PSXII-9 - Effects of lauric acid- and hops-based products on select microbial populations of aerobically exposed silage

Abstract: Air exposed silages can harbor spoilage and pathogenic microbes which can reduce the palatability, nutritive quality and microbial safety of these feedstuffs. Accordingly, effective, environmentally friendly interventions are sought to rescue the biological and economical value of spoiled silages. The objectives of this study were to test the effects of treating air exposed corn silage with LipoVital GL-45, a Berg + Schmidt GmbH & Co. KG (Hamburg, Germany) product containing 45% monoglyceride of lauric acid (mixed within a 50% di/triglyceride base) alone or mixed with either Chinook or Galena hops or with an experimental extract containing hops β-acids. All treatments were administered as a warm water spray to deliver 1.6% product to the silage on a dry matter basis. Silage samples collected after 24 h ambient incubation were serially diluted in 0.4 M sodium phosphate buffer (pH 6.4) and plated to 3M Petrifilm for enumeration of yeast and molds and total aerobes as well as to Rogosa SL for enumeration of lactic acid bacteria and streptococci. Fluid samples from sampled silage were also inoculated in 10-fold increments to triplicate sets of tubes containing anaerobically prepared Reinforced Clostridial agar supplemented cellobiose and xylose (0.05% wt/vol each) for most probable number enumeration of total anaerobes. Populations of presumptive spore-forming aerobes and anaerobes were measured as described above except inocula were heated to 80^oC for 10 minutes to kill vegetative cells. An analysis of variance (Statistix Analytical Software, Tallahassee, FL, USA) revealed no treatment effects on yeasts and mold populations (P > 0.05) after 24 h air exposure of the silage, with counts averaging (± SD) 5.0 ± 0.7 log₁₀ CFU/g. Silage treated with combinations of LipoVital GL-45 with Galena hops or the β-acid extract had 0.8 to 0.9 log₁₀ units fewer (P < 0.05) lactic acid bacteria after 24 h air exposure than untreated controls (7.4 ± 0.1 log₁₀ CFU/g). Similarly, silage treated with the LipoVital GL-45/Galena hops combination had 0.6 to 0.7 log₁₀ units fewer (P < 0.05) heat-sensitive and presumptive spore-forming aerobes after 24 h air exposure when compared to controls (5.5 ± 0.2 and 5.2 ± 0.2 log₁₀ CFU/g, respectively). Conversely, most probable numbers of nonheated anaerobe populations were lower (P < 0.05) in silage treated with LipoVital GL-45 combined with the β-acid extract when compared to controls (8.6 ± 0.x and 9.9 ± 0.7 log₁₀ cells/g) with all other treatments being similar to controls. Populations of presumptive spore-forming anaerobes in the air exposed silage were unaffected by treatments, averaging 8.3 ± 0.7 log₁₀ cells/g. Results warrant further research to investigate whether optimized dosages and formulations of LipoVital GL-45, Galena hops and β-acid extracts may ultimately yield treatments to prevent spoilage of air-exposed silages.