Characterization of Lactobacillus rhamnosus GG and its effects on improving the fermentation quality of silages as a novel inoculant

Abstract

The aim of the present study was to characterize the fermentation properties of Lactobacillus rhamnosus GG (LGG; ATCC 53103) in vitro, and investigate the effects of inoculation with LGG on fermentation quality of whole plant corn silage (WPCS) and fermented total mixed ration (FTMR). The antifungal activity of LGG against 4 prevalent fungi isolated from corn stalk was determined using the Oxford cup method. The binding capacity of LGG to aflatoxin B1, zearalenone and deoxynivalenol was examined by in vitro adsorption experiments using a batch mode in phosphate buffered saline. The antioxidant activity of LGG in vitro was evaluated by determining the resistance to hydrogen peroxide, free radical scavenging capacity and reducing activity. Three batches of whole plant corn and total mixed ration were collected separately. Each batch of raw material was divided into equal portions and applied to 2 treatments: (1) control with distiller water (CON), and (2) treatment inoculated with LGG (LGG). After 48 d of ensiling, the chemical composition, ruminal degradability, microbial community and mycotoxin concentrations of WPCS and FTMR were determined. The results showed that lactic acid was the predominant component among organic acids in LGG culture process, with a rapid generated occurring at 4 h after inoculation and reaching a stable state at approximately 48 h. Lactobacillus rhamnosus GG could effectively inhibit the growth of 4 prevalent fungi isolated from corn stalk, the diameter of inhibition zone was higher for Mucor circinelloides than that of the other moulds (P = 0.016). With increasing of LGG cell amount, the binding capacity to 3 mycotoxins increased (P < 0.01); the heat and acid treated LGG also enhanced the binding capacity to mycotoxins (P < 0.01). Lactobacillus rhamnosus GG displayed tolerance to hydrogen peroxide (0.8 mmol/L) for 8 h at 37 °C (96%, viability), but the viability decreased sharply (52.39%, viability) under the concentration of H2O2 increased to 1.2 mmol/L (P < 0.001). The free radical scavenging activity and reducing activity of viable LGG were greatest, followed by cell-free extracts and inactivated cells (P < 0.001). Ensiling of WPCS and FTMR inoculated with LGG decreased dry matter loss (P < 0.05), increased lactic acid and acetic acid production (P < 0.05), enhanced some nutrients ruminal degradability (P < 0.05). Meanwhile, the inoculation of LGG reduced the counts of yeast, mold and coliform bacteria (P < 0.05) and, more importantly, alleviated mycotoxin contamination (P < 0.05). These results indicated that LGG could be a novel inoculant to improve the quality and safety of WPCS and FTMR.