Antimicrobial activities of saponin-rich guar meal extract

Abstract

Three saponin-rich extracts (20, 60, 100% methanol), four 100% methanol subfractions and seven independently acquired fractions (A-G) from guar meal, Cyamopsis tetragonoloba L. (syn. C. psoraloides), were evaluated for antimicrobial and hemolytic activities. These activities were compared against quillaja bark (Quillaja saponaria), yucca (Yucca schidigera), and soybean (Glycine max) saponins in 96-well plates using eight concentrations (0.01 to 1.0 and 0.1 to 12.5 mg extract/mL). Initial guar meal butanol extract was 4.8 ± 0.6% of the weight of original material dry matter (DM). Butanol extract was purified by preparative reverse-phase C-18 chromatography. Two fractions eluted with 20, and one each with 60, and 100% methanol with average yields of 1.72 ± 0.47, 0.88 ± 0.16, 0.91 ± 0.16 and 1.55 ± 0.15% of DM, respectively. Further purification of the 100% methanol fraction using normal-phase silica gel preparatory high pressure liquid chromatography eluted 4 peaks at 16, 39, 44 and 46 min. Only the 100% methanol fraction, its 16 min peak, F and G fractions, and quillaja saponin, exhibited both hemolytic and antibacterial activities against Staphylococcus aureus, Salmonella Typhimurium and E. coli, but 20 and 60% methanol fractions stimulated Lactobacillus spp. growth. Guar meal (0 or 5%) was added to diets fed to chicks from 1 to 21 days of age. Chicks fed both diets were unchallenged or challenged with 5 x 103 Eimeria tenella sporulated oocysts at 10 days. Guar meal diets reduced oocysts shed per gram of feces, body weight, and feed efficiency. Adding 2.5% guar meal, 1% guar gum, or 0.125% saponin-rich guar meal extract to diets fed to chicks to 21 days of age showed that guar meal increased the cfu concentrations of digesta more than controls following a challenge with 107 cfu of Clostridium perfringens at 14 days. Body weights of chicks fed guar meal and saponin-rich extract were significantly lower than control body weights at 21 days of age, whereas the weekly feed to gain ratio of chicks fed saponin-rich extract was higher than controls. Guar meal reduced severity of Eimeria tenella infection and guar saponin-rich extract exhibited antimicrobial activity against several common poultry pathogens.