90% under the following conditions: 10% skim milk (with 1% added glucose) concentration, 37℃ incubation temperature, 17.8 h incubation time, and 0.2% added starter. Based on the RSM, using predicted best ACE conditions for fermentation of 13.49% skim milk (with 1% added glucose) with 0.0578% starter at 33.4℃ for 21.5 h, the predicted ACE inhibitory activity and pH values were 86.69% and 4.6, respectively. Actual ACE inhibitory activity and pH values were 85.5% and 4.58, respectively.