Abstract
Two lactic acid bacteria (LAB) strains with different ferulic acid esterase (FAE) activities were isolated: Lactobacillus farciminis (LF18) and Lactobacillus plantarum (LP23). The effects of these strains on the fermentation quality, in vitro digestibility and phenolic acid extraction yields of sorghum (Sorghum bicolor L.) silage were studied at 20, 30 and 40 °C. Sorghum was ensiled with no additive (control), LF18 or LP23 for 45 days. At 40 °C, the lactic acid content decreased, whereas the ammonia nitrogen (NH3-N) content significantly increased (p < 0.05). At all three temperatures, the inoculants significantly improved the lactic acid contents and reduced the NH3-N contents (p < 0.05). Neither LP23 nor LF18 significantly improved the digestibility of sorghum silages (p > 0.05). The LP23 group exhibited higher phenolic acid extraction yields at 30 °C (p < 0.05), and the corresponding yields of the LF18 and control groups were improved at 40 °C (p < 0.05). FAE-producing LABs might partially ameliorate the negative effects of high temperature and improve the fermentation quality of sorghum silage. The screened FAE-producing LABs could be candidate strains for preserving sorghum silage at high temperature, and some further insights into the relationship between FAE-producing LABs and ensiling temperatures were obtained.
Highlights
Several research studies have attempted to study the effects of ferulic acid esterase (FAE)-producing lactic acid bacteria (LAB) strains on ensiling and fiber degradability, and some of the findings have shown that LAB-treated silage exhibits higher neutral detergent fiber digestibility (NDFD) [11,12,13]
The two LAB strains were identified as Lactobacillus plantarum (LP23) and Lactobacillus farciminis (LF18) via 16S rRNA sequencing
The control and LF18 groups presented high ferulic acid and p-coumaric acid extraction yields at 40 ◦ C; as a result, no significant difference in the phenolic acid extraction yields were found among the three treatments at this temperature, the LP23 strain used in this study presented its highest FAE enzymatic activity at 40 ◦ C
Summary
Silage is a product obtained through a fermentation process during which lactic acid bacteria (LAB) convert water-soluble carbohydrates (WSCs) to organic acids under anaerobic conditions. The production of silage is an efficient method for preserving animal feed but is a process used for the biological pretreatment of lignocellulose materials [1]. The main factor limiting the use of sorghum silage by ruminants is the digestibility of the fiber. Cellulolytic enzymes, including cellulases and xylanases, are superior fermentation activators for improving fiber degradation [3]. The preliminary enzymatic degradation of the plant cell wall is limited by the complex cross-linked structure formed by ferulic acid, which inhibits the digestion of the cell wall by ruminants [4]. Ferulic acid and p-coumaric acid are ubiquitous residues in the plant cell wall and account for 80%
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