Effects on microbial diversity of fermentation temperature (10°C and 20°C), long-term storage at 5°C, and subsequent warming of corn silage

Objective: To evaluate the effects on microbial diversity and biochemical parameters of gradually increasing temperatures, from 5 to 25 °C on corn silage which was previously fermented at ambient or low temperature. Methods: Whole-plant corn silage was fermented in vacuum bag mini-silos at either 10 or 20 °C for two months and stored at 5 °C for two months. The mini-silos were then subjected to additional incubation from 5 to 25 °C in 5 °C increments. Bacterial and fungal diversity was assessed by PCR-DGGE profiling and biochemical analysis from mini-silos collected at each temperature. Results: A temperature of 10 °C during fermentation restricted silage fermentation compared to fermentation temperature of 20 °C. As storage temperature increased from 5 to 25 °C, little changes occurred in silages fermented at 20 °C, in terms of most biochemical parameters as well as bacterial and fungal populations. However, a fairly high number of enterobacteria and yeasts (4-5 log10 CFU g FM-1) were detected at 15 °C and above. PCR-DGGE profile showed that Candida humilis predominated the fungi flora. For silage fermented at 10 °C, no significant changes were observed in most silage characteristics when temperature was increased from 5 to 20 °C. However, above 20 °C, silage fermentation resumed as observed from the significantly increased number of LAB colonies, acetic acid content, and the rapid decline in pH and WSC concentration. DGGE results showed that Lactobacillus buchneri started to dominate the bacterial flora as temperature increased from 20 to 25 °C. Conclusion: Temperature during fermentation as well as temperature during storage modulates microorganism population development and fermentation patterns. Silage fermented at 20 °C indicated that these silages should have lower aerobic stability at opening because of better survival of yeasts and enterobacteria.