Survival of Lactic Acid Bacteria and Yeasts in Refrigerated and Frozen Silage Samples

• Andrea Field, Biological Sciences, University of Delaware

• Tanya Gressley, Animal and Food Sciences, University of Delaware

Silage is an anaerobically fermented forage used to feed dairy cattle. For an ideal silage fermentation, the goal is to increase lactic acid bacteria (LAB) growth while inhibiting spoilage organisms like fungi. These organisms are measured by plating on selective media that takes multiple days. It would be desirable to store samples during this period in case the quantification needs to be repeated, but the impact of storage on microbial survivability is unknown. The objective of this experiment was to determine the survival of LAB and fungi over time in refrigerated and frozen silage samples. Corn and alfalfa silage samples were collected and immediately processed or stored at 4°C and -20°C for 24 or 48 hours. At each time point, 25 g of silage was added to 225 mL of Ringer’s solution, processed in a stomacher for 2 min, then the water extract was serially diluted before plating. To measure LAB and fungi, De Man-Rogosa-Sharpe agar was incubated at 35°C for 48 hours and acidified malt extract agar was incubated at 30°C for 72 hours, respectively. Microbial counts were analyzed in JMP Pro 17 using the Fit Model procedure for standard least squares, with main factors being silage type, storage method, storage time and their interactions. Fungal counts were not affected by silage type, storage method or storage time. There was an interaction between storage time and storage method for LAB counts (P<0.01). After 48 hours in the freezer, LAB counts were decreased as compared to those from samples in the fridge or freezer for 24 hours or samples in the fridge for 48 hours. This suggests that there is a limited window of time (below 48 hours in the freezer) where samples from an experiment can be repeated and offer similar LAB counts compared to the day they were collected.