Bacteriocin Production Correlates with Epidemiological Prevalence of Phylotype I Sequevar 18 Ralstonia pseudosolanacearum in Madagascar

Bacterial wilt caused by the Ralstonia solanacearum species complex (RSSC) is a major threat to vegetable crops in Madagascar. For more effective disease management, surveys were carried out in the main vegetable production areas of the country, leading to the collection of 401 new RSSC isolates. Phylogenetic assignment of the isolates revealed a high prevalence of phylotype I sequevar 18. This result contrasts sharply with the epidemiological pattern of RSSC in neighboring islands, including Reunion Island, Comoros, Mayotte, Mauritius, Rodrigues, and the Seychelles, where phylotype I sequevar 31 is widespread. Molecular typing characterization of the Malagasy isolates allowed the identification of 96 haplotypes. Some are found in various plots located in different provinces, which suggests that they were probably disseminated via infected plant material. To find out a potential explanation for the observed epidemiological pattern, we examined the capacity of the Malagasy strains to produce bacteriocin. Interestingly, the highly prevalent genetic lineages I-18 produce bacteriocins that are active against all the genetic lineages present in the country. This work sheds light on the potential impact of bacteriocins in the epidemiology of Malagasy RSSC. IMPORTANCE Knowledge of the epidemiology of a plant pathogen is essential to develop effective control strategies. This study focuses on the epidemiological pattern of Ralstonia pseudosolanacearum phylotype I populations responsible for bacterial wilt in Madagascar. We identified, with the newly collected isolates in three provinces, four genetic lineages probably propagated via infected plant material in Madagascar. We revealed that the epidemiological situation in Madagascar contrasts with that of neighboring Indian Ocean islands. Interestingly, our study on the bacteriocin-producing capacity of Malagasy isolates revealed a correlation between the inhibitory activity of the producing strains and the observed epidemiology. These results suggested that the epidemiology of plant pathogens may be impacted by bacteriocin production.

Emerging starch composite nanofibrous films for food packaging: Facile construction, hydrophobic property, and antibacterial activity enhancement

Polymers synthesized from green resources have many advantages in food packaging and hence their development is very important. Herein, starch/polyvinyl alcohol (PVA) nanofibrous composite films were fabricated by electrospinning technology. Steam-induced cross-linking reaction with glutaraldehyde (GTA) and silver sodium zirconium phosphate (Ag-ZrP) was employed to improve the hydrophobic and antibacterial properties of the constructed nanofibrous films, respectively. The effects of starch/PVA ratio on the micro-morphology and mechanical properties of the binary composite film were investigated. The composite film showed optimal uniformity, bead-free electrospun nanofibers, with enhanced mechanical strength for the 60/40 (v/v) starch/PVA composite. Moreover, the crystallinity of PVA was reduced during the electrospinning process, whereas the introduction of PVA strengthened the hydrogen interactions and improved the thermal stability of the composite films. After the cross-linking with GTA, the starch/PVA films became more hydrophobic. Furthermore, the starch/PVA films embedded with Ag-ZrP had outstanding antibacterial property against both Gram-negative and Gram-positive bacteria. This work demonstrated the potential prospects of electrospun starch nanofibrous films in the food packaging field.

Cell-free supernatants produced by lactic acid bacteria reduce Salmonella population in vitro

The genus Salmonella is closely associated with foodborne outbreaks and animal diseases, and reports of antimicrobial resistance in Salmonella species are frequent. Several alternatives have been developed to control this pathogen, such as cell-free supernatants (CFS). Our objective here was to evaluate the use of lactic acid bacteria (LAB) CFS against Salmonella in vitro. Seventeen strains of LAB were used to produce CFS, and their antimicrobial activity was screened towards six strains of Salmonella. In addition, CFS were also pH-neutralized and/or boiled. Those with the best results were lyophilized. MICs of lyophilized CFS were 11.25-22.5 g l^-1. Freeze-dried CFS were also used to supplement swine and poultry feed (11.25 g kg^-1) and in vitro simulated digestion of both species was performed, with Salmonella contamination of 5×10⁶ and 2×10⁵ c.f.u. g^-1 of swine and poultry feed, respectively. In the antimicrobial screening, all acidic CFS were able to inhibit the growth of Salmonella. After pH neutralization, Lactobacillus acidophilus Llorente, Limosilactobacillus fermentum CCT 1629, Lactiplantibacillus plantarum PUCPR44, Limosilactobacillus reuteri BioGaia, Lacticaseibacillus rhamnosus ATCC 7469 and Pediococcus pentosaceus UM116 CFS were the only strains that partially maintained their antimicrobial activity and, therefore, were chosen for lyophilization. In the simulated swine digestion, Salmonella counts were reduced ≥1.78 log c.f.u. g^-1 in the digesta containing either of the CFS. In the chicken simulation, a significant reduction was obtained with all CFS used (average reduction of 0.59±0.01 log c.f.u. ml^-1). In general, the lyophilized CFS of L. fermentum CCT 1629, L. rhamnosus ATCC 7469 and L. acidophilus Llorente presented better antimicrobial activity. In conclusion, CFS show potential as feed additives to control Salmonella in animal production and may be an alternative to the use of antibiotics, minimizing problems related to antimicrobial resistance.

Bioactive peptides supplemented raw buffalo milk: Biological activity, shelf life and quality properties during cold preservation

This study aimed to prolong the raw buffalo milk handling and cold storage period by controlling the microbes, enhancing sensory properties and their functionality after supplementing bioactive peptides. The additions included hen and duck egg white protein isolates (HPI and DPI), pepper seed protein (PSP), and pepsin-kidney bean protein hydrolysate (PKH). Five milk treatments were prepared and evaluated as non-supplemented milk (M- Control), hen egg white protein isolate-supplemented milk (M-HPI), duck egg white protein isolate-supplemented milk (M-DPI), pepper seeds protein-supplemented milk (M-PSP), and kidney bean hydrolysate-supplemented milk (M-PKH). Pyrogallol, protocatechuic, catechin, benzoic and caffeine were the main phenolic compounds, Apignin-6-arabinose, naringin, hesperidin, naringenin, kaempferol 3-2-p-comaroyl were the dominant flavonoids in milk samples based on HPLC profile. During 30 days of cold storage, the antioxidant potential of peptides-supplemented milk samples was significantly decreased (p ≤ 0.05) as decrement of phenolic compounds and flavonoids; the pH was nearly stable, the titratable acidity and total soluble solids (TTS) were (p ≤ 0.05) raised. PSP and PKH were inhibited (p ≤ 0.05) the decay of sugars in M-PSP, and M-PKH by reducing 45% of bacterial load as compared to other milk samples. PSP was significantly (p ≤ 0.05) scavenged 87% of DPPḢ compared to other peptides. Besides, PSP followed by PKH reduced considerably (p ≤ 0.05) the growth of tested bacteria, molds, and yeasts. The PSP has significantly increased the whiteness of M-PSP as compared to other milk samples. M-PSP had the highest score in color, taste, and flavor, followed by M-PKH.

Antioxidant and Antimicrobial Activity of Porcine Liver Hydrolysate in Meat Emulsion and Their Influence on Physico-Chemical and Color Deterioration During Refrigeration Storage

Present study explored the quality changes in meat emulsion during storage at refrigerated temperature prepared with inclusion of three different levels of liver protein hydrolysate (LPH) in meat emulsion (LPH-1: 0.03, LPH-2: 0.06, and LPH-3: 0.09%) and compared with control (LPH: 0.00%) and positive control (butylated hydroxytoluene: 0.02% w/w meat emulsion). Physico-chemicals, antioxidant activities, lipid oxidation, color profile, microbial quality, and microbial challenge test (MCT) were assessed for all groups. Results indicated that all evaluated attributes were considerably improved with increase in LPH concentration. Among treated groups, LPH-3 was maintained comparatively better for every attribute assessed during storage studying. Regarding microbial quality, LPH-3 showed (P ≤ 0.05) lower aerobic plate count, coliforms, and yeast mold counts than others. Likewise for MCT, significantly (P ≤ 0.05) lower microbial counts were recorded in LPH-3 during storage. Results concluded that LPH can be a good alternative substance for the preservation of meat for lower oxidation activity and bacterial growth. PRACTICAL APPLICATION: Meat emulsion is more prone to lipid oxidation and microbial contamination than fresh meat. However, for the preparation of convenient, value added meat products, better utilization of freezed meat and reduced cooking time have enhanced the demand of emulsion-based meat products. Liver protein hydrolysate can be a good alternative substance for the preservation of emulsion-based meat products. Treated groups better retained their physico-chemical properties, color indices, and showed lower oxidation and microbial counts than control. It can be exploited commercially for the preparation of functional foods, nutraceuticals, and cosmeceuticals.

Antibacterial Effect of Black Pepper Petroleum Ether Extract against Listeria monocytogenes and Salmonella typhimurium

The aim of the present study was to evaluate the antibacterial effect of black pepper petroleum ether extract (BPPE) against Listeria monocytogenes ATCC 19115 and Salmonella typhimurium ATCC 14028. The results showed that the BPPE had a strong antimicrobial activity against L. monocytogenes and S. typhimurium, and 2-methylene-4,8,8-trimethyl-4-vinyl-bicyclo[5.2.0]nonane (9.36%) and caryophyllene oxide (4.85%) were identified as the two primary components of BPPE. The ability of cells to break down hyperoxide was decreased, and the activities of POD and CAT were inhibited. The activities of key metabolic enzymes shed some light on the biochemical mechanism of aglycon cell growth inhibition, indicating that the energetic metabolism of L. monocytogenes and S. typhimurium was markedly influenced by the BPPE. The contents of key organic acids varied significantly, resulting in remarkable abnormalities in the energetic metabolism of L. monocytogenes and S. typhimurium. Thus, the consecution of energetic metabolism was destroyed by the BPPE, which contributed to metabolic dysfunction, the suppression of gene transcription, and cell death.

Stability of Bacteriocin-Like Inhibitory Substance (BLIS) Produced by Pediococcus acidilactici kp10 at Different Extreme Conditions

Nowadays, bacteriocin industry has substantially grown replacing the role of chemical preservatives in enhancing shelf-life and safety of food. The progress in bacteriocin study has been supported by the emerging of consumer demand on the applications of natural food preservatives. Since food is a complex ecosystem, the characteristics of bacteriocin determine the effectiveness of their incorporation into the food products. Among four commercial media (M17 broth, MRS broth, tryptic soy broth, and nutrient broth) tested, the highest growth of Pediococcus acidilactici kp10 and bacteriocin-like-inhibitory substance (BLIS) production were obtained in the cultivation with M17. BLIS production was found to be a growth associated process where the production was increased concomitantly with the growth of producing strain, P. acidilactici kp10. The antimicrobial property of BLIS against three indicator microorganisms (Listeria monocytogenes, Escherichia coli, and Staphylococcus aureus) remained stable upon heating at 100°C but not detectable at 121°C. The BLIS activity was also observed to be stable and active at a wide pH range (pH 2 to pH 7). The BLIS activity remained constant at -20°C and -80°C for 1 month of storage. However, the activity dropped after 3 and 6 months of storage at 4°C, -20°C, and -80°C with more than 80% reduction. The ability of bacteriocin from P. acidilactici kp10 to inhibit food-borne pathogens while remaining stable and active at extreme pH and temperature is of potential interest for future applications in food preservatives.

Isolation of antibacterial protein from Lactobacillus spp. and preparation of probiotic curd

The study was aimed to isolate antagonistic lactobacilli and the molecules responsible for their antagonistic ability from curd. Preparation of probiotic curd and the ability of the selected lactobacilli to suppress the pathogen therein was also assessed. All the 116 isolates were identified as Lactobacillus spp. based on morphological, biochemical and curdling assays. Five of these lactobacilli (Lb-17, Lb-33, Lb-108, Lb-112, and Lb-N3) were found most promising to inhibit all test pathogens (Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Salmonella typhi and Shigella sonnei). The cell-free culture supernatants of these five lactobacilli were recorded as thermo-tolerant when subjected to heat treatment at 100 °C for 20 min. The loss in the activity after protease treatment indicated the proteinaceous nature of the antimicrobial molecule present in the culture supernatants. Active protein (19 kDa) produced by lactobacilli was confirmed by SDS-PAGE followed by agar-overlay method. Antibiotic sensitivity assay revealed that the selected Lactobacillus spp. isolates were resistant to methicillin and vancomycin. Probiotic curd prepared by using Lb-108 and Lb-N3 was found to be superior to rest of the three isolates based on organoleptic tests and shelf-life. Complete inhibition of all the test pathogens in curd was shown by Lb-108 and Lb-N3. Inhibition spectrum, production of thermostable protein and preparation of quality curd suggest Lb-108 and Lb-N3 as promising candidates to prepare probiotic curd.

Antimicrobial peptides as natural bio-preservative to enhance the shelf-life of food

Antimicrobial peptides (AMPs) are diverse group of natural proteins present in animals, plants, insects and bacteria. These peptides are responsible for defense of host from pathogenic organisms. Chemical, enzymatic and recombinant techniques are used for the synthesis of antimicrobial peptides. These peptides have been found to be an alternative to the chemical preservatives. Currently, nisin is the only antimicrobial peptide, which is widely utilized in the preservation of food. Antimicrobial peptides can be used alone or in combination with other antimicrobial, essential oils and polymeric nanoparticles to enhance the shelf-life of food. This review presents an overview on different types of antimicrobial peptides, purification techniques, mode of action and application in food preservation.