Investigating the mechanisms of Lactiplantibacillus plantarum-mediated optimization of alfalfa silage fermentation and enhancement of antioxidant capacity based on 16 S sequencing technology

Lactiplantibacillus plantarum (L. plantarum) is a safe and eco-friendly additive capable of improving the yield and quality of silage. Currently, research on the use of antioxidative lactic acid bacteria in silage production remains limited. Silage inoculated with antioxidative L. plantarum retains more nutrients and exhibits relatively high antioxidant capacity, demonstrating significant potential for enhancing animal health and improving the quality of animal-derived products. The objective of this research was to assess how four strains of L. plantarum with antioxidant properties impact the fermentation characteristics, bacterial composition, and antioxidant capacity of alfalfa silage. Freshly chopped alfalfa was subjected to five different treatments: I.) no inoculation (control); II.) inoculation with L. plantarum S2; III.) inoculation with L. plantarum LP1; IV.) inoculation with L. plantarum LP8; and V.) inoculation with L. plantarum H8. The additives were all added with a dosage of 1 × 106 cfu/g fresh weight and stored for 90 days for sampling and analysis. The research results indicated that, compared with the control group, the addition of four L. plantarum strains had a significant impact on both the quality and microbial community of silage (P < 0.05). The crude protein content in silage inoculated with L. plantarum was significantly higher than that in the control group (P < 0.05). Among all the L. plantarum treatment groups, the LP1 group exhibited the largest increase in crude protein content, with a rise of 10.06%. Compared with the control group, the total phenolic content in silage supplemented with L. plantarum LP8 significantly increased (P < 0.05), with an increase of 13.98%. The silage supplemented with L. plantarum H8 had significantly lower pH and ammonia nitrogen content than the control group (P < 0.05), with decreases of 6.21% and 120%, respectively. Its lactic acid and flavonoid contents significantly increased, with rises of 18.21% and 18.47%, respectively. Moreover, the contents of 1,1-diphenyl-2-picrylhydrazyl radical and 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging activities in the silage supplemented with L. plantarum H8 were significantly higher than those in the control group (P < 0.05). In the treatment groups supplemented with L. plantarum, the relative abundance of the Lactobacillus genus significantly increased (P < 0.05), inhibiting the growth and reproduction of undesirable microorganisms (such as Chryseobacterium and Stenotrophomonas) (P < 0.05). The addition of L. plantarum H8 and LP8 simplified the microbial network of alfalfa silage, while the addition of L. plantarum S2 and LP1 increased the complexity of the microbial network structure. Metabolic function prediction showed that the addition of L. plantarum promoted carbohydrate and amino acid metabolism (P < 0.05). In conclusion, the addition of all four L. plantarum species improved alfalfa silage quality, but L. plantarum H8 was more effective at improving fermentation quality and antioxidant activity.