Impact of ferulic acid esterase-producing L. plantarum strains on fermentation characteristics and nutritional value of sweetcorn stover silages

Abstract

The application effects of ferulic acid esterase-producing (FAE+) lactobacilli on forage silages are inconsistent among published trials, including its intended impact on fiber composition and degradability. Most studied FAE+ species is Lentilactobacillus buchneri, an obligated heterolactic fermenter that is usually present in detectable quantities when the fermentation process is stable and pH is too low for FAE enzymes to hydrolyze ester bonds in plant cell walls. Little is known regarding the effect as silage inoculant of FAE+ Lactiplantibacillus (L.) plantarum, a major dominant species in the initial fermentation process of animal feed. Therefore, our objective was to identify possible benefits of using FAE+ strains of this species to preserve sweetcorn stover in laboratory scale silos. Fresh cells of selected FAE+ L. plantarum strains (CRL046, ETC180 and ETC182) were individually sprayed on sweetcorn stover (25% dry matter content, DM) batches (n=3), at a dose of 3x105 CFU/g fresh material (FM). A control group sprayed with sterile suspension buffer was prepared. Mini silos (≈300 g, two per batch) were vacuum-sealed (650 g FM/m3) using high-barrier bags, and stored for 300 days before opening for analysis. When compared to Control group, results indicated a statistically significant reduction of DM loss in silages inoculated with CRL046 (4.4 vs 2.5%, respectively) and higher organic matter content for the ETC180 experimental group (885 vs 905 g. kg DM-1, respectively). Plate counts showed lactic acid bacteria (LAB) present above detection limit (3 Log CFU/ g FM) in all inoculated silages, as opposed to Control group; yeasts were only detected in ETC180 and ETC182 experimental groups. There were no significant alterations in the fiber fraction composition (NDF, ADF, ADL) or its digestibility analysis (IVDMD, NDFd, ADFd using Daisy II- ANKOM®) among treatments. Overall results reinforce previous observations of little or no effect in fiber fraction of FAE+ LAB when applied as single inoculants to silages; even though, it must be noticed that initial forage IVDMD was 683 g. kg DM-1, which is close to maximum values reported for corn stover. It is possible that, in addition to the benefits observed in this study of using L. plantarum CRL046 and ETC180 as inoculants, positive effects in digestibility measures could be detected when applied to less digestible forages, or when combined with other fibrolytic enzymes such as cellulases.