Dynamics associated with fermentation and aerobic deterioration of high-moisture Italian ryegrass silage made using Lactobacillus plantarum and caproic acid

AIMS

To determine the fermentation quality, aerobic stability, and chemical composition of Italian ryegrass silage prepared with Lactobacillus plantarum (LP), caproic acid (CA), and their combination during ensiling and feed-out phase.

METHODS AND RESULTS

Six treatments: control (CON), LP, 0.15% caproic acid (LCA), 0.2% caproic acid (HCA), LCA + LP, and HCA + LP were employed for 30 days ensiling and an 8-days aerobic stability test. LP had similar pH value and lactic acid content with LCA + LP, while the contents of NH3-N and total VFAs in LCA + LP were significantly lower than those in LP and CON, and the fermentation quality of LCA + LP performed best among all silages. As air-exposure extended, contents of water-soluble carbohydrates (WSC), lactic, and acetic acids decreased, while pH, and NH3-N content increased significantly. The population of lactic acid bacteria gradually decreased in contrast to increased counts of aerobic bacteria and yeasts. Compared with LCA, 0.2% CA delayed the aerobic deterioration as judged by a slower increase in pH and high residual of WSC and lactic acid, and negligible ethanol content and anaerobe spores counts remained in HCA at the end of air exposure. Compared with CON (73 h), LP showed less aerobic stability (38 h), whereas HCA and HCA + LP prolonged aerobic stability for 210 and 152 h, better than LCA (109 h) and LCA + LP (146 h).

CONCLUSIONS

Lactobacillus plantarum apparently improved the fermentation quality, and combined with CA exhibited greater efficiency in inhibiting undesirable microorganism during ensiling. CA at 0.2% optimally extended the aerobic stability.

A novel image-based method for simultaneous counting of Lactobacillus and Saccharomyces in mixed culture fermentation

Mixed microorganism cultures are prevalent in the food industry. From sour beer to sourdough bread, mixed culture popularity has been growing steadily. A variety of microbiological mixtures have been used in these unique fermenting processes to create distinctive flavor profiles and potential health benefits. Although mixed cultures may seem ubiquitous, they are typically not well characterized, which may be due to the lack of user-friendly and simple measurement tools. Image-based cytometry systems have been employed to count bacteria or yeast cells directly and rapidly in plastic chambers, as opposed to traditional cell counting methods that can take days to grow and count. In this work, we aim to develop a novel image cytometry method to distinguish and enumerate mixed cultures of yeast and bacteria in beer products. We demonstrate that the proposed image cytometry method can be used to rapidly distinguish and simultaneously count the bacteria and yeast cells mixed cultures. The Cellometer X2 from Nexcelom was used to automate the counting of Lactobacillus plantarum and Saccharomyces cerevisiae in a mixed culture using fluorescent dyes and size exclusion image analysis algorithm. The proposed image cytometry method was tested with a series of experiments. (1) Yeast and bacteria monoculture titration, (2) mixed culture with various ratios, and (3) monitoring a Berliner Weisse mixed culture fermentation. All experiments were validated by comparing directly to manual counting of yeast and bacteria colony formation on agar plates. The two counting methods were highly comparable with ANOVA analysis showing p-value > 0.05 for all trials. The image cytometry method was the most accurate for yeast concentrations between 105-107 cells/mL and 106-108 cells/mL for lactic acid bacteria. Overall, the novel image cytometry method was able to distinguish and count mixed cultures consistently and accurately, which may provide better characterization and assessment of mixed culture brewing applications that may produce more consistent and higher quality products.

Effect of different dry matter content on fermentation characteristics and nutritional quality of Napier grass silage with novel lactic acid bacteria strains

To investigate the characteristics of different LAB strains isolated from subtropics and their effects on Napier grass (Pennisetum purpureum Schum.) silage with two dry matter (DM) levels, sugar fermentation pattern, and growth profiles of three screened lactic acid bacteria (LAB) strains [Pediococcus pentosaceus (PP04), Weissella cibaria (WC10), and Lactobacillus plantarum (LP694)] were characterized, and then used either individually or in combination at 1.0 × 106 cfu g-1 fresh weight to inoculate grass having 15% or 25% DM. Treatments were applied: (1) no inoculant (control); (2) PP04; (3) WC10; (4) LP694; (5) M-1 (PP04: WC10 = 2:1); (6) M-2 (PP04: LP694 = 1:2); (7) M-3 (WC10: LP694 = 2:1); (8) M-4 (PP04: WC10: LP694 = 2:1:1). The results showed that all inoculations increased LAB, DM recovery, and lactic acid (LA) concentration, while decreasing pH, the ammonia nitrogen/total nitrogen (NH3-N/TN), and butyric acid (BA) concentration compared to control group in both DM. However, the effect of inoculations was very limited at 15% DM. Silages with inoculants achieved higher silage quality at 25% DM than 15% DM. The different LAB inoculants result in significant differences in silage quality, while W. cibaria decreased the pH and inhibited the growth of undesirable bacteria and those characteristics were not affected by the DM content.

Production of Lactobacillus plantarum ghosts by conditional expression of a prophage-encoded holin

Bacterial ghosts (BGs) are nonviable empty bacterial cell envelopes with intact cellular morphology and native surface structure. BGs made from pathogenic bacteria are used for biomedical and pharmaceutical applications. However, incomplete pathogenic cell inactivation during BG preparation raises safety concerns that could limit the intended use. Therefore, safer bacterial cell types are needed for BG production. Here, we produced BGs from the food-grade Gram-positive bacterium Lactobacillus plantarum TBRC 2-4 by conditional expression of a prophage-encoded holin (LpHo). LpHo expression was regulated using the pheromone-inducible pSIP system and LpHo was localized to the cell membrane. Upon LpHo induction, a significant growth retardation and a drastic decrease in cell viability were observed. LpHo-induced cells also showed membrane pores by scanning electron microscopy, membrane depolarization by flow cytometry, and release of nucleic acid contents in the cell culture supernatant, consistent with the role of LpHo as a pore-forming protein and L. plantarum ghost formation. The holin-induced L. plantarum BG platform could be developed as a safer alternative vehicle for the delivery of biomolecules.

Optimization and adsorption characteristics of beads based on heat-inactivated bacterial biomaterial towards the pesticide Cypermethrin

AIMS

Beads containing heat-inactivated bacterial biomaterial (BBBs) were prepared for removal of cypermethrin (CPM) and the conditions for this removal were evaluated and optimized via single-factor coupled orthogonal experiments based on five factors. The adsorption characteristics of BBBs and the binding mechanism were then explored.

METHODS AND RESULTS

Results showed that the adsorption rate of CPM could reach 98% with beads prepared under optimized conditions: equal volumes of Lactobacillus cell debris derived from 1×1011 CFU; 2% hydroxypropyl-β-cyclodextrin and 2.5% activated carbon concentration, were mixed to give mixture TM, and this and SA, was mixed 1:4 with sodium alginate (SA) and beads were prepared using a 26-Gauge needle). The best adsorption conditions were initial CPM concentration of 10 mg l-1, incubation time of 24 h, and rotational speed of 180 rpm. BBBs have a well-formed structure and abundant surface functional groups, such as -COOH, -OH, -NH, -CH, -CO, -C=C. The adsorption process conformed to pseudo-second-order kinetic, and it was also a Freundlich monolayer adsorption, and the calculated maximum adsorption capacity was 9.69 mg g-1 under optimized conditions.

CONCLUSIONS

BBBs showed the highest CPM removal capacity and a good tolerance ability.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results provided a theoretical foundation for developing an adsorbent with heat-inactivated Lactobacillus plantarum (L. plantarum) RS60 for removing CPM in wastewater or drinks.

Screening of Antifungal Lactic Acid Bacteria as Bioprotective Cultures in Yogurt and a Whey Beverage

ABSTRACT

The demand for preservative-free food products is rising, and biopreservation is a potential alternative to replace or reduce the use of chemical preservatives. The objectives of this study were to assess the antifungal activity of lactic acid bacteria (LAB; n = 98) and the efficacy and applicability of the chosen bioprotective cultures against fungal spoilers in dairy products. First, 14 antifungal strains were preliminarily screened by in vitro tests against Pichia pastoris D3, Aspergillus niger D1, Geotrichum candidum N1, Kluyveromyces marxianus W1, and Penicillium chrysogenum B1 and validated by challenge tests in yogurt, indicating that the fungal-inhibiting activity of LAB was species specific and yogurt fermented with antifungal LAB cultures was more effective in extending shelf life. Second, the chosen 14 LAB strains were identified by the 16S rDNA sequence analysis and carbohydrate fermentation test. The results were as follows: nine strains were Lactobacillus plantarum, three were Lactobacillus paracasei, one was Enterococus faecium, and one was Lactobacillus rhamnosus. Among them, active L. plantarum N7 was the chosen and studied factor affecting antifungal activity by using the response surface methodology. Finally, in situ tests were conducted to validate the activity of L. plantarum N7 in actual dairy products (whey beverages). Physicochemical and microbial indices of whey beverages during storage indicated that antifungal L. plantarum N7 could slow yeast growth and be candidates of interest for industrial applications.

HIGHLIGHTS

Recombinant Lactobacillus plantarum NC8 strain expressing porcine rotavirus VP7 induces specific antibodies in BALB/c mice

The major etiologic agent that causes acute gastroenteritis worldwide in young animals and children is Group A rotavirus. Currently, commercially available vaccines do not often prevent porcine rotavirus (PRV) infection. In this study, we evaluated the efficacy of oral recombinant Lactobacillus vaccine against PRV in a mouse model. Lactobacillus plantarum NC8 was used as the host strain, and bacterial vectors were constructed, because the NC8 isolated has shown the capability to survive gastric transit and to colonize the intestinal tract of humans and other mammals. To explore the immunological mechanisms, lactic acid bacterial vectors were used to express VP7 antigen from PRV. We constructed an L. plantarum strain with surface-displayed VP7, named NC8-pSIP409-pgsA-VP7-DCpep. The expressed recombinant protein had a molecular weight of ∼37 kDa. The strain was used to immunize BALB/c mice to evaluate their immunomodulatory characteristics. Mice were orally immunized with recombinant L. plantarum NC8-pSIP409-pgsA-VP7-DCpep at a dose of 2 × 109 colony forming units/200 µl. The results showed that NC8-pSIP409-pgsA-VP7-DCpep significantly stimulated the differentiation of dendritic cells (DCs) in Peyer's patches (PPs) and increased the serum levels of IL-4 and IFN-γ, as measured by enzyme-linked immunosorbent assay in mice treated with NC8-pSIP409-pgsA-VP7-DCpep. Compared to the empty vector group, NC8-pSIP409-pgsA-VP7-DCpep significantly increased the production of B220+ B cells in mesenteric lymph nodes (MLNs) and PPs and also increased the titer levels of the VP7-specific antibodies, including IgG and sIgA. The administration of NC8-pSIP409-pgsA-VP7-DCpep mediated relatively broad cellular responses. This study reveals that clear alternatives exist for PRV control strategies and provides information on PRV infection.

plantarum ZLP001 and fructo-oligosaccharide in post-weaning piglets1

In this study, we evaluated the effects of seven oligosaccharides on the growth rate and stress tolerance of Lactobacillus plantarum ZLP001 in vitro, and the potential synbiotic effects of the most effective oligosaccharide [fructo-oligosaccharide (FOS)] and L. plantarum ZLP001 on the growth performance, apparent nutrient digestibility, fecal microbiota, and serum immune index in weaning piglets. Most oligosaccharides were utilized as carbohydrate sources by L. plantarum ZLP001, but we observed obvious differences in the bacterial growth depending on oligosaccharide type and concentration. Oligosaccharides and glucose significantly alleviated the decrease in L. plantarum ZLP001 viability in artificial gastric fluid, whereas none of the sugars affected viability in artificial intestinal fluid. FOS and galacto-oligosaccharide significantly improved the viability of L. plantarum ZLP001 under heat stress (65 °C for 15 and 30 min). FOS and soybean oligosaccharide significantly increased the viability of L. plantarum ZLP001 in response to cold stress (4 °C for 30 and 60 days). On the basis of the findings of in vitro experiments, we selected FOS for in vivo studies. Eighty-four weaned piglets were randomly assigned to one of the following groups: control (basal diet, no additives), freeze-dried L. plantarum ZLP001 (4.2 × 109 CFU/g, 2 g/kg diet), FOS (5 g/kg diet), and combination (0.2% L. plantarum ZLP001 + 0.5% FOS). Body weight and feed consumption were recorded for determinations of the average daily gain (ADG), average daily feed intake (ADFI), and feed-to-gain ratio (F/G). On day 28, fresh fecal samples were collected to evaluate the apparent digestibility of nutrients and microbiota, and serum samples were collected to determine the immune status. L. plantarum ZLP001 plus FOS significantly increased ADG and decreased the F/G ratio compared with the no-additive control. The combination treatment also increased the apparent nutrient digestibility of dry matter and crude protein. Compared with the control and single supplementation, the combination treatment had a significant regulatory effect on the intestinal microbiota, as evidenced by increases in Lactobacillus spp. and a decrease in Enterobacteriaceae. In addition, the combination treatment increased the concentrations of serum IFN-γ and immunoglobulin G. In conclusion, FOS can be utilized well by L. plantarum ZLP001 and can be combined with it as a potential synbiotic that shows synergistic effects in weaning piglets.