Applicability of Neural Networks for the Fermentation of Propionic Acid by Propionibacterium acidipropionici

According to our best knowledge, this is the first report applying Artificial neural networks (ANN) for simulation of batch propionic acid (PA) fermentation. Therefore, the main focus of this research was to investigate the applicability of ANN on PA fermentations. To demonstrate this, we used the results of 40 Propionibacterium acidipropionici fermentations (ca 2,000 data points) to build up the ANN, and additional two independent fermentations to demonstrate the prediction capability of the observed ANN. Analyzing the predicted output parameters we observed, that ratio of propionic acid to acetic acid (PA/AA) variables can only be used for ANN after normalization. Finally, the fit of the ANN model to the measured data was fine (average correlation coefficients over 0.9). A special feature was also tested: fermentation time was also used as an input parameter, thus making the ANN suitable to predict time course of PA fermentations as well which was also satisfying.

Efficient Production of Propionic Acid in the Fed-Batch Fermentation of Propionibacterium acidipropionici and Its Metabolic Flux Analysis

To improve the fermentation efficiency of Propionibacterium acidipropionici, a simplified metabolic network was established to provide theoretical guidance for medium optimization and process regulation. The effect of glucose and glycerol on propionic acid production and metabolic flux distribution was investigated and the combination of glucose and glycerol was optimized. The results showed that the productivity of propionic acid could be improved by enhancing the synthesis of pyruvate and its flux distribution to the oxaloacetate branch. Finally, the scaled-up fed-batch fermentation of P. acidipropionici was conducted. The concentration of propionic acid reached 51.75 ± 3.62g/L with a glucose/glycerol ratio of 4:1, an improvement of 79.25% relative to the use of glucose alone, and the corresponding productivity and yield were 0.39g/(L· h) and 0.52g/g, respectively. Therefore, the combination of glucose and glycerol significantly improved the productivity of propionic acid and provides a new strategy for industrial production.

Fermentation Profile, Nutritional Value, and Microbial Population of C4 Grasses Silages with or Without Bacterial Additive

The objective of the present study was to evaluate the use of bacterial additive (Lactobacillus plantarum and Propionibacterium acidipropionici) on chemical composition, in vitro gas production, pH, losses, aerobic stability, and microbial population of corn, pearl millet, and sorghum silages in plastic bags silos (without vacuum). The experiment was carried out in a randomized block design, in a 2 × 3 factorial scheme, with or without additive ([Control] without additive and Lactobacillus plantarum [2.5 × 1010 cfu/g] and Propionibacterium acidipropionici [2.5 × 1010 cfu/g] Biomax corn, Lallemand, Saint-Simon, France [LP]) and three crops of agricultural interest; pearl millet, sorghum, and corn, with four replicates per treatment. We performed chemical analyses and in vitro gas production to determine the nutritional value of the silages. We also evaluated the aerobic stability, ammoniacal nitrogen (NH3), pH, and microbial population of the silages. The additive increased the crude protein content (P = 0.0062) in corn and sorghum and decreased the LIG content (P = 0.0567). The gas production was not affected (P > 0.05) by the additive and neither between crops. In aerobic stability, we observed that the additive affected the temperature of the sorghum silage (P = 0.0123). The additive decreased NH3 (P = 0.0095) content. The additive increased (P = 0.0441) the lactic acid bacteria population in the pearl millet, corn, and sorghum silages. Thus, the bacterial additive did not improve the fermentation profile and nutritional value of corn, pearl millet, and sorghum silages in plastic bag silos.

High-moisture corn grain silage inoculated with Propionibacterium acidipropionici and Lactobacillus plantarum in different storage times

The aim of this study was to evaluate the chemical composition, growth of microorganisms, and the aerobic stability of high-moisture corn grain silage inoculated with Lactobacillus plantarum + Propionibacterium acidipropionici. The experimental design was completely randomized in a 2 x 5 factorial arrangement with four replications (50 experimental units) and the treatments were: use or not of microbial inoculant (2 x 105 colony forming unit (CFU) g-1 Lactobacillus plantarum + Propionibacterium acidipropionici) and the storage length for 0, 1, 3, 7, and 14 d. Aerobic stability of silage was evaluated at 28 and 56 d of storage length. The lactic acid bacteria population was influenced by storage length and the greatest values were estimated at 8 d of storage length. Regardless of inoculant application, no enterobacteria were present from 3 d post-ensiling. With respect to mold growth, an interaction between inoculant and storage length was observed wherein molds were most abundant after 3 d of storage in silage that received inoculant. However, at 14 d of storage the use of bacterial inoculant reduced the occurrence of molds. pH values obtained after 3 d of ensiling were less than 4.0 for all the treatments. The high-moisture corn grain silage possessed good fermentative quality. Further, adequate pH values were achieved from the third day of ensilage and were not influenced by the presence of bacterial inoculant.

Effect of rehydration with whey and inoculation with Lactobacillus plantarum and Propionibacterium acidipropionici on the chemical composition, microbiological dynamics, and fermentative losses of corn grain silage

The objective of this study was to compare rehydrated corn grain silages using water or whey and inoculated (Lactobacillus plantarum and Propionibacterium acidipropionici) or not. We also verified whether rehydration with whey associated with the bacterial inoculant improves material conservation. The treatments were as follows: silages rehydrated with water without inoculant (SWa); silages rehydrated with water and inoculated (SWaI); silages rehydrated with whey without inoculant (SWe); silages rehydrated with whey and inoculated (SWeI). A completely randomized design was used, with three replications, treatments in a 2 × 2 factorial scheme (RE: rehydration with water or whey, and IN: inoculation or addition of water without chlorine), during the following storage periods (T): 0, 4, 8, 16, 32, and 64 days. There was an RE x IN x T interaction (P < 0.001) for dry matter (DM), with lower values over time for SWe and higher values in SWeI. An interaction between RE x IN (P < 0.001) and IN x T (P < 0.001) was observed for pH, with higher values for SWe at 64 days of storage and a reduction from the first days of ensiling for SWaI and SWeI. The microbiological variables showed an RE x IN x T interaction (P < 0.001), with the highest counts of lactic acid bacteria for SWaI and SWeI up to 8 days of storage and subsequent higher counts in SWa and SWe. Higher counts were obtained in SWe. For the variables of fermentative losses, there was an RE x IN x T interaction (P < 0.001), with SWeI showing lower losses. The inoculation associated with whey for rehydration of corn grain improved the fermentation profile of the silage, with lower pH values and reduced losses.