Antioxidant status, chemical composition and fermentation profile of alfalfa silage ensiled at two dry matter contents with a novel Lactobacillus plantarum strain with high-antioxidant activity

摘要

The objective of this study was to evaluate the effects of a novel Lactobacillus plantarum strain with high-antioxidant activity on antioxidant status, chemical composition and fermentation profiles of alfalfa silage ensiled at two dry matter (DM) contents. Fresh chopped alfalfa was wilted to two targeted dry matter (DM) contents of approximately 300 (low DM) and 400 (high DM) g/kg fresh weight and treated without or with a strain of L. plantarum 24-7 with high antioxidant activity. Forages were ensiled in vacuum-sealed polyethylene bags containing similar to 600 g wilted forage for 60 d, with 5 replicates for each treatment. Alfalfa silage ensiled at low DM had higher concentrations of acetic acid and non-protein nitrogen (NPN) and lower concentrations of lactic acid, propionic acid and water soluble carbohydrates (WSC) than silages with high DM. Inoculation of L. plantarum 24-7 led to lower silage pH and lower concentrations of NPN, neutral detergent fiber (aNDF), acid detergent fiber (ADF), and higher WSC compared to the control silage at two DM contents. Inoculation increased aerobic stability of the forage ensiled at low DM but decreased that ensiled at high DM. In control silages, almost half of the alpha-tocopherol and beta-carotene was degraded during ensiling, whereas inoculation with L. plantarum 24-7 increased alpha-tocopherol and beta-carotene concentrations as well as the proportion of polyunsaturated fatty acids (PUFA) in ensiled alfalfa at both DM contents. Greater concentrations of beta-carotene were observed in L. plantarum 24-7 treated-silage at low DM compared to silage at high DM. The application of L. plantarum 24-7 strain also increased total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-Px) and catalase (CAT) activities of the alfalfa silage but decreased superoxide dismutase (SOD) and lipoxygenase (LOX) activities. These results indicate that L. plantarum 24-7 improved the fermentation quality and antioxidant status of ensiled alfalfa forage relative to the control silage.