PS4-7. Interactions Between Water Hardness and pH on the Stability and Antimicrobial Efficacy of Tannic Acid in Swine Drinking Water

Hard water is a common issue across the United States with up to 85% of regions exhibiting water hardness ranging from slightly to extremely hard. Tannic acid (TA), a polyphenolic compound with strong antimicrobial, antioxidant, and anti-inflammatory properties, has been used as a novel feed additive for monogastric animals. However, tannins can form complexes with minerals present in water; thus, high water hardness may reduce the efficacy of TA through precipitation. The purpose of this study was to investigate the recovery rate and in vitro antimicrobial effects of 1% TA in different water sources using a 2 × 6 factorial arrangement, with the main factors being: (1) water source [Western Texas (WTX; hard water) and Georgia (GA; soft water)], and (2) pH levels (3, 4, 5, 6, 7, and 8). Water samples were collected from the swine farms of Texas Tech University and the University of Georgia. A 1% TA solution was prepared in WTX and GA water, and the pH of each water source was adjusted using NaOH or HCl. The optical density at 525 nm (OD525) was measured after pH modulation to detect potential reactions between TA and iron ions in the water. The concentration of free TA in the supernatant after centrifugation was quantified using a colorimetric method. The in vitro antimicrobial effects of the supernatant were evaluated using a well-diffusion assay. Statistical analyses were conducted using a two-way ANOVA to evaluate the effects of pH, water source, and their interaction. At pH 7 and 8, OD525 of the supernatant was significantly greater in WTX water compared with GA water (interaction: P < 0.01). The recovery rate of TA significantly decreased with increasing pH (P < 0.001) and was lower in WTX than in GA water (P < 0.01). The antimicrobial effects of TA were markedly reduced in WTX water, showing limited inhibition against feedborne Escherichia coli at pH 7 and 8 (interaction: P < 0.01), while there were no differences in antimicrobial activity against Salmonella Typhimurium among different pH and water sources (P > 0.05). These results suggest that TA forms complexes with minerals in hard water, leading to reduced antimicrobial efficacy at pH 7 to 8. Since pH 7 to 8 approximates the pH environment of the lower gut, these findings imply that the efficacy of TA in animals consuming hard water may be compromised, warranting further in vivo investigation.