Enhanced shelf-life of tofu by using bacteriocinogenic Weissella hellenica D1501 as bioprotective cultures

Bacteriocinogenic Weissella hellenica D1501 was originally isolated from Chinese Dong fermented meat, showing a relatively good growth and sufficient acid development in soymilk. Investigation of the antagonistic activities of W. hellenica D1501 was conducted by co-culturing with spoilage and pathogenic bacteria (i.e. Kurthia gibsonii, Staphylococcus aureus and Escherichia coli) in soymilk. The proliferations of the three undesired strains were suppressed and the bacterial populations decreased to undetectable level after 36 h of co-cultures. An innovative tofu (designated as LAB tofu) was a novel type of tofu coagulated by both acid and enzyme together through the using of W. hellenica D1501 combined with MTGase (microbial transglutaminase). Compared with tofu prepared with traditional coagulants, W. hellenica D1501 in LAB tofu could significantly suppress the microbial spoilage and extend the shelf-life based on microbiological analyses. During the storage periods at different temperatures, LAB tofu was observed bacteriocin activities and significantly increased amounts of various antimicrobial volatile compounds, which might be in partly responsible for spoilage retardation and shelf-life extension. In conclusion, W. hellenica D1501 can be used as bioprotective cultures for extending shelf-life and improving the safety of tofu.     

Partial characterisation of bacteriocins produced by lactic acid bacteria isolated from Thai fermented meat and fish products

Lactic acid bacteria (LAB) from Thai fermented meat and fish products were isolated. From a total of 93 samples, 152 isolates of lactic acid bacteria were obtained. Antimicrobial activity screening was performed using the agar spot test and the agar well diffusion method. Of the six isolates which produced antimicrobial activities against Weissella confusa N31, only isolate N23 was identified as Weissella cibaria (GenBank accession number AB494716.1) with 99% similarity by 16S rDNA sequence analyses. Complete inactivation of antimicrobial activity produced by W. cibaria N23 was observed after treatment of the bacteriocins with trypsin, actinase, protease XIII, ficin, trypsin from porcine pancreas, α-chymotrypsin and pepsin. In addition, the inhibitory activities were not affected by the addition of catalase. Taken together, these results confirmed that the inhibitory compounds produced by this strain were proteinaceous in nature and possessed typical characteristics of bacteriocins. The highest yield of bacteriocin produced by W. cibaria N23 was recorded at 20 h. The bacteriocin N23 remained stable after 2 h of incubation at pH values between 2.0 and 8.0, and also for 15 min at 121 °C. The bacteriocin produced by W. cibaria N23 was found to have a narrow antibacterial spectrum, being able to inhibit only W. confusa N31. In addition, bacteriocin N23 did not adhere to the surface of the producer cells. The results produced from this study will contribute to the existing body of knowledge and enhance the databases of bacteriocin-producing Weissella.     

Novel bacteriocin produced by Lactobacillus alimentarius FM-MM4 from a traditional Chinese fermented meat Nanx Wudl: Purification,identification and antimicrobial characteristics

The present study aims to purify and characterize a novel bacteriocin (designated as lactocin MM₄) produced by Lactobacillus alimentarius FM-MM₄, which was isolated from Nanx Wudl, a traditional Chinese fermented meat. Lactocin MM₄ was extracted by ethyl acetate and purified through cation exchange chromatography and semi-preparative high-performance liquid chromatography (RP-HPLC). As revealed by LC-MS/MS, lactocin MM₄ has a molecular mass of 1104.58 Da with the N-terminal sequence QGVGPLGQGHR, demonstrating low homology with previously reported class II bacteriocins. Lactocin MM₄ exhibited broad-spectrum antimicrobial activity against both Gram-positive and Gram-negative food-borne pathogens, as well as several yeasts. It was considerably thermo-stable with 84.7% residual antimicrobial activity after exposure to121 °C for 15 min, and it was highly stable at acidic pH (2–5). Proteases, such as trypsin, protease K, papain and pepsin, could completely inactivate the bacteriocin, while other enzymes, such as lipase and amylase, had no effect on its antimicrobial activity. These results indicate the potential of lactocin MM₄ for application in food preservation.     

Technological properties and bacteriocins production by Lactobacillus curvatus 54M16 and its use as starter culture for fermented sausage manufacture

Lactobacillus curvatus 54M16 was isolated from traditional fermented sausages of Campania region (Italy) and identified by 16S rRNA and hsp60 gene sequencing and by SDS-PAGE of whole cell proteins. The strain produced more than one bacteriocin, carrying the genes for sakacin X, T and P as demonstrated by PCR studies. The ability of L. curvatus 54M16 to produce multiple bacteriocins is confirmed by molecular mass spectrometry analysis and N-terminal amino acid sequencing. Among the bacteria tested, the pathogens Listeria monocytogenes and Bacillus cereus and the meat spoilage Brochotrix thermosphacta were sensitive to the bacteriocins. No inhibition of tested Gram-negative bacteria, some strains of Lactobacillus and of strains of Staphylococcus aureus was observed.All the in vitro conditions tested for the production of the bacteriocins (temperature, pH and NaCl), indicate that the strain of L. curvatus 54M16 is able to grow and to produce the antagonistic substances at pH 4.5 and in the presence of 4% NaCl. The strain has good acidifier capability and it is able to hydrolyse sarcoplasmic but not myofibrillar proteins, lipids and to reduce nitrates. Moreover it shown high values of SOD, while the aminopeptidase activity is restricted to whole cells that hydrolyse at high rates the amino acids l-arginine, l-valine, l-phenylalanine and l-lysine. The suitability of L. curvatus 54M16 as starter culture was assayed during sausage fermentation. Its use can improve the quality and safety of the traditional fermented sausages prepared without antimicrobial additives.     

Partial characterization of a class IIa pediocin produced by Pediococcus parvulus 133 strain isolated from meat (Mexican “chorizo”)

Pediocin-like bacteriocins are antimicrobial substances produced by some bacteria with high antilisterial activity. Several isolates of Pediococcus acidilactici and two Pediococcus parvulus strains of vegetable origin have been reported to produce this kind of peptide. This work presents the partial characterization of the bacteriocin produced by P. parvulus 133 found in meat and confirms its identity as a heat resistant, antilisterial bacteriocin. This peptide has a relatively narrow inhibitory spectrum but a high antilisterial activity. Pediocin remained active after heating to 121 °C, but its thermoresistance varied with pH. The pH selective adsorption method resulted in a 150-fold concentration of antimicrobial activity. The final extract was obtained by ultrafiltration and resulted in an additional 10-fold concentration of activity. Molecular weight was estimated as 5 kDa and isoelectric point was 8.65. The sequence of the first 17 aminoacids at the N-terminal end of the bacteriocin showed complete coincidence with that previously reported for pediocin A1 (AcH) and with an antilisterial peptide produced by Bacillus coagulans. High sequence similarity was also found with two other antilisterial bacteriocins.     

Purification and partial characterization of a novel bacteriocin produced by Lactobacillus casei TN-2 isolated from fermented camel milk (Shubat) of Xinjiang Uygur Autonomous region,China

Identification, characterization and assessment of novel bacteriocins for their potential use as biopreservatives continue to be highlighted in LAB research from past to present. A bacteriocin-producing Lactobacillus casei TN-2 strain was isolated from fermented camel milk (Shubat) of Xinjiang Uygur Autonomous region, China, after which the bacteriocin (designated as caseicin TN-2) was purified by performing ammonium sulfate precipitation, gel filtration, anion exchange chromatography and reversed-phase HPLC separation. According to MS spectrum, the molecular mass of caseicin TN-2 was 6352 Da, which was significantly different from previous reported bacteriocins produced by L. casei strains. Antibacterial activity of caseicin TN-2 was retained over a wide pH range and survived a heat treatment of 121 °C for 20 min. It was sensitive to proteases, such as trypsin and papain. Caseicin TN-2 exhibited a broad antimicrobial spectrum against Gram-positive and Gram-negative food-borne pathogenic strains including some antibiotic-resistant strains. It was found that the minimum inhibitory concentration of caseicin TN-2 to Escherichia coli ATCC25922 and Staphylococcus aureus ATCC25923 was 2.5 mg/mL and 5 mg/mL respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses were carried out to investigate the effect of caseicin TN-2 on the target cells, where it was demonstrated that the bacteriocidal mode of action was pore formation in the cytoplasmic membrane.     

Purification and characterization of a novel bacteriocin CAMT2 produced by Bacillus amyloliquefaciens isolated from marine fish Epinephelus areolatus

A novel bacteriocin named CAMT2 was produced by strain ZJHD3-06 which was isolated from the marine fish Epinephelus areolatus and identified as Bacillus amyloliquefaciens, Bacteriocin CAMT2 inhibits important food spoilage and food-borne pathogens such as Listeria monocytogenes, Staphylococcus aureus, Escherichia coli and Vibrio parahaemolyticus. Bacteriocin CAMT2 was purified by ammonium sulfate precipitation, gel filtration chromatography on Sephadex G-50 and reversed phase chromatography on a C₁₈ column. The molecular mass of the purified bacteriocin CAMT2 was about 20.0 kDa and N-terminal sequencing of the peptides revealed low similarity with existing antimicrobial peptides, as determined by an LC–MS/MS system. Bacteriocin CAMT2 was resistant for up to 100 °C and pH ranging 2–10, but lost its activity when treated with protease K. The bacteriocin also showed significant antimicrobial activity against L. monocytogenes in a meat model system. These obtained results suggest that bacteriocin CAMT2 has potential for use as a food biopreservative.     

A novel bacteriocin with a broad inhibitory spectrum produced by Lactobacillus sake C2, isolated from traditional Chinese fermented cabbage

By excluding the effects of organic acids and hydrogen peroxide, strain C2 producing a bacteriocin strongly inhibited Staphylococcus aureus ATCC 63589 and Escherichia coli ATCC 25922 was selected from 300 lactic acid bacteria isolated from traditional Chinese fermented cabbage. Strain C2 was identified as Lactobacillus sakei by phenotypical and physiological tests and 16S rDNA identification. This bacteriocin, which was designated sakacin C2, was purified by cold ethanol and Sephadex G50 column chromatography for further studies. The molecular weight of sakacin C2 was 5.5 kDa by Tris-Tricine SDS–PAGE, which was the largest among all known sakacins. Sakacin C2 exhibited a wide range of antimicrobial activity, strong heat stability (15 min at 121 °C) and pH stability (pH 3.0–8.0). Sakacin C2 was sensitive to protease but insensitive to lipase, α-amylase and β-amylase. These characters suggested that sakacin C2 was a novel Class II bacteriocin with a broad inhibitory spectrum and might broaden the application range of bacteriocins from LAB in the food industry.     

Characterization of bacPPK34 a bacteriocin produced by Pediococcus pentosaceus strain K34 isolated from “Alheira”

Different lactic acid bacteria were isolated during different stages in the production of “Alheiras”, a traditionally fermented sausage produced in the north of Portugal, between 2005 and 2007, in a total of 484 isolates. One of 484 isolates (K34) produced a bacteriocin, designated as bacPPK34, and was identified as a strain of Pediococcus pentosaceus by 16S rRNA sequencing. The highest bacteriocin production was noted at late log/early stationary phase after 15–18 h of growth in MRS broth at 37 °C (3200 AU/ml) against Enterococcus faecalis ATCC 29212 and 12800 AU/ml against Listeria monocytogenes (L1, L2, L3). bacPPK34 was between 2.5 kDa and 6.2 kDa in size, as determined by tricine-SDS-PAGE. Complete inactivation or significant reduction in antimicrobial activity was observed after treatment of cell-free supernatants with proteinase K, pepsin and trypsin. No change in activity was recorded when treated with catalase. The bacteriocin was resistant to treatments with lipase and detergents Triton X-100, Tween 20, SDS, NaCl, urea and EDTA. Furthermore, the bacteriocin remained active after 2 h at pH 2–12 and temperature treatments at 60, 80, 100 °C, 1 month of storage at ?20 and 4 °C and 20 min at 121 °C. Addition of bacPPK34 to a mid-log culture of L. monocytogenes and E. faecalis ATCC 29212 inhibited growth. The bacteriocin did not adhere to the surface of the producer cells.     

Sardinian goat’s milk as source of bacteriocinogenic potential protective cultures

Goat breeding in Sardinia constitutes an important source of income for farming and shepherding activities. In this study 170 LAB strains were isolated from Sardinian goat’s milk and tested for bacteriocins production against several food-borne pathogenic microorganisms. Four isolates (SD1, SD2, SD3 and SD4) were selected for their effective inhibition on Listeria monocytogenes. The strains were classified as members of Enterococcus genus, according to their biochemical and physiological characteristics, and then genetically identified as Enterococcus faecium. In MRS broth at 37 °C, bacteriocins SD1 and SD2 were produced at much higher levels (51200 AU/ml) compared to bacteriocin SD3 (3200 AU/ml) and bacteriocin SD4 (800 AU/ml). Their peptides were inactivated by proteolytic enzymes, but not when treated with α-amylase, catalase and lipase. The four bacteriocins remained stable at pH from 2.0 to 12.0, after exposure to 100 °C for 120 min and were not affected by the presence of surfactants and salts (N-Laourylsarcosine, NaCl, SDS, Triton X-100, Tween 20, Tween 80 and urea). Their molecular size was determined to be approximately 5 kDa by tricine-SDS-PAGE.Since the strains exhibited a strong antimicrobial activity against 21 L. monocytogenes strains and 6 Salmonella spp. isolates, they should be considered as potential bio-preservatives cultures for fermented food productions. Moreover, due to their technological features, the four strains could be taken in account for using as adjunct NSLAB (non-starter lactic acid bacteria) rather than as starter culture.     

Characterization of an anti-Listeria bacteriocin produced by Lactobacillus plantarum LB-B1 isolated from koumiss,a traditionally fermented dairy product from China

Lactobacillus plantarum LB-B1, isolated from a traditionally fermented dairy product koumiss, produced a bacteriocin active against strains of Listeria, Lactobacillus, Streptococcus, Enterococcus, Pediococcus and Escherichia. Pediocin LB-B1 was sensitive to proteolytic enzymes, but stable between pH 2.0–10.0 and heat resistant (15 min at 121 °C). It did not adhere to the surface of the producer cells. However, adsorption to both resistant and sensitive cells was observed. Production of the bacteriocin started at the early exponential phase and reached its maximum at the early stationary phase. This result suggested that pediocin LB-B1 was produced as a primary metabolite. Its mode of action was bactericidal, as determined against Listeria monocytogenes 54002. Pediocin LB-B1 was estimated between 2.5 kDa and 6.5 kDa by tricine–SDS–PAGE. Furthermore, the gene cluster encoding pediocin LB-B1 showed 99.8% homology with the operon encoding pediocin PA-1, suggesting that the two bacteriocins are identical.     

Suspected mode of antimycotic action of brevicin SG1 against Candida albicans and Penicillium citrinum

Brevicin SG1, a novel, broad spectrum bacteriocin produced by Lactobacillus brevis SG1 isolated from ‘ogi’, a traditional Nigerian fermented cereal, was studied for its effects on fungal hyphal growth and morphology. The bacteriocin caused some morphological changes and a decrease in the total mass of Candida albicans and, cellular damage and an inhibition of pre-formed germ tubes in Penicillium citrinum. The inhibitory action was concentration- dependent, confirming that antibiosis was the mode of antagonism.Transmission scanning electron microscopy (TSEM) study revealed that the bacteriocin caused hyphal destruction and lysing of the cell wall in P. citrinum and distortion of shape in C. albicans. TSEM result suggested that the fungal cell wall and the cell membrane were the main target of this antifungal compound and the suspected mode of action was fungiolytic. Disintegration of fungal hyphae was probably due to a membrane disorder causing increased membrane permeability and the consequent osmotic effect.The bacteriocin was stable over a wide range of pH (1–10) especially between pH 5–7 while its production was maximal at pH 6.5. The production and stability of the bacteriocin at a broad pH makes it a suitable agent for controlling spoilage organisms of most foods and for using it as starter cultures of fermented foods. It also has the potential for probiotic usage.     

Characterization of a novel bacteriocin produced by Lactobacillus sakei LSJ618 isolated from traditional Chinese fermented radish

A novel bacteriocin, sakacin LSJ618, produced by the strain Lactobacillus sakei LSJ618 isolated from traditional Chinese fermented radish, was studied. L. sakei LSJ618 was identified by both phenotypical and physiological tests combined with 16S rDNA sequence analysis. Sakacin LSJ618 is sensitive to hydrolytic enzymes including lipase, is stable between pH 2-8, and is heat resistant (30 min at 121 °C). Sakacin LSJ618 exhibits inhibitory activity against food-spoiling bacteria and food-borne pathogens, including the Gram-positive Listeria monocytogenes, Staphylococcus aureus, Sarcina sp., Micrococcus luteus, and the Gram-negative Proteus sp. and Escherichia coli, but not against most of the lactic acid bacteria tested. Maximal production of bacteriocin was reached in the late stationary phase, and inhibitory activity declined within 26 h. The mode of action of sakacin LSJ618 was determined to be bactericidal, as evidenced by its action upon Micrococcus tetragenus. After partial purification by ammonium sulfate precipitation and Sephadex G-25 chromatography, the molecular weight of sakacin LSJ618 was determined to be 5.2 kDa by Tricine-SDS-PAGE. The identified properties of sakacin LSJ618 indicate that it is a novel bacteriocin with potential application as a biopreservative in the food industry.     

Inhibition of Listeria monocytogenes in vitro and in goat milk by liposomal nanovesicles containing bacteriocins produced by Lactobacillus sakei subsp. sakei 2a

Lactobacillus sakei subsp. sakei 2a is a bacteriocinogenic lactic acid bacteria isolated from a Brazilian meat product, capable to inhibit Listeria monocytogenes in vitro and in foods. In this study, bacteriocin produced by this strain were encapsulated in phosphatidylcholine (FC) and 1,2-dioleoyloxy-3-trimethylammonium-propane (DOTAP) liposomes, separately and in combination, were characterized and evaluated for activity against L. monocytogenes in vitro and in experimentally contaminated UHT goat milk, during storage at 7 °C for 14 days and 30 °C for 24 h. The FC and DOTAP/FC (3:1) nanovesicles containing bacteriocins (12.800 AU mL⁻¹) presented zeta potential of −1.54 and + 38.13 mV, Entrapment Efficiency of 80.0% and 94.1%, and diameter of 91.19 and 81.49 nm, respectively. DOTAP/FC nanovesicle presented excellent stability, and maintained the same physicochemical characteristics over 28 days. Both free and encapsulated bacteriocins controlled L. monocytogenes growth in BHI medium and goat milk stored at 30 °C for at least 8 h, in a similar pattern. After 24 h in BHI medium, bacteriocins encapsulated in FC nanovesicles were more effective (p < 0.05) than free bacteriocins. However, in goat milk, no significant differences (p ≥ 0.05) were observed for the two types of nanovesicles. At 7 °C, both free and encapsulated bacteriocins retarded the L. monocytogenes growth, and after 5 days, counts were 5 log lower than in the controls, both in BHI and in goat milk. Encapsulation of bacteriocin in FC and DOTAP/FC nanovesicles did not affect the antimicrobial activity, but the advantages of their application for control of L. monocytogenes in goat milk based dairy products, when compared to free bacteriocins, remain unclear and more studies are needed.     

Isolation and characterization of bacteriocin-producing Pediococcus acidilactici HW01 from malt and its potential to control beer spoilage lactic acid bacteria

A bacteriocin-producing lactic acid bacterium was isolated from malts. The isolate was identified as Pediococcus acidilactici by morphological, API 50 CHL kit and 16S rRNA analysis, and designated as strain HW01. The antimicrobial activity was maintained over a broad pH range (pH 2–11). Proteolytic enzymes and α-amylase treatments inactivated the bacteriocin activity; while catalase, heat, detergents, and solvents did not. The molecular weight of the crude bacteriocin was approximately 6 kDa by SDS-PAGE. The bacteriocin production phenotype (Bac⁺) was linked to a 9.8 kb plasmid and was not increased by co-culture with an indicator microorganism. Bacteriocin HW01 inhibited several Gram-positive bacteria, including health-threatening microorganisms (Staphylococcus aureus, Streptococcus mutans, Lactobacillus curvatus, Listeria monocytogenes, and L. innocua). Particularly, Pediococcus damnosus and P. claussenii, which were isolated from spoiled beer, were strongly antagonised by the bacteriocin. P. acidilactici HW01 has tolerance to hop compounds but is unable to grow in a simulated beer environment. The potential of the HW01 strain, as a starter culture in brewing, to control beer spoilage lactic acid bacteria, is discussed.     

Characterization and application of an anti-Listeria bacteriocin produced by Pediococcus pentosaceus 05-10 isolated from Sichuan Pickle,a traditionally fermented vegetable product from China

Pediococcus pentosaceus 05-10, isolated from a traditionally fermented Sichuan Pickle, produced a bacteriocin (Pediocin 05-10) active against Listeria, Lactobacillus, Streptococcus, Enterococcus, Pediococcus and Leuconostoc. Pediocin 05-10 was sensitive to proteolytic enzymes, but stable between pH 2–10 and heat resistant (15 min at 121 °C). It did not adhere to the surface of the producer cells. However, adsorption to both resistant and sensitive cells was observed. Production of the bacteriocin started at the early exponential phase and reached its maximum at the early stationary phase. This result suggested that Pediocin 05-10 was produced in a growth-associated manner. Its mode of action was bactericidal, as determined against Listeria monocytogenes 54002. Pediocin 05-10 was estimated below 6.5 kDa by tricine–SDS–PAGE. The application experiment showed that Pediocin 05-10 could significantly reduce the counts of L. monocytogenes 54002 in pork ham during storage at 4 °C for 10 days. Thus, Pediocin 05-10 has potential for application in food preservation, especially in the meat products industry.     

Biodiversity,dynamics and antimicrobial activity of lactic acid bacteria involved in the fermentation of maize flour for doklu production in Côte d'Ivoire

Doklu is a maize-based spontaneously fermented dough produced and consumed in parts of West Africa, particularly in Côte d'Ivoire. The characterization of the microbial ecosystem of doklu was carried out using a polyphasic approach. First, culture-dependent methods were used for bacterial enumeration and the phenotypic and molecular identification of 250 lactic acid bacteria (LAB) isolates. Then, culture-independent methods, including PCR-TTGE (V3 region of the 16S rRNA gene), provided a fingerprinting of bacterial DNA directly extracted from doklu. Bio preservative abilities were also tested and strains producing antimicrobial compounds were genotyped using PFGE. During maize dough fermentation, LAB became dominant and their load increased from 4.2 ± 0.2 log CFU/g to 9.0 ± 0.7 log CFU/g only after 48 h. Culture-dependent methods highlighted the presence of five LAB groups with the species Lactobacillus plantarum (28%), Lactobacillus fermentum (41.6%), Pediococcus acidilactici (6.8%), Pediococcus pentosaceus (18%) et Weissella cibaria (5.6%), succeeding during the fermentation. Lb. fermentum being practically the only species present at the end of fermentation, is with Lb. plantarum, the predominant species of fermenting dough. Culture-independent analysis underlined the undoubted role of Lb. fermentum, actively involved in the dough fermentation. These Lb. fermentum species, with a diversity of strains also showed important antimicrobial activity, due to production of bacteriocins. Being able to produce antimicrobial compounds, Lb. fermentum species may act as both bio protective culture as well as fermenting agent in cereal products and could be exploited to create functional starter cultures.     

Purification and characterization of bacteriocin F1, a novel bacteriocin produced by Lactobacillus paracasei subsp. tolerans FX-6 from Tibetan kefir,a traditional fermented milk from Tibet,China

A bacteriocin-producing lactic acid bacteria, FX-6, was isolated from Tibetan kefir using the agar well diffusion assay. Strain FX-6 was identified as Lactobacillus paracasei subsp. tolerans on the basis of 16S rDNA sequence analyses. This bacteriocin, which was designated bacteriocin F1, was purified by a three-step purification procedure. The molecular mass of bacteriocin F1 was 2113.842 Da by MALDI-TOF–MS analyses. It was also discovered to have blocked N-termini, hampering analysis by Edman degradation. Bacteriocin F1 exhibited a wide range of antimicrobial activity, strong heat stability (20 min at 121 °C, or 60 min at 100 °C) and pH stability (pH 3.0–9.0). Following treatment by pepsin and trypsin, the antibacterial activity was partly reduced. Bacteriocin F1 is the first reported bacteriocin produced by L. paracasei subsp. tolerans which can not only inhibit fungi but also bacteria. The characterization of bacteriocin F1 suggested that it was a novel bacteriocin with potential research and application value in food industry.     

Technological properties of Lactobacillus plantarum strains isolated from Chinese traditional low salt fermented whole fish

A total of 21 Lactobacillus plantarum were isolated from a Chinese traditional low salt fermented whole fish product “Suan yu” and identified by biochemical and molecular methods. The isolates were screened for acidifying and amino-biogenic ability for proteolysis, lipolysis, antimicrobial activity, and sensory in order to select the most suitable candidates as the starter cultures. All the strains had high acidifying activities and were able to reduce the pH to lower than 4.5 in 36, 24 and 16 h at 15, 25 and 37 °C respectively. Major strains showed antimicrobial activities against Listeria monocytogenes, Staphylococcus aureus and Escherichia coli, and ten L. plantarum strains could produce bacteriocins. Five L. plantarum strains exhibited weak proteolytic activities against myofibrillar proteins, as evidenced by the agar plate assay and sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE). None of the strains showed lipolytic activity. Major L. plantarum strains displayed different enzymatic profiles. Besides, the isolates mostly showed negative-decarboxylase activities, but Lp-10 had a decarboxylase activity against l-tyrosine. Furthermore, the fermented fish surimi inoculated with Lp-15 and Lp-21 strains respectively scored high for overall acceptability. Therefore, Lp-15 and Lp-21 presented the best technological properties, which should be given first priority as the starter culture for manufacturing fermented fish products.     

Control of Listeria monocytogenes on sliced bologna sausage using a novel bacteriocin,amysin, produced by Bacillus amyloliquefaciens isolated from Thai shrimp paste (Kapi)

Listeria monocytogenes is a foodborne pathogen causing listeriosis, a disease of great concern due to high fatality rates. Furthermore the bacterium has the ability to survive under stressful conditions. The objectives of this study were to characterize and evaluate the effectiveness of new antilisteria bacteriocin designated as amysin produced by Bacillus amyloliquefaciens strain SP-1-13LM isolated from Thai shrimp paste or “Kapi”. The partially purified bacteriocin or PPB containing amysin prepared from strain SP-1-13LM showed a broad range of inhibition including L. monocytogenes, Salmonella sp. and Shigella sp. It was found that the antimicrobial activity of PPB was heat stable up to 100 °C for 60 min and active within the pH range of 3–9. The activity of PPB disappeared when treated with proteinase K, α-chymotrypsin and trypsin demonstrating its proteinaceous nature. Tris-Tricine SDS-PAGE analysis revealed that amysin prepared from B. amyloliquefaciens strain SP-1-13LM had an apparent molecular weight of 5.2 kDa. PCR analysis revealed the presence of malonyl CoA transacylase (ituD), lichenysin synthetase C (lchAC) and surfactin synthetase (sfp) coding for iturin, lichenysin C and surfactin, respectively. The potent antilisterial effect of amysin on the growth of L. monocytogenes in sliced bologna sausage was observed during seven days of storage at 4 °C. The potential application of amysin, non-nisin bacteriocin, might be exploited as a safe food biopreservative for used with nisin to inhibit all foodborne pathogens and minimize the nisin-resistant problem of L. monocytogenes in the food industry.