Characterization of the dominant bacterial communities of traditional fermentation starters for Hong Qu glutinous rice wine by means of MALDI-TOF mass spectrometry fingerprinting, 16S rRNA gene sequencing and species-specific PCRs

The main goal of this work was to investigate the bacterial flora present in the traditional fermentation starters using matrix-assisted laser desorption/ionisation time of flight (MALDI-TOF) mass spectrometry fingerprinting combined with 16S rRNA gene sequencing and species-specific PCRs. A total of 1314 bacterial strains were obtained from ten kinds of representative wine fermentation starters (5 Hong Qu and 5 Yao Qu) and classified by MALDI-TOF mass spectrometry. Sixteen different bacterial species belonging to six different genera (Bacillus, Staphylococcus, Leuconostoc, Pediococcus, Lactobacillus and Lactococcus) were identified with high accuracy by comparing them with generated spectra of MALDI Biotyper database. Comparison of 16S rRNA gene phylogeny and MALDI-TOF mass spectrometry analysis showed that MALDI-TOF mass spectrometry fingerprinting was a good complementary approach to 16S rRNA sequencing and even a more powerful tool in the accurate differentiation and classification of Bacillus species, especially for differentiating between Bacillus subtilis, Bacillus amyloliquefaciens and Bacillus methylotrophicus. MALDI-TOF mass spectrometry was also found to provide valuable information at species levels for the genus of Lactobacillus. The identification revealed that most strains isolated from traditional fermentation starters were B. amyloliquefaciens (31.81%), followed by Bacillus megaterium (16.89%), Lc. lactis subsp. lactis (8.60%) and B. subtilis (8.14%). In the culture-dependent quantitative analysis, 69.01% of the detected isolates were Bacillus species, and 30.44% of the detected isolates belonged to the class of lactic acid bacteria (LAB), including Leu. mesenteroides, Pediococcus pentosaceus, Lactobacillus plantarum, Lactobacillus paracasei, Lactobacillus brevis, Pediococcus acidilactici, Lactobacillus coryniformis and Lc. lactis subsp. lactis. This study provides detailed evaluation of bacterial communities in the traditional fermentation starters for Hong Qu glutinous rice wine using a fast and cost-effective technique—MALDI-TOF mass spectrometry fingerprinting. Information provided by this study is fundamental and useful to develop effective strategies for the selection of beneficial bacterial strains and improve of quality of Hong Qu glutinous rice wine.     

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.     

Isolation of lactic acid bacteria with antifungal activity against the common cheese spoilage mould Penicillium commune and their potential as biopreservatives in cheese

Moulds are the most common cheese spoilage organisms which can lead to economic loss as well as raising public health concerns due to the production of mycotoxins. In this study, 897 lactic acid bacteria (LAB) isolated from different herbs, fruits and vegetables were screened for their antifungal activity in an agar plate overlay assay. Thirty-six isolates had weak activity, 11 had moderate activity and 12 were confirmed as having strong activity. The strong antifungal isolates were obtained from a range of different sources but were all identified by 16S rDNA sequencing as being Lactobacillus plantarum. The antifungal spectra for these 12 isolates were determined against eight other moulds commonly associated with cheese spoilage and all isolates were found to possess inhibition against Penicillium solitum, Aspergillus versicolor and Cladosporium herbarum, but not against Penicillium roqueforti, Penicillium glabrum, Mucor circinelloides, Geotrichum candidum or Byssochlamys nivea. The absence of sodium acetate from MRS agar resulted in no inhibition of Penicilium commune, suggesting the synergistic effect of acetic acid with the antifungal LAB, similarly to that previously reported. To determine their potential as biopreservatives in cheese, LAB isolates were inoculated into cottage cheese prior to the addition of P. commune. All Lb. plantarum isolates were found to prevent the visible growth of P. commune on cottage cheese by between 14 and >25 days longer than cottage cheese that contained either no added LAB or LAB that did not have antifungal activity (Lactococcus lactis, Weissella soli, Leuconostoc inhae and Leuconostoc mesenteroides isolates). The results of this study shows that LAB isolated from various herbs, fruits and vegetables possess antifungal activity and have potential for use as biopreservatives in cheese.     

Characterization of the natural microflora of artisanal Mexican Fresco cheese

The objective was to characterize the microflora of Mexican artisanal Fresco cheese, as a first step towards the development of a starter culture, which would allow the making of a safe and uniform product from pasteurized milk. The numbers of several microbial groups (aerobic mesophilic flora, total and fecal coliforms, Salmonella spp., Staphylococcus spp., molds, yeasts and lactic acid bacteria) were investigated. The dominating isolates were characterized as being Lactococcus lactis ssp. lactis, Enterococcus faecium and Lactobacillus casei. The results suggest that an adequate starter in the production of Mexican Fresco cheese may be composed of strains of these species.     

Biochemical and microbial characterization of cassava inocula from the three main attieke production zones in Côte d'Ivoire

Attieke is one of the few products whose fermentation is not spontaneous but involves the use of an inoculum. In Côte d'Ivoire, country of attieke origin, as various traditional inocula are used for attieke production, the present study on inocula from the three main attieke producers ethnic groups (Adjoukrou, Alladjan and Ebrié) was performed to establish a scientific database of characteristics of these inocula, in order to highlight the way in which these inocula could contribute to set the diversity in quality of attieke produced and sold in Côte d'Ivoire. Thus, the biochemical and microbial characteristics of 54 traditional inocula were monitored and lactic acid bacteria involved in the fermentation were investigated using morphological, biochemical as well as molecular approaches to identify the predominant species. Results showed that traditional cassava inocula used to produce the 3 main types of attieke in Côte d'Ivoire differ quantitatively and qualitatively in their biochemical and microbial composition. Representative lactic acid bacteria (LAB) were grouped into 4 clusters included 5 species: Leuconostoc mesenteroides, Pediococcus acidilactici, Lactobacillus plantarum, Lactobacillus fermentum and Weissella cibaria. Inocula from Adjoukrou group were dominated by Leuconostoc mesenteroides and Pediococcus acidilactici, while L. fermentum was preponderant in inocula from Alladjan group and L. plantarum in those from Ebrie group. Weissella cibaria was specific to inocula from Ebrie group. The dominating LAB strains can be potential starter cultures for cassava fermentation during the production of each type of attieke.     

Screening of adhesive lactobacilli with antagonistic activity against Campylobacter jejuni

In the present study, 78 lactic acid bacteria (LAB) strains were screened for the antagonistic activity against Campylobacter jejuni and 15 LAB strains with high bactericidal capacity were selected for further study through the analysis of the inhibition zone of LAB spent culture supernatant on the growth of C. jejuni. Among these strains, four isolates, Lactobacillus plantarum N8, N9, ZL5 and Lactobacillus casei ZL4 exhibited high adhesion ability to HT-29 cells. All the cell free supernatant (CFS) of these four strains contained high concentration of organic acid and their inhibition effects against C. jejuni were pH sensitive. Furthermore, these four strains could strongly antagonize the adhesion and invasion of C. jejuni to HT-29 cells and showed good tolerance to artificial gastric and small intestinal juices. This study suggests that Lactobacillus strains N8, N9, ZL4 and ZL5 could be used as potential probiotics in food applications against C. jejuni infection.     

Prevention of bread mould spoilage by using lactic acid bacteria with antifungal properties

The ability of lactic acid bacteria (LAB) to inhibit Aspergillus, Fusarium, and Penicillium, the main contaminants in bread, was evaluated. Only four strains (Lactobacillus plantarum CRL 778, Lactobacillus reuteri CRL 1100, and Lactobacillus brevis CRL 772 and CRL 796) from 95 strains tested displayed antifungal activity. The major antifungal compounds were acetic and phenyllactic acids. The fermentation quotient (FQ = 2.0) and the leaven volume (80 cm³) of doughs with LB and yeasts were higher than doughs without LB. The inclusion of antifungal LAB strains in the starter culture allowed a reduction in the concentration of calcium propionate by 50% while still attaining a shelf life similar to that of traditional bread containing 0.4% CP.     

Molecular characterisation and antimicrobial activity of bacteria associated with submerged lactic acid cassava fermentation

Molecular identification of microorganisms associated with submerged cassava fermentation was carried out and isolates of lactic acid bacteria (LAB) were examined for antimicrobial activity, including ability to produce antimicrobial peptides as a first step to define starter cultures for controlled cassava fermentations. A total of 75 isolates, including 41 LAB, 31 aerobic bacteria (AB) and three anaerobic bacteria were isolated from unfermented and fermenting cassava roots, cassava leaves and fermented cassava dough and identified by a combination of phenotypic tests and sequencing of 16S rRNA, rpoA, rpoB and pheS genes. Microbial diversity at interspecies and intraspecies level was screened by, respectively, PCR amplification of the 16S-23S rDNA intergenic transcribed spacer (ITS-PCR) and repetitive sequence based PCR (rep-PCR). Antimicrobial activity of LAB cultures and supernatants against indicator bacteria; Escherichia coli, Salmonella enterica serotype Typhimurium (S. Typhimurium), Bacillus cereus and Staphylococcus aureus was studied using agar diffusion tests. Furthermore, inactivation of indicator bacteria was investigated in both liquid medium and during controlled cassava fermentation. Results revealed a diversity of bacterial genera, species and subspecies associated with submerged cassava fermentation. DNA sequencing enabled identification of LAB isolates as Lactobacillus plantarum, Weissella confusa, Weissella paramesenteroides, Lactobacillus rhamnosus, Lactobacillus hilgardii, Lactobacillus paracasei, Leuconostoc mesenteroides, Enterococcus faecium, Enterococcus casseliflavus, and Pediococcus acidilactici. Lactobacillus spp. were the predominant LAB and were present in all cassava samples studied. Aerobic bacteria were predominantly Bacillus spp., including Bacillus subtilis, Bacillus amyloliquefaciens and B. cereus. Other species identified included Staphylococcus pasteuri and Clostridium beijerinkii. Cells, supernatants and cell free supernatants (CFS) of selected LAB isolates were able to inhibit both Gram positive and Gram negative pathogenic bacteria. LAB isolates inactivated all indicator organisms during controlled cassava fermentations, with a 4–6 log reduction after 48 h fermentation. The antimicrobial effect of the LAB was attributed to acid production.     

Microbiological quality of raw-fermented sausages with Lactobacillus casei LOCK 0900 probiotic strain

The objective of this study was to evaluate the microbiological quality, defined as health safety, microbiological stability, sensory acceptability and dietary value, of raw-fermented sausages with Lactobacillus casei LOCK 0900 probiotic strain. The study assessed the impact of the number of probiotic starter culture suspension (Lc1 ≈ 6 log cfu/g; Lc2 ≈ 7.3 log cfu/g) on the microbiological quality of sausages after the fermentation and following 6 months' storage. The number of used probiotic in the examined raw-fermented sausages was approx. 9 log cfu/g after the fermentation and following 6 months' storage. The number of lactic acid bacteria in the Lc1 and Lc2 samples after the fermentation was similar, however, the smaller number of Staphylococcus aureus, Escherichia coli and Enterobacteriaceae in the Lc2 sample shows that a greater addition of the starter culture suspension is more beneficial. The sensory evaluation results showed that the overall quality was positively correlated with the aroma of cured meat, the taste of dried meat and muscle tissue fragmentation following the fermentation. Negative evaluation of the product was based on such parameters as bitter or other taste, acrid odour, fatty taste. The environment of raw-fermented sausages is suitable for the growth and survival of probiotic.     

Induction of plantaricin MG under co-culture with certain lactic acid bacterial strains and identification of LuxS mediated quorum sensing system in Lactobacillus plantarum KLDS1.0391

A bacteriocin named plantaricin MG was produced by Lactobacillus plantarum KLDS1.0391 which was isolated from “jiaoke”, a traditional, naturally fermented cream from Inner Mongolia in China. Bacteriocin production was increased significantly when L. plantarum KLDS1.0391 co-cultured with certain lactic acid bacteria (LAB) strains. Among 76 strains belonging to the genera Lactobacillus, Lactococcus, Leuconostoc and Streptococcus, four strains namely Lactobacillus helveticus KLDS1.9207, Enterococcus faecium KLDS4.0352, Lactobacillus reuteri KLDS1.0737 and Enterococcus faecalis KLDS4.0313 were shown to induce bacteriocin production of L. plantarum KLDS1.0391. Cell numbers of L. plantarum KLDS1.0391 were greatly enhanced when co-cultured with four bacteriocin-inducing strains. Bacteriocin production was not induced by autoclaved cultures and cell-free supernatants (CFS) of inducing strains, indicating that living cells of inducing strains might be necessary for enhancement of bacteriocin production. The presence of plnD and luxS genes was detected by polymerase chain reaction (PCR), and the existence of plNC8HK gene was detected by single oligonucleotide nested PCR (SON-PCR).     

Screening for bacteriocin-producing lactic acid bacteria from kurut,a traditional naturally-fermented yak milk from Qinghai–Tibet plateau

The objective of this study was to screen the bacteriocin-producing lactic acid bacteria (LAB) strains from kurut collected from six regions in Qinghai–Tibet Plateau. Upon the elimination of the effects of organic acids and hydrogen peroxide on tested microorganisms, 5 strains, among a total of 256 presumptive LAB strains screened, belonging to the species of Lactobacillus casei (strains T1, T11 and S9), Lactobacillus lactis (strain S2), and Leuconostoc lactis (strain T14), showed inhibition activities against both Staphylococcus aureus and Escherichia aerogenes. The inhibition activities were destroyed after treated with proteinase K, pepsin and trypsin separately, suggesting the proteinaceous nature of the antimicrobial compounds produced from the strains. The bacteriocins from strains T1 and T14 remained stable for 20 min at 121 °C and after 2 h of incubation at pH values between 3.0 and 11.0, compared with those from strains S2 and T11 that were stable during pH 3.0–6.0, and that from strain S9 stable between pH 3.0 and 9.0. Bacteriocins produced from strains S2, S9 and T11 were resistant to heating treatment at 100 °C for 20 min. Bacteriocins did not adhere to the surface of the producer cells. The results suggest that the extracellular bacteriocins produced from special LAB strains from kurut, of high antibacterial activity, as well as high thermal and pH stability, may be applied to dairy products manufactory to inhibit the growth of spoilage and pathogens during fermentation.     

Bacteriocin production by Lactobacillus curvatus MBSa2 entrapped in calcium alginate during ripening of salami for control of Listeria monocytogenes

Bacteriocins of lactic acid bacteria (LAB) have been extensively studied due to their possible applications in food preservation. However, components of the food matrix may interfere or inhibit bacteriocin production, and entrapment of the bio-protective strains may protect them of the adverse conditions in the food environment. In this study, a bacteriocinogenic LAB (Lactobacillus curvatus MBSa2) isolated from salami was entrapped in calcium alginate and tested for functionality in MRS broth and in salami experimentally contaminated with Listeria monocytogenes AL602/08 (a meat isolate), during 30 days simulating manufacture process conditions, including fermentation and maturation steps. The entrapment process did not affect bacteriocin production by Lb. curvatus MBSa2 in MRS broth and in salami. Both, free and entrapped Lb. curvatus MBSa2 caused reduction in a similar manner in the counts of L. monocytogenes AL602/08 in salami during manufacture process.     

Inhibition of Fusarium culmorum by carboxylic acids released from lactic acid bacteria in a barley malt substrate

The effect of carboxylic acids, composed by both organic and phenolic acids, released in a barley malt substrate fermented by lactic acid bacteria was tested against Fusarium culmorum macroconidia and compared under different fermentation conditions. Phenolic acids released by Lactobacillus plantarum FST1.7 and Lactobacillus brevis R2Δ were quantified using a QuEChERS method coupled with a HPLC-UV/PDA system. Their concentration improved with increasing extract content of the barley malt-based substrate and reached maximal concentrations after 48 h of fermentation performed at optimum growth temperature. Generally, phenolic acids were produced at levels far below their minimal inhibitory concentration (MIC), and limited synergistic effects were observed when mixed with organic acids. The fungal growth suppression by the wort fermented by Lb. brevis R2Δ (95 ± 9 h total inhibition) could be fully explained by the presence of antifungal carboxylic acids, whereas only partially accounted for Lb. plantarum FST1.7 (198 ± 19 h). Organic acids were mainly responsible for the ability of LAB fermented wort to cause fungal inhibition, whereas phenolic acids took only a secondary role at the low concentrations released. Longer fermentation times favoured primarily organic acid release, whereas fermentation of higher malt extract substrates encouraged both organic and phenolic acids production. The understanding on how synergy works between antifungal compounds could help to identify strategies to further increase their concentration in wort, with potential to replace synthetic broths and for direct application in food application.     

Effect of autochthonous starter cultures on microbiological and physico-chemical characteristics of Suan yu,a traditional Chinese low salt fermented fish

In this study, three groups of mixed starter cultures (S1: Lactobacillus plantarum 120, Staphylococcus xylosus 135 and Saccharomyces cerevisiae 31; S2: L. plantarum 145, S. xylosus 135 and S. cerevisiae 22; S3: Pediococcus pentosaceus 220; S. xylosus 135 and S. cerevisiae 22), isolated from Suan yu, were inoculated to produce the traditional fermented fish. After 42 days fermentation at 24 °C, Suan yu inoculated with different mixed starter cultures underwent rapid growth of lactic acid bacteria (LAB), declined pH, suppressed increase of thiobarbituric acid (TBARS) and total volatile base nitrogen (TVB-N) as well as growth of spoilage bacteria and pathogens. Besides, Suan yu had higher contents of non-protein nitrogen (NPN) and total free amino acids (FAA) compared to the control (P < 0.05). The muscle proteins were severely hydrolyzed during fermentation (SDS-PAGE). Moreover, the sensory evaluation indicates the fermented fish was more widely accepted than the control. The results suggest that the inoculation with S1, S2 and S3 reduced the lag time that fermentation began and improved the quality of Suan yu.     

Suppression of bacteriocin production in mixed-species cultures of lactic acid bacteria

In the present work, the effect of co-culture on bacteriocin production by selected lactic acid bacteria (LAB) was studied. Thus, the co-culture of two bacteriocin-producer strains, Lactobacillus plantarum NC8C and Enterococcus faecium 6T1a, resulted in a significant reduction or even suppression of bacteriocin production by both strains. The phenomenon was not restricted to these two strains since we have further proved that it was more general and also occurred in several other co-cultures with LAB isolated from different food fermentations. This decrease in bacteriocin production was confirmed to be non cell–cell contact-dependent by using a two-compartment system in which the microorganisms were separated by a 0.2-μm-pore-size membrane. In addition, cell-free supernatants from certain co-cultures were able to suppress bacteriocin production in other strain cultures. In light of these findings, we hypothesize that such interactions between microorganisms should be taken into account to improve the development of bacteriocin-producing starter cultures used in food fermentations in order to avoid a negative effect on the quality of the fermented product.     

Whole soybean as probiotic lactic acid bacteria carrier food in solid-state fermentation

For the purpose of preparing lactic acid bacteria (LAB) carrier food, the solid-state fermentation of whole soybean was performed using Bifidobacterium animalis 937, Lactobacillus casei Zhang and Lactobacillus plantarum P-8 mixed with Bacillus subtilis natto, respectively. The physicochemical properties, the amino nitrogen content and peptide molecular weight distribution of the fermented whole soybean products were examined during this process. After 48 h of fermentation, the viable counts of the three samples were 1.41 × 10⁸ CFU/g (B. animalis 937), 1.74 × 10¹⁰ CFU/g (L. casei Zhang) and 2.19 × 10¹⁰ CFU/g (L. plantarum P-8), with the pH declined rapidly from 6.32 to 5.78, 5.60 and 5.44 at the early stage of the fermentation and increased to 6.71, 6.47 and 6.60 at the later stage of the fermentation. The fermentation caused a sharply increase in the content of the free amino nitrogen from 99.7 μmol/g to 301.9 μmol/g, 390.1 μmol/g and 529.1 μmol/g in the solid fermented soybean products, due to the multiplication of microorganism and the effect of enzyme system. Furthermore, the levels of soybean peptide with molecular weight less than 1000 Da increased 30.7%, 71.2% and 81.3% relative to that of the control group at 48 h. The result of the present work implied that whole soybean fermented by LAB can provide the different probiotics for the host, and there is potential to develope nutritious fermented soybean products.     

Fermented tofu: Enhancement of keeping quality and sensorial properties

In this study a new way to produce tofu by means of soymilk fermentation by specific lactic acid bacteria, Lactobacillus casei and Lactobacillus acidophilus alone or in combination, and subsequent precipitation has been developed, in order to prevent undesired microbial and chemical spoilage, as well as improve the stability and the quality of the product. In particular, the combination L. casei and L. acidophilus generated tofu having shelf life exceeding 20 days and able to prevent the growth of the spoilage strains inoculated. This fermented tofu was characterized by the production of antimicrobial molecules, such as acetic acid, limonene, 2-nonen-1-ol, 1-nonanol, 2(5H)-furanone, benzyl alcohol, phenylethyl alcohol and heptanoic acid. Depending on the Lactobacillus species used, the fermentation process generated different metabolites profiles and sensorial properties. Another promising properties conferred by the lactic acid bacteria fermentation was the inhibition of unsaturated fatty acids (UFAs) peroxidation or reduction of the aldehydes originated to their corresponding alcohols.     

Biogenic amine inhibition and quality protection of Harbin dry sausages by inoculation with Staphylococcus xylosus and Lactobacillus plantarum

This study was conducted to evaluate the effects of inoculation with Staphylococcus xylosus, Lactobacillus plantarum, or a mixture of strains (L. plantarum + S. xylosus) on the formation of biogenic amines (BAs) and quality characteristics in Harbin dry sausage. Microbial analysis shows that total aerobic bacteria and lactic acid bacteria (LAB) counts were higher in the inoculated sausages, especially in those inoculated with a mixture of strains, but the growth of enterobacteriaceae was inhibited (P < 0.05). A sharp decrease in the pH value of the sausages was observed, and the moisture content and water activity were significantly decreased during fermentation. Sausages inoculated with a mixture of bacterial strains had the lowest pH, moisture content and water activity (P < 0.05). Inoculation of dry sausages with S. xylosus or L. plantarum, especially a mixture of strains (L. plantarum + S. xylosus), significantly delayed lipid oxidation, improved sensory characteristics, and inhibited BA accumulation. Six types of BAs (cadaverine, putrescine, tryptamine, 2-phenylethylamine, histamine, and tyramine) were inhibited by the presence of L. plantarum and S. xylosus, and a mixture of them had the most inhibitive effect. Correlation analysis showed that the BA concentrations correlated well with enterobacteriaceae counts, and some BAs were negatively correlated with LAB counts. These results demonstrate that S. xylosus and L. plantarum could be used as starter cultures in Harbin dry sausage production to inhibit BA accumulation and improve quality characteristics.     

Heterologous production of pediocin for the control of Listeria monocytogenes in dairy foods

Pediocin is an antimicrobial peptide naturally produced by Pediococci with the potential to serve as a food-grade preservative for controlling Listeria contamination. The use of Pediococci in dairy products is limited due to their inability to ferment lactose, thus lactic acid bacteria (LAB) have been considered as potential hosts for the heterologous production of pediocin. In this study the four gene operon (papA-D) required for pediocin production was cloned on the nisin-inducible expression vector pMSP3535H3. The resulting vector, pRSNPed2, was electrotransformed into Streptococcus thermophilus, Lactococcus lactis ssp. lactis and Lactobacillus casei. Transformants containing the properly constructed vector were identified by PCR analysis and shown to inhibit the growth of Listeria monocytogenes Scott A. S. thermophilus transformants were all shown to constitutively express pediocin; however, in L. lactis and L. casei both constitutive and inducer-dependent expression was observed. In all cases nisin-induction resulted in optimal pediocin production. Transformants from each LAB host were also shown to inhibit the growth of L. monocytogenes NR30, a nisin-resistant variant of L. monocytogenes Scott A. These results suggest pediocin has the potential to serve as a hurdle component along with nisin for prevention of Listeria contamination of foods.     

Screening for potential new probiotic based on probiotic properties and α-glucosidase inhibitory activity

In this study, 11 lactic acid bacteria (LAB) strains were screened for potential new probiotics using in vitro methods, including acid and bile salt tolerance, adhesion, antioxidative and α-glucosidase inhibitory activity. The results indicated that Lactobacillus casei 2W and Lactobacillus rhamnosus Z7 showed better potential probiotic properties and α-glucosidase inhibitory activity in vitro. The characteristics of L. casei 2W were better than those of L. rhamnosus GG, and L. rhamnosus Z7 was the most similar strain to L. rhamnosus GG, which had an antidiabetic capability. This finding suggested that L. casei 2W and L. rhamnosus Z7 could be used as potential antidiabetic probiotics. Further research is required to examine the α-glucosidase inhibitory activity of these strains.