Factors affecting the adsorption of Lactobacillus plantarum bacteriocin bacST8KF to Enterococcus faecalis and Listeria innocua

Bacteriocin ST8KF (bacST8KF), produced by Lactobacillus plantarum ST8KF isolated from kefir, inhibits the growth of Enterococcus faecalis E88, Lactobacillus casei LHS, Lactobacillus curvatus DF38, Lactobacillus sakei DSM 20017^T, Lactobacillus salivarius 241 and Listeria innocua LMG 13568. Eighty per cent of bacST8KF adsorbed to La. casei LHS and La. sakei DSM 20017^T. However, the same level of adsorption was recorded to bacST8KF-resistant Lactobacillus paraplantarum ATCC 700211^T and Streptococcus caprinus ATCC 700066, suggesting that adherence to the cell surface occurs at random and not always at specific receptor sites. Adsorption of bacST8KF is affected by inorganic salts, acids, surfactants, alcohols, temperature and pH, as observed for E. faecalis E88 and Li. innocua LMG 13568. The target of bacST8KF is the cytoplasmic membrane, as indicated by changes in cell morphology and leakage of DNA and β-galactosidase from cells of E. faecalis E88 and Li. innocua LMG 13568 treated with bacST8KF. However, the mode of activity against E. faecalis E88 and Li. innocua LMG 13568 is bacteriostatic, as concluded from slight increases in optical density levels after a few hours in the presence of bacST8KF. Activity of bacST8KF doubled (from 12 800 AU mL⁻¹ to 25 600 AU mL⁻¹) when strain ST8KF was grown in the presence of Li. innocua LMG 13568, which may indicate some sort of quorum sensing.     

Competitiveness and antibacterial potential of bacteriocin-producing starter cultures in different types of fermented sausages

Application of bacteriocin-producing starter cultures of lactic acid bacteria in fermented sausage production contributes to food safety. This is sometimes hampered by limited efficacy in situ and by uncertainty about strain dependency and universal applicability for different sausage types. In the present study, a promising antilisterial-bacteriocin producer, Lactobacillus sakei CTC 494, was applied as a coculture in addition to commercial fermentative starters in different types of dry-fermented sausages. The strain was successful in both Belgian-type sausage and Italian salami that were artificially contaminated with about 3.5 log CFU g(-1) of Listeria monocytogenes. After completion of the production process, this led to listerial reductions of up to 1.4 and 0.6 log CFU g(-1), respectively. In a control sausage, containing only the commercial fermentative starter, the reduction was limited to 0.8 log CFU g(-1) for the Belgian-type recipe, where pH decreased from 5.9 to 4.9, whereas an increase of 0.2 log CFU g(-1) was observed for Italian salami, in which the pH rose from 5.7 to 5.9 after an initial decrease to pH 5.3. In a Cacciatore recipe inoculated with 5.5 log CFU g(-1) of L. monocytogenes and in the presence of L. sakei CTC 494, there was a listerial reduction of 1.8 log CFU g(-1) at the end of the production process. This was superior to the effect obtained with the control sausage (0.8 log CFU g(-1)). Two commercial antilisterial cultures yielded reductions of 1.2 and 1.5 log CFU g(-1). Moreover, repetitive DNA sequence-based PCR fingerprinting demonstrated the competitive superiority of L. sakei CTC 494.     

清酒乳杆菌对发酵风干肠品质的影响

该研究采用清酒乳杆菌（Lactobacillus sakei，L. sakei）作为发酵菌株制备发酵风干肠，研究其对发酵风干肠品质的影响，以自然发酵产品作为对照组，在发酵成熟过程中的第0、3、6、9天测定产品的菌落总数、乳酸菌数、pH值、水分含量、水分分布、嫩度、色差、过氧化物值（Peroxide Value，POV）、硫代巴比妥酸值（Thiobarbituric Acid Value，TBARS）、脂肪酸含量和感官评分等指标，研究发酵菌株对风干肠品质的影响。试验表明，L. sakei接种组的乳酸菌数和菌落总数显著高于对照组（P<0.05），L*值、a*和b*显著低于对照组（P<0.05）；L. sakei接种组在发酵终点时，水分含量降至32.15%，pH值降至4.41，保证了发酵风干肠的安全性；POV值和TBARS值显著低于对照组（P<0.05），表明L. sakei具有较好的抑制脂肪氧化作用；L. sakei接种组的总体可接受性更高，发酵后期酯类物质种类和含量均高于对照组。综上，L. sakei的添加改善了产品的品质和风味。     

Screening for Listeria monocytogenes surrogate strains applicable to food processing by ultrahigh pressure and pulsed electric field

Ultrahigh pressure (UHP) and pulsed electric field (PEF) are emerging processing technologies developed to enhance the safety while maintaining the fresh-like quality of food. For each food and process combination, a pathogen of concern (i.e., target pathogen) must be determined, and a low-risk microorganism that serves as the pathogen surrogate for process validation must be identified. The objective of this study was to identify a surrogate for Listeria monocytogenes for UHP and PEF process validation. Potential surrogates tested include four Lactobacillus spp., a Pediococcus sp., and a Listeria innocua strain. These were compared with nine L. monocytogenes strains, with regard to sensitivity to UHP and PEF processing. For UHP treatment, the strains were suspended in citrate-phosphate buffer (pH 7.0 or 4.5), sweet whey, or acidified whey and pressure processed at 500 MPa for 1 min. For PEF treatment, the strains were suspended in NaCl solution, acid whey, or sweet whey and processed at 25 kV/cm. The lethality of UHP or PEF treatment varied considerably, depending on medium types and pH and the treated strain. Treating the tested microorganisms with UHP inactivated 0.3 to 6.9 log CFU/ml for L. monocytogenes strains and 0.0 to 4.7 log CFU/ml for the potential surrogates. When PEF was employed, populations of tested microorganisms decreased < 1.0 to 5.3 log CFU/ml. L. monocytogenes V7 and OSY-8578 were among the most resistant strains to UHP and PEF treatments, and thus are candidate target strains. Lactobacillus plantarum ATCC 8014 demonstrated similar or greater resistance compared with the target organisms; therefore, the bacterium is proposed as a surrogate of L. monocytogenes for both processes under the conditions specified in the food matrices tested in this study.     

不同乳酸菌发酵剂对发酵红肠品质的影响

为研究乳酸菌发酵对红肠品质的影响,将发酵技术应用于本无发酵工艺的红肠制品中,筛选出能够提高红肠品质的乳酸菌发酵剂。分别将常应用于发酵肉制品的7 种商业乳酸菌发酵剂（木糖葡萄球菌＋戊糖片球菌（THM-17）、木糖葡萄球菌＋清酒乳杆菌＋类植物乳杆菌（PRO-MIX5）、木糖葡萄球菌＋肉葡萄球菌＋清酒乳杆菌（WBL-45）、木糖葡萄球菌＋戊糖片球菌＋植物乳杆菌（VHI-41）、木糖葡萄球菌＋戊糖片球菌＋植物乳杆菌（SHI-59）、肉葡萄球菌＋木糖葡萄球菌（WBX-43）和戊糖片球菌＋木糖葡萄球菌＋肉葡萄球菌＋乳酸片球菌（VBM-60））及8 种单菌（弯曲乳杆菌、戊糖乳杆菌、清酒乳杆菌-1、戊糖片球菌、木糖葡萄球菌、肉葡萄球菌、清酒乳杆菌-2、植物乳杆菌）以107 CFU/g的接种量接种至腌制后的肉馅中,拌馅灌肠后于35 ℃、80%湿度条件下发酵12 h,取样测定发酵后样品的乳酸菌数和细菌总数,再经干燥、蒸煮、烟熏、烘烤制得成品,测定其感官、pH值、色差、质构、亚硝酸盐、硝酸盐、生物胺及N-亚硝胺含量等指标。结果表明：15 种发酵剂中以木糖葡萄球菌和植物乳杆菌2 种乳酸菌发酵剂应用效果较好,所制得产品pH值分别为5.26和5.04,色泽美观,弹性适中,亚硝酸盐残留量（10.84、10.13 mg/kg）低,可显著抑制N-亚硝胺的形成（N-二甲基亚硝胺含量分别为1.29、2.51 μg/kg）,生物胺总量较低。由此说明,木糖葡萄球菌和植物乳杆菌能够显著提高红肠产品的安全品质。     

Evaluation of different starter cultures (Staphylococci plus Lactic Acid Bacteria) in semi-ripened Salami stuffed in swine gut

The ripening properties were evaluated in semi-ripened pork Salami started by different cultures: CXP (Pediococcus pentosaceus, Staphylococcus xylosus and Staphylococcus carnosus); RAP (Lactobacillus plantarum, Lactobacillus sakei, S. xylosus and S. carnosus); and GY2 (L. sakei, S. xylosus and S. carnosus). These starters were chosen by their technological activities: CXP (rapid acidifying); RAP (medium acidifying); and GY2 (slow acidifying plus intense reddening-flavouring). Salami was enhanced with Ponceau 4R red and sodium glutamate, stuffed in pig gut and aged for 12 days at 15 °C/65-85%RH. Dehydration, reddening, proteolysis, fat acidity and lipid oxidation were hardly affected by the starters. Acidification by LAB strongly influenced the flavour. L. sakei plus L. plantarum provided a better flavouring than a low dose of L. sakei, and, especially, than over-acidifying P. pentosaceus. A final pH of 5 seems to be suitable for preventing aroma and taste defects in semi-ripened Salami. Spontaneous lactic microflora showed great acidifying potential.     

Inactivation of Escherichia coli O1 57:H7, Listeria monocytogenes, and Lactobacillus leichmannii by combinations of ozone and pulsed electric field

Pulsed electric field (PEF) and ozone technologies are nonthermal processing methods with potential applications in the food industry. This research was performed to explore the potential synergy between ozone and PEF treatments against selected foodborne bacteria. Cells of Lactobacillus leichmannii ATCC 4797, Escherichia coli O157:H7 ATCC 35150, and Listeria monocytogenes Scott A were suspended in 0.1% NaCl and treated with ozone, PEF, and ozone plus PEE Cells were treated with 0.25 to 1.00 microg of ozone per ml of cell suspension, PEF at 10 to 30 kV/cm, and selected combinations of ozone and PEF. Synergy between ozone and PEF varied with the treatment level and the bacterium treated. L. leichmannii treated with PEF (20 kV/cm) after exposure to 0.75 and 1.00 microg/ml of ozone was inactivated by 7.1 and 7.2 log10 CFU/ml, respectively; however, ozone at 0.75 and 1.00 microg/ml and PEF at 20 kV/cm inactivated 2.2, 3.6, and 1.3 log10 CFU/ml, respectively. Similarly, ozone at 0.5 and 0.75 microg/ml inactivated 0.5 and 1.8 log10 CFU/ml of E. coli, PEF at 15 kV/cm inactivated 1.8 log10 CFU/ml, and ozone at 0.5 and 0.75 microg/ml followed by PEF (15 kV/cm) inactivated 2.9 and 3.6 log10 CFU/ml, respectively. Populations of L. monocytogenes decreased 0.1, 0.5, 3.0, 3.9, and 0.8 log10 CFU/ml when treated with 0.25, 0.5, 0.75, and 1.0 microg/ml of ozone and PEF (15 kV/cm), respectively; however, when the bacterium was treated with 15 kV/cm, after exposure to 0.25, 0.5, and 0.75 microg/ml of ozone, 1.7, 2.0, and 3.9 log10 CFU/ml were killed, respectively. In conclusion, exposure of L. leichmannii, E. coli, and L. monocytogenes to ozone followed by the PEF treatment showed a synergistic bactericidal effect. This synergy was most apparent with mild doses of ozone against L. leichmannii.     

Inhibition of Escherichia coli O157:H7 in ripening dry fermented sausage by ground yellow mustard

Compounds generated by the enzymatic hydrolysis of glucosinolates naturally present in mustard powder are potently bactericidal against Escherichia coli O157:H7. Because E. coli O157:H7 can survive the dry fermented sausage manufacturing process, 2, 4, and 6% (wt/wt) nondeheated (hot) mustard powder or 6% (wt/wt) deheated (cold) mustard powder were added to dry sausage batter inoculated with E. coli O157:H7 at about 7 log CFU/g to evaluate the antimicrobial effectiveness of the powders. Reductions in E. coli O157:H7 populations, changes in pH and water activity (aw), effects on starter culture (Pediococcus pentosaceus and Staphylococcus carnosus) populations, and effects of mustard powder on sausage texture (shear) were monitored during ripening. Nondeheated mustard powder at 2, 4, and 6% in dry sausage (0.90 aw) resulted in significant reductions in E. coli O157:H7 (P < 0.05) of 3.4, 4.4, and 6.9 log CFU/g, respectively, within 30 days of drying. During fermentation and drying, mustard powder did not affect P. pentosaceus and S. carnosus activity in any of the treatments. Extension of drying to 36 and 48 days reduced E. coli O157:H7 by >5 log CFU/g in the 4 and 2% mustard powder treatments, respectively. The 6% deheated mustard powder treatment provided the most rapid reductions of E. coli O157:H7 (yielding <0.20 log CFU/g after 24 days) by an unknown mechanism and was the least detrimental (P < 0.05) to sausage texture.     

不同接种量的清酒乳杆菌对低钠盐风干肠品质的改善作用研究

本实验研究了不同清酒乳杆菌的接种量(10⁵、10⁶和10⁷ CFU/g)对低钠盐风干肠品质特性的影响。以不接种的风干肠为对照,分别在发酵的第0、3、6和9 d测定4组风干肠的水分含量、水分活度、pH、乳酸菌数、色差和剪切力,并采用气相色谱-质谱技术结合电子鼻对第9 d样品进行风味特征的分析。结果表明,接种量为10⁶和10⁷ CFU/g降低了风干肠发酵结束时的pH(P<0.05),与对照组相比,10⁶ CFU/g的接种促进了终产品水分含量和水分活度的提升,而色差和剪切力并未在组间发现显著差异(P>0.05)。清酒乳杆菌的接种降低了醛类物质含量,且仅接种10⁶ CFU/g增加了醇类、酸类和酯类物质含量(P<0.05),进而使电子鼻“感知”到了比对照组更为浓烈的特征气味。感官评价结果表明,接种量为10⁶ CFU/g对低钠盐风干肠苦味和金属味的改善效果最佳,整体可接受性最好。理化特性和感官特性的偏最小二...     

Effect of starter culture and storage temperature on the content of biogenic amines in dry fermented sausage poličan

Water activity, pH, microbial counts (total counts/TCM/, coliforms, Enterobacter, Proteus, Pseudomonas, Escherichia and Lactobacillus spp., respectively), and seven biogenic amines (BA) were determined in dry fermented sausage 'poli?an' produced using starter culture A (Lactobacillus sakei, Staphylococcus carnosus, S. xylosus) or B (L. sakei, S. carnosus, Pediococcus pentosaceus), ripened 42 days, and subsequently stored at 8 or 22°C 60 days. Counts of lactobacilli were higher and TCM lower in the A-sausage when ripening was finished. Tyramine (quantitatively most important BA) content was not different (P>0.05) in A- (90 mg/kg of dry matter, DM) or B-sausage (91 mg/kg DM) at the end of ripening. The effect of the storage temperature on BA content was not significant (P>0.05) in the case of either tyramine or any other tested BA. The increase of total BA content during ripening was not different (P>0.05) between A- and B-sausages (final value 190 and 222 mg/kg DM, respectively). However, sum of BA was significantly higher (P<0.05) in B-sausage as compared with A-sausage at the end of either refrigerated storage (304 and 236 mg/kg DM) or room temperature storage (468 and 206 mg/kg DM, respectively). It is concluded that legislative limits should be established for tyramine and total BA content in dry fermented meat products.     

Survival of Listeria monocytogenes, Listeria innocua, and Lactic Acid Bacteria in Chill Brines

ABSTRACT:  Listeria monocytogenes is the pathogen of concern in ready-to-eat (RTE) meat products. Salt brines are used to chill processed meats. L. monocytogenes and lactic acid bacteria (LAB) can grow under saline conditions, and may compete with each other for nutrients. The objective of this study was to determine the effect of lactic acid bacteria ( Enterococcus faecalis , Carnobacterium gallinarum , and Lactobacillus plantarum ) on the survival of L. monocytogenes and Listeria innocua in brines stored under low temperatures for 10 d. Sterile tap water (STW) and 2 brine solutions (7.9% and 13.2% NaCl) were inoculated with 1 of 5 cocktails ( L. monocytogenes , L. innocua , LAB, L. monocytogenes + LAB, or L. innocua + LAB) at initial concentrations of 7 log CFU/mL. Brines were stored for 10 d at 4 or 12 °C. Three replications of each brine concentration/cocktail/temperature combination were completed. No significant reductions of L. monocytogenes occurred in 7.9%[w/v] or 13.2%[w/v] brines when LAB were present; however, there were significant reductions after 10 d of L. monocytogenes in the STW solution when LAB were present (1.43 log CFU/mL at 4 °C and 3.02 log CFU/mL at 12 °C). L. innocua was significantly less resilient to environmental stresses of the brines than L. monocytogenes , both with and without LAB present ( P ≤ 0.05). These strains of lactic acid bacteria are not effective at reducing L. monocytogenes in brines at low temperatures. Furthermore, use of L. innocua as a model for L. monocytogenes is not appropriate under these environmental conditions.     

Effect of Commercial Starter Cultures on the Myofibrillar Proteins of Pastirma, a Turkish Dry Meat Product

ABSTRACT: The effect of 3 different commercial starter cultures ( Staphylococcus carnosus, Staphylococcus carnosus + Lactobocillus pentosus and Staphylococcus xylosus + Lactobacillus sakei ) on the myofibrillar proteins of pastirma was investigated. It was observed that using commercial starter cultures in pastirma manufacture had a significant effect on myofibrillar fragmentation. However, the effect of each starter culture on myofibrillar fragmentation in pastirma was different. Most of the changes in myofibrillar proteins were produced with S. carnosus + L. pentosus.     

新疆传统香肠中抗李斯特菌乳酸菌的分离

香肠在贮藏末期,乳酸菌检出量很高,其中还有一些具有抑制其他微生物的乳酸菌。在北疆市场上抽到8批样品,真空包装后,将其贮藏在4℃条件下,分别在贮藏前后检测其理化指标。各样品的pH值、水分活度和盐分基本一致;香肠中微生物的生长也比较一致,初期乳酸菌水平比较低(102CFU/g),贮藏末期,乳杆菌占多数(107CFU/g),肠杆菌相对较低(105CFU/g)。这表明,乳酸菌具有相对的竞争优势。其中,贮藏前后,样品中均没有检出李斯特菌。抑菌圈试验发现,分离出的乳酸菌中有41%对李斯特菌有抑菌特性,经过进一步试验,发现大部分的乳酸菌不具有产细菌素能力,但这些乳酸菌仍然具有竞争优势,对于香肠的贮藏仍有积极的作用。     

PROTEOLYTIC ACTIVITY OF BACTERIAL STARTER CULTURES FOR MEAT FERMENTATION

Proteolytic activity of fermented meat starter cultures Pediococcus acidiliactic, Lactobacillus sake, Lactobacillus curvatus, Streptomyces griseus, Staphylococcus xylosus and Staphylococcus carnosus was examined after inoculation of sterile beef protein extracts containing 1% dextrose. Analysis for primary amines in extracts generated during fermentation of glucose showed that L. sake had the highest (P<0.05) proteolytic activity. The other cultures ranked from highest to lowest activity as follows : L. curvatus < S. carnosus < S. griseus < P. acidilactici < S. xylosus. All inoculated extracts showed a pH decline by 96 h to pH 3.76-4.31 whereas the control extract remained at 6.0-5.95. All cultures except S. xylosus had CFU increases within 24 h of inoculation. Only L. sake and S. xylosus had counts less than their initial level after 96 h. The results provide evidence that these commercially available starters for meat fermentation do possess significant proteolytic activity when tested using beef protein extracts.     

Surface application of lysozyme, nisin, and EDTA to inhibit spoilage and pathogenic bacteria on ham and bologna

A study was conducted to determine if the effectiveness of an antimicrobial treatment for cooked ham and bologna would be increased or maintained when applied in a surface coating. Cooked 10-g disks of ham and bologna sausage received one of three treatments: no coating (control), coating with 0.2 g of 7% (wt/vol) gelatin gel (gel-control), or coating with 0.2 g of 7% gelatin gel containing 25.5 g/liter of lysozyme-nisin (1:3) plus 25.5 g/liter of EDTA (gel-treated). The samples were then inoculated with one of six test organisms: Brochothrix thermosphacta, Escherichia coli O157:H7, Lactobacillus sakei, Leuconostoc mesenteroides, Listeria monocytogenes, or Salmonella Typhimurium. Inoculated samples were vacuum packed and stored at 8 degrees C for 4 weeks. The antimicrobial gel treatment had an immediate bactericidal effect up to 4 log CFU/cm2 on the four gram-positive organisms tested (B. thermosphacta, Lactobacillus sakei, Leuconostoc mesenteroides, and Listeria monocytogenes) and inhibited the growth of these organisms during the 4 weeks of storage. The antimicrobial gel treatment also had a bactericidal effect on the growth of Salmonella Typhimurium during storage. The numbers of E. coli O157:H7 on ham were reduced by 2 log CFU/cm2 following treatment with both antimicrobial-containing and non-antimicrobial-containing gels during the 4-week storage period. No effect was observed on the growth of E. coli O157:H7 on bologna.     

Inactivation of Listeria innocua on frankfurters that contain potassium lactate and sodium diacetate by flash pasteurization

ABSTRACT:  Listeria monocytogenes , a psychrotrophic foodborne pathogen, is a recurring postprocess contaminant on ready-to-eat meat (RTE) products, including frankfurters. Potassium lactate (PL) and sodium diacetate (SDA) are FDA-approved antimicrobials that inhibit the growth of L. monocytogenes when incorporated into the formulation of fine emulsion sausage. Flash (steam) pasteurization (FP) has been shown to reduce levels of L. monocytogenes , and its surrogate L. innocua , on frankfurter surfaces. The ability of FP to inactivate and prevent the growth of the L. monocytogenes surrogate L. innocua in a pilot plant setting was investigated. FP treatment (1.5 s, 121 °C) of single layers of frankfurters that were surface-inoculated with either 5, 4, or 3 log CFU/g of L. innocua immediately before FP (1.5 s, 121 °C) resulted in log reductions of 1.97 (± 0.11), 2.03 (± 0.10), or 2.07 (± 0.14), respectively. Inoculum level had no effect on the inactivation of L. innocua . Following 8 wk of refrigerated storage (4 °C), L. innocua levels decreased by 0.5 log in non-FP-treated frankfurter packs, while the 2 log reduction of L. innocua was maintained for FP-treated frankfurters. FP (1.5 s, 121 °C) had no effect on frankfurter color or texture. Because the numbers of L. monocytogenes associated with contaminations of ready-to-eat meats are typically very low, the use of FP in combination with PL and SDA has the potential to reduce the number of frankfurter recalls and foodborne illness outbreaks.     

In vitro evaluation of the probiotic potential of bacteriocin producer Lactobacillus sakei 1

Lactobacillus sakei 1 is a food isolate that produces a heat-stable antimicrobial peptide (sakacin 1, a class IIa bacteriocin) inhibitory to the opportunistic pathogen Listeria monocytogenes. Bacterial isolates with antimicrobial activity may be useful for food biopreservation and also for developing probiotics. To evaluate the probiotic potential of L. sakei 1, it was tested for (i) in vitro gastric resistance (with synthetic gastric juice adjusted to pH 2.0, 2.5, or 3.0); (ii) survival and bacteriocin production in the presence of bile salts and commercial prebiotics (inulin and oligofructose); (iii) adhesion to Caco-2 cells; and (iv) effect on the adhesion of L. monocytogenes to Caco-2 cells and invasion of these cells by the organism. The results showed that L. sakei 1 survival in gastric environment varied according to pH, with the maximum survival achieved at pH 3.0, despite a 4-log reduction of the population after 3 h. Regarding the bile salt tolerance and influence of prebiotics, it was observed that L. sakei 1 survival rates were similar (P > 0.05) for all de Man Rogosa Sharpe (MRS) broth formulations when tests were done after 4 h of incubation. However, after incubation for 24 h, the survival of L. sakei 1 in MRS broth was reduced by 1.8 log (P < 0.001), when glucose was replaced by either inulin or oligofructose (without Oxgall). L. sakei 1 was unable to deconjugate bile salts, and there was a significant decrease (1.4 log) of the L. sakei 1 population in regular MRS broth plus Oxgall (P < 0.05). In spite of this, tolerance levels of L. sakei 1 to bile salts were similar in regular MRS broth and in MRS broth with oligofructose. Lower bacteriocin production was observed in MRS broth when inulin (3,200 AU/ml) or oligofructose (2,400 AU/ml) was used instead of glucose (6,400 AU/ml). L. sakei 1 adhered to Caco-2 cells, and its cell-free pH-neutralized supernatant containing sakacin 1 led to a significant reduction of in vitro listerial invasion of human intestinal Caco-2 cells.     

Microbiological and sensory quality of dry fermented sausages containing alginate-microencapsulated Lactobacillus reuteri

The probiotic bacterium Lactobacillus reuteri was added to dry sausage batter, without or after being microencapsulated in alginate using either extrusion or emulsion technology. Pediococcus pentosaceus and Staphylococcus carnosus were added at 7 log cfu/g as starter cultures for fermentation. The sausage batter was stuffed in 55 mm fibrous casings and fermented, with smoking, at 相似文献   

Inactivation of barotolerant Listeria monocytogenes in sausage by combination of high-pressure processing and food-grade additives

Food-grade additives were used to enhance the efficacy of high-pressure processing (HPP) against barotolerant Listeria monocytogenes. Three strains of L. monocytogenes (Scott A, OSY-8578, and OSY-328) were compared for their sensitivity to HPP, nisin, tert-butylhydroquinone (TBHQ), and their combination. Inactivation of these strains was evaluated in 0.2 M sodium phosphate buffer (pH 7.0) and commercially sterile sausage. A cell suspension of L. monocytogenes in buffer (10(9) CFU/ml) was treated with TBHQ at 100 ppm, nisin at 100 IU/ml, HPP at 400 MPa for 5 min, and combinations of these treatments. Populations of strains Scott A, OSY-8578, and OSY-328 decreased 3.9, 2.7, and 1.3 log with HPP alone and 6.4, 5.2, and 1.9 log with the HPP-TBHQ combination, respectively. Commercially sterile sausage was inoculated with the three L. monocytogenes strains (10(6) to 10(7) CFU/g) and treated with selected combinations of TBHQ (100 to 300 ppm), nisin (100 and 200 ppm), and HPP (600 MPa, 28 degrees C, 5 min). Samples were enriched to detect the viability of the pathogen after the treatments. Most of the samples treated with nisin, TBHQ, or their combination were positive for L. monocytogenes. HPP alone resulted in a modest decrease in the number of positive samples. L. monocytogenes was not detected in any of the inoculated commercial sausage samples after treatment with HPP-TBHQ or HPP-TBHQ-nisin combinations. These results suggest that addition of TBHQ or TBHQ plus nisin to sausage followed by in-package pressurization is a promising method for producing Listeria-free ready-to-eat products.     

Survival of Bacillus cereus vegetative cells during Spanish-style fermentation of conservolea green olives

The aim of this research was to investigate the survival of artificially inoculated Bacillus cereus during Spanish-style green olive fermentation. Olives were initially treated with lye and subjected to different fermentation procedures including (i) heat shock (85 degrees C for 10 min) and inoculation with Lactobacillus plantarum ACA-DC 287, (ii) heat shock and inoculation with L. plantarum ACA-DC 146, (iii) heat shock and inoculation with Lactobacillus pentosus isolated during previous studies, and (iv) fermentation by indigenous flora (control process). Microbial growth and survival, pH, titratable acidity, and organic acid evolution were monitored. Inactivation of B. cereus was observed during all processes. The pathogen population declined during all fermentations, but a tailing effect was observed in the brines when the population reached 2 log CFU/ml, at which point the pathogen does not pose a risk to human health. The rate of inactivation was higher in heat-shocked inoculated olives (mean of -2.21 log CFU/day) compared with control olives (-1.26 log/day), indicating an advantage of heat shock and inoculation over spontaneous fermentation. The production of organic acids (primarily lactic acid) during fermentation seemed to be the main factor that determined the behavior of the pathogen under stress conditions prevailing in the brine. Principal components analysis was useful for distinguishing among the different fermentation processes on the basis of the relevant organic acid profile.