Citric Acid Influences the Dynamics of the Fermentation Quality, Protease Activity and Microbial Community of Mulberry Leaf Silage

Inoculation of Lactobacillus parafarraginis enhances silage quality, microbial community structure, and metabolic profiles in hybrid Pennisetum

BACKGROUND

This study investigated the effects of inoculating Lactobacillus parafarraginis alone or in combination with citric acid on the silage quality, microbial community structure, and metabolic characteristics of hybrid Pennisetum. The experiment included three treatments: (1) addition of 10 ml distilled water (CON); (2) addition of 1 × 106 cfu/g L. parafarraginis (LP); (3) addition of 1 × 106 cfu/g L. parafarraginis and 1% citric acid (LCA). The fermentation was maintained at 25 ℃ for 60 days.

RESULTS

The addition of L. parafarraginis increased the dry matter, water-soluble carbohydrates, and crude protein content of the silage and decreased the fiber contents. Moreover, lactic acid content was notably higher, and pH values were lower in the L. parafarraginis group, with higher lactic acid bacteria (LAB) compared with the CON. The microbial community analysis indicated that adding L. parafarraginis promoted the proliferation of beneficial LAB and inhibited spoilage bacteria, such as Clostridium. In the LCA, amino acid metabolism was improved, particularly with an increase in L-tyrosine concentration, along with significant enrichment of pathways related to tryptophan metabolism.

CONCLUSIONS

The addition of L. parafarraginis improved the fermentation quality of the silage, reduced undesirable microorganisms, and increased the content of organic acids, indicating its potential to enhance the flavor of the silage. Compared with individual treatments, the combination of L. parafarraginis and citric acid improved amino acid metabolism and enriched pathways related to tryptophan metabolism, further enhancing the quality of the silage. These findings highlight the potential of L. parafarraginis, especially in combination with citric acid, as an effective additive for producing high-quality, nutritious hybrid Pennisetum silage.

Effects and function of citric acid on fermentation quality and microbial community in sugarcane tops silage with high and low water-soluble carbohydrate content

Sugarcane tops silage (STS), as a source of roughage for ruminants, is rich in water-soluble carbohydrate (WSC) content, which significantly affects silage quality. Citric acid (CA) is a low-cost natural antimicrobial agent that can inhibit undesirable microbes and improve silage quality. The objectives of this study were to investigate the effects of CA on the chemical composition, fermentation quality, microbial communities, and metabolic pathways of STS with high and low WSC contents before or after aerobic exposure. Fresh sugarcane tops with low-WSC [143.05 g/kg dry matter (DM)] and high-WSC (249.99 g/kg DM) contents were treated with and without CA and then ensiled for 125 days, followed by aerobic exposure for 4, 8, and 16 days. The results showed that high-WSC STS had lower crude protein (CP) content and higher DM, neutral detergent fiber (NDF), and acid detergent fiber (ADF) contents, whether treated with CA or not. CA-inoculated silage exhibited decreased DM loss and enterobacteria (EB) counts compared to the control. High-WSC STS treated with CA had higher WSC content and lower yeast count than those without CA inoculation. During the 0-16 days of aerobic exposure, the propionic acid and butyric acid contents in CA-inoculated silage were almost unchanged and ranged from 0 to 1 g/kg DM. Meanwhile, the ethanol content was almost unchanged and ranged from 0 to 1 g/kg DM only in low-WSC STS, irrespective of CA addition. Before aerobic exposure, CA inoculation decreased the abundances of undesirable microbes (e.g., Clostridium_sensu_stricto_12 and Paecilomyces) and animal pathogens, while amino acid metabolism was lower in high-WSC STS regardless of CA treatment. After aerobic exposure, CA inoculation increased the abundance of bacteria with antibacterial effects, including Paenibacillus and Bacillus. Moreover, the metabolism of energy and nucleotides was lower in high-WSC STS treated with CA, and the animal pathogens was lower in low-WSC STS treated with CA. In conclusion, CA inoculation could be effective in decreasing nutrients loss, improving fermentation quality, inhibiting harmful microorganisms, and modulating the metabolic pathways of microorganisms in STS with high and low WSC contents prior to and after aerobic exposure.

Current approaches on the roles of lactic acid bacteria in crop silage

Lactic acid bacteria (LAB) play pivotal roles in the preservation and fermentation of forage crops in spontaneous or inoculated silages. Highlights of silage LAB over the past decades include the discovery of the roles of LAB in silage bacterial communities and metabolism and the exploration of functional properties. The present article reviews published literature on the effects of LAB on the succession, structure, and functions of silage microbial communities involved in fermentation. Furthermore, the utility of functional LAB in silage preparation including feruloyl esterase-producing LAB, antimicrobial LAB, lactic acid bacteria with high antioxidant potential, pesticide-degrading LAB, lactic acid bacteria producing 1,2-propanediol, and low-temperature-tolerant LAB have been described. Compared with conventional LAB, functional LAB produce different effects; specifically, they positively affect animal performance, health, and product quality, among others. In addition, the metabolic profiles of ensiled forages show that plentiful probiotic metabolites with but not limited to antimicrobial, antioxidant, aromatic, and anti-inflammatory properties are observed in silage. Collectively, the current knowledge on the roles of LAB in crop silage indicates there are great opportunities to develop silage not only as a fermented feed but also as a vehicle of delivery of probiotic substances for animal health and welfare in the future.

Effects of Mulberry Leaves and Pennisetum Hybrid Mix-Silage on Fermentation Parameters and Bacterial Community

The silage quality and bacterial community of hybrid Pennisetum (P. hydridum × P. americanum) with or without 30% and 50% mulberry leaves for 3, 7, 14, and 30 days were investigated. Results showed that compared with the 100% hybrid Pennisetum group, more lactic acid (40.71 vs. 80.81 g/kg dry matter (DM)), acetic acid (10.99 vs. 31.84 g/kg DM), lactic acid bacteria (8.46 vs. 8.51 log10 cfu/g fresh matter), water-soluble carbohydrates (2.41 vs. 4.41 g/100 g DM), crude protein (4.97 vs. 10.84 g/100 g DM), and true protein (3.91 vs. 8.52 g/100 g DM) content as well as less neutral detergent fiber (67.30 vs. 47.26 g/100 g DM), acid detergent fiber (33.85 vs. 25.38 g/100 g DM), and yeast counts (4.78 vs. 2.39 log10 cfu/g fresh matter) and an appropriate pH (3.77 vs. 4.06) were found in silages added with 50% mulberry leaves at 30 days of ensiling. Moreover, the addition of mulberry leaves also influenced the relative abundance of the bacterial community. The relative abundance of Firmicutes increased and Proteobacteria decreased when mulberry leaves were added. Weissella and Lactobacillus abundance also increased. To sum up the above, mixing with 50% mulberry leaves yielded the greatest fermentation quality in this study. In conclusion, mixing with mulberry leaves could be a reasonable way to improve the quality of hybrid Pennisetum silage.